GEOTECHNICAL EVALUATION OF QUESTA MINE MATERIAL, … · 2009-04-28 · GEOTECHNICAL EVALUATION OF QUESTA MINE MATERIAL, TAOS COUNTY, NEW MEXICO . by . ... showed that rock fragments

GEOTECHNICAL EVALUATION OF QUESTA MINE MATERIAL,

TAOS COUNTY, NEW MEXICO

by

Samuel Nunoo

Submitted in partial fulfillment of the requirements for the Degree of Master of Science in Mineral Engineering

with Specialization in Geotechnical Engineering

New Mexico Institute of Mining and Technology Department of Mineral Engineering

Socorro, New Mexico May, 2009

Abstract

In this research work, geotechnical properties of Questa rock piles and their natural

analogs were investigated, along with the relationships between the various geotechnical

tests. Particle shape analysis, wet and dry sieving, and direct shear tests were conducted.

In addition, the results of 12-inch direct shear tests and 4-inch diameter triaxial tests from

published documents and Golder laboratory were studied. The particle shape analysis

showed that rock fragments at the test locations of Questa mine are mainly subangular,

subdiscoidal and subprismoidal. Furthermore, the sphericity and angularity of the rock

fragments of the older analogs are similar to those of the younger rock piles indicating

that short-term weathering (100 years) and longer hydrothermal alteration has not

noticeably changed the particle shapes at the test locations. Wet sieving methods results

in more fines than the dry sieving. The increase in fines is a result of the presence of

water in wet sieving that dissolves the cementation and cohesion between particles and

causes disintegration of clumps that act as solid rock fragments during dry sieving

methods. The shear strength of Questa mine material is affected by the particle size and

shape. In general, larger samples contain lesser amount of fines that result in higher

friction angles. For example, 12-inch samples show higher friction angles compared to

the 2.4 or 2-inch samples. The peak friction angle of the materials from Questa rock piles

and analogs reduces as the water content increases. The greatest friction angles belong to

air-dried samples. 12-inch direct shear and 4-inch diameter triaxial tests show similar

peak friction angles of 40° or above. An exception is for sample SSW-SAN-0006 that

indicates a 6° difference in the measured friction angle using direct shear and triaxial

testing. This sample has greatest percentage of fines that could be responsible for this

discrepancy.

Acknowledgements

I would like to express my sincere appreciation to Dr. McLemore and Dr. Ali

Fakhimi for providing guidance, insight, and support throughout the course of this

research. Appreciation is also extended to Dr. Mojtabai who is on the thesis advisory

committee and who encouraged me to do my thesis research at New Mexico Tech and the

Questa Molybdenum Mine.

I would like to thank many people who provided insight and suggestions on this

research: Dr. Dirk Van Zyl, Dr. Dave Jacobs, and other members of the Chevron Questa

project weathering study. I especially want to thank Prosper Feli, Kojo Anim and

Gertrude Ayakwah for assistance with the laboratory testing program. Last but not least, I

would like to thank Solomon Ampim, Ariel Dickenson, and Kelly Donahue for all their

support by reviewing some of my chapters.

This thesis is dedicated to God Almighty for making it possible to complete my

masters’ degree program. “It is not of him that wills or of him that runs but it is the Lord

that showeth mercy”, Romans 9:16. I also dedicate this degree to my parents Maxwell

Nunoo and Dora Nunoo, my brothers Moses Nunoo and Joshua Nunoo and my one and

only sister Mary Nunoo, and to my lovely wife Josephine Nunoo.

ii

Table of Content List of Tables ..................................................................................................................... vi

List of Figures ................................................................................................................... vii

1. Introduction ................................................................................................................ 1

1.1. Background ............................................................................................................. 1 1.2 Site Description ....................................................................................................... 3 1.3 Project Scope and Objectives .................................................................................. 5 1.4 Sample Collection and Sample Preparation ............................................................ 6 1.5 Thesis organization ................................................................................................ 7

2. Mineralogy and Petrographic Description of Samples .............................................. 8

2.1 Description of Sample MIN-SAN-0002 ................................................................. 8 2.1.1 Location ............................................................................................................ 8 2.1.2 Hand Specimen Description ............................................................................. 8 2.1.3 Petrographic Description .................................................................................. 9 2.1.4 Laboratory Analyses ....................................................................................... 10

2.2 Description of Sample QPS-SAN-0002................................................................ 12 2.2.1 Location .......................................................................................................... 12 2.2.2 Hand Specimen Description ........................................................................... 12 2.2.3 Petrographic Description ................................................................................ 13 2.2.4 Laboratory Analyses ....................................................................................... 14

2.3 Description of Sample SPR-SAN-0002 ................................................................ 16 2.3.1 Location .......................................................................................................... 16 2.3.2 Hand Specimen Description ........................................................................... 16 2.3.3 Petrographic Description ................................................................................ 17 2.3.4 Laboratory Analyses ....................................................................................... 18

2.4 Description of Sample SSW-SAN-0002 ............................................................... 20 2.4.1 Location .......................................................................................................... 20 2.4.2 Hand Specimen Description ........................................................................... 20 2.4.3 Petrographic Description ................................................................................ 21 2.4.4 Laboratory Analyses ....................................................................................... 23

2.5 Description of Sample SSW-SAN-0006 ............................................................... 24 2.5.1 Location .......................................................................................................... 24 2.5.2 Hand Specimen Description ........................................................................... 24 2.5.3 Petrographic Description ................................................................................ 25 2.5.4 Laboratory Analyses ....................................................................................... 27

3. The Effect of Weathering on Particle Shape of Questa Mine Material .................... 28

3.1 Introduction .......................................................................................................... 28 3.2 Sample Description .............................................................................................. 30 3.3 Background .......................................................................................................... 31 3.4 Methodology ......................................................................................................... 32

3.4.1 Sample Collection and Sample Preparation .................................................... 32 3.5 Description of Index Parameters of Rock Fragments .......................................... 35

3.5.1 Point Load Test ............................................................................................... 35

iii

3.5.2 Slake Durability Test ...................................................................................... 35 3.6 Results .................................................................................................................. 36 3.7. Index Parameters of Rock Fragments .................................................................. 38

3.7.1 Slake Durability Test ...................................................................................... 38 3.7.2 Point Load Test ............................................................................................... 39

3.8 Conclusion ........................................................................................................... 40

4. Comparison of Wet and Dry Sieving Particle Size Analyses ................................... 42

4.1. Introduction ........................................................................................................... 42 4.2. Objective ............................................................................................................... 42 4.3. Previous Work ...................................................................................................... 43 4.4. Background ........................................................................................................... 44 4.5. Methodology ......................................................................................................... 45 4.6. Results ................................................................................................................... 46 4.7. Discussion ............................................................................................................. 48 4.8. Conclusion ............................................................................................................ 49

5. Effect of Particle Size on Cohesion and Friction Angle of Questa Mine Material ... 50

5.1. Introduction ........................................................................................................... 50 5.2. Previous Work ...................................................................................................... 51 5.3. Previous Work on Shear Strength of Questa Mine Material ................................ 53 5.4. Methodology ......................................................................................................... 55 5.5. Background ........................................................................................................... 56 5.6. Results ................................................................................................................... 57 5.7. Discussion and Conclusion ................................................................................... 63

6. Moisture-Softening Effect ........................................................................................ 64

6.1. Introduction ........................................................................................................... 64 6.2. Previous Work ...................................................................................................... 65 6.3. Background ........................................................................................................... 67 6.4. Methodology ......................................................................................................... 67 6.5. Results ................................................................................................................... 68 6.6. Discussion and Conclusion ................................................................................... 72

7. Comparison of Triaxial and Direct Shear Test Results of Questa Mine Material .... 73

7.1. Introduction ........................................................................................................... 73 7.2 Previous Work ...................................................................................................... 74 7.3 Background ........................................................................................................... 77 7.4 Methodology ......................................................................................................... 77 7.5. Results and Discussion ......................................................................................... 77

8. Conclusions and Recommendation .......................................................................... 81

8.1 Conclusion ............................................................................................................ 81

References ......................................................................................................................... 83

Appendixes ....................................................................................................................... 88

Appendix 1. Petrographic Descriptions and the Mineralogy of Samples .................... 88

iv

Appendix 2. Particle Shape of Samples ........................................................................ 94 Appendix 3. Standard Operating Procedure (SOP) .................................................... 102 Appendix 4. Dry and Wet Sieving Analysis ............................................................... 128 Appendix 5. Shear Displacements, and Normal Displacement Plots for Dry, Moist, and Wet Conditions ........................................................................................................... 136 Appendix 6. Golder Associates Triaxial Test Results ................................................ 159

v

List of Tables

Table 2.1. Various laboratory analyses for sample MIN-SAN-0002. ...................... 10 Table 2.2. Chemical and mineralogical analysis for sample MIN-SAN-0002. ........ 11 Table 2.3. Various laboratory analyses for sample QPS-SAN-0002. ....................... 14 Table 2.4. Chemical and mineralogical analysis for sample QPS-SAN-0002. ........ 15 Table 2.5. Various laboratory analyses for sample SPR-SAN-0002. ....................... 18 Table 2.6. Chemical and mineralogical analysis for sample SPR-SAN-0002. ......... 19 Table 2.7. Various laboratory analyses for sample SSW-SAN-0002. ...................... 23 Table 2.8. Chemical and mineralogical analysis for sample SSW-SAN-0002. ........ 23 Table 2.9. Various laboratory analyses for sample SSW-SAN-0006. ...................... 27 Table 2.10. Chemical and mineralogical analysis for sample SSW-SAN-0006. ...... 27 Table 3.1. Samples and the particle sizes used for particle shape analysis. ............. 33 Table 3.2. Point load strength index classification (Broch and Franklin, 1972). ..... 35 Table 3.3. Slake durability index classification (Franklin and Chandra, 1972). ...... 36 Table 3.4. Summary of slake durability results. ....................................................... 38 Table 3.5. Summary of point load test results. ......................................................... 39 Table 4.1. Wet sieve analysis results on the samples collected from a bore hole in Sugar Shack South rock pile (Norwest Corporation, 2005). .................................... 44 Table 4.2. The minimum sample weight required for particle size analysis based on the size of the largest particle in the sample (U.S. Army Corps of Engineers, 1970)……... .............................................................................................................. 45 Table 4.3. Summary table of particle size results conducted at New Mexico Tech. Note that two separate samples were collected from Sugar Shack West rock pile. . 47 Table 4.4. Summary table of particle size conducted by Golder Associates-Burnaby Laboratory ................................................................................................................. 48 Table 4.5. Ranges and means of gravel, sand, and fines from wet sieving of Questa materials reported by different laboratories. ............................................................. 48 Table 5.1. Golder Associates-Burnaby Laboratory (2.4-inch samples) and NMT (2-inch samples) shear test results for air-dried samples. .............................................. 58 Table 5.2. Shear strength parameters from direct shear tests using the 12-inch shear box……..................................................................................................................... 58 Table 5.3. Shear strength parameters from direct shear tests using the 2.4-inch shear box………................................................................................................................. 59 Table 6.1. Shear strength parameters from direct shear tests using the 12-inch shear box……..................................................................................................................... 69 Table 6.2. Shear strength parameters from direct shear tests using the 2.4-inch shear box……..................................................................................................................... 70 Table 7.1. Summary of Golder Triaxial Test Results. σ´1= effective axial stress, σ´3= effective confining stress, q = (σ´1 - σ´3)/2, p´ = (σ´1 + σ´3)/2. ................................ 78 Table 7.2. Percent Fines of Samples of Questa Mine Material Obtained from Golder Laboratory Results .................................................................................................... 79

vi

List of Figures

Figure 1.1. Questa rock piles and other mine features ................................................ 3 Figure 2.1. Photograph of sampling location of MIN-SAN-0002. ............................ 8 Figure 2.2. Photograph of washed rock fragments. Field of view is 2.5 inches across........................................................................................................................... 9 Figure 2.3. Sample overview image showing altered rock and mineral fragments in clay rich soil matrix. ................................................................................................... 9 Figure 2.4. Highly altered quartz-rich clast (darker areas) with relict pyrite cubes replaced by jarosite (brighter areas). ......................................................................... 10 Figure 2.5. Altered rock & mineral fragments in clay rich matrix; note Fe-cemented (goethite+ quartz) grain & goethite+ jarosite) grain. ................................................ 10 Figure 2.6. Photograph of sampling location for QPS-SAN-0002. NO SCALE .... 12 Figure 2.7. Photograph of rock fragments. Field of view is 3 inches across. .......... 13 Figure 2.8. Fe-cemented rock fragments, dominantly quartz fragments, with some jarosite cement. ......................................................................................................... 13 Figure 2.9. Clay-rich clast with rock and minerals fragments cemented by clays. .. 14 Figure 2.10. Clay rich clast with relict pyrite cube replaced by jarosite. ................. 14 Figure 2.11. Photograph of sampling location for SPR-SAN-0002. Tennis ball, at right, is for scale. ....................................................................................................... 16 Figure 2.12. Photograph of washed rock fragments from hand sample. Field of view is 3 inches across. ...................................................................................................... 17 Figure 2.13. Overview image of rock fragments with soil matrix adhering to the larger rock fragments. ............................................................................................... 17 Figure 2.14. A close-up image of a rock fragment with an Fe-oxide (goethite) coating. A small rounded jarosite grain can be seen in the matrix. The jarosite and Fe-oxides are the brighter hues. ................................................................................ 18 Figure 2.15. A close-up image displaying relict pyrite crystals (completely oxidized) that are being replaced by jarosite and Fe-oxides. .................................................... 18 Figure 2.16. Photograph of sampling location SSW-SAN-0002. Tennis ball (right) is for scale. ................................................................................................................ 20 Figure 2.17. Photograph of washed rock fragments from sample SSW-SAN-0002. Field of view is 2.5 inches across. ............................................................................ 20 Figure 2.18. Figure shows image SSW-SAN-0002-02 showing a close-up of matrix clay……... ................................................................................................................. 21 Figure 2.19. Figure shows image SSW-SAN-0002-03 with a high magnification. The bright areas are jarosite and the “wavy” areas are clay. .................................... 22 Figure 2.20. Figure shows image SSW-SAN-0002-08 where multiple clay phases in an altered rock fragment can be seen. ....................................................................... 22 Figure 2.21. Figure shows image SSW-SAN-0002-11 where a partially dissolved gypsum can be seen in the center (bright area). ........................................................ 22 Figure 2.22. Sampling location for sample SSW-SAN-0006. Scale is a person’s legs in background. ................................................................................................... 24 Figure 2.23. Washed rock fragments. Field of view is 2.5 inches across. ............... 24 Figure 2.24. Close up image of matrix clay with jarosite poor and rich areas. ........ 25

vii

Figure 2.25. Image shows matrix clay with bands of jarosite cement running along grains. ........................................................................................................................ 26 Figure 2.26. Image of rutile (bright area) in a clay matrix ....................................... 26 Figure 2.27. Image displays cubic areas where pyrite has been dissolved in a rhyolite rock fragment. ........................................................................................................... 26 Figure 3.1. The effect of particle shape on friction angle for sand (Cho et al., 2006). Open circles and closed circles are for sand with sphericity greater than 0.7, and sphericity lower than 0.7, respectively. .................................................................... 31 Figure 3.2. Comparison chart for estimating particle shape and roundness (Powers, 1982). ........................................................................................................................ 34 Figure 3.3. (a) Distribution of sphericity and (b) distribution of roundness of particles in sample MIN-SAN-0001. ........................................................................ 37 Figure 3.4. Overall distribution of sphericity and roundness class for all samples. . 38 Figure 3.5. Slake durability of Rock piles and analogs. ........................................... 39 Figure 3.6. Point load strength for Rock piles. ......................................................... 40 Figure 3.7. A photo of the material from the surface of a Questa rock pile showing the angularity of the rock fragments compared to a spherical ball 50 mm in diameter…................................................................................................................. 41 Figure 4.1. Some of the steps followed for the wet sieving. ..................................... 46 Figure 5.1. Relationship between percent gravel and angle of internal friction (Goel, 1978). ........................................................................................................................ 52 Figure 5.2. Friction angles of 12-inch samples versus the friction angles of 2.4-inch samples showing the size effect in the direct shear test results. ............................... 55 Figure 5.3. Curve failure envelope for 12-inch dry sample (Golder Associates-Burnaby Laboratory) ................................................................................................. 59 Figure 5.4. Curve failure envelope for 2.4-inch dry samples (Golder Associates-Burnaby Laboratory) ................................................................................................. 60 Figure 5.5. Curve failure envelope for 2-inch dry samples (NMT) .......................... 60 Figure 5.6. Curve failure envelope showing the effect of particle size on shear strength for both 12-inch and 2.4-inch dry samples. ................................................ 61 Figure 5.7. Size effect on friction angle for all rock piles (normal stress of 50 to 702kPa). .................................................................................................................... 62 Figure 5.8. Size effect on cohesion for all rock piles (normal stress of 50 to 702kPa)…... .............................................................................................................. 62 Figure 6.1. Schematic diagram showing the behavior of soil when sheared using direct shear testing method. ...................................................................................... 65 Figure 6.2. Cohesion intercept versus water content for a) 12-inch samples, b) 2.4-inch samples. ............................................................................................................. 70 Figure 6.3. Friction angle versus water content for a) 12-inch samples, b) 2.4-inch samples. ..................................................................................................................... 71 Figure 6.4. Curved failure envelope showing the effects of moisture on shear strength of 12-inch samples ...................................................................................... 71 Figure 6.5. Curved failure envelope showing the effects of moisture on shear strength of 2.4-inch samples ..................................................................................... 72 Figure 7.1. Shear strength versus normal stress. Note the triaxial tests were 6 inch in diameter (not 4 inch as shown in the figure legend by Norwest Corporation). ........ 76

viii

ix

Figure 7.2. Friction angle of saturated rock piles and analogs ................................. 80

This thesis is accepted on behalf of the Faculty of the Institute by the following committee:

_________________________________________________________ Research Advisor

__________________________________________________________ Academic Advisor

__________________________________________________________ Committee Member

___________________________________________________________ Date

I release this document to the New Mexico Institute of Mining and Technology.

_____________________________________________________________ Student's Signature Date

1. Introduction

1.1. Background

Numerous geotechnical data have been collected for this project (URS

Corporation, 2003; Norwest Corporation, 2004, 2005; Gutierrez, 2006; Viterbo, 2007;

Boakye, 2008; McLemore et al., 2008), and many different geotechnical laboratory

techniques have been employed in these studies. In this study, five samples were

collected from the Questa rock piles and analog materials and tested using various

laboratory techniques to identify the geotechnical properties of these samples and the

relationships between the various geotechnical tests. The purpose of this thesis is to

compare the shear strength parameters of rock pile and analog materials with previous

results and different test methods and to determine the effect of weathering on

geotechnical properties of Questa mine material. The objective is to determine if the

shear strength of the Questa rock piles and weathering analogs are similar or different to

each other and to compare the results with previous work. Shear strength of the rock pile

materials depends upon the friction angle and cohesion of these materials. In this research

work three types of weathering analogs are recognized; alteration scars, debris flows, and

colluvium/weathered bedrock soil profiles.

Alteration scar, debris flow, and colluvium/weathered bedrock samples represent

hydrothermally-altered samples that have been weathering under similar surface

weathering processes as the rock piles, but for significantly longer periods of time than

the rock piles. These analog sites are analogous to the Questa mine site, because they are

similar in lithology, hydrothermal alteration assemblages, mineralogy, chemistry, and

1

clay types to the rock-pile samples and similar processes have occurred in them

(Campbell and Lueth, 2008; Graf, 2008). One hypothesis is since that the rock piles are

made up of the same rock types and mineralogies as the analogs, the analogs serve as

proxies of what the mineralogical, hydrological and geochemical composition will be as

the rock piles weather.

Most studies at Questa mine have used laboratory test methods to determine the

shear strength parameters of rock pile material with the use of disturbed samples because

it is less expensive, not as labor intensive and easier to perform. In majority of

geotechnical studies at Questa mine, existence of cohesion within the rock pile was not

considered thereby assuming zero cohesion. However, cohesion does affect the overall

stability of rock piles. In situ test shear method was previously performed on Questa mine

rock pile by Boakye (2008). He concluded that cohesion of rock pile material has

increased with age of the Questa rock piles at the test locations; this is believed to be due

to gravitational compaction of these materials since their placement, the presence of the

cementing minerals at the surface of the rock piles, and the weathering effects.

In this research work, the laboratory test methods are used to investigate the shear

strength (i.e. internal friction angle and cohesion) of the rock piles. The laboratory test

methods include 2-inch direct shear box testing that was conducted on dry samples at

NMT, 2.4-inch and 12-inch direct shear box testing that were used for testing the dry,

moist and saturated samples and also 4-inch diameter triaxial tests on saturated samples

that were conducted by Golder Associates-Burnaby Laboratory. Note that only disturbed

samples near in-situ test locations were examined. In addition to shear and triaxial tests,

2

particle shape analysis was performed to identify how weathering has affected the

particle shape of the rock fragments at Questa mine.

This project is part of the Questa Rock Pile Stability Study and is funded by

Chevron Mining Inc., the New Mexico Bureau of Geology and Mineral Resources

(NMBGMR) and the Department of Mineral Engineering, both at the New Mexico

Institute of Mining and Technology (NMT).

1.2 Site Description

The Questa Mine, now owned and operated by Chevron, is located five miles east

of the town of Questa, Taos County, New Mexico in the Taos range of the Sangre de

Cristo Mountains (Fig. 1.1). The site is located at approximately latitude 36o41’40” north

and longitude 105o30’20” west. The mine site is within the mountain zone mixed with

conifer forest with the main head frame located on the south-facing slopes of the Red

River Valley at approximately 2,438 m (8000 ft) above sea level.

Figure 1.1. Questa rock piles and other mine features

3

Mining operations first began at the site in the 1916 and open pit mining was

conducted between 1965 and 1983. During this period, mine rock associated with

development of the open pit was disposed of in a series of mine rock piles in the vicinity

of the open pit. This material was placed in nine rock piles (valley fill and slope) using

end dumping methods as shown in Figure 1.1. The rock piles, including Sugar Shack

South, Middle and Old Sulphur (or Sulphur Gulch South), were deposited along the

slopes and in mountain drainages along State Highway 38. These piles are referred to as

the “Front Rock Piles” or “Roadside rock piles”. These are some of the highest rock piles

in the United States. Since the rock piles were emplaced, a number of shallow-seated

failures, or slumps, have occurred at Questa and a foundation failure occurred at Goathill

North rock pile that resulted in sliding of the rock pile (Norwest Corporation, 2004; URS,

2003). Note that rock piles refer to structures consisting of non-ore material removed

during the extraction of ore. These materials, referred to in older literature as mine waste,

mine soils, overburden, sub-ore, or proto-ore, do not include the tailings material that

consists of non-ore waste remaining after milling. Robertson (1982) described mine rock

piles as some of the largest man-made structures at a mine by volume and height.

The deposit mined at Questa mine is a porphyry molybdenum deposit and formed

about 25 million years ago. Molybdenite (along with other minerals) precipitated from

magmatic-hydrothermal fluids to fill fractures and breccias and form the veins that

characterize the Questa ore bodies. These ore bodies are a small portion of large regional

zones of pyrite along the Red river valley. Overlying the pyrite zone is a zone of

weathered argillized rock extending along the Red river valley. This zone is up to 3,000

feet wide. The lithologies found in the Questa rock piles ranges from metarmophic rocks,

4

granite to shale, to limestone and sandstone, all of which are hydorthermally altered to

varying degrees: rhyolite tuff (Amalia Tuff), aplite porphyry (and other granitic rocks),

andesite porphyry and andesite to quartz latite porphyry flows. The regional geology can

be subdivided into five general tectonics periods: Preterozoic, Paleozoic Ancestral Rocky

Mountains, Laramide Orogeny, recent Rio Grande Rift Fill, and Rio Grande Rift

Volcanism (including the Questa caldera). The Rio-Grande Rift related volcanic rocks are

considered to be the most important rocks in the area. The volcanic rocks are extrusive

rocks ranging in composition from basaltic and quartz-latitic flow to welded ash flow

sheets of high silica alkaline rhyolite (Amalia tuff) that erupted from the Questa caldera

(Norwest Corporation, 2004; URS, 2003).

The climate at the mine site is temperate to semi-arid with mild summers and cold

winters with an average annual precipitation of about 20 inches (505 mm). The average

daily maximum temperatures range from 2.7º to 25ºC (37º to 77ºF) with average daily

minimum temperatures ranging from -14.4º to 5ºC (6º to 41ºF). During five months of the

year (November through March) the average monthly temperature is below freezing

(Robertson GeoConsultants Inc., 2000). The rainy season is during July and August.

Heavy localized rainfalls during July and August often cause flash floods and mudflows,

which sometimes block the highway between the Village of Questa and the Town of Red

River (Molycorp Inc., 2002).

1.3 Project Scope and Objectives

In July 2007, samples for this research work were collected from the same Questa

locations where in-situ shear tests were performed. The purpose of using samples

5

collected from the same locations where in-situ shear testing was completed is to be able

to compare the similarities or the differences in shear strength parameters of both rock

piles and analogs with other available shear test data. Minus 1-inch representative

samples were taken to a geotechnical laboratory for direct shear and consolidated

undrained triaxial tests. Some of the critical questions to be answered by this research

project are:

• How shear strength of Questa rock pile material is affected by the shear box size

and scalping of the material?

• How the shear strengths of Questa rock pile material are comparable to those of

older natural analogs?

• How moisture affects the shear strength of Questa material?

• How particle shapes of Questa material have been affected by weathering?

1.4 Sample Collection and Sample Preparation

Five samples collected from five different locations from the Spring Gulch, Sugar

Shack West rock piles and the analog sites, the Goat Hill debris flow and Questa Pit

alteration scar of the Questa mine were used for this study. The locations were selected

based on accessibility, safety, and near the locations where in situ direct shear tests were

performed (Boakye, 2008). No scalping was performed on the samples in the field other

than removing very large rock fragments that could not be placed in the 5 gallon buckets.

The samples were transported to the New Mexico Tech lab and air dried. Note that two

samples from the Sugar Shack rock pile were collected at two different locations with

6

different weathering intensity. The petrographic description of the samples is presented in

chapter 2.

In addition to the above samples, samples of minus 1-inch material from the same

locations were collected in the field and were placed into three 30-gallon plastic drums

and shipped to Golder Associates-Burnaby Laboratory for triaxial and direct shear

testing. A total of fifteen 30-gallon plastic drums of material were shipped to this

commercial lab (i.e. Golder Associates-Burnaby Laboratory).

1.5 Thesis organization

This thesis is organized into eight chapters as follows:

Chapter 1: Introduction to the general concept of the research project, the project

background and site description

Chapter 2: Mineralogy and Petrographic Description of Samples

Chapter 3: The effect of Weathering on Particle Shape of Questa Mine Materials, New

Mexico (Nunoo et al., 2009)

Chapter 4: Comparison of Wet and Dry Sieving using Particle size analyses

Chapter 5: Effect of Particle Size on Cohesion and Internal Friction angle

Chapter 6: Moisture- Softening Effect

Chapter 7: Comparison of Triaxial and Direct Shear Test Results of Questa Mine

Material

Chapter 8: Conclusions and Recommendation

7

2. Mineralogy and Petrographic Description of Samples

2.1 Description of Sample MIN-SAN-0002

2.1.1 Location

Sample MIN-SAN-0002 was collected from the top of the Goat Hill Debris Flow

at UTM 13N4059919, 452369E. (Fig. 2.1)

Figure 2.1. Photograph of sampling location of MIN-SAN-0002.

2.1.2 Hand Specimen Description

The hand sample is light brown in color before washing, and is dark brown to

grey in color after washing, depending on the clast examined. The shapes of the rock

fragments are sub-angular to sub-rounded, and the size ranges from gravel to clay size.

The rock fragments are poorly cemented in a clay matrix, and there appears to be iron

staining on some of the rock fragments. In outcrop, the sample is well graded with poor

sorting and has some cementation.

8

Figure 2.2. Photograph of washed rock fragments. Field of view is 2.5 inches across.

2.1.3 Petrographic Description

Petrographic examination of the thin section reveals that the sample is brown to

tan in color with fine sand- to gravel-sized rock fragments; the fragments are sub-rounded

and sub-discoidal in shape. The sample itself is composed of ~50% clay size and ~50%

rock fragments. The rock fragments are composed of ~95% intrusive rock and ~5% are

from the rhyolitic Amalia Tuff. The sample has undergone two types of alteration, with

~30% being QSP alteration and ~3% as argillic; the intensity of alteration is about

30/100. In the sample there is no trace of chlorite, epidote, or pyrite although there are

relict eroded pyrite cubes that have been replaced by jarosite in some rock fragments

(Figure 2.2 to Figure 2.5).

Figure 2.3. Sample overview image showing altered rock and mineral fragments in clay

rich soil matrix.

9

Figure 2.4. Highly altered quartz-rich clast (darker areas) with relict pyrite cubes

replaced by jarosite (brighter areas).

Figure 2.5. Altered rock & mineral fragments in clay rich matrix; note Fe-cemented

(goethite+ quartz) grain & (goethite+ jarosite) grain.

2.1.4 Laboratory Analyses

The laboratory results for mineralogy and chemistry are summarized in Tables 2.1

and 2.2.

Table 2.1. Various laboratory analyses for sample MIN-SAN-0002. pastepH 3.53 pasteCond (mS/cm) 0.16 pasteTDS 0.08 AP 4.17 NP 1.87 netNP -0.62 NPAP 0.62 QMWI (McLemore et al 2008a) 6 SWI (McLemore et al 2008a) 3

10

Table 2.2. Chemical and mineralogical analysis for sample MIN-SAN-0002. Chemistry WT. % MIN-SAN-

0002 Mineralogy %

SiO2 71.07 Quartz 45 TiO2 0.45 K-spar/orthoclase 13 Al2O3 12.74 Plagioclase 2 Fe2O3T 2.96 Albite FeOT 2.69 Anorthite - FeO 1.39 Biotite - Fe2O3 1.43 Clay - MnO 0.02 Illite - MgO 0.64 Chlorite 2 CaO 0.1 Smectite 1 Na2O 0.69 kaolinite 3 K2O 4.23 mixed layered - P2O5 0.12 Epidote - S 0 Magnetite - SO4 0.54 Fe oxides 1 C 0.3 Goethite - LOI 4.68 Hematite - Total 98.54 Rutile 0.4 Trace elements (ppm) Apatite 0.2 Pb 88.2 Pyrite - Th 13.1 Calcite 0.1 U 3.9 Gypsum 0.2 Y 35 Zircon 0.04 Sc 4.5 Sphalerite - V 56.8 Molybdenite - Ni 2.6 Fluorite - Cu 24.9 Jarosite 3 Zn 19.2 Copiapite - Ga 21.6 Organic C 1 La 53.4

11

2.2 Description of Sample QPS-SAN-0002

2.2.1 Location

The sample QPS-SAN-0002 was collected from the Questa pit scar in between 2

in-situ test pits. The sample is from a road cut with the UTM coordinates 13N4062551,

54146E (Fig. 2.6).

Figure 2.6. Photograph of sampling location for QPS-SAN-0002.


The hand sample is composed of rock fragments and clay sized material; rock

fragments range in size from gravel to sand. The clays that coat the rock fragments are

yellow to tan to brown in color. After rinsing off the clays, the rock fragments are white

to grey in color. The rock fragments are angular to sub-angular, poorly cemented, and do

not display any oxide staining. The rock fragments are also competent and do not break

by hand. In outcrop the sampling location is well graded, poorly sorted, and cemented by

gypsum.

12

Figure 2.7. Photograph of rock fragments. Field of view is 3 inches across.


In thin section, the sample is brown to grey in color, with fine sand- to gravel-

sized rock fragments that are sub-rounded and sub-discoidal in shape. The sample is

composed of ~82% rock fragments, ~13% iron oxides, ~4% gypsum, and trace amounts

of carbonate, jarosite, and chlorite. The rock fragments are composed of ~95% lithic and

~5% intrusive fragments. The sampled unit has undergone ~30% QSP alteration and 7%

propylitic alteration. Ninety-eight percent of the gypsum crystals in the sample are clear

and authigenic, whereas the chlorite in the sample appears as soapy green grains. Rock

fragments are cemented together primarily by Fe-oxides, and locally by jarosite (Figure

2.7 to Figure 2.10).

Figure 2.8. Fe-cemented rock fragments, dominantly quartz fragments, with some

jarosite cement.

13

Figure 2.9. Clay-rich clast with rock and minerals fragments cemented by clays.

Figure 2.10. Clay rich clast with relict pyrite cube replaced by jarosite.



and 2.4.

Table 2.3. Various laboratory analyses for sample QPS-SAN-0002. pastepH 2.84 pasteCond (mS/cm) 3.04 pasteTDS 1.52 AP 0 NP -0.52 netNP 0.52 NPAP -0.52 QMWI (McLemore et al 2008a) 7 SWI (McLemore et al 2008a) 4

14

Table 2.4. Chemical and mineralogical analysis for sample QPS-SAN-0002. Chemistry Wt. % QPS-

SAN-0002 Mineralogy %

SiO2 67.69 Quartz 42 TiO2 0.5 K-spar/orthoclase 3 Al2O3 13.66 Plagioclase 10 Fe2O3T 3.36 Albite - FeOT 3.06 Anorthite - FeO 1.61 Biotite - Fe2O3 1.59 Clay - MnO 0.02 Illite 32 MgO 0.93 Chlorite 3 CaO 0.68 Smectite 3 Na2O 1.24 kaolinite 0.9 K2O 3.71 mixed layered - P2O5 0.17 Epidote 0.01 S 0 Magnetite - SO4 0.97 Fe oxides 0.6 C 0.04 Goethite - LOI 5.13 Hematite - Total 98.1 Rutile 0.4 Trace elements (ppm) Apatite 0.3 Pb 32.6 Pyrite - Th 11.1 Calcite 0.3 U 5.1 Gypsum 0.8 V 68.9 detrit gypsum - Ni 7.8 auth gypsum - Cu 33.7 Zircon 0.04 Zn 33.7 Sphalerite - Ga 22.8 Molybdenite - Cr 48.3 Fluorite 0.2

15

2.3 Description of Sample SPR-SAN-0002

2.3.1 Location

Sample SPR-SAN-0002 was collected from the top of the Spring Gulch rock pile

at UTM coordinates 13N4062285, 455255E (Fig. 2.11).

Figure 2.11. Photograph of sampling location for SPR-SAN-0002. Tennis ball, at right,

is for scale.


In hand sample, the sample is brown in color, and after washing the hand sample

is dark brown in color. The sample’s lithology is 100% andesite and clay. The particle

size for the rock fragments ranges from cobble to clay, the fragments are angular to sub-

angular and there appears to be minor oxide staining on the outside of some fragments.

The clays associated with this sample do not cement the rock fragments together,

although smaller rock fragments are cemented to larger fragments in some instances. At

the sampling location, the sample is well graded with poor sorting.

16

Figure 2.12. Photograph of washed rock fragments from hand sample. Field of view is 3

inches across.


In thin section, the sample is brown to grey in color, has silt- to gravel- sized

particles that are sub-angular and sub-discoidal in shape. The lithology is 100% andesite

with 35% QSP and 7% propyllitic alteration. The rock is composed of ~80% rock

fragments, ~15% iron oxides, ~4% clays, ~1% gypsum, with trace amounts of pyrite and

epidote. Epidote is seen in trace amounts on rock surfaces, chlorite is described as soapy

green grains, and 98% of the gypsum crystals are clear and authigenic. The primary

cement in this sample is Fe-oxides with minor amounts of clay and jarosite. Pyrite

crystals have numerous small inclusions of apatite and quartz, and many pyrite crystals

display eroded and scalloped grain edges, oxidized rims, and goethite replacement


Figure 2.13. Overview image of rock fragments with soil matrix adhering to the larger

rock fragments.

17

Figure 2.14. A close-up image of a rock fragment with an Fe-oxide (goethite) coating. A small rounded jarosite grain can be seen in the matrix. The jarosite and Fe-oxides are the

brighter hues.

Figure 2.15. A close-up image displaying relict pyrite crystals (completely oxidized) that

are being replaced by jarosite and Fe-oxides.



and 2.6.

Table 2.5. Various laboratory analyses for sample SPR-SAN-0002. pastepH 4.22 pasteCond (mS/cm) 3.98 pasteTDS 1.71 AP 5.63 NP 18.96 netNP -13.33 NPAP 13.33 QMWI (McLemore et al 2008a) 7 SWI (McLemore et al 2008a) 2

18

Table 2.6. Chemical and mineralogical analysis for sample SPR-SAN-0002. Chemistry Wt. % SPR-

SAN-0002 Mineralogy %

SiO2 59.74 Quartz 25 TiO2 0.73 K-spar/orthoclase 21 Al2O3 14.39 Plagioclase 18 Fe2O3T 5.9 Albite - FeOT 5.36 Anorthite - FeO 3.27 Biotite - Fe2O3 2.3 Clay - MnO 0.11 Illite 14 MgO 2.96 Chlorite 8 CaO 2.31 Smectite 3 Na2O 2.79 kaolinite 0.9 K2O 3.5 mixed layered - P2O5 0.38 Epidote 2 S 0.18 Magnetite - SO4 0.46 Fe oxides 4 C 0.05 Goethite - LOI 4.22 Hematite - Total 97.72 Rutile 0.5 Trace elements (ppm) Apatite 0.9 Pb 20.7 Pyrite 0.3 Th 8 Calcite 0.4 U 3 Gypsum 2 Sc 13.8 detrit gypsum - V 122 auth gypsum - Ni 62.8 Zircon 0.03 Sphalerite - Molybdenite - Fluorite 0.5 Jarosite - Copiapite - Chalcopyrite -

19

2.4 Description of Sample SSW-SAN-0002

2.4.1 Location

Sample SSS-SAN-0002 was collected from the top of the Sugar Shack West rock

pile at the UTM coordinates 13N4060534, 453682E (Fig. 2.16).

Figure 2.16. Photograph of sampling location SSW-SAN-0002. Tennis ball (right) is for scale.


The hand sample consists of gravel to clay size particles, angular grain shapes,

and it is light brown in color. After rinsing the sample, the rock fragments are dark brown

in color. In outcrop it is well-graded with poor sorting. The rock fragments are 100%

andesite and the sample has associated clay. There is weak cementation for this sample,

although large rock fragments are not cemented together.

Figure 2.17. Photograph of washed rock fragments from sample SSW-SAN-0002. Field

of view is 2.5 inches across.

20


In thin section, the sample is brown-tan in color, has silt to gravel-sized rock

fragments, and the fragments are sub-angular and sub-discoidal in shape. The rock

fragments are 100% andesite, and have been altered ~25% by QSP and ~7% by propylitic

alteration, with an alteration intensity of about 25/100. There are traces of epidote

crystals on the outsides of rock fragments, chlorite is seen as soapy green grains, and

gypsum is 100% authigenic and clear. Rocks are cemented together by a combination of

matrix clay and jarosite cement. Pyrites in the sample are granular, cubic, and up to 50

microns in size; there are distinct “moats that surround some pyrites although in other

rock fragments the pyrites are unaltered. There is also a Na-bearing clay phase in this

sample, as well as small apatite crystals, and abundant altered magnetite and ilmenite


Figure 2.18. Figure shows image SSW-SAN-0002-02 showing a close-up of matrix

clay.

21

Figure 2.19. Figure shows image SSW-SAN-0002-03 with a high magnification. The

bright areas are jarosite and the “wavy” areas are clay.

Figure 2.20. Figure shows image SSW-SAN-0002-08 where multiple clay phases in an

altered rock fragment can be seen.

Figure 2.21. Figure shows image SSW-SAN-0002-11 where a partially dissolved

gypsum can be seen in the center (bright area).

22



and 2.2.

Table 2.7. Various laboratory analyses for sample SSW-SAN-0002. pastepH 2.9 pasteCond (mS/cm) 3.97 pasteTDS 1.98 AP 6.25 NP -17.23 netNP 23.47 NPAP -23.47 QMWI (McLemore et al 2008a) 7

SWI (McLemore et al 2008a) 4

Table 2.8. Chemical and mineralogical analysis for sample SSW-SAN-0002. Chemistry Wt. % SSW-SAN-0002 Mineralogy % SiO2 62.56 Quartz 32 TiO2 0.59 K-spar/orthoclase 8 Al2O3 14.28 Plagioclase 18 Fe2O3T 5.03 Albite - FeOT 4.57 Anorthite - FeO 2.69 Biotite 0.01 Fe2O3 2.07 Clay - MnO 0.07 Illite 23 MgO 1.79 Chlorite 5 CaO 1.29 Smectite 4 Na2O 2.38 kaolinite 0.9 K2O 3.78 mixed layered - P2O5 0.25 Epidote 0.01 S 0.2 Magnetite - SO4 1.26 Fe oxides 2 C 0.03 Goethite - LOI 5.44 Hematite - Total 98.95 Rutile 0.5 Trace elements (ppm) Apatite 0.3 Ba 1090 Pyrite 0.3 Rb 130.9 Calcite 0.09 Sr 388.7 Gypsum 2 Pb 30.9 detrit gypsum - Th 7.9 auth gypsum - U 3.5 Zircon 0.03 Zr 155.5 Sphalerite - Nb 9.5 Molybdenite - Y 12.5 Fluorite 0.2 Sc 8.9 Jarosite 4

23

2.5 Description of Sample SSW-SAN-0006

2.5.1 Location

Sample SSS-SAN-0006 was collected from the top of the Sugar Shack West rock

pile at UTM coordinates 13N4060822, 453975E (Fig. 2.22).

Figure 2.22. Sampling location for sample SSW-SAN-0006. Scale is a person’s legs in

background.


The hand sample is light yellow to light brown in color, and after rinsing the

sample is dark grey to off-white in color depending on the examined clast. The rock

fragments are poorly cemented by clays, are cobble to clay size, have angular to sub-

rounded shapes, and are mainly comprised of rhyolite (Amalia Tuff). In the field the

sample location was well graded with poor sorting.

Figure 2.23. Washed rock fragments. Field of view is 2.5 inches across.

24


In thin section, the sample is brown in color, rock fragments are silt to gravel

sized, and the fragments are sub-angular and sub-prismoidal in shape. The lithology of

the rock is 95% rhyolite (Amalia Tuff), 3% andesite, and 2% intrusive rocks. The sample

has undergone ~50% QSP and 1% argillic alteration, with an alteration intensity of about

50/100. The clay matrix of this sample is widely cemented with jarosite, and veins of

pure jarosite are observed. Pyrite in this sample displays a sugary texture, and there are

some cubic voids from where pyrite has been removed. Epidote is seen as small deeply

altered fragments, 95% of the gypsums observed are milky, small amounts of rutile are

observed as well as trace amounts of rutile. Authigenic gypsum appears as a coating on

some rock fragments (Figure 2.23 to Figure 2.27).

Figure 2.24. Close up image of matrix clay with jarosite poor and rich areas.

25

Figure 2.25. Image shows matrix clay with bands of jarosite cement running along

grains.

Figure 2.26. Image of rutile (bright area) in a clay matrix

Figure 2.27. Image displays cubic areas where pyrite has been dissolved in a rhyolite

rock fragment.

26



and 2.10.

Table 2.9. Various laboratory analyses for sample SSW-SAN-0006. pastepH 2.4 pasteCond 4.38 pasteTDS 1.49 AP 1.56 NP -2.53 netNP 4.09 NPAP -4.09 QMWI 7 SWI 4

Table 2.10. Chemical and mineralogical analysis for sample SSW-SAN-0006.

Chemistry Wt. % SSW-SAN-0006 Mineralogy % SiO2 65.71 Quartz 37 TiO2 0.47 K-spar/orthoclase 22 Al2O3 13.16 Plagioclase 2 Fe2O3T 3.7 Albite - FeOT 3.36 Anorthite - FeO 1.86 Biotite - Fe2O3 1.65 Clay - MnO 0.06 Illite 23 MgO 0.93 Chlorite 3 CaO 0.87 Smectite 0.9 Na2O 0.9 kaolinite 0.9 K2O 4.03 mixed layered - P2O5 0.12 Epidote 3 S 0.05 Magnetite - SO4 1.45 Fe oxides 0.6 C 0.03 Goethite - LOI 6.84 Hematite - Total 98.32 Rutile 0.4 Trace elements (ppm) Apatite 0.3 Ba 777 Pyrite 0.09 Rb 146.1 Calcite 0.3 Sr 189.1 Gypsum 1 Pb 70 detrit gypsum - Th 8 auth gypsum - U 3.6 Zircon 0.04 Zr 191.4 Sphalerite - Nb 16.9 Molybdenite - Y 28.2 Fluorite 0.3 Sc 6.8 Jarosite 5 V 66.6 Copiapite -

27

3. The Effect of Weathering on Particle Shape of Questa Mine

Material

3.1 Introduction

Research studies have shown that the shape of particles can significantly modify

the shear strength (i.e. friction angle) and deformational characteristics of granular

materials. Das (1983) reported that friction angle for medium dense sandy gravel and

medium dense sand have values ranging from 34º to 48º and 32º to 38º, respectively, due

to difference in particle shape. Morris (1959) studied the effects of particle shape on the

strength of aggregate material and concluded that “perfectly spherical particles give the

weakest aggregate, whereas chunky aggregates offer increase in strength up to a point

where the very roughness imposes limiting conditions of density (or void ratio), where

after additional irregularity of shape limits the obtainable density and the strength falls

off.”. Cho et al. (2006) concluded that the decrease in particle sphericity and/or roundness

leads to increase in the constant volume critical state friction angle.

The shape of particles reflects the material composition, the release of the grains

from the matrix, the formation history of the particles, transportation of the particles,

depositional environments of the material, and mechanical and chemical processes acting

on the particles, including weathering (Cho et al., 2006). Weathering is the set of physical

and chemical changes, up to and including disintegration of rock by physical, chemical,

and/or biological processes occurring at or near the earth’s surface (e.g., in the vadose

zone within approximately 300 ft of ground surface at temperatures less than or equal to

approximately 70°C) that result in reductions of grain size, changes in cohesion or

28

cementation, and change in mineralogical composition (modified from Neuendorf, et al.,

2005). Weathering can change the particle shape. For example, more weathered sands

tend to be rounder regardless of particle size (Cho et al., 2006), mostly due to mechanical

abrasion during transport. Particle shape of sediments and sedimentary rocks is described

by the following three parameters: form or sphericity, roundness/angularity and

smoothness/roughness (Krumbein, 1941; Barrett, 1980; Powers, 1982; Dodds, 2003;

Oakey et al., 2005). Sphericity (described as spherical, needle-like, tabular, and flat)

refers to the similarity of a particle to a sphere with equal volume. Roundness/angularity

describes the degree of abrasion of a particle as shown by the sharpness of its edges and

corners. It is expressed by Wadell (1932) as the ratio of the average radius of curvature of

the several edges or corners of the particle to the radius of curvature of the maximum

inscribed sphere or to one-half the nominal diameter of the particle.

Smoothness/roughness refers to the texture of the surface of the particle.

The purpose of this chapter is to (1) determine the particle shape of some of the

Questa mine rock pile and analog materials and (2) investigate the effect of weathering

on the shape of the particles. Analog materials are from sites in the vicinity of the Questa

mine that are similar in composition and weathering process as the rock piles, but are

older than the rock piles. Processes operating in the natural analogs share many

similarities to those processes in the rock pile, although certain aspects of the physical

and chemical system are different (Graf, 2008; Ludington et al., 2004). The alteration

scar (sample QPS-SAN-0001) and debris flow (sample MIN-SAN-0001) are considered

natural analogs for future weathering of the rock piles because they have undergone

hydrothermal alteration, weathering, and erosion since they were formed and could

29

represent the future weathering of the rock piles. The pit alteration scar is younger than

0.24 ± 0.12 Ma (40Ar/39Ar age of jarosite, Virgil Lueth, written communication,

November 2008) and the debris flow is younger than 4220 + 40 years (14C age of wood

from the debris flow, Virgil Lueth, written communication, November 2008).

3.2 Sample Description

The samples collected for this study were from the surface of two rock piles

(Sugar Shack West, Spring Gulch) and from within the interior of the Goathill North rock

pile and consisted of a heterogeneous mixture of rock fragments ranging in size from

~0.1 m to <1 mm in diameter in a finer-grained matrix. The talus/scree deposit from the

alteration scar is a rock fall or landslide material that formed when the natural slope of

the scar slid, possibly as a result of heavy rainfall. The Goathill debris flow is a

heterogeneous mixture of sediment that was deposited by a slurry of water and sediment

during flood erosion of the alteration scars (Ludington et al., 2004). Most rock fragments

within the sample exhibit varying degrees of hydrothermal alteration (Appendix 1) and

have been exposed to weathering since the construction of the rock pile (approximately

25-40 years). Petrographic descriptions and the mineralogy are summarized in chapter 2

and Appendix 1. Samples for the particle shape analysis were sieved from the original

samples and were >2 mm (no. 10 sieve) in size. Samples for point load and slake

durability testing were 4-10 cm in size.

30

3.3 Background

Cho et al. (2006) studied the effect of particle shape on internal friction angle, as

shown in Figure 3.1. Open circles are sand grains with sphericity >0.7 and closed circles

are sand grains with sphericity <0.7. The plot shows a negative correlation between

internal friction angle and roundness. As roundness varied from 0.1 (very angular) to 1

(well rounded), the internal friction angle decreased from approximately 40º to 28º.

Sphericity (described as spherical, needle-like, tabular, and flat) refers to the similarity of

a particle to a sphere with equal volume. Roundness/angularity describes the degree of

abrasion of a particle as shown by the sharpness of its edges and corners (Powers, 1982;

Dodds, 2003).

In summary, there appears to be a general agreement in the literature that the

more angular the particles, the higher the shear strength, if all other factors remained

constant (Cho et al., 2006; Leps, 1970; Marsal et al, 1965). Materials with higher shear

strength tend to be more stable. This is because more angular particles form an

interlocking that results in a more stable slope than more rounded particles.

Figure 3.1. The effect of particle shape on friction angle for sand (Cho et al., 2006). Open circles and closed circles are for sand with sphericity greater than 0.7, and

sphericity lower than 0.7, respectively.

31

3.4 Methodology

3.4.1 Sample Collection and Sample Preparation

In order to study the particle shape of the Questa rock piles and analogs materials,

five sieve sizes (2 inch, 1 inch, ½ inch, No.4 and No. 10 sieves) were employed to

separate the particles or rock fragments with different sizes. Samples were collected from

different locations (Goathill North, Spring Gulch, Sugar Shack West, debris flow and Pit

Alteration Scar) at the Questa mine. The alteration scar (sample QPS-SAN-0001) and

debris flow (sample MIN-SAN-0001) are considered as natural analogs for future

weathering of the rock piles because they have undergone hydrothermal alteration,

weathering, and erosion since they were formed <100,000 yrs to 4.5 million years ago

(determined using 40Ar/39Ar ages of jarosite from the alteration scars, Virgil Lueth, written

communication, August 2008). Note that samples from each rock pile or natural analog

have different identification numbers (e.g. QPS-SAN-0001 and QPS-SAN-0002), but are

from the same location. These numbers indicate sample splits of the same material that

are used for different purposes such as mineralogical and geotechnical testing. Some of

the sample locations were selected near locations where in situ direct shear tests were

performed (Fakhimi et al, 2008). Note that two samples from the Sugar Shack rock pile

and three samples from Goathill North rock pile were collected at different locations.

Twenty grains were selected from the retained material on each sieve. For some samples

less than 20 particles were left on the sieves with large opening. Some particles retained

on other sieves with smaller opening were used to compensate for shortage in the number

of larger particles and to make the total selected rock particles equal to 100 out of each

32

sample. Table 3.1 shows the number of particles and their sizes from each sample that

was used for particle shape analysis.

Sphericity and roundness can be estimated visually using comparison charts (Fig.

3.2). These charts make it easier to examine the influence of particle shape on

geotechnical properties (Powers, 1982; Cho et al, 2006). More sophisticated modeling

techniques using Fourier, fractal, or image analyses are available (Clark, 1987; Hyslip

and Vallejo, 1997; Smith, 1999; Bowman et al., 2001; Sukumaran and Ashmawy, 2001;

Alshibli and Alsaleh, 2004), but were not used in this study, because these methods were

not part of the scope of the project.

According to Folk (1955), an error associated with particle shape analysis by

visual methods is that a grain that seems to be subangular to one individual can seem

subrounded to another individual since each individual has different perspective of

visualizing things. He also emphasized that the error in terms of roundness was

significant as compared to the sphericity of the grains. In order to limit the errors

described by Folk (1955), four individuals, including two geologists and two mining

engineers described the particle shapes using the chart (Fig. 3.2) introduced by Powers

(1982). This approach reduced the bias in the description of particle shapes based on an

individual visual inspection.

Table 3.1. Samples and the particle sizes used for particle shape analysis. Sample ID Grain Size and Number of Particles

2-inch 1-inch 1/2-inch No. 4 sieve No.10 sieve MIN-SAN-001 (Debris Flow) 5 25 25 25 20

SPR-SAN-0001 (Spring Gulch) 5 25 25 25 20

SSW-SAN-001 (Sugar Shack West) 0 20 28 27 25

SSW-SAN-005 (Sugar Shack West) 0 25 25 25 25

33

QPS-SAN-0001 (Alteration Scar) 7 25 25 25 23

GHN-KMD-0017 (Goathill North) 0 0 33 33 34



Figure 3.2. Comparison chart for estimating particle shape and roundness (Powers, 1982).

The definitions we used for description of particle shapes are as follows:

• Subrounded – Particles have more round edges than sharp edges

• Rounded – Particles have round edges with no sharp edges

• Angular – Particles have sharp edges with no round edges

• Subangular – Particles have more sharp edges than round edges

• Spherical –Particles are similar to a ball or a sphere in three dimensions

• Discoidal – Particles are similar to a disc in one dimension

• Subdiscoidal – Particles are somewhat similar to the discoidal description

• Prismoidal – Particles are similar to a prism with long or needle-like shapes

• Subprismoidal – Particles are somewhat similar to the prismoidal description

34

Based on the chart in Figure 3.2, the sphericity and roundness of each grain was

determined and the results were analyzed as described in the next sections.

3.5 Description of Index Parameters of Rock Fragments

3.5.1 Point Load Test

The point load test is a simple test for estimating rock strength. The equipment

consists of a loading frame that measures the force required to split the sample and a

system for measuring the distance between the two contact loading points. The point load

test can be performed on samples with different shapes (Broch and Franklin, 1972). All

samples were classified according to the classification index in Table 3.2.

Table 3.2. Point load strength index classification (Broch and Franklin, 1972).

Is50 (MPa) Strength classification < 0.03 Extremely low 0.03 – 0.1 Very low 0.1 – 0.3 Low 0.3 – 1.0 Medium 1.0 – 3.0 High 3.0 – 10 Very high > 10 Extremely high

3.5.2 Slake Durability Test

The slake durability test was developed by Franklin and Chandra (1972) and

recommended by the International Society for Rock Mechanics (ISRM, 1979) and

standardized by the American Society for Testing and Materials (ASTM, 2001). The

purpose of the test is to assess the influence of physical weathering on rocks as simulated

by subjecting rocks to dry and wet cycles in a rotating drum, thereby measuring their

resistance to wear and tear and breakdown. Durability of rocks can be described as the

35

resistance to deterioration under physical weathering conditions over time. Slaking is

defined as the extent of swelling of rocks containing clay minerals when in contact with

water (Franklin and Chandra, 1972). The slake durability index (ID2) is a measure of

durability and provides quantitative information on the mechanical behavior of rocks

according to the amount of clay and other secondary minerals produced in them due to

exposure to climatic conditions (Fookes et al., 1971). All samples were classified

according to the classification index in Table 3.3. For each test, 10 rock fragments

weighing between 40 to 60 grams were used.

Table 3.3. Slake durability index classification (Franklin and Chandra, 1972). ID2 (%) Durability classification 0 – 25 Very low 25 – 50 Low 50 – 75 Medium 75 – 90 High 90 – 95 Very high 95 – 100 Extremely high

3.6 Results

Sample descriptions are summarized in chapter 2 and appendix 1. The samples

represent a range of lithologies and weathering intensities as determined by petrographic

and electron microprobe analyses, color, paste pH, presence or absence of pyrite, calcite,

gypsum, and jarosite.

Based on the visual comparison method (Powers, 1982), sphericity and roundness

of the rock fragments from the samples were obtained (Appendix 2). Figure 3.3 shows

the results of particle shape analysis for sample MIN-SAN-0001. Figure 3.3a suggests

that irrespective of particle size, the sphericity of a particle can be described as

subdiscoidal and subprismoidal. In Figure 3.3b, the angularity of particles is shown; the

majority of the particles are subangular to subrounded. Note that in this specific sample,

36

37

the finer particles are more angular. Similar bar graphs for the other samples have been

provided and are reported in the appendix 2.

Figure 3.4 shows the overall distribution of roundness and sphericity for all eight

samples. The bar graph in Figure 3.4 for each sample was obtained by taking the particle

shape analysis for all the 100 particles without considering the particle size. From Figure

3.4, it is clear that the majority of the particles are subangular. Note also that

subprismoidal and subdiscoidal particles are predominant in each sample. It is interesting

to note that the maximum number of spherical particles is in MIN-SAN-0001 (the sample

collected from the Goathill debris flow). The reason for more spherical particles in the

debris flow is probably a result of these materials being partially transported by water

(Ayakwah et al., 2008).

Grain Size vs Roundness(MIN-SAN-0001)

0

10

20

30

40

50

60

70

80

90

SUBANGULAR

ANGULAR

SUBROUNDED

ROUNDED

Roundness

Num

ber o

f Gra

ins

(%)

2-INCH1-INCH1/2-INCHNo. 4No. 10

Grain Size vs Sphericity (MIN-SAN-0001)

0

5

10

15

20

25

30

35

40

45

SUBDISCOIDA

2-INCH 1-INCH1/2-INCHNo. 4

L

DISCOIDAL

SPHERICAL

SUBPRISMOIDA

Sphericity

Num

ber o

f Gra

ins

(%)

No. 10

L

PRISMOIDAL (a) (b) Figure 3.3. (a) Distribution of sphericity and (b) distribution of roundness of particles in

sample MIN-SAN-0001.

0

10

20

30

40

50

60

70

80

90

100

SUB

AN

GU

LAR

AN

GU

LAR

SUB

RO

UN

DED

RO

UN

DED

SUB

DIS

CO

IDA

L

DIS

CO

IDA

L

SPH

ERIC

AL

SUB

PRIS

MO

IDA

L

PRIS

MO

IDA

L

ROUNDNESS SPHERICITY

Num

ber o

f gra

ins

(%)

MIN-SAN-0001SPR-SAN-0001SSW-SAN-0001SSW-SAN-0005QPS-SAN-0001GHN-KMD-0017GHN-KMD-0055GHN-KMD-0095

Figure 3.4. Overall distribution of sphericity and roundness class for all samples.

3.7. Index Parameters of Rock Fragments

3.7.1 Slake Durability Test

Table 3.4 is a summary of the slake durability results. The slake durability values

of the samples ranged from 89% to 99%. Similar results were obtained by Viterbo (2007)

and Gutierrez et al. (2008). Figure 3.5 illustrates the scatter of the slake durability index

of the rock piles and analogs.

Table 3.4. Summary of slake durability results.

Sample ID Slake Durability

(%) Durability classification MIN-SAN-0001 98.6 Extremely high QPS-SAN-0001 92.4 Very high SSW-SAN-0005 95.2 Extremely high SPR-SAN-0001 98.0 Extremely high SSW-SAN-0001 96.1 Extremely high GHN-KMD-0017 89.3 High GHN-KMD-0055 95.0 Very high GHN-KMD-0095 97.9 Extremely high

38

88

90

92

94

96

98

100

MIN-S

AN-0001

QPS-SAN-00

01

SSW-S

AN-0005

SPR-SAN-00

01

SSW-S

AN-0001

GHN-KMD-00

17

GHN-KMD-00

55

GHN-KMD-00

95

Rock piles

Slak

e D

urab

ility

(%)

Figure 3.5. Slake durability of Rock piles and analogs.

3.7.2 Point Load Test

Table 3.5 is a summary of point load strength results indicating point load

strength in the range of 0.6 to 5.0 MPa. Each point load test value in Table 3.5 is the

average of at least six tests. The point load test results (Fig. 3.6) suggest that the rock

fragments are strong except for rock fragments from sample GHN-KMD-0017. The high

point load strength and slake durability of rock pile and analog materials support the

particle shape analysis results. The higher the rock fragments strength, the greater their

resistance to weathering. Therefore, the particles resist to become rounded due to

weathering effects.

Table 3.5. Summary of point load test results. Sample ID Mean Point Load Strength

(MPa) Number of Tests Strength Classification

MIN-SAN-0001 5.04 9 Very high QPS-SAN-0001 3.50 6 Very high SSW-SAN-0005 2.03 8 High SPR-SAN-0001 2.08 6 High SSW-SAN-0001 2.51 6 High GHN-KMD-0017 0.61 6 Medium GHN-KMD-0055 1.56 6 High GHN-KMD-0095 n/a n/a n/a

39

0

1

2

3

4

5

6

MIN-S

AN-0001

QPS-SAN-00

01

SSW-S

AN-0005

SPR-SAN-00

01

SSW-S

AN-0001

GHN-KMD-00

17

GHN-KMD-00

55

Rock piles

Poin

t loa

d st

reng

th (M

Pa)

Figure 3.6. Point load strength for Rock piles.

3.8 Conclusion

Particle shape analyses were performed on samples collected from the Questa

rock piles and two analog materials (the Goathill debris flow and a talus/scree deposit

within the Pit Alteration Scar). Most rock fragments selected exhibit varying degrees of

hydrothermal alteration (Appendix 1) and have been exposed to weathering since the

construction of the rock pile (approximately 25-40 years). Petrographic analysis (chapter

2 and appendix 1) and high point load and slake durability indices indicate that, although

some of the samples are weathered, the rock fragments from rock piles and analogs are

quite strong and have relatively similar ranges in slake durability and point load indices

(Tables 3.4 and 3.5). The results of this study indicate that rock fragments in the selected

samples are mainly subangular, subdiscoidal and subprismoidal (Fig. 3.7). Note that the

sphericity and angularity of the rock fragments of the analog materials are similar to

those of the rock piles. This suggests that there is no relationship between particle shape

40

and short-term weathering (<100 years) at the test locations. Rock piles made of more

angular particles are more stable compared to rock piles with rounded particles, because

the more angular the material, the more interlocking of grains, which increases the

resistance to shearing and increases friction angle

Figure 3.7. A photo of the material from the surface of a Questa rock pile showing the

angularity of the rock fragments compared to a spherical ball 50 mm in diameter.

41

4. Comparison of Wet and Dry Sieving Particle Size Analyses

4.1. Introduction

Particle size analysis is performed to assess the particle size distribution of a

granular material and to understand its hydrological and structural properties. Two

general methods are considered for particle size analysis; dry sieving and wet sieving (or

wash sieving) analyses. The standard test method for laboratory determination of particle

size of the Questa material was performed in accordance with ASTM D422-63. The

standard operating procedure (SOP 33) for the test is presented in Appendix 3. This

method covers the quantitative determination of the distribution of particle size in soils.

Both wet and dry sieve analysis were employed.

4.2. Objective

The Questa rock pile materials are heterogeneous with particle sizes ranging from

minute clay-size fractions up to boulders (Gutierrez, 2006). An important question that

needs to be addressed is: How does the percentage of fines change between wet sieving

compared to that of dry sieving of Questa rock pile material? In general, higher

percentage of fines reduces the friction angle of rock-pile material that affects its

gravitational stability. To investigate this issue, wet and dry sieving were conducted on

the materials collected from the Questa mine rock piles and analogs. The results of this

specific study are reported in this chapter.

42

4.3. Previous Work

Particle size distribution within the Questa rock piles forms an important

component of the geotechnical characterization evaluation. Gutierrez (2006) performed

both dry and wet particle size analysis on Goathill North rock pile material, one of the

nine rock piles at the Questa mine site, in accordance to the ASTM (2002) and U.S.

Army Corps of Engineers (1970) standards. Gutierrez (2006) reported that there were

differences in the percent fines, i.e. the percentage passed sieve No. 200, when dry and

wet sieving were performed on the same material. The percent fines for the sample she

tested changed from 2.5% in dry sieving to 17.8% when wet sieving was conducted.

Gutierrez (2006) decided to use dry sieving analyses for her work. Graf (2008) also

performed both wet and dry sieving of samples from the alteration scars and found

similar results.

Norwest Corporation (2005) collected test pit samples as well as split-spoon

samples during drilling of a roadside rock pile (i.e. Sugar Shack South) that were tested

using wet sieving. The percent fines for samples ranged from 6% to 21% with an

average of 14%. The summary of the Norwest Corporation (2005) results is shown in

Table 4.1.

Boakye (2008) performed only dry particle size analysis and had percent fines (the

percentage of particles passing the No. 200 sieve) range from 0.1% to 14%. This wide

range in percentage of fines might be due to the heterogeneous nature of the rock pile and

analogs materials at Questa.

43

Table 4.1. Wet sieve analysis results on the samples collected from a bore hole in Sugar Shack South rock pile (Norwest Corporation, 2005).

4.4. Background

Grain size distribution is an important physical characteristic of a soil. The

gradation curve and the percentage of fines control the shear strength and compressibility

of soil. The hydraulic conductivity of granular soils can be related to D10.

It can be argued that wet sieving results in the “true” particle size distribution of

the material. The fine-sized particles in the rock-pile samples are weakly cemented with

the coarse particles or form moderately- to well-cemented clumps. The wet sieving

method allows for the separation of the fines from the coarse particles. The rock pile

material therefore will behave differently from the “true” particle size distribution and

dry sieving may result in a better representation of the unsaturated in situ rock pile

material behavior.

44

4.5. Methodology

Two representative splits were taken from each sample by the method of cone and

quartering (ASTM, 1987) for wet and dry sieving. The minimum mass of a sample used

for particle size analysis was related to the maximum particle size present in the bucket.

Table 4.2 shows different size particles and the corresponding minimum mass of sample

necessary to perform the test (U.S. Army Corps of Engineers, 1970).

Samples from the same locations were screened through 1-inch sieve in the field

and were sent to a commercial laboratory (i.e. Golder Associates-Burnaby Laboratory)

for additional geotechnical testing, including additional wet sieving analysis.

Table 4.2. The minimum sample weight required for particle size analysis based on the

size of the largest particle in the sample (U.S. Army Corps of Engineers, 1970). Nominal diameter of the largest

particle inches (mm) Approximate minimum mass

of the sample (g)

3 (76.2) 6000 2 (50.8) 4000 1 (25.4) 2000 ½ (12.7) 1000

0.18 (4.75) 200

0.079 (2) 100

For the dry sieving, the air-dried sample was weighed and then poured into the

top sieve (3-inch sieve) of the stack of sieves that was placed on a mechanical shaker.

The shaking time ranged from 45 to 60 minutes to assure that the retained material on

each sieve remained unchanged.

The first step in the sample preparation for wet sieving was weighing the air-dried

sample and then soaking it in the water for more than 60 minutes. Three sieves, No. 6,

No. 10, and No. 200 were put into a stack with a bucket placed underneath. The soaked

sample was poured into the top sieve (No. 6) of the stack, and was washed gently by hand

45

with running tap water to separate the fines from the coarse materials. The soaked

material was put into the sieves in several steps and then washed to allow better

separation of the particles. The fine material that passed through the No. 200 sieve was

collected in the bucket that was placed underneath the sieve stack. The wet sieving

process was conducted with caution to assure that this bucket did not overflow as this

causes loss of the fine material. The slurry collected in the bucket was left for a while for

the water to become clear. The clear water was gradually siphoned from the bucket

leaving behind the slurry. The fine material was then placed in the oven and the dry

weight of the fines was measured. The retained material on the sieves was oven dried as

well. Dry sieving was conducted on this coarse portion of the sample to result in the

gradation curve. Figure 4.1 shows some of the steps involved in this study (ASTM, 1971,

Head, 1980).

Washing the samples through sieves

Three sieves used Soil sample saturated in water

Oven dried samples after washing

Figure 4.1. Some of the steps followed for the wet sieving.

Water runs clean after washing tsample

he Retained samples after washing

4.6. Results

The wet and dry sieving test results are summarized in Table 4.3. These results

suggest that the percent fines of 1.9, 2.0, 3.1, 2.7, and 1.4 due to dry sieving were

46

increased to those of 12.6, 9.0, 18.1, 11.0, and 22.1 due to wet sieving (samples MIN-

SAN-0001, Debris Flow; QPS-SAN-0001, Pit Alteration Scar; SSW-SAN-0005, Sugar

Shack West Rock Pile; SPR-SAN-0001, Spring Gulch Rock Pile; and SSW-SAN-0001,

Sugar Shack West Rock Pile), respectively. The gradation curves for dry and wet sieving

for these five locations are reported in appendix 4.

The percent fines of minus 1-inch field samples reported by Golder was between

13% to 25%. The Golder Associates-Burnaby Laboratory results have been summarized

in Table 4.4 and the corresponding gradation curves are also reported in appendix 4. Note

that the percent fines in wet sieving conducted by Golder Associates-Burnaby Laboratory

are in general higher than those from NMT tests because larger particles were present in

NMT samples. The ranges and means of percent gravel, sand, and fines from Norwest

(Table 4.1), Golder Associates-Burnaby Laboratory and NMT are compared in Table 4.5.

Table 4.3. Summary table of particle size results conducted at New Mexico Tech. Note that two separate samples were collected from Sugar Shack West rock pile.

SAMPLE ID DESCRIPTION

PARTICLE SIZE, DRY SIEVING

PARTICLE SIZE, WET SIEVING

% GRAVEL

% SAND

% FINE % GRAVEL

% SAND

% FINE

MIN-SAN-0001 Debris Flow 52.4 45.7 1.9 53.2 34.3 12.6

QPS-SAN-0001 Alteration Scar 64.9 33.1 2.0 62.0 29.1 9.0

SSW-SAN-0005

Sugar Shack West 56.7 40.2 3.1 49.8 32.2 18.1

SPR-SAN-0001 Spring Gulch 71.4 25.9 2.7 66.4 22.6 11.0

SSW-SAN-0001

Sugar Shack West 46.4 52.3 1.4 33.2 44.7 22.1

47

Table 4.4. Summary table of particle size conducted by Golder Associates-Burnaby Laboratory

SAMPLE ID DESCRIPTION

PARTICLE SIZE (GRADATION) (-1-INCH)

WET SIEVING

PARTICLE SIZE (GRADATION) (-No. 4)

WET SIEVING %

GRAVEL %

SAND %

FINE %

GRAVEL %

SAND % FINE

MIN-SAN-0002 Debris Flow 62.3 20.7 17.0 0.0 72.6 27.4

QPS-SAN-0002 Alteration Scar 40.9 42.5 16.6 0.0 71.9 28.1

SSW-SAN-0006

Sugar Shack West 66.4 8.8 24.8 0.0 62.6 37.4

SPR-SAN-0002 Spring Gulch 41.8 44.9 13.3 0.0 68.2 31.8

SSW-SAN-0002

Sugar Shack West 39.2 43.5 17.3 0.0 71.6 28.4

Table 4.5. Ranges and means of gravel, sand, and fines from wet sieving of Questa materials reported by different laboratories.

Laboratory % Gravel %Sand %Fines Range Mean Range Mean Range Mean

Norwest 27-58 42.3 24-68 43.0 6-21 14.6 Golder 39.2-66.4 50.1 8.8-44.9 32.1 13.3-24.8 17.8 NMT 33.2-66.4 52.9 22.6-44.7 32.6 9.0-22.1 14.6

4.7. Discussion

The amount of cementation of fines to coarse particles and “clumping” in the

rock-pile materials was not quantitatively measured in this study, but visual observations

and electron microprobe analysis indicate that these processes are common in the

rockpiles.. The wet and dry sieving results reported here provide better insight in these

characteristics.

The differences in the fines from the particle size distribution between wet and

dry sieving relates to the behavior of the rock-pile materials. However, the wet sieving

results do not represent the behavior of the rock-pile materials as there is cementation of

48

fines to coarse particles and clumping of fines throughout the rock piles. Unless there is a

major change to the geohydrological regime in the piles, e.g. large zones of saturated

flow, the cementation and clumping will not be impacted.

4.8. Conclusion

Wet and dry sieve analyses were conducted on the material collected from the

rock piles and analogs at the Questa mine. It was observed that the wet sieving resulted in

higher percentages of fines compared to dry sieving. These results are consistent with

those from other laboratory tests. The increase in fines is a result of the presence of water

in wet sieving that dissolves the cementation and cohesion between particles and

disintegration of clumps. However, it is believed that the increased percentage of fines

observed in the wet sieve analysis may not represent the true behavior of the unsaturated

rock-pile material.

49

5. Effect of Particle Size on Cohesion and Friction Angle of Questa

Mine Material

5.1. Introduction

One of the fundamental objectives of soil mechanics is the determination of the

strength of soil. Knowledge of strength properties is needed to give proper answers to the

following questions (Pa’lossy et al., 1993):

• What is the allowable loading or force acting on a structure?

• What are the stability and bearing capacities of a structure embedded in subsoil?

• What is the deformation and displacement of loaded soil masses and structures?

The shear strength of a soil sample can be defined by equation 5.1,

(5.1) φστ tan'+= c

where c is the cohesion intercept (in kPa, MPa or psf), σ' is the effective stress ( in kPa,

MPa or psf), and φ is the internal angle of friction of the soil. Equation 5.1 is generally

referred to as the Mohr-Coulomb failure criterion.

Different shear box sizes were used to investigate the effect of particle size and

scalping on the measured friction angle and cohesion of Questa rock pile materials.

Scalping is the process of removing larger particles from soil samples by sieving the soil

through a particular sieve and testing on samples passed through the sieve. Scalping is

performed because the size of a laboratory shear box is normally smaller than the natural

rock fragment sizes in a rock-pile material sample. ASTM D3080-98 (2003) requires that

the largest rock fragment in a direct shear box to be smaller than 0.1 of the box width and

50

1/6 of the box height. Scalping of the rock-pile material changes the gradation curve of

the material and modifies its shear strength. To investigate the effect of scalping, direct

shear tests using 2 inch, 2.4 inch, and 12 inch wide shear boxes were conducted on the

air-dried samples of Questa Mine material. The results of these direct shear tests are

discussed in this chapter.

5.2. Previous Work

Vallerga et al. (1957) discussed a systematic study on the effect of particle shape,

size and surface roughness on the shear strength of granular materials using triaxial

testing. They used smooth, hard, and subrounded river gravel composed of recrystallised

sandstone. The subrounded particles were washed and sieved into four geometrically

similar grading. Angular particles used for this test were prepared by crushing 1.2 cm

(0.5 in) gravels into smaller angular particles and then sieving them into the required

grades similar to that of subrounded material. The tests were performed using confining

pressures of 2.4, 5.7 and 10 psi (16.5, 39.3 and 68.9 kPa, respectively). Under these test

conditions, they reported that there is no evidence of any particle size effect on the value

of the angle of internal friction. They also indicated that the sample with angular particles

has a higher angle of internal friction than subrounded material, the difference was as

large as 7.5 degrees at a void ratio of 0.80. They also noted from the results obtained

from the test that the range of size of the particles were too small to extrapolate to the 60

cm (24 in) particle size often used in a rock fill dam design.

51

Lewis (1956) concluded that the friction angle increases with increasing particle

sizes. He attributed this to increase in interlocking of particles and an increase in

dilatational tendencies of the larger particles.

Goel (1978) studied the effect of particle size on shear strength by increasing the

gravel content in shear test samples. The direct shear test results showed that by

increasing the gravel content of gravelly sand from 30% to 50%, the friction angle is

increased approximately 2o. Figure 5.1 shows the relationship between percent gravel and

the angle of internal friction.

Figure 5.1. Relationship between percent gravel and angle of internal friction (Goel, 1978).

Early studies by Lewis (1956) using direct shear tests showed that the angle of

internal friction increased from 34o to 38o with an increase in maximum particle size from

0.2 mm to 7.6 mm. He used drained direct shear test partly because of its simplicity and

also because of the availability of the 12-inch square machine, which allowed larger

stones to be tested than the triaxial test allowed for. He also used small direct shear boxes

of 6 cm (2.4-inches) square. The samples he used were composed of uniformly sized

52

crushed granite. Large increases in shear strength developed with increasing particle size.

Lewis (1956) states that the interlocking and interference of particles during shear have a

greater proportional effect with large size particles than with smaller sizes. This could be

due to the dilation being greater for larger particle sizes.

Bishop (1948) performed direct shear tests on two types of uniform soils with

different particle sizes. He reported no change in the shear strength due to the change in

particle sizes.

Koerner (1970) studied the effect of particle size on eight different saturated

quartz soils. The soils tested were in triaxial compression with samples 4-inch high and

4-inch in diameter at densities differing from loose through dense. He found an opposite

conclusion from Bishop (1948) in that the internal friction angle increases as the

maximum particle size decreases. The increase is significant with particle sizes less than

0.6 mm (medium sand and finer).

In summary, there is no common agreement on the effect of scalping on shear

strength after evaluating the literature on this topic. Internal friction angle can decrease

with increase in particles size while other studies have opposite views.

5.3. Previous Work on Shear Strength of Questa Mine Material

Gutierrez (2006) performed laboratory direct shear tests on the Goathill North

(GHN) rock-pile material from the Questa mine. The shear tests were conducted on the

air dried samples passed sieve No.4 and No. 6, using 2-inch and 4-inch shear boxes for

each sample. A displacement rate of 8.5×10-3 mm/sec (0.02 in/min) and a normal stress

varying from 159 to 800 kPa were used for the tests. Gutierrez (2006) reported a residual

53

friction angle (φr) ranging from 37º to 41º and a peak internal friction angle (φ) ranging

from 40º to 47º assuming zero cohesion, thus the Mohr-Coulomb failure envelope was

assumed to pass through the origin. Gutierrez (2006) did not observe any noticeable

change in the measured friction angle using 2 and 4-inch shear boxes.

URS Corporation (2003) reported the results of a number of shear tests on Questa

rock piles material, using 12-inch in width and 2.4-inch in diameter shear boxes that were

conducted by AMEC geotechnical laboratory and Advanced Terra Testing in Arizona

and Colorado, respectively. The tests were performed under different normal stresses

ranging from 119.7 to 478.8 kPa (2.5 to 10ksf) and 98.6 to 526.7 kPa (2.06 to 11 ksf) for

12-ich and 2.4-inch samples, respectively. The materials of minus 1.5 inch for the 12-

inch box and minus No. 4 sieve for 2.4-inch in diameter box were used for the shear tests.

The materials for 12-inch samples were prepared under dry densities ranging from 1522

to 1682 kg/m3 (95 to 105pcf) at water content ranging from 8 to 12%. The 2.4-inch

samples had dry densities of 1522 to 1890 kg/m3 (95 to 118 pcf) and water content of 10

to 14%. The friction angle and cohesion for 12-inch shear box ranged from 26° to 59o and

0 to 111 kPa, respectively. For the 2.4-inch shear box, the friction angle and cohesion

ranged from 30° to 41o and 0 to 34 kPa, respectively. Based on the above shear test

results, URS Corporation (2003) concluded that as larger particles are allowed in the

shear box, higher shear strengths are obtained; scalping of the Questa rock pile material

causes reduction in the measured shear strengths (Fig 5.2).

54

25

30

35

40

45

50

25 30 35 40 45 50

FRICTION ANGLE OF 2.4-INCH SAMPLES (DEGREES)

FRIC

TIO

N A

NG

LE O

F 12

-INC

H S

AM

PLES

(DEG

REE

S)

MOIST

SATURATED

Figure 5.2. Friction angles of 12-inch samples versus the friction angles of 2.4-inch

samples showing the size effect in the direct shear test results.

5.4. Methodology

Two types of shear boxes were used for testing i.e. a 12 × 12 × 9-inch shear box

and a circular shear box, 2.4 inch in diameter and about 1 inch in height. Each test series

included four individual shear tests using different normal stresses. For the 12-inch shear

box, minus 1-inch material was placed in the shear box and normal stresses of 50, 150,

250, and 400 kPa were used; each sample was compacted to a dry density of 1800 kg/m3

at dry, moist, and saturated conditions, corresponding to the water contents of 0.1 to 2%,

9 to 12% and 9 to 15%, respectively. For 2.4-inch diameter shear box, minus No.6 sieve

material was used under normal stresses of 50, 150, 400, and 700 kPa; the samples were

compacted to a dry density of 1700 kg/m3 at dry, moist, and saturated conditions

corresponding to the water content of 1 to 3%, 9 to 15%, and 9 to 19%, respectively. The

shear displacement rates for 12-inch and 2.4-inch shear tests were 0.01 mm/sec and 0.003

mm/sec, respectively.

55

Additional direct shear tests on the same air dried samples as tested by Golder

were conducted at New Mexico Tech (NMT), using a 2-inch square shear box. Minus

sieve No. 6 material was compacted at the dry density of 1700 kg/m3 and was subjected

to a shear displacement rate of 8.5 × 10-4 mm/sec. Two sets of shear tests were conducted;

in the first set, four shear tests with the normal stress in the range of 50 to 150 kPa and in

the second set, four shear tests with the normal stress of 50kPa to 700 kPa were

performed. All the shear tests were performed in accordance with the general guidelines

of ASTM D-3080 (1998).

5.5. Background

The well known Mohr-Coulomb failure criterion was used to interpret the shear

tests results. This failure criterion has two constants namely cohesion (c) and friction

angle (φ). Non-linear Coulomb failure criterion (equation 5.2) has been used to interpret

the shear strength of soil as well (Charles and Watts, 1980):

τ= Aσnb (5.2)

where A and b are material constants and σn is the applied normal stress in a shear test.

This failure criterion is especially more practical if a wide range of normal stresses is

being used; as the normal stress increases, the corresponding shear strength does not

grow linearly possibly due to particle breakage. This non-linear failure criterion was

successfully used by Linero et al (2007) in describing the shear strength of some rock

piles in Chile.

56

5.6. Results

Cohesion and friction angle parameters for each sample were obtained by drawing

the best fit straight line (failure envelope) through the four shear stress-normal stress

points in the shear strength vs. normal stress plot (Figs 5.7 and 5.8). The shear strength

parameters for air-dried samples from Golder Associates-Burnaby Laboratory and NMT

are reported in Table 5.1. The Golder lab results for 12-inch and 2.4-inch shear boxes are

in Tables 5.2 and 5.3, respectively. The nonlinear Coulomb failure criterion of the

samples from the Golder Associates-Burnaby Laboratory and NMT are shown in Figures

5.3 to 5.6. The detailed results are reported in appendix 5. These results suggest that:

• The measured peak friction angles for dry samples from the 12-inch box are

above 45° (Fig. 5.7) and are higher than those measured using 2.4-inch box,

suggesting the size effect in the measurement. Friction angles on the small shear

box are too conservative to be used in stability analysis. The reason for the lower

friction angles for the smaller box is the presence of higher percentage of fines in

the samples in this situation.

• The results in Table 5.1 show a fairly good agreement between the friction angles

obtained by Golder Lab and NMT.

57

Table 5.1. Golder Associates-Burnaby Laboratory (2.4-inch samples) and NMT (2-inch samples) shear test results for air-dried samples.

SAMPLE ID (GOLDER)

SAMPLE ID (NMT) DESCRIPTION

2.4 inch DRY, GOLDER LAB

RESULTS

2 inch DRY, NMT RESULTS

Normal Stress (50-700kPa)

Normal Stress (50-700kPa)

c (kPa) φ (degrees) c

(kPa) φ (degrees)

MIN-SAN-0002 MIN-SAN-0001 Debris Flow 32.2 39.3 26.1 39.7

QPS-SAN-0002 QPS-SAN-0001 Alteration Scar 54.4 38.5 33.4 38.4

SSW-SAN-0006 SSW-SAN-0005

Sugar Shack West 30.3 39.2 28.9 35.3

SPR-SAN-0002 SPR-SAN-0001 Spring Gulch 33.9 38.4 26.6 38.1

SSW-SAN-0002 SSW-SAN-0001

Sugar Shack West 64.4 35.8 17.7 41.6

Table 5.2. Shear strength parameters from direct shear tests using the 12-inch shear box.

Sample ID Description %FINE

12-inch dry

Cohesion (kPa)

Friction Angle

(degrees)

A (kPa**(1-

b)) b

MIN-SAN-0002 Debris Flow 17.0 45.8 45.7 3.98 0.79

QPS-SAN-0002

Alteration Scar 16.6 18.4 48.3 1.98 0.91

SSW-SAN-0006

Sugar Shack West 24.8 12.0 48.1 2.40 0.87

SPR-SAN-0002

Spring Gulch 13.3 11.5 52.1 2.24 0.91

SSW-SAN-0002

Sugar Shack West 17.3 29.4 47.0 3.48 0.81

Note A and b are shear strength parameters in equation 5.2

58

Table 5.3. Shear strength parameters from direct shear tests using the 2.4-inch shear box.

Sample ID Description %FINE

2.4-inch dry

Cohesion (kPa)

Friction Angle

(degrees)

A (kPa**(1-

b)) b

MIN-SAN-0002

Debris Flow 32.2 32.2 39.3 2.85 0.81

QPS-SAN-0002

Alteration Scar 32.2 54.4 38.5 6.14 0.69

SSW-SAN-0006

Sugar Shack West 42.3 30.3 39.2 2.32 0.84

SPR-SAN-0002

Spring Gulch 37.3 33.9 38.4 2.96 0.80

SSW-SAN-0002

Sugar Shack West 33.4 64.4 35.8 4.75 0.73

1;y=3.9826x0.7888

2 ;y=1.9817x0.9109

3 ;y = 2.3969x0.8688

5;y=3.4847x0.808

4;y=2.2382x0.9063

0

100

200

300

400

500

600

700

0 50 100 150 200 250 300 350 400 450

NORMAL STRESS (kPa)

PEA

K S

HEA

R S

TRES

S (k

Pa)

1-MIN-SAN-0002_12INCH DRY_GOLDER TEST2-QPS-SAN-0002_12INCH DRY_GOLDER TEST3-SSW-SAN-0006_12INCH DRY_GOLDER TEST4-SPR-SAN-0002_12INCH DRY_GOLDER TEST5-SSW-SAN-0002_12INCH DRY_GOLDER TEST

Figure 5.3. Curve failure envelope for 12-inch dry sample (Golder Associates-Burnaby

Laboratory)

59

1;y=2.8454x0.8114

3;y=2.3201x0.8448

4;y=2.9626x0.8013

5;y=4.7484x0.7282

2;y=6.142x0.6896

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700

NORMAL STRESS (kPa)

PEA

K S

HEA

R S

TRES

S (k

Pa)

1-MIN-SAN-0002_2.4INCH DRY_GOLDER TEST2-QPS-SAN-0002_2.4INCH DRY_GOLDER TEST3-SSW-SAN-0006_2.4INCH DRY_GOLDER TEST4-SPR-SAN-0002_2.4INCH DRY_GOLDER TEST5-SSW-SAN-0002_2.4INCH DRY_GOLDER TEST

Figure 5.4. Curve failure envelope for 2.4-inch dry samples (Golder Associates-Burnaby Laboratory)

1;y = 2.4189x0.8376

R2 = 0.998

2;y = 3.1464x0.7905

R2 = 0.9959

3;y = 2.5552x0.8065

R2 = 0.9968

4;y = 2.5371x0.8211

R2 = 0.997

5;y = 2.0025x0.8743

R2 = 0.9978

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700 800

NORMAL STRESS (kPa)

PEA

K S

HEA

R S

TRES

S (k

Pa)

1-MIN-SAN-0001(DRY_NMT TEST)2-QPS-SAN-0001(DRY_NMT TEST)3-SSW-SAN-0005(DRY_NMT TEST)4-SPR-SAN-0001(DRY_NMT TEST)5-SSW-SAN-0001(DRY_NMT TEST)

Figure 5.5. Curve failure envelope for 2-inch dry samples (NMT)

60

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700

NORMAL STRESS (kPa)

PEA

K S

HEA

R S

TRES

S (k

Pa)

MIN-SAN-0002_2.4INCH DRY_GOLDER TESTQPS-SAN-0002_2.4INCH DRY_GOLDER TESTSSW-SAN-0006_2.4INCH DRY_GOLDER TESTSPR-SAN-0002_2.4INCH DRY_GOLDER TESTSSW-SAN-0002_2.4INCH DRY_GOLDER TESTMIN-SAN-0002_12INCH DRY_GOLDER TESTQPS-SAN-0002_12INCH DRY_GOLDER TESTSSW-SAN-0006_12INCH DRY_GOLDER TESTSPR-SAN-0002_12INCH DRY_GOLDER TESTSSW-SAN-0002_12INCH DRY_GOLDER TEST

12-inch box

2.4-inch box

Figure 5.6. Curve failure envelope showing the effect of particle size on shear strength

for both 12-inch and 2.4-inch dry samples.

61

30

35

40

45

50

55

60

MIN-SAN-0002

QPS-SAN-0002

SSW-SAN-0006

SPR-SAN-0002

SSW-SAN-0002

Rock Piles

Fric

tion

Ang

le (d

egre

es)

12-inch dry sample(Golder)

2.4-inch dry sample (Golder)

2-inch dry sample (NMT)

Figure 5.7. Size effect on friction angle for all rock piles (normal stress of 50 to 702kPa).

0

10

20

30

40

50

MIN-SAN-0002

QPS-SAN-0002

SSW-SAN-0006

SPR-SAN-0002

SSW-SAN-0002

Rock Piles

Coh

esio

n in

terc

ept (

kPa)

12inch dry sample (Golder)

2.4inch dry sample (Golder)

2inch dry sample (NMT)

Figure 5.8. Size effect on cohesion intercept for all rock piles (normal stress of 50 to

702kPa).

62

5.7. Discussion and Conclusion

As explained in section 5.2 of this chapter, there is not a general agreement on the

effect of particle size on the shear strength of soil in the literature. Therefore, it was

decided to study the size effect of Questa mine material through direct shear testing using

different sample sizes as discussed above. The results suggest that indeed the Questa

mine material when tested show size effects; scalping the material causes reduction in the

measured friction angle. The effect of scalping on cohesion except for samples (MIN-

SAN-0002 and SSW-SAN-0002) indicates that larger air-dried samples show lower

cohesion intercept values (Fig. 5.8). This could be the result of having less fines material

in the larger samples. The 12-inch dry samples have higher resistance corresponding to

higher friction angle compared to the 2.4-inch dry sample (Fig. 5.7). The size effect

observed in this study is consistent with those reported by Kirkpatrick (1965), Koerner

(1970) and Marsal (1965a).

63

6. Moisture-Softening Effect

6.1. Introduction

Shear strength of geomaterials depends on many factors such as particle size

distribution, water content, and the weathering intensity of the grains. In particular, the

water content can modify the shear strength by changing the way that particles interact

with each other. If the water content of soil sample is high enough to saturate the sample,

pore pressure can develop during a shear testing that results in reduction of the shear

strength. For situations where soil is not completely saturated, positive pore pressure may

not develop, but still the presence of water between soil grains can act as a lubricating

agent that affects the strength of the material.

When a soil is sheared slowly in a drained condition giving enough time for

dissipation of pore pressures induced by shearing, the mechanical behavior of the

material can be either like a normally-consolidated (i.e. no softening) or overconsolidated

(i.e. with softening) material (Fig. 6.1). The behavior is mainly controlled by the amount

of fines material, the compaction density of the sample, and the amount of normal stress

in a shear test. Softening behavior is observed when the material is overconsolidated or

compacted at high density. The perfect plastic behavior is observed for materials with

either low compacted density or when the material is normally consolidated.

The softening behavior studied in this chapter is not concerned with the gradual

reduction in shear strength in the post peak in a shear test as shown in Figure 6.1, but it

addresses the reduction in peak strength due to the effect of soil moisture. In general

moist soil samples are weaker than the dry samples. This issue is studied in this chapter

64

by considering the direct shear test results on Questa mine materials that were tested

using different moisture contents. Result of shear tests on samples 2 inch, 2.4 inch, and

12 inch wide are studied.

Shear Displacement (mm)

Hardening - plastic behavior

Hardening – softening behavior

Shea

r Stre

ss (k

Pa)

Perfect plastic behavior

Softening behavior

Figure 6.1. Schematic diagram showing the behavior of soil when sheared using direct shear testing method.

6.2. Previous Work

Several studies have been performed to investigate the effect of moisture on shear

strength of soils. Direct shear test on rock fill materials was performed by Yu et al (2006)

to investigate the effect of moisture, particle size, gradation and shearing rate. The

material which was mainly gravels ranged from 2 mm to 9.4 mm in size and normal

stresses of 20 to 1000 kPa was used. The addition of 2% moisture to the gravels

indicated slightly lower shear strength than that for the dry gravels. The authors

concluded that water can lubricate the gravel grains and reduce the sliding friction

coefficient between particles that results in reduction in the peak shear stress (Yu et al,

2006).

65

Bishop and Eldin (1953) performed drained triaxial compression test on fine to

clean medium sand with wide range of densities under both dry and saturated conditions

using confining pressures of 101.3 to 5.35 psi (698.4 to 36.9 kPa). The results showed

that the internal friction angle for the dry sand was consistently higher than that of the

saturated sand.

Horn and Deere (1962) investigated the friction characteristics of minerals

performing direct shear on powdered muscovite under over dry, air dried and saturated

conditions at a shear rate of 0.003 in/min. The results showed that the internal friction

angle decreases with increasing water content. The internal friction angle was 27o, 24.2o

and 16.2o for the oven dried, air dried and saturated conditions, respectively. They cited a

personal communication by Terzaghi (1958), who described several failures that occurred

in rock-tunneling operations that could not be explained except by the reduction in the

shear strength of the rock. There would have been a reduction in friction resistance along

the joints if moisture had been introduced hence reducing shear strength of the rock that

can cause failure.

Isotropically consolidated triaxial compression tests with confining pressures

ranging from 1 to 140 kg/cm2 (98 to 13729 kPa) with constant strain rate of 0.6% / min

were used to investigate the effect of water on the behavior of Antioch sand at relative

density of 100. The soil was tested under three conditions of moisture; oven dried, air

dried, and saturated. The results of the test indicated that the oven dried sample is 35%

stronger than the saturated samples with the air dried sample falling between the two

extremes. Data on changes in volume suggested more dilation in the oven dried sand than

the saturated sand (Lee et al, 1967).

66

In general, water can act as a lubricating agent between the rock particle surfaces

and change the strength and compressibility of rock fill material. Studies by Zellar and

Wullimann (1957) on non-cohesive gravelly sand and boulder material have shown that

the shear strength decreases with increasing the water content; a shear strength loss of

10% to 15% was found as the rock fill material became wet at all densities.

6.3. Background

The well known Mohr-Coulomb failure criterion was used to interpret the shear

tests results. This failure criterion has two constants, namely cohesion intercept (c) and

friction angle (φ). The cohesion intercepts and friction angles are reported separately for

the 2-inch, 2.4-inch and 12-inch shear boxes as different sample sizes have different

amount of fines material that affect their shear strength. The curved failure envelope is

used as well and is described in section 5.5 of chapter 5.

6.4. Methodology

Direct shear tests were performed on the rock-pile and analog samples of the

Questa mine. Details of the sample locations and the method employed are described in

chapter 5. The entire shear tests were performed in accordance with the general

guidelines of ASTM (1998) D-3080. The standard operating procedure (SOP 50) for the

test is presented in Appendix 3.

67

6.5. Results

Direct shear tests were performed on dry, moist and wet samples for both 2.4-inch

and 12-inch width boxes by Golder Inc. The shear stress versus shear displacement, and

normal (vertical) displacement versus shear displacement for the direct shear tests are

reported in Appendix 5. It is clear from the results in Appendix 5 that under the given

normal stresses and the dry densities used, the material behavior is close to a perfectly

plastic material, i.e. the post peak softening is negligible.

The Golder results for 12-inch and 2.4-inch shear boxes are shown in Tables 6.1

and 6.2, respectively. These results suggest that:

• The measured peak friction angles from the 12-inch box are greater than 40°

except for the two moist and wet samples collected from the Sugar Shack West

rock pile.

• Moist and wet samples showed lower friction angles compared to those from dry

samples, suggesting moisture softening of Questa rock pile materials.

Figures 6.2 and 6.3 illustrate the relationship between cohesion intercept and friction

angle at different water content. The cohesion intercept and friction angles reported in

these figures were obtained by using the four shear strength-normal stress points in

plotting the Mohr-Coulomb failure envelope, corresponding to normal stresses of 50

to700 kPa for 2.4-inch and 50 to 400 kPa for 12-inch. It is clear from Figure 6.3 that the

friction angle reduces as the water content increases. Douglas and Bailey (1982) showed

that the friction angle of rock-pile material reduces as water content increases. The

situation is similar for the case of cohesion intercept, even though the data is more

68

scattered in this case, especially for the cohesion intercept values from the 12-inch shear

box.

Curved failure envelopes of Figures 6.4 and 6.5 suggest that shear strength reduces

with increasing water content of the samples.

Table 6.1. Shear strength parameters from direct shear tests using the 12-inch shear box. A Water

Content (%) c

(kPa) φ (degrees) (kPa**(1-

b)) b Sample ID Description Condition


QPS-SAN-0002

Alteration Scar

Dry

0.5 18.4 48.3 1.98 0.91

SSW-SAN-0006

Sugar Shack West 0.4 12.0 48.1 2.40 0.87

SPR-SAN-0002 Spring Gulch 11.5 52.1 2.24 0.91 1.9

SSW-SAN-0002

Sugar Shack West 0.2 29.4 47.0 3.48 0.81


QPS-SAN-0002

Alteration Scar 9.6 35.5 44.9 3.36 0.81

SSW-SAN-0006

Sugar Shack West Moist 11.4 41.3 36.8 3.54 0.76


SSW-SAN-0002

Sugar Shack West 9.9 37.1 43.5 4.40 0.75


QPS-SAN-0002

Alteration Scar 11.4 20.8 41.7 1.67 0.91

SSW-SAN-0006

Sugar Shack West 12.4 18.0 34.2 Wet 1.25 0.91


SSW-SAN-0002

Sugar Shack West 11.8 13.7 42.6 2.36 0.84

69

Table 6.2. Shear strength parameters from direct shear tests using the 2.4-inch shear box.

Sample ID Description Condition Water Content (%)

c (kPa) φ (degrees)

A (kPa**(1-b))

b

MIN-SAN-0002 Debris Flow

Dry

1.5 32.2 39.3 2.85 0.81

QPS-SAN-0002 Alteration Scar 2.3 54.4 38.5 6.14 0.69 SSW-SAN-

0006 Sugar Shack West 2.9 30.3 39.2 2.32 0.84

SPR-SAN-0002 Spring Gulch 2.5 33.9 38.4 2.96 0.80 SSW-SAN-

0002 Sugar Shack West 2.1 64.4 35.8 4.75 0.73


Moist

9.9 29.3 38.4 1.70 0.89


0006 Sugar Shack West 12.0 47.7 34.0 3.68 0.75


0002 Sugar Shack West 11.4 38.8 35.8 2.47 0.82


Wet

13.0 20.2 35.9 1.66 0.88


0006 Sugar Shack West 16.6 22.9 30.7 1.32 0.89


0002 Sugar Shack West 14.5 26.1 35.6 1.68 0.88

2.4 INCH SHEAR BOX

0

20

40

60

0 2 4 6 8 10 12 14 16 18

Water content (%)

Coh

esio

n in

terc

ept (

kPa)

MIN-SAN-0002QPS-SAN-0002SSW-SAN-0006SPR-SAN-0002SSW-SAN-0002

12 INCH SHEAR BOX

0

20

40

60

0 2 4 6 8 10 12 14 16 18

Water content (%)

Coh

esio

n in

terc

ept (

kPa)


(a) (b)

Figure 6.2. Cohesion intercept versus water content for a) 12-inch samples, b) 2.4-inch samples.

70

2.4 INCH SHEAR BOX

30

40

50

60

0 2 4 6 8 10 12 14 16 18

WATER CONTENT (%)

FRIC

TIO

N A

NG

LE (

DEG

REE

S)


12 INCH SHEAR BOX

30

40

50

60

0 2 4 6 8 10 12 14 16 18

WATER CONTENT (%)

FRIC

TIO

N A

NG

LE (

DEG

REE

S)

MIN-SAN-0002QPS-SAN-0002SSW-SAN-0006SPR-SAN-0002

SSW-SA N-0002

(a) (b)

Figure 6.3. Friction angle versus water content for a) 12-inch samples, b) 2.4-inch samples.

0

100

200

300

400

500

600

700

0 50 100 150 200 250 300 350 400 450

NORMAL STRESS (kPa)

PEA

K S

HEA

R S

TRES

S (k

Pa)

MIN-SAN-0002_12INCH DRY_GOLDER TESTQPS-SAN-0002_12INCH DRY_GOLDER TESTSSW-SAN-0006_12INCH DRY_GOLDER TESTSPR-SAN-0002_12INCH DRY_GOLDER TESTSSW-SAN-0002_12INCH DRY_GOLDER TESTMIN-SAN-0002_12INCH MOIST_GOLDER TESTQPS-SAN-0002_12INCH MOIST_GOLDER TESTSSW-SAN-0006_12INCH MOIST_GOLDER TESTSPR-SAN-0002_12INCH MOIST_GOLDER TESTSSW-SAN-0002_12INCH MOIST_GOLDER TESTMIN-SAN-0002_12INCH WET_GOLDER TESTQPS-SAN-0002_12INCH WET_GOLDER TESTSSW-SAN-0006_12INCH WET_GOLDER TESTSPR-SAN-0002_12INCH WET_GOLDER TESTSSW-SAN-0002_12INCH WET_GOLDER TEST

Figure 6.4. Curved failure envelope showing the effects of moisture on shear strength of

12-inch samples

71

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700

NORMAL STRESS (kPa)

PEA

K S

HEA

R S

TRES

S (k

Pa)

MIN-SAN-0002_2.4INCH DRY_GOLDER TESTQPS-SAN-0002_2.4INCH DRY_GOLDER TESTSSW-SAN-0006_2.4INCH DRY_GOLDER TESTSPR-SAN-0002_2.4INCH DRY_GOLDER TESTSSW-SAN-0002_2.4INCH DRY_GOLDER TESTMIN-SAN-0002_2.4INCH MOIST_GOLDER TESTQPS-SAN-0002_2.4INCH MOIST_GOLDER TESTSSW-SAN-0006_2.4INCH MOIST_GOLDER TESTSPR-SAN-0002_2.4INCH MOIST_GOLDER TESTSSW-SAN-0002_2.4INCH MOIST_GOLDER TESTMIN-SAN-0002_2.4INCH WET_GOLDER TESTQPS-SAN-0002_2.4INCH WET_GOLDER TESTSSW-SAN-0006_2.4INCH WET_GOLDER TESTSPR-SAN-0002_2.4INCH WET_GOLDER TESTSSW-SAN-0002_2.4INCH WET_GOLDER TEST

Figure 6.5. Curved failure envelope showing the effects of moisture on shear strength of

2.4-inch samples

6.6. Discussion and Conclusion

Shear tests were conducted on samples collected from the rock piles and analogs

at the Questa mine using different water content values. It appears that there are

evidences to support the moisture softening of Questa Mine material. The peak friction

angle of the materials from Questa rock piles and analogs reduces as the water content

increases.

72

7. Comparison of Triaxial and Direct Shear Test Results of Questa

Mine Material

7.1. Introduction

A triaxial compression test is normally used to measure the shear strength of a soil

under controlled drainage conditions. In a conventional triaxial test, a cylindrical sample

of soil encased in a rubber membrane is placed in a triaxial compression chamber,

subjected to a confining fluid pressure, and then loaded axially to failure. Connections at

the ends of the sample permit controlled drainage of pore water from the sample.

There are 3 types of triaxial tests:

1. Unconsolidated-undrained test, which is also called the quick test (abbreviations

commonly used are UU and Q test). This test is performed with the drain valve

closed for all phases of the test. Axial loading is commenced immediately after

the chamber pressure σ3 is stabilized.

2. Consolidated-undrained test, also termed consolidated-quick test or R test

(abbreviated as CU or R). In this test, drainage or consolidation is allowed to take

place during the application of the effective confining pressure σ´3. Loading does

not commence until the sample ceases to drain (or consolidate). The axial load is

then applied to the sample, with no attempt made to control the formation of

excess pore pressure. For this test, the drain valve is closed during axial loading,

and excess pore pressures can be measured.

3. Consolidated-drained test, also called slow test (abbreviated as CD or S). In this

test, the drain valve is opened and is left open for the duration of the test, with

73

The focus on this study is on consolidated undrained test. The advantages of a

triaxial test over a direct shear test are:

• Progressive effects are less significant in a triaxial test.

• The measurement of sample volume changes is more accurate in a triaxial test.

• The complete state of stress is assumed to be known at all stages during a triaxial

test.

• The triaxial machine is more adaptable to special requirements.

The advantages of a direct shear test over triaxial tests are:

• Direct shear machine is simpler, cheaper and faster to operate.

• A thinner soil sample is used in the direct shear test, thus facilitating drainage of

the pore water from a saturated sample.

7.2 Previous Work

Triaxial testing of soil and rock fill samples is a well established approach to

obtain shear strength parameters under well-controlled stress and drainage conditions

(Bishop and Henkel, 1962, Leps, 1970, Marsal, 1973). Recent testing for large scale tests

(1 m diameter by 2 m tall triaxial samples) on mine rock-pile materials have been

reported by Linero, et al. (2007) and Valenzuela, et al. (2008). The major advantage of

74

testing large-scale samples is that larger particles can be included in the testing that better

simulate field conditions.

Uhle (1986) performed statistical evaluations on a large range of laboratory test

results obtained for rock-filled dam materials and concluded that:

• Axial and volumetric strains at failure and particle breakage, tend to increase

with: (1) increasing uniformity of a rock fill sample, (2) increasing grain size of

uniform rock fill, (3) increasing angularity of particles, (4) increasing void ratio,

(5) decreasing strength of rock fill material, (6) increasing confining pressure, (7)

increasing normal stress at a given confining pressure, (8) decreasing compressive

strength of intact rock from which rock fill is obtained, and (9) increasing the rock

fill saturation.

• Angle of internal friction φ, tends to increase with : (1) increasing compressive

strength of intact rock from which rockfill is obtained, (2) increasing coefficient

of uniformity of the rockfill, (3) increasing or decreasing maximum particle size

(no universal conclusion) , (4) increasing particle angularity, (5) decreasing void

ratio, (6) decreasing confining pressure, (7) decreasing rockfill saturation, (8)

increasing particle surface roughness.

Dawson and Morgenstern (1998) evaluated the liquefaction behavior of three

kinds of carbonaceous waste rock materials under saturated conditions where static

liquefaction had been identified as a failure mode resulting in run outs over long

distances. The test resulted in a typical strain-weakening (also known as strain softening)

under the undrained isotropic condition indicating that despite differences in waste

material, the steady-state friction angles were basically the same and close to the field

75

0

200

400

600

800

1000

1200

1400

1600

0 500 1000 1500 2000 2500

Normal Stress (kPa)

Shea

r Stre

ngth

(kP

a)

Small Box Direct Shear (2.4'')

Large Box Direct Shear (12'')

Triaxial (4'')

Φ' = 36°

gradation waste dump angle of repose value of 37-38o. In evaluating the liquefaction of

sands and other finer-grained materials, Jefferies and Been (2006) emphasized the

importance of loose contractive behavior of such materials as a pre-requisite to

liquefaction.

Norwest Corporation (2005) reported the results of isotropically consolidated

undrained triaxial tests performed by Thurber Engineering Ltd using a 6-inch diameter

triaxial apparatus. Minus 1.5-inch rock-pile material was used and compacted to a target

density of 1922.3 kg/m3 (120 pcf) at 5 and 9% water contents. Effective confining

pressures of 68.9, 344.7, 689.5, 1379, and 2757.9 kPa (10, 50, 100, 200 and 400 psi) were

used for the tests. Figure 7.1 summarize the results of direct shear tests and triaxial tests

reported by Norwest (2005) suggesting higher friction angles for the 12-inch shear box.

The results of direct shear tests (2.4-inch wide) and triaxial tests are relatively consistent.

Figure 7.1. Shear strength versus normal stress. Note the triaxial tests were 6 inch in diameter (not 4 inch as shown in the figure legend by Norwest Corporation).

76

7.3 Background

The well known Mohr-Coulomb failure criterion was used to interpret the shear and

triaxial tests results. This failure criterion has two constants, namely cohesion intercept

(c) and friction angle (φ). The cohesion intercepts and friction angles are reported

separately for the 2.4-inch and 12-inch shear boxes and 4-inch diameter triaxial apparatus

as different sample sizes have different amount of fines material that affect their shear

strength.

7.4 Methodology

Sample collection and preparation are described in section 1.4 in chapter 1. All

triaxial samples 4-inch in diameter and 8-inch in height were saturated and tested under

consolidated undrained (CU) condition with pore pressure measurement. The maximum

particle size in the samples was minus 0.5-inch. Each test series included four individual

shear tests using different total cell pressures ranging from 38 to 678 kPa. The applied

axial strain rate was 2%/hour. The samples were compacted to a dry density of 1800

kg/m3 for testing.

7.5. Results and Discussion

The triaxial tests were conducted by Golder Associates-Burnaby Laboratory. The

triaxial test results are shown in Appendix 6 where axial stress and pore pressure versus

axial strain are reported. Notice that the samples show no or little softening behavior

under the applied confining pressures. To obtain the cohesion intercept and friction angle

of each sample, the effective axial stress (σ´1) and the effective confining stress (σ´3)

77

corresponding to the situation that the ratio of q to p´ is maximum is obtained and used

for both approaches where q and p´ are defined as (σ´1 - σ´3)/2 and (σ´1 + σ´3)/2

respectively. Two approaches were used in showing the results. In the first approach,

Mohr circles are plotted while in the second approach axial stresses versus confining

pressures are sketched using the best fit line (Appendix 6). Table 7.1 summarizes the

effective friction angles and cohesion intercepts obtained using these two approaches.

Note that the friction angles from these two approaches are close to each other while the

cohesion intercept values show large differences. The reason for these differences in

cohesion intercept is that the Mohr circles are not all tangent to the failure envelope

(Appendix 6).

Table 7.1. Summary of Golder Triaxial Test Results. σ´1= effective axial stress, σ´3= effective confining stress, q = (σ´1 - σ´3)/2, p´ = (σ´1 + σ´3)/2.

Sample ID Test q/p'MAX σ´1(kPa) σ´3(kPa) Best fit Mohr Circle φ' (deg) c' (kPa) φ' (deg) c' (kPa)

MIN-SAN-0002

1 1.04 45.79 -0.96

39.3 3.4 41.0 10.0 2 0.69 123.64 22.76 3 0.51 241.49 77.52 4 0.68 626.95 120.74

QPS-SAN-0002

1 0.78 73.31 9.11

40.4 7.9 40.0 10.0 2 0.75 132.26 18.48 3 0.67 333.82 66.54 4 0.66 728.74 147.15

SSW-SAN-0006

1 0.78 54.63 6.78

39.4 10.8 40.5 4.0 2 0.91 102.38 5.01 3 0.66 296.27 61.49 4 0.66 654.67 133.86

SPR-SAN-0002

1 1 35.86 0.09

43.2 5.8 43.0 5.0 2 0.73 110.75 17.03 3 0.7 322.58 56.28 4 0.7 653.32 116.62

SSW-SAN-0002

1 1.12 40.22 -2.28

41.5 5.3 41.0 15.0 2 0.81 107.3 10.94 3 0.56 180.75 50.63 4 0.69 677.64 125.37

78

Figure 7.2 shows internal friction angle values from the triaxial and direct shear tests

under saturated conditions. The direct shear tests were conducted using 2.4-inch and 12-

inch samples by Golder laboratory. This figure suggests that the friction angles from 12-

inch shear box and the triaxial cell are consistent (except for tests on sample SSW-San-

0006) while the small shear box results in lower friction angles. In Table 7.2, the percent

fines for different samples are compared indicating that smaller samples contain higher

percent fines. This explains the reason for lower friction angles obtained for 2.4-inch

samples emphasizing the importance of size effect in shear testing of Questa mine

material.

Table 7.2. Percent Fines of Samples of Questa Mine Material Obtained from Golder Laboratory Results

Percent Fines

Sample ID 12-inch Shear Box

4-inch triaxial samples

2.4-inch Shear Box

MIN-SAN-0002 17 19.9 32.2 QPS-SAN-0002 16.6 20 32.2 SSW-SAN-0006 24.8 28.2 42.3 SPR-SAN-0002 13.3 18.4 37.3 SSW-SAN-0002 17.3 19.6 33.4

79

30

33

36

39

42

45

MIN-SAN-0002

QPS-SAN-0002

SSW-SAN-0006

SPR-SAN-0002

SSW-SAN-0002

Rock Piles

Fric

tion

Ang

le (d

egre

es)

Friction Angle (degrees) 12"Friction Angle (degrees) 2.4"Friction Angle (degrees) Triaxial (4")

Figure 7.2. Friction angle of saturated rock piles and analogs

80

8. Conclusions and Recommendation

8.1 Conclusion

In this research work, geotechnical properties of Questa rock piles and their

natural analogs were investigated. Particle shape analysis, wet and dry sieving, and direct

shear tests were conducted. In addition, the results of 12-inch direct shear tests and 4-inch

diameter triaxial tests from published documents and Golder laboratory were studied. The

results of this study can be summarized as follows:

• The particle shape analysis showed that rock fragments at the test locations of

Questa mine are mainly subangular, and subdiscoidal and subprismoidal.

Furthermore, the sphericity and angularity of the rock fragments of the older

analogs are similar to those of the younger rock piles indicating that short-term

weathering (100 years) and longer hydrothermal alteration have not noticeably

changed the particle shapes at the test locations (section 3.8 of chapter 3).

• Wet sieving results in more fines than the dry sieving. The increase in fines is a

result of the presence of water in wet sieving that dissolves the cementation and

cohesion between particles and causes disintegration of clumps (section 4.8).

• The shear strength of Questa mine material is affected by the particle size and

shape. In general, larger samples contain less amount of fines that result in higher

friction angles. For example, 12-inch samples show higher friction angles

compared to the 2.4 or 2-inch samples (Fig. 5.7).

81

• The peak friction angle of the materials from Questa rock piles and analogs

reduces as the water content increases. The greatest friction angles belong to air-

dried samples (Fig. 6.3).

• 12-inch direct shear and 4-inch diameter triaxial tests show similar peak friction

angles of 40° or above. An exception is for sample SSW-SAN-0006 that indicates

a 6° difference in the measured friction angle using direct shear and triaxial

testing. This sample has the greatest percentage of fines that could be responsible

for this discrepancy.

82

References Ayakwah, G., Dickens, A., and McLemore, V.T., 2008, Characterization of a debris flow

profile, Questa, New Mexico: revised unpublished report to Molycorp Task B1.4. Alshibli, K.A. and Alsaleh, M.I., 2004, Characterizing surface roughness and shape of

sands using digital microscopy: Journal of Computing in Civil Engineering, v. 18(1), p. 36-45.

ASTM, 2002a, Standard Test Method for Particle-Size Analysis of Soils (D422): Annual Book of ASTM Standards. American Society for Testing and Materials (ASTM), West Conshohocken, PA.

ASTM, 2001, American Society for Testing Materials. Procedures for testing soils (1964). Standard Test Method for Slake Durability of Shales and Similar Weak Rocks: D464487 (Reapproved 1992): Annual Book of ASTM Standards, West Conshohocken, PA.

ASTM, 1998, Standard Test Method for Direct Shear Test of Soils Under Consolidated Drained Conditions (D3080), Annual Book of ASTM Standards, American Society for Testing and Materials (ASTM), West Conshohocken, PA.

ASTM, 1987, Standard Preparation of Soil Samples for Particle Size Analysis and Determination of Soil Constants (D421): Annual Book of ASTM Standards. American Society for testing and Materials (ASTM), West Conshohocken, PA.

ASTM, 1971 (Reapproved), Standard Test Method for Amount of Material in Soils Finer than No. 200(75μm) (D1140): Annual Book of ASTM Standards. American Society for Testing and Materials (ASTM), West Conshohocken, PA.

Barrett, P.J., 1980, The shape of rock particles—A critical review: Sedimentology, v. 27, p. 291-303.

Bishop, A.W. and Henkel, D.J. (1962) The measurement of soil properties in the triaxial test, Second Edition, Arnold, London.

Bishop, Alan W. and Eldin, A.K. Gamel, 1953, The effect of Stress History on the Relation between Friction Angle and Porosity in Sand, Proceedings, 3rd International Conference on Soil Mechanics and Foundation Engineering, Zurich, Vol. 1, pp. 100-105.

Bishop, A W., (1948), A Large Shear Box for Testing Sand and Gravels, Proceedings of the 2nd International Conference on Soil Mechanics and Foundation Engineering, Vol. 1, pp. 207-211.

Boakye, K., 2008, Large In situ Direct Shear Tests on Rock Piles at the Questa Mine, Taos County, New Mexico: M. S. thesis, New Mexico Institute of Mining and Technology, Socorro, 154 p., http://geoinfo.nmt.edu/staff/mclemore/Molycorppapers.htm, accessed August 08, 2008.

Bowman, E. T., Soga, K., and Drummnond, W., 2001, Particle shape characterization using Fourier descriptor analysis: Geotechnique, v. 51(6), p. 545–554.

Broch, E. and Franklin, J. A., 1972, The Point Load Strength Test: International Journal of Rock Mechanics and Mineral Sciences, v. 9, p. 669-697.

83

http://geoinfo.nmt.edu/staff/mclemore/Molycorppapers.htm

Campbell, A.R. and Lueth, V.W., 2008, Isotopic and textural discrimination between hypogene, ancient supergene, and modern sulfates at the Questa mine, New Mexico: Applied Geochemistry, v. 23, no. 2, p. 308- 319.

Charles, J. A., and Watts, K. S., 1980, The influence of Confining Pressure on the Shear Strength of Compacted Rock fill, Geotechnique 30, No. 4, pp. 353 – 367.

Cho, G.C., Dodds, J., and Santamarina, J.C., 2006, Particle shape effects on packing density, stiffness, and strength: Natural and crushed sands: Journal of Geotechnical and Geoenvironmental Engineering, v. 132, Issue 5, p. 591-602.

Clark, N. N., 1987, A new scheme for particle shape characterization based on fractal harmonics and fractal dimensions: Powder Technology, v. 51, p. 243–249.

Das, B.M., 1983, Advanced Soil Mechanics: New York, McGraw Hill Book Company, 511 p.

Dawson, R.F., Morgenstern, N.R., and Stokes, A.W., 1998, Liquefaction flowslides in Rocky Mountains coal mine waste dumps: Canadian Geotechnical Journal, 35(2), 328-343.

Dodds, J., 2003, Particle shape and stiffness—effects on soil behavior: M.S. thesis, Georgia Institute of Technology, Atlanta, 190 p.

Douglass, P.M. and Bailey, M.J., 1982, Evaluation of surface coal mine spoil pile failures, Stability in surface mining: Brawner, C.O., (ed.), v. 3, Printed by Edwards Brothers, Inc., Michigan, USA.

Fakhimi A., Boakye K., Sperling D., and McLemore V., 2008, Development of a modified in situ direct shear test technique to determine shear strength of mine rock piles: Geotechnical Testing Journal, v. 31, no. 3, paper on line www.astm.org.

Folk, R.L., 1955, Student operator error in determination of roundness, sphericity, and grain size: Journal of Sedimentary Petrology, v. 25, no. 4, p. 297-301.

Fookes, P. G., Dearman, W. R., and Franklin, J. A., 1971, Some engineering aspects of rock weathering with field examples from Dartmoor and elsewhere: Quarterly Journal of Engineering Geology, v. 4, p. 139-185.

Franklin, J.A., and Chandra, A., 1972, The slake durability test: International Journal of Rock Mechanics and Mineral Sciences: v. 9, p. 325–341.

Goel, M.C. (1978), Evaluation of Shear Strength of Coarse Grained Soils, Indian Geotechnical Journal, Vol. 8, No.3 July, pp.141-152.

Graf, G.J., 2008, Mineralogical and geochemical changes associated with sulfide and silicate weathering, natural alteration scars, Taos County, New Mexico: M. S. thesis, New Mexico Institute of Mining and Technology, Socorro, 193 p., http://geoinfo.nmt.edu/staff/mclemore/Molycorppapers.htm, accessed April 28, 2008.

Gutierrez, L.A.F., Viterbo, V.C., McLemore, V.T., and Aimone-Martin, C.T., 2008, Geotechnical and Geomechanical Characterisation of the Goathill North Rock Pile at the Questa Molybdenum Mine, New Mexico, USA; in Fourie, A., ed., First International Seminar on the Management of Rock Dumps, Stockpiles and Heap Leach Pads: The Australian Centre for Geomechanics, University of Western Australia, p. 19-32.

84


Head, K.H., 1980, Manual of Soil Laboratory Testing: Volume 1, Soil Classification and Compaction Test Engineering Laboratory Equipment Limited, Pentech Press Limited, Estover Road, Plymouth, Devon.

Holtz, R.D. and Kovacs, W.D., 2003. An Introduction to Geotechnical Engineering. Civil Engineering and Engineering Mechanics Series. Pearson Education Taiwan Ltd., 733 pp.

Horn, H.M., and Deere, D.U., Frictional Characteristics of Minerals, Geotechnique, Vol. XII, No.4, December 1962, pp 319-335.

Hyslip, J. P. and Vallejo, L. E., 1997, Fractal analysis of the roughness and size distribution of granular materials: Engineering Geology, v. 48, no. 34, p. 231-244.

International Society for Rock Mechanics (ISRM), 1979, Suggested Methods for determination of the slake durability index: International Journal of Rock Mechanics and Mineral Sciences Geomech., v. 16, 154-156.

Jefferies, M.G. and Been, K. (2006) Soil liquefaction, a critical state approach, Taylor and Francis, London, UK.

Kirkpatrick, W. M., 1965, Effect of Grain Size and Grading on the Shearing Behavior of Granular Material, Proceedings 6th International Conference on Soil Mechanics and Foundation Engineering, Vol. I, pp. 273-277.

Koerner, R. M., (1970), Effect of Particle Characteristic on Soil Strength, Proceedings of the American Society of Civil Engineers, Journal of the Soil Mechanics and Foundations Division, SM4, pp. 1221-1235. Krumbein, W.C., 1941, Measurement and geological significance of shape and roundness

of sedimentary particles: Journal of Sedimentary Petrology, v. 11(2), p. 64-72. Lee,K.L., Seed, H.B., and Dunlop, P.,1967, Effect of Moisture on the Strength of Clean

Sand, Journal of the Soil Mechanics and Foundations Division, Vol. 93,No. SM6,pp 17-40.

Leps, T.M. (1970) Review of shearing strength of rockfill, Journal of Soil Mechanics and Foundation Division, ASCE, Vol. 96, No. SM4, July, pp 1159-1170.

Lewis, J. G., (1956), Shear Strength of Rock fill, Proceedings of the 2nd Australia-New Zealand Conference on Soil Mechanics and Foundation Engineering, pp, 181-202. Linero, S., Palma, C., and Apablaza, R., 2007, Geotechnical characterization of waste

material in very high dumps with large scale triaxial testing, Proceedings of International Symposium on Rock Slope Stability in Open Pit Mining and Civil Engineering, 12-14 September 2007, Perth, Australia, p. 59-75. Marsal, R.J. (1973) Mechanical properties of rockfill, In: Embankment-Dam Engineering

(Casagrande Volume) Hirschfeld R.C. and Poulos, S.J. (Eds.), John Wiley and Sons, pp 109-200.

Marsal, R.J., E.M. Gomez, A. Nunez G., R. Cuellar B. and R.M. Ramos, 1965, Research on the Behavior of Granular Soils and Rockfill Samples, CFE, Publication, Mexico.

Marsal, R. J., 1965a, Discussion, Proceedings, 6th International Conference on Soil Mechanics and Foundation Engineering, Vol. 3, pp. 310-316. Morris, H.C., 1959, Effect of particle shape and texture strength of non-cohesive

aggregates: ASTM STP. No. 254, p. 350- 364. Norwest Corporation, 2004, Goathill North slide investigation, evaluation and mitigation report: unpublished report to Molycorp Inc., 99 p., 3 vol.

85

Norwest Corporation, 2005, Questa Roadside Rock Piles 2005 Operation Geotechnical Stability Evaluation: unpublished report to Molycorp Inc., 210 p., 3 vol.

Oakey, R.J., Green, M., Carling, P.A., Lee, M.W.E., Sear, D.A., and Warburton, J., 2005, Grain shape analyses—a new method for determining representative particle shapes for populations of natural grains: Journal of Sedimentary Research, v. 75, p. 1065-1073.

Pa’lossy, L., Scharle, P., and Szalatkay, I., Earth Walls, Ellis Horwood, New York, ISBN 0-13-223876-4, 246 p. Powers, M.C., 1982, Comparison chart for estimating roundness and sphericity: AGI

(American Geological Institute), Alexandria, Va., data sheet 18.1 Quine, R.L., 1993. Stability and deformation of mine waste dumps in north-central

Nevada. M. S. Thesis, University of Nevada, Reno, 402 pp. Robertson, A.M., 1982, Deformation and Monitoring of Waste Dump Slopes, p. 16. Robertson GeoConsultants Inc., 2000. Interim Mine Site Characterization Study, Questa

Mine, New Mexico. 052008/10, Robertson Geoconsultants Inc. Unpublished Report toMolycorp Inc.

Seedsman, S.A. and Emerson, W.W., 1985. The Role of Clay-rich Rocks in Spoil Pile Failures at Goonyella Mine, Queensland, Australia. International Journal of Rock Mechanicas and Mining Science, 22: 113-118.

Shaw, S.C., Wels, C., Roberston, A. and Lorinczi, G., 2002. Physical and Geochemical Characterization of Mine Rock Piles at the Questa Mine, New Mexico: An Overview, 9th International Conference on Tailings and Mine Waste ’02. Balkema., Rotterdam.

Smith, M.L., 1999, The analysis of surface texture using photometric stereo acquisition and gradient space domain mapping: Image Vis. Comput., v. 17, p. 1009–1019.

Sukumaran, B., and Ashmawy, A. K., 2001, Quantitative characterization of the Geometry of discrete particles: Geotechnique, v. 51(7), p. 171–179.

Uhle, R.J. (1986) A statistical analysis of rockfill data – shear strength and deformation parameters with respect to particle size, M.S. Thesis, Department of Civil Engineering, Colorado State University, 212 p.

URS Corporation, 2003, Mine rock pile erosion and stability evaluations, Questa mine: Unpublished Report to Molycorp, Inc. Project No. 22236156.00100, 4 volumes.

U.S. Army Corps of Engineers, 1970, Grain Size Analysis: Engineering Design: Laboratory Soil Testing: Department of the Army Headquarters, Washington, DC, p. V1-V28.

Valenzuela, L., Bard, E., Campana, J. and Anabalon, M.E. (2008) High waste dumps – challenges and developments, In: Rock Dumps 2008, Fourie, A. (Ed.), Australian Centre for Geomechanics, Perth, Australia, pp 65-78.

Vallerga, B. A., Seed, H. B., Monismith, C. L., and Cooper, R. S., (1957), Effect of Shape Size and Surface Roughness of Aggregate Particles on the Strength of Granular Materials, Special Technical Publication No. 212, ASTM, pp. Viterbo, V.C., 2007, Effects of pre-miming hydrothermal alteration processes and post-

mining weathering on rock engineering properties of Goathill North rock pile at Questa mine, Taos County, New Mexico: M.S. thesis, New Mexico Institute of Mining and Technology, Socorro, 274 p.,

86

http://geoinfo.nmt.edu/staff/mclemore/Molycorppapers.htm, accessed December 06, 2007.

Wadell, H., 1932, Volume, shape, and roundness of rock particles: Journal of Geology, v. 40, p. 443–451.

Yu, Xinboa, Ji, Shunying and Janoyan, Kerop D., 2006, Direct Shear Testing of Rock fill Material, Soil and rock behavior and modeling; Proceedings of sessions of GeoShanghai, Shanghai, China.

Zeller, J. and R. Willimann, 1957, The Shear Strength of the Shell Materials for Goschenalp Dam Switzerland, Proc. IV International Conference on Soil Mechanics and Foundation Engineering, Volume II, London, England, p. 399-404.

87


Appendixes Appendix 1. Petrographic Descriptions and the Mineralogy of Samples

Brief descriptions of the samples, including indications of weathering are below.

The lithology, hydrothermal alteration, and mineralogy are in Table 1-2. Explanation of

the SWI (Simple Weathering Index) is in Table 1-3.

Sample GHN-KMD-0017 was collected from Unit I, trench LFG-006, bench 9

(UTM 4062143.2N, 453695.9E, zone 13. The sample was located approximately 2 ft east

of the outer edge of the rock pile. Sample GHN-KMD-0017 is a select, bulk sample of a

layer that consists of soil matrix and rock fragments that vary in size from 3 inches to less

than 1 mm. It is pale yellow, oxidized, poorly-sorted, medium consistency, and high

plasticity. Chlorite is found as rare green individual grains. Gypsum is found as primarily

rounded milky grains with some euhedral clear crystals. Pyrite is found as small cubic

crystals within rock fragments and soil matrix. The sample has a paste pH of 2.19, low

NP (Neutralizing Potential, 0.73), and SWI of 4 (weathered). The relatively high gypsum

+ jarosite (5.5%, Table 1-1) is consistent with a weathered intensity.

Sample GHN-KMD-0055 was collected from Unit I, trench LFG-007, bench 12

(UTM 4062146.5N, 453676.5E, zone 13). Sample GHN-KMD-0055 is a select, bulk

sample of a layer that consists of soil matrix and rock fragments that vary in size from 3

inches to less than 1 mm. It is pale yellow, coarse sand to gravel, and well graded (poor

sorting). Edge of rock fragments shows Fe oxide and clay-rich material adhered to the

edge of the sample. Pyrite cubes within the rock fragments are relatively fresh (Fig. 1-1).

The sample has a paste pH of 4.27, low NP (Neutralizing Potential, -15.03), and SWI of 4

88

(weathered). The relatively low gypsum + jarosite (2%, Table 1-2) suggest a weathering

intensity of moderately weathered.

Sample GHN-KMD-0095 was collected from Unit C, trench LFG-008, bench 18

(UTM 4062118.6N, 453656E, zone 13). Sample GHN-KMD-0095 is a select, bulk

sample of a layer that consists of soil matrix and rock fragments that vary in size from 3

inches to less than 1 mm. It is yellow brown, coarse sand to gravel, and well graded (poor

sorting). The sample has a paste pH of 2.73 and SWI of 4 (weathered). The relatively low

gypsum + jarosite (1.2%, Table 1-2) suggest a weathering intensity of moderately

weathered.

GHN-KMD-0055-31-01 Unit I

Figure 1-1. BSE image of fresh pyrite in rock sample. Brightest areas on image are pyrite grains, which are of uniform brightness and display distinct grain margins.

89

Table 1-1. Summary of sample preparation for specific laboratory analyses. XRF–X-ray fluorescence analyses, XRD–X-ray diffraction analysis, ICP–Induced-coupled plasma spectrographic analysis, NAG–net acid producing tests, ABA–acid base accounting tests. Laboratory analysis Type of sample Sample Preparation Method of obtaining

accuracy and precision

SOP

Petrographic analyses Collected in the field, used split from chemistry sample

Uncrushed, typically smaller than gravel size material used, thin sections made of selected rock fragments

Selected samples were analyzed by outside laboratory

24

Microprobe analyses Collected in the field or split from chemistry sample

Uncrushed, generally 2 splits; rock fragments and soil matrix

Use reference standards 26

Whole-rock chemical analysis (XRF, S/SO4)

Collected in the field in separate bag

Crushed and pulverized Use reference standards and duplicates and triplicates

8

Whole-rock chemical analysis (ICP)

Collected in the field in separate bag

Crushed, pulverized, and dissolved in a liquid for analysis

Use reference standards and duplicates and triplicates

8, 30, 31

X-ray diffraction (XRD) analyses (including remaining pyrite analysis)

Used split from chemistry sample

Crushed Compared to detailed analysis by electron microprobe

27, 34

Clay mineralogy analyses

Used split from chemistry sample

Uncrushed, typically smaller than gravel size material used, thin sections made of selected rock fragments, clay separation obtained by settling in a beaker of DI water

Use duplicate analysis, compared to other results performed by consultant companies, compared to detailed analysis by electron microprobe

29

Particle-size analysis Bulk sample collected in the field

Sample sieved for each size fraction weighed

Use duplicate analysis, compared to other results performed by consultant companies

33

Paste pH and paste conductivity

Collected in the field, used split from chemistry sample or gravimetric sample

Uncrushed, typically smaller than gravel size material used

Use duplicates, compared with field measurements using Kelway instrument (SOP 63), compare to mineralogical analysis

11

ABA/NAG tests Used split from chemistry sample

Uncrushed, typically smaller than gravel size material used

Use duplicate analysis, compared to other results performed by consultant companies

52, 62

DI leach Collected in the field

Crushed and split Use reference standards and duplicate analyses

38

90

Table 1-2. Description of samples. Hydrothermal alteration and composition of rock fragments was determined by petrographic techniques using a binocular microscope and electron microprobe. The mineral composition was determined by a modified ModAn technique using petrographic analysis, clay mineralogy by X-ray diffraction, and whole rock chemistry (McLemore et al., 2009). Phyllic or QSP (quartz-sericite-pyrite) alteration consists of quartz, sericite (a form of illite), and pyrite. Propylitic alteration consists of essential chlorite (producing the green color), epidote, albite, pyrite, quartz, carbonate minerals, and a variety of additional minerals. Argillic or clay alteration consists of kaolinite, smectite (montmorillonite clays), chlorite, epidote, and sericite.

Composition of rock fragments

(%) Sample

MIN-SAN-0001

SPR-SAN-0001

SSW-SAN-0001

SSW-SAN-0005

QPS-SAN-0001

GHN-KMD-0017

GHN-KMD-0055

GHN-KMD-0095

Description debris flow

rock pile

rock pile

rock pile

alteration scar

GHN rock pile

GHN rock pile

GHN rock pile

rhyolite (Amalia Tuff) 5 95 10 100andesite 100 100 3 95 65 100 intrusive 95 2 5 25

Amount of Hydrothermal Alteration (%)

QSP 30 35 25 50 30 50 50 70propylitic 7 5 7 2 argillic 3 1 20

Mineral Composition

(%)

quartz 45 25 32 37 42 32 48 48K-feldspar/ 13

21

8

22

4

3

14

25 orthoclase

plagioclase

2

18

18

2

10

21

biotite 0.01 illite 28 14 23 23 31 25 28 20chlorite 2 8 5 3 3 4 2 1smectite 1 3 4 1 3 3 1 2kaolinte 3 1 1 1 1 1 1 2epidote 2 0.01 3 Fe oxides 1 4 2 0.6 0.8 0.6 0.7 0.7rutile 0.4 0.6 0.5 0.4 0.4 0.6 0.3 0.1apatite 0.2 0.9 0.3 0.3 0.2 0.4 0.2 0.01pyrite 0.01 0.3 0.3 0.1 3 3 0.3calcite 0.1 0.5 0.1 0.3 0.2 0.1 0.5 0.3gypsum 0.2 2 2 1 1 1.5 1 0.2zircon 0.04 0.03 0.03 0.04 0.04 0.03 0.04 0.06sphalerite 0.01 fluorite 0.03 jarosite 3 4 5 4 4 1 1copiapite 0.06 organic carbon

1

SUM MINERALS 99.95 100.33 100.25 99.74 100.64 99.3 101 101

91

Table 1-3. Simple weathering index for rock-pile material (including rock fragments and matrix) at the Questa mine (McLemore et al., 2008a).

SWI Name Description 1 Fresh Original gray and dark brown to dark gray colors of igneous rocks; little to

no unaltered pyrite (if present); calcite, chlorite, and epidote common in some hydrothermally altered samples. Primary igneous textures preserved.

2 Least weathered Unaltered to slightly altered pyrite; gray and dark brown; very angular to angular rock fragments; presence of chlorite, epidote and calcite, although these minerals not required. Primary igneous textures still partially preserved.

3 Moderately weathered

Pyrite altered (tarnished and oxidized), light brown to dark orange to gray, more clay- and silt-size material; presence of altered chlorite, epidote and calcite, but these minerals not required. Primary igneous textures rarely preserved.

4 Weathered Pyrite very altered (tarnished, oxidized, and pitted); Fe hydroxides and oxides present; light brown to yellow to orange; no calcite, chlorite, or epidote except possibly within center of rock fragments (but the absence of these minerals does not indicate this index), more clay-size material. Primary igneous textures obscured.

5 Highly weathered No pyrite remaining; Fe hydroxides and oxides, shades of yellow and red typical; more clay minerals; no calcite, chlorite, or epidote (but the absence of these minerals does not indicate this index); angular to subround rock fragments

The SWI accounts for changes in color, texture, and mineralogy due to weathering, but it

is based on field descriptions. Some problems with this weathering index are:

• It is subjective and based upon field observations.

• This index does not always enable distinction between pre-mining supergene

hydrothermal alteration and post-mining weathering.

• The index is developed from natural residual soil weathering profiles, which

typically weathered differently from the acidic conditions within the Questa rock

piles and, therefore, this index may not adequately reflect the weathering

conditions within the rock piles.

• This index refers mostly to the soil matrix; most rock fragments within the

sample are not weathered except perhaps at the surface of the fragment and

along cracks.

92

• The index is based primarily upon color and color could be indicative of other

processes besides weathering intensity.

• This index was developed for the Questa rock piles and may not necessarily

apply to other rock piles.

• Weathering in the Questa rock piles is an open not a closed system (i.e. water

analysis indicates the loss of cations and anions due to oxidation).

93

94

Appendix 2. Particle Shape of Samples

Figure 2-1. Particles from Debris Flow Sample (MIN-SAN-0001)

Grain Size vs Roundness(MIN-SAN-0001)

0

10

20

30

40

50

60

70

80

90

SUBANGULAR

ANGULAR

SUBROUNDED

ROUNDED

Roundness

Num

ber o

f Gra

ins

(%)


Grain Size vs Sphericity (MIN-SAN-0001)

0

5

10

15

20

25

30

35

40

45

SUBDISCOIDAL

DISCOIDAL

SPHERICAL

SUBPRISMOIDAL

PRISMOIDAL

Sphericity

Num

ber o

f Gra

ins

(%)

2-INC

H

1-INCH1/2-INCH No. 4No. 10

(b) (a)

Figure 2-2. Distribution of a) sphericity b) roundness of particles from the debris flow Sample.

95

Figure 2-3. Particles from Pit Alteration Scar Sample (QPS-SAN-0001)

Grain Size vs Roundness(QPS-SAN-0001)

0

10

20

30

40

50

60

70

80

90

100

SUBANGULAR

ANGULAR

SUBROUNDED

ROUNDED

Roundness

Num

ber o

f Gra

ins

(%)


Grain Size vs Sphericity(QPS-SAN-0001)

0

10

20

30

40

50

60

70

SUBDISCOIDAL

DISCOIDAL

SPHERICAL

SUBPRISMOIDAL

PRISMOIDAL

Sphericity

Num

ber o

f Gra

ins

(%)

2-INCH1-I CHN

1/ NCH2-I No. 4N 0o. 1

(a) (b)

Figure 2-4. Distribution of a) sphericity b) roundness of particles from the Pit Alteration Scar Sample.

Figure 2-5. Particles from Sugar Shack West Sample (SSW-SAN-0005)

Grain Size vs Sphericity(SSW-SAN-0005)

0

10

20

30

40

50

60

70

SUBDISCOIDAL

DISCOIDAL

SPHERICAL

SUBPRISMOIDAL

PRISMOIDAL

Sphericity

Num

ber o

f Gra

ins

(%)

2-INCH1-INCH1/2-INCHN

Grain Size vs Roundness(SSW-SAN-0005)

0

10

20

30

40

50

60

70

80

90

SUBANGULAR

ANGULAR

SUBROUNDED

ROUNDED

Roundness

Nm

ber o

f Gra

ins

(%)


o. 4No. 10

(a) (b) Figure 2-6. Distribution of a) sphericity b) roundness of particles from the Sugar Shack rock pile Sample (SSW-SAN-0005).

96

97

Figure 2-7. Particles from Spring Gulch Sample (SPR-SAN-0001)

Grain Size vs Spehricity(SPR-SAN-0001)

0

10

20

30

40

50

60

SUBDISCOIDAL

DISCOIDAL

SPHERICAL

SUBPRISMOIDAL

PRISMOIDAL

Sphericity

Num

ber o

f Gra

ins

(%)

2-INCH1-INCH1/2-INCHNo.

Grain Size vs Roundness(SPR-SAN-0001)

0

10

20

30

40

50

60

70

80

90

100

SUBANGULAR

ANGULAR

SUBROUNDED

ROUNDED

Roundness

Num

ber o

f Gra

ins

(%)


4No. 10

(a) (b)

Figure 2-8. Distribution of a) sphericity b) roundness of particles from the Spring Gulch rock pile Sample.

98

Figure 2-9. Particles from Sugar Shack West Sample (SSW-SAN-0001)

Grain Size vs Sphericity(SSW-SAN-0001)

0

10

20

30

40

50

60

SUBDISCOIDAL

DISCOIDAL

SPHERICAL

SUBPRISMOIDAL

PRISMOIDAL

Sphericity

Num

ber o

f Gra

ins

(%)

2-INCH1-INCH1/2-INCHNo. 4No.

Grain Size vs Roundness(SSW-SAN-0001)

0

10

20

30

40

50

60

70

80

90

SUBANGULAR

ANGULAR

SUBROUNDED

ROUNDED

Roundness

Num

ber o

f Gra

ins

(%)


10

(a) (b)

Figure 2-10. Distribution of a) sphericity b) roundness of particles from the Sugar Shack rock pile Sample (SSW-SAN-0001).

99

Figure 2-11. Particles from Goathill North Sample (GHN-KMD-0017)

Grain Size vs Roundness(GHN-KMD-0017)

0

10

20

30

40

50

60

70

80

SUBANGULAR

ANGULAR

SUBROUNDED

ROUNDED

Roundness

Num

ber o

f Gra

ins

(%)


Grain Size vs Sphericity (GHN-KMD-0017)

0

10

20

30

40

50

60

SUBDISCOIDAL

DISCOIDAL

SPHERICAL

SUBPRISMOIDAL

PRISMO

2-INCH

IDAL

Sphericity

Num

ber o

f Gra

ins

(%) 1-INCH

1/2-INCH No. 4

No. 10

(a) (b)

Figure 2-12. Distribution of a) sphericity b) roundness of particles from the Goathill North Sample (GHN-KMD-0017).

100



0

10

20

30

40

50

60

70

80

90

100

SUBANGULAR

ANGULAR

SUBROUNDED

ROUNDED

Roundness

Num

ber o

f Gra

ins

(%)


Grain Size vs Sphericity(GHN-KMD-0055)

0

10

20

30

40

50

60

70

80

90

100

SUBDISCOIDAL

DISCOIDAL

SPHERICAL

SUBPRISMOIDAL

PRISMOIDAL

Sphericity

Num

ber o

f Gra

ins

(%)


(a) (b)


101



0

20

40

60

80

100

120

SUBANGULAR

ANGULAR

SUBROUNDED

ROUNDED

Roundness

Nm

ber o

f Gra

ins

(%)


Grain Size vs Sphericity(GHN-KMD-0095)

0

10

20

30

40

50

60

70

80

90

SUBDISCOIDAL

DISCOIDAL

SPHERICAL

SUBPRISMOIDAL

PRISMOIDAL

Sphericity

Num

ber o

f Gra

ins

(%)

2-IN CH

1-INCH

1/2- HINC

No. 4No.

(b) (a)

10


Appendix 3. Standard Operating Procedure (SOP)

STANDARD OPERATING PROCEDURE NO. 33

PARTICLE SIZE ANALYSIS (Including both Dry and Wet Mechanical Sieving and Hydrometer Analyses)

REVISION LOG

Revision Number Description Date

33 Original SOP

33.1 Revisions by Dr. Catherine T. Aimone-Martin

Aug 19, 2004

33v2 GMLR 9-27

33.3 Addition of ASTM, and revisions JRM 01/12/2005

33.4 Revisions by HRS 01/18/05

33v4 Extensive Edits & comments by LMK 2/14/05

33v5 Revisions by RDL 5/30/2006

33v5 Minor edits LMK, sent to jack Hamilton to replace the old one on the Utah Molycorp project website

7/11/06

33v6 APPENDIX FOR MECHANICAL PARTICLE SIZE ANALYSES (NO. 200 SIEVE) written by Kwaku Boekye, January 2007, edited by LMK and added to original SOP 33v5 by LMK. SOP 33v6 finalized by LMK and sent to Jack Hamilton to post on project website

1/29/07

33v6 LMK finalized to post on Project Website and to send to George Robinson for lab audit, no new edits

4/2/07

102

33v7 LMK added wet sieving procedure appendix 10/26/07

33v7 LMK added modification to dry sieving procedure that increases sieve shaking time

10/29/07

33v8 Editorial by SKA 10/24/08

1.0 PURPOSE AND SCOPE

This Standard Operating Procedure (SOP) is based on ASTM D422-63 Standard Test Method for Particle-Size Analysis of Soils. This SOP covers the quantitative determination of the distribution of particle sizes in soils. The distribution of particle sizes larger than 2.0 mm is determined by sieving, while the distribution of particle sizes smaller than 2.0 mm is determined by a sedimentation process using a hydrometer to secure the necessary data. It provides technical guidance and procedures to be employed for particle size analyses, including the required equipment, procedures, and personnel responsibilities.

2.0 RESPONSIBILITIES AND QUALIFICATIONS The Characterization Team Leader shall have the overall responsibility for implementing this SOP. He/she will be responsible for assigning appropriate staff to implement this SOP and ensuring that procedures are followed accurately. All personnel performing these procedures are required to have the appropriate health and safety training. In addition, all personnel are required to have a complete understanding of the procedures described within this SOP and receive specific training regarding these procedures, if necessary. All staff are responsible for reporting deviations from this SOP to the Characterization Team Leader.

3.0 DATA QUALITY OBJECTIVES Particle size analysis is required to understand the hydrologic and structural properties of the rock pile and to estimate the soil-water characteristic curve (SWCC), which is used in modeling the seepage and stability of the rock piles. Accordingly, this SOP addresses objectives 2 and 8 in the data quality objectives outlined by Virginia McLemore for the "Geological and Hydrological Characterization at the Molycorp Questa Mine, Taos County, New Mexico”.

103

4.0 RELATED STANDARD OPERATING PROCEDURES The procedures set forth in this SOP are intended for use with the following SOPs:

• SOP 1 Data management (including verification and validation) • SOP 2 Sample management (including chain of custody) • SOP 6 Drilling, logging, and sampling of subsurface materials (solid) • SOP 9 Test pit excavation, logging, and sampling (solid) • SOP 36 Sample preservation, storage, and shipment • SOP 54 Atterberg Limits

5.0 EQUIPMENT LIST The following materials and equipment are required to perform mechanical and hydrometer grain size analyses: • Sieve shaker • A series of sieves, (stainless steel sieves if chemical analyses will also be required):

3 inch (75 mm) 2 inch (50 mm) 1 ½ inch (37.5 mm) 1 inch (25.0 mm) ¾ inch (19.0 mm) 3/8 inch (9.5 mm) No. 4 (4.75 mm) No. 6 (3.35 mm) No. 10 (2.00 mm) No. 16 (1.18 mm) No. 30 (600 μm) No. 40 (425 μm) No. 50 (300 μm) No. 70 (212 μm) No. 100 (150 μm) No. 200 (75 μm) Include a cover plate and bottom pan. The number and sizes of sieves used for testing a given soil sample will depend on the range of soil sizes in the material.

• Balances, sensitive to 0.01g for samples weighing less than 500g, and to 1.0g for samples weighing over 500g

• Container of known weight in which to weigh the fractions • Paintbrush or soft wire brush, for cleaning sieves • Sample splitter or riffle • Hydrometer 151H or 152H model • Sedimentation cylinder with a volume of 1,000 ml • Thermometer with accuracy to 1°F (0.5°C) • Timing device, a watch or clock with a second hand

104

• Beaker with 250ml capacity • Containers for drying samples • Drying oven • Dispersing or antifloculating agent, 4N of sodium hexametaphosphate (NaPO4), trade

name Calgon • Distilled or demineralized water • A mechanically operated stirring device • Dispersion cup • Wash bottle • Plastic bags for different particle size fractions • Waterproof labels and indelible pens • Particle size fraction forms (Appendix 1) • Parafilm

6.0 PROCEDURES 6.1 Mechanical particle size analyses Fill out chain of custody forms. Air-dry the sample to be analyzed (if necessary). See ASTM D 421 – Dry Preparation of

Soil Samples for Particle-Size Analysis and Determination of Soil Constants Split the sample using the sample splitter or the cone and quarter method and obtain a

representative sample for particle size analysis. The size of the sample shall depend on the diameter of the largest particle in the sample according to the following schedule (Department of the Army, Army Corps of Engineers, 1965):

Maximum Particle Size Minimum Weight of Sample (g)

3 inches 2 inches 1 inch ½ inch

Finer than No. 4 sieve Finer than No. 10 sieve

6000 4000 2000 1000 200 100

Record the total sample weight on the sample form. Select the top sieve as the one with openings that are slightly larger than the diameter of

the largest particle in the sample. If chemical analysis of the sample is to be performed, stainless steel sieves must be used.

Arrange the series of sieves so that they have decreasing opening sizes from the top to the bottom of the stack (largest openings at the top of the stack, decreasing sieve openings through the stack, with the smallest openings at the bottom of the stack). Attach the catch pan to the bottom of the sieve stack. Place the sample in the top sieve and put the cover plate over the top of the sieve stack.

105

Place the sieve stack in the shaking machine and shake it for at least 10 minutes or until additional shaking does not produce appreciable changes in the amounts of material on each sieve screen.

As of August 2007, this procedure has been modified to add a wet sieving procedure (See APPENDIX VI in this SOP for the wet sieving procedure) before the dry sieving and to increase the sieve shaking time for the dry sieving from minimum 10 minutes to maximum 60 minutes. From this date on the wet sieving and the longer shaking time were used and will continue to be used for this project. This is because the shorter shaking time and no wet sieving did not yield accurate grain size distribution curves because the fines clung to the larger particles.

Remove the sieve stack from the mechanical shaker. Beginning with the top sieve, transfer the soil particles to a weighed container/tare (which you have already noted the weight of or for which you have tared the balance). Carefully invert the sieve and gently brush the bottom of the sieve to remove any particles caught in the screen, catching them in the weighed container as well.

Weigh the container and sample and subtract the weight of the container from the soil material retained by that sieve. Record the weight of the soil particles retained on the sieve on the data sheet.

Save the material from each sieve in a plastic bag labeled with the sample ID information (See the Sieve Analysis Data Sheet in Appendix 1), the size of the sieve, and the sample weight.

Repeat steps 7 and 8 to determine the weight of soil particles retained on each sieve, including the total amount of the material in the catch pan.

When finished, place approximately 125g of sample passing the No. 10 sieve in a plastic bag. Mark the bag with the sample ID and the words “Hydrometer Test”.

Thoroughly remix the portion of the sample retained by the No. 10 sieve with the portion passing the No. 10 sieve.

Place approximately 125g of the remixed sample in a plastic bag. Mark this bag with the sample ID and the words “Specific Gravity”.

Using the remixed portion of the sample, obtain approximately 500g of sample passing the No. 6 sieve. Place this material in a plastic bag marked with the sample ID and the words “Direct Shear”.

From the remixed portion of the sample, obtain approximately 250g of material passing the No. 40 sieve. Place this material in a plastic bag marked with the sample ID and the words “Atterberg Limits”.

6.2 Hydrometer analyses 1. Record all the identifying information for the sample on the Hydrometer Analysis

Data Sheet (see Appendix 1). 2. The approximate size of sample to be used for the hydrometer analysis varies

according to the size of soil particles being tested. If the soil is predominately clay and silt, use approximately 50g, but if the soil is mostly sand, use approximately 100g.

3. Weigh out a sample of the air-dry fine fraction.

106

4. Place the sample in a 250ml beaker and add distilled or demineralized water until the sample is submerged. Add 15ml of the dispersing agent (antifloculant) at this time. Allow the sample to soak overnight or until all soil lumps have disintegrated.

5. At the end of the soaking period, disperse the sample further by transferring the complete sample to the dispersion cup. Wash any residue from the beaker with distilled or demineralized water so that all the sample is transferred.

6. Add distilled water to the dispersion cup, if necessary, so the cup is more than half full.

7. Place the cup in the dispersing machine and disperse the suspension for 1 to 10 minutes.

8. Transfer the solution to the sedimentation cylinder and add distilled water or demineralized water to the 1000ml mark.

9. Cover the end of the cylinder with Parafilm and shake the suspension vigorously for a few seconds in order to transfer the sediment on the bottom of the cylinder into a uniform suspension. Continue the agitation for the remainder of the minute by turning the cylinder upside down and back.

10. At the end of the 1-minute shaking period, set the cylinder on a stable surface, noting the time. Slowly immerse the hydrometer into the liquid over a period of 20 to 25 seconds before taking the first reading.

11. Take hydrometer readings after 1 and 2 minutes have elapsed from the time the cylinder was placed on the table.

12. As soon as each reading is taken, carefully remove the hydrometer from the suspension and place it in a sedimentation cylinder full of clean water.

13. Repeat steps 9 to 12 to make sure that the same readings are obtained. Many errors can occur during the first two readings. If the same values are read for 1 minute and two minutes during the second hydrometer test, reshake the sample and perform as above. Then proceed to the next steps to perform the rest of the hydrometer grain size distribution test.

14. At the end of the second 2 minutes and after each subsequent hydrometer reading, place a thermometer in the suspension and record the temperature reading on the data sheet.

15. You have already recorded the hydrometer reading at 1 minute and two minutes. Now record hydrometer readings at the following time intervals: 4, 15, 30, 60 (1 hour), 120 (2 hours), 240 (4 hours), 960 (16 hours) and 1440 (24 hours) minutes, removing the hydrometer from the suspension after each reading and placing it in a sedimentation cylinder of clean water.

16. If the dry weight of the samples is to be obtained at the end of the test, carefully wash all the suspensions into a container of known weight. Oven-dry the material, allow it to cool, weigh the sample, and record the weight on the sample form.

Selected size fractions will be submitted for bulk mineral analyses (XRD) and chemical analyses (XRF, ICP) to assess the mineralogy of the size fractions. If chemical analyses are required, then stainless steel sieves must be used for those samples.

107

NOTE: Wash your hands periodically. Follow normal procedures to prevent cross-contamination of grain sizes. Maintain field sample numbers throughout sample preparation. 6.3 PROCEDURAL ADDENDUM ADDENDUM TO MECHANICAL PARTICLE SIZE ANALYSES (NO. 200 SIEVE PORTION OF SOP 33V5 PARTICLE SIZE ANALYSIS) 1. PURPOSE AND SCOPE OF ADDENDUM This addendum modifies part of the procedure for the mechanical dry sieving of samples and is effective as of January 22, 2007, replacing the procedure described in SOP 33vr 2. RELATED STANDARD OPERATING PROCEDURES The procedure set forth in this SOP is intended for use with the following SOPs:

• SOP 1 Data management (including verification and validation) • SOP 2 Sample management (including chain of custody) • SOP 5 Sampling outcrops, rock piles, and drill core (solid) [ Suggest deleting:

method is for soil-not rock] • SOP 6 Drilling, logging, and sampling of subsurface materials (solid) • SOP 9 Test pit excavation, logging, and sampling (solid) • SOP 36 Samples preservation, storage, and shipment • SOP 54 Atterberg Limits

3. EQUIPMENT LIST The following materials and equipments are required to perform mechanical and hydrometer analysis:

• Sieve shaker • A series of sieves, ( stainless steel if chemical analyses will also be required):

3-in (75-mm) 2-in (50-mm)

121 - in (37.5-mm)

1-in (25.00-mm)

43 -in (19.00-mm)

83 -in (9.5-mm)

No.4 (4.75-mm) No.8 (2.36-mm) No.10 (2.00-mm)

108

No.16 (1.18-mm) No.20 (850-µm) No.30 (600-µm) No.40 (425-µm) No.50 (300-µm) No.60 (250-µm) No.100 (150-µm) No.140 (106-µm) No.200 (75-µm) 4. PROCEDURES 4.1 Mechanical particle size analyses (No. 200 sieve) 1. Fill out chain of custody 2. Air-dry the sample to be analyzed (if necessary). See ASTM D 421- Dry

Preparation of the Soil Samples for Particle Analysis and Determination of Soil Constant

3. Split the sample using the sample splitter and obtain a representative sample for particle size analysis. The size of the sample shall depend on the diameter of the largest particle in the sample according to the following schedule (Department of the Army, 1965):

4.

Maximum Particle Size Minimum Weight of Sample (g)

3-in 6000 2-in 4000 1-in 2000 1/2-in 1000

Finer than No.4 sieve 200 Finer than No.10 sieve 100

5. Record the total sample weight on the sample form. 6. Select the top sieve based on the weight of the sample as the one with openings

that are slightly larger than the diameter of the largest particle in the sample. 7. Arrange the series of sieves so that they have decreasing opening size from the

top to the bottom of the stack (largest openings at the top of the stack, decreasing sieves opening through the stack, with the smallest openings at the bottom of the stack). Include No. 200 sieve in every stack to determine whether to run a hydrometer test on the sample as well (Any sample that has size fractions passing through the no. 200 sieve will require a hydrometer test to determine the grain

109

size distribution of the < 75 µm fraction of the sample.). Attach the catch pan to the bottom of the sieve stack.

8. Place the sieve stack in the shaking machine and shake it for at least 10 min or until additional shaking does not procedure appreciable changes in the amounts of material on each sieve screen.

9. Remove the sieve stack from the mechanical shaker. Beginning with the top sieve, transfer the soil particles to a weighed container (which you have already noted the weight of or tared the balance to). Carefully invert the sieve and gently brush the bottom of the sieve to remove any particles caught in the screen, catching them in the weighed container as well.

10. Weigh the container and sample and subtract the weight of the container from the soil material retained by that sieve. Record the weight of the soil particles retained on the sieve on the data sheet.

11. Save the material from each sieve in an envelope labeled with the sample ID information, the size of the sieve, and the sample weight. Include the same information plus the words “for hydrometer test ” on the material collected from the no. 200 sieve

12. Save the fraction passing the No. 200 sieve in a plastic bag and label it with the sample ID and the words “hydrometer test”. Make sure it is 125 g.

13. If you do not have enough material for the hydrometer test, hand shake more sample through the No. 200 sieve and add the material obtained to the material obtained from sieving to measure 125g

14. When finished, place approximately 200g of sample passing the No. 6 sieve in a plastic bag. Mark the bag with the sample ID and the words “Direct Shear Test”.

15. Place approximately 125g of the sample passing the No.4 sieve in a plastic bag. Mark this bag with the sample ID and the words “Specific Gravity”.

16. Place approximately 125g of the sample passing the No.40 sieve in a plastic bag. Mark this bag with the sample ID and the words “Atterburg Limits”.

7.0 DOCUMENTATION Fill out particle size analysis form (Appendix 1). Each size fraction is assigned a separate sample identification number. The first part is identical to the field identification number (reference SOP for field identification number) and is followed by a sequential two numbers, for example SSW-HRS-001-03, shown in Table 1.

Table 1. Sample identification numbering (Sample ID) as outlined in SOP 2 Sample Management.

Component 1 Component 2 Component 3 Component 4

Three letter abbreviation for the mine feature, for example SSW for Sugar Shack West.

Three letter initials of the sample collector, for example HRS for Heather R. Shannon.

Sequential four number designation, for example 0001.

Sequential two-number designation, for example 03 for split sample 3.

110

In the example above, the sample ID would be SSW-HRS-0001-03.

8.0 QUALITY ASSURANCE/QUALITY CONTROL NMBGMR will archive all samples for future studies. • The lab manager or other supervisory personnel experienced with the test will review

the results, checking calculations, and check for consistency with the approved test methodology.

• Depending on the DQO being satisfied, a greater frequency of tests may need to be performed on a particular material. The reviewer needs to check that the frequency of tests is consistent with the DQO.

9.0 DATA ANALYSIS AND CALCULATIONS • Mechanical Analyses

a) The weight percent of the material retained on the various sieves is computed as follows: Weight percent retained = air-dry weight in g retained on a sieve x 100 air-dry weight in g of total sample b) Percent finer by weight is obtained by subtracting the cumulative percent retained

from 100%. c) Plot the relationship between sieve openings and percent finer by weight on a

semi-logarithmic graph with the sieve openings as ordinates on the arithmetical scale, and the percent finer by weight as abscissas on the logarithmic scale.

• Hydrometer Analyses

a) Correct hydrometer reading, R, by adding the meniscus correction to the actual hydrometer reading, R’. Record the correct reading, R, on the data sheet.

b) Calculate the particle diameter corresponding to a given hydrometer reading on the basis of Stoke’s equation, using the monograph shown in Appendix II.

c) Plot the results as the continuation of the grain-size distribution curve from the larger size fractions of that sample on a semi-logarithmic chart

The results of the particle size analysis are presented in the form of a grain size distribution curve on a semi-logarithmic chart. The curves obtained from the sieve analysis and hydrometer tests are joined by constructing a smooth curve between them.

10. REFERENCES Aimone-Martin, C. T., 2003, Soil Mechanics: Laboratory Manual, Department of Mineral and Engineering, New Mexico Institute of Mining and Technology, Socorro, NM. Liu, C. and Evett, J. B. 2003, Soil Properties: Testing, Measurements, and Evaluation, 5th edition, Upper Saddle River, NJ., pg 103 – 125.

111

ASTM, 2001, American Society for Testing Materials. Annual Book of ASTM Standards, West Conshohocken, PA, Cited by Liu, C. and Evett, J. B., 2003. Department of the Army, 1965, Engineering Design: Laboratory Soil Testing, Department

of the Army Headquarters, Washington, D.C., pg V1 – V28. Saskatchewan Highways and Transportation, 1993, Standard Test Procedures Manual- STP205-10: Mechanical Analysis, Hydrometer, http://www.highways.gov.sk.ca/docs/reports_manuals/STP_DOC/stp205-10.pdf (accessed 06/08/2004).

112

http://www.highways.gov.sk.ca/docs/reports_manuals/STP_DOC/stp205-10.pdf

APPENDIX 1 FORMS

113

APPENDIX II, HYROMETER CALIBRATION EQUATIONS (APPLICABLE FOR THE HYDROMETERS IN THE SOIL MECHANICS LABORATORY AT NEW MEXICO TECH.)

0 20 40CORRECTED HYDROMETER READING, R

605

10

15

20H

EIG

HT,

H

(cm

)Hydrometer

A

B

H = -0.1917 R + 18.5

H = -0.18 R + 18.0

APPENDIX III. TEMPERATURE CURRECTION FACTORS, m, FOR HYDROMETER DATA REDUCTION

Degrees Degrees Correction



C F m C F C F m 14 57.2 -0.9 21 69.8 0.2 28 82.4 1.8

14.5 58.1 -0.8 21.5 70.7 0.3 29 84.2 2.1 15 59 -0.8 22 71.6 0.4 29.5 85.1 2.2

15.5 59.9 -0.7 22.5 72.5 0.5 30 86 2.3 16 60.8 -0.6 23 73.4 0.6 30.5 86.9 2.5

16.5 61.7 -0.6 23.5 74.3 0.7 31 87.8 2.6 17 62.6 -0.5 24 75.2 0.8 31.5 88.7 2.8

17.5 63.5 -0.4 24.5 76.1 0.9 32 89.6 2.9 18 64.4 -0.4 25 77 1 32.5 90.5 3

18.5 65.3 -0.3 25.5 77.9 1.1 33 91.4 3.2 19 66.2 -0.2 26 78.8 1.3 33.5 92.3 3.3

19.5 67.1 -0.1 26.5 79.7 1.4 34 93.2 3.5 20 68 0 27 80.6 1.5

20.5 68.9 0.1 27.5 81.5 1.6

1.1.

114

115

APPENDIX IV. Grain Size Sub Form

APPENDIX V. WET SIEVING PROCEDURE This wet sieving procedure is used to remove the fine particles clinging to the larger pieces in the sample before dry sieving the sample to determine the grain size distribution. ADDITIONAL EQUIPMENT NEEDED

• Bucket • Piece of hose long enough to reach sieve area and bucket with connection to fit

water source you’re using • Set of no. 6, no. 10, and 200 sieves • Extra person to help • Spatula or similar to stir fines when 200 sieve gets clogged

PROCEDURE 1. Weigh container and sample in dry form first and record weights. The amount of the

sample needed is determined by the largest grain size in the sample (see Table on Page 4 or Page 7 in the dry sieving section of this SOP).

2. After weighing, put sample in a pan, cover with tap water, and soak for at least an hour

3. Stack these three sieves: No. 6, No. 10., and 200, with bucket under these three sieves 4. Then pass sample thru these three sieves while running water to remove all of the

fines, with one person holding the sieve set and the other directing the water from the hose and watching for overflow

5. Fines may clog up the 200 sieve and cause the water to overflow, so watch the water levels and stop the water flow until the clog is removed

116

6. Use a spatula or similar to stir fines clogging sieve until water can flow through it again

7. Catch the water in the bucket 8. Make sure all the particles are clean (run water thru until water runs clean. 9. Using the three sieves keeps the larger particles from ruining the 200 sieve. 10. Then recombine the material from the No. 6, No. 10 and 200 sieves 11. Air dry or oven dry the sample in a pan 12. Follow the dry sieving procedure in this SOP from here ADDITION TO THIS SOP IS U.S. ARMY CORPS OF ENGINEERS 1970 SIEVING PROCEDURE

Standard Operating Procedure No. 50

Direct Shear Test

REVISION LOG Revision Number Description Date SOP 50.0 Original SOP by LFG,

revisions/rewrite by FFJ 8/1/04, 9/22/04

SOP 50.1 Revisions by BEB 12/07/04 SOP 50.2 Revisions by FFJ/BEB 12/14/04 SOP 50.3 Rev. by JRH/GMLR 12/15/04 SOP 50.4 Rev. by FFJ/BEB 01/31/05 SOP 50v4 Final edits by LMK, revisions

and approved by VTM, LFG 2/2/05

SOP 50v5 Appendix I written and added by LMK

13Oct06

SOP 50v5 Reviewed by Dr. Ali Fakhimi and Kwaku Boakye

20-24Oct06

SOP 50v5 LMK edited Fakhimi and Boakye changes

25Oct06

SOP 50v5 Finalized by LMK to post on Molycorp project website and to send to George Robinson for lab audit, LMK addressed comments in previous version

3Apr07

50v6 Editorial by SKA 10/24/08 1. PURPOSE AND SCOPE This Standard Operating Procedure describes the method for determining the consolidated drained shear strength of a soil material in direct shear. In spite of the general procedures described in this SOP, specific procedures for the tests can be further

117

defined. The lab technician should check to see if specific test conditions are requested regarding saturation state and initial density of the specimens. The test consists of deforming a specimen at a controlled strain rate on or near a single horizontal shear plane determined by the configuration of the apparatus. Three or more specimens are tested, each under a different normal load, to determine the effects on shear resistance and displacement, and strength properties such as Mohr strength envelopes. The test can be made on all soil materials including undisturbed, remolded or compacted materials. There is, however, a limitation on maximum particle size as described below. The direct shear test can also be performed on soil samples containing moisture content. This procedure is described in Appendix I in this SOP. 2. RESPONSIBILITIES AND QUALIFICATIONS The Team Leader will have the overall responsibility for implementing this SOP. He/she will be responsible for assigning appropriate staff to implement this SOP and for ensuring that the procedures are followed accurately. All personnel performing these procedures are required to have the appropriate health and safety training. In addition, all personnel are required to have a complete understanding of the procedures described within this SOP, and receive specific training regarding these procedures, if necessary. All environmental staff and assay laboratory staff are responsible for reporting deviations from this SOP to the Team Leader. 3. DATA QUALITY OBJECTIVES • Perform direct shear tests under low and high normal loads, to determine the effects

on shear resistance and displacement, as well as strength properties such as Mohr strength envelopes.

• Determine the influence of weathering on the shear strength properties of the material.

4. RELATED STANDARD OPERATING PROCEDURES The procedures set forth in this SOP are intended for use with the following SOPs: • SOP 1 - Data management (including verification and validation) • SOP 2 - Sample management (including chain of custody) • SOP 4 - Taking photographs • SOP 5 - Sampling outcrops, rock piles, and drill core (solid) • SOP 6 - Drilling, logging and sampling of subsurface materials (solid)

118

• SOP 9 - Test pit excavation, logging and sampling • SOP 36 - Particle size analysis • SOP 40 - Gravimetric water content The procedures set forth in this SOP are also intended for use with the ASTM standard designation D-3080-98 (Appendix 1). 5. EQUIPMENT LIST The following materials are required for performing the direct shear test:

- Shear device - 4 inch square or circular shear box - Porous inserts - Loading devices (pneumatic or dead weight) - Load cell and readout to measure shear force - Vertical and horizontal displacement dial indicators - Controlled high humidity room, if required, for preparing specimens - Trimmer or cutting rings - Scales - Oven - Vernier or micrometer - Laboratory forms (Appendix 2) - Miscellaneous equipment including timing device, distilled or

demineralized water, spatulas, knives, straightedge and wire saws - Vibrotool - Ziploc bags®

6. COLLECTION OF SAMPLES Refer to SOP 5 (Sampling outcrops, rock piles, undisturbed blocks and drill cores), and SOP 9 (Test pit excavation, logging and sampling) to collect unconsolidated or undisturbed samples. Samples are collected, labeled, preserved and transported in accordance with SOP 1, 5 and 9. Log samples into the laboratory following chain of custody procedures (see SOP 2). Photographs should be taken before the sample is collected, consistent with SOP 4. 7. TEST SPECIMEN - The sample used for specimen preparation should be sufficiently large such that a

minimum of three similar specimens can be prepared. Prepare the specimens in a controlled temperature and humidity environment to minimize moisture loss or gain.

119

- Sieve the sample through a No. 4 sieve (4.75 mm) and use the passing fraction to perform the test.

- The minimum sample diameter for circular specimens, or width for square specimens, shall be 3.0 in. (75 mm), or not less than 10 times the maximum particle size diameter. The use of a 4.0 in. (100 mm) square shear box is preferable. The minimum initial specimen thickness shall be 1.0 in. (25 mm), but not less than six times the maximum particle diameter.

- The minimum specimen diameter to thickness, or width to thickness ratio, shall be 2:1.

- For either undisturbed or disturbed samples, prior to inserting the loading cap, weigh the shear box before and after the sample is loaded such that the weight and density of the sample can be calculated (e.g. weight of sample is weight of loaded shear box minus weight of empty shear box, and density of sample is weight of sample divided by the volume of sample).

- Compute the initial void ratio, dry unit weight, and degree of saturation based on the specific gravity (ASTM D854-02), gravimetric water content (SOP 40), and bulk density of the specimen. Specimen volume is determined by measurements of the shear box lengths or diameter and the measured thickness of the specimen.

7.1 Specimen Preparation 7.1.1 Undisturbed Samples - Extreme care should be taken in preparing undisturbed specimens of sensitive soils to

prevent disturbance to the natural soil structure. - Prepare undisturbed specimens from the sample boxes collected in accordance with

SOP 5. - Trim the specimen carefully to fit the dimensions of the shear box by using preparing

knives, wire saws, and spatulas. To mold the sample to the exact size, it might be necessary to remove coarse gravel from the corners. When removing coarse particles, be careful not to fragment or damage the soil structures.

- Place moist porous inserts over the exposed ends of the specimen in the shear box. Place the shear box containing the undisturbed specimen and porous inserts into the shear box bowl and attach the shear box.

7.1.2 Disturbed (unconsolidated) Samples - Loose samples: Put the soil evenly into the shear box from a drop height of about 6 to

8 inches. It is best to continuously pour the sample through a funnel. Stop pouring when the sample reaches the desired thickness. After leveling the surface of the sample, carefully insert the loading cap and seat it evenly with gentle pressure. Be careful not to jar the sample.

- Dense samples: Pour the sample into the shear box and simultaneously vibrate the side of the box by using a vibro-tool. After the sample reaches the desired thickness, stop pouring but continue with the vibrations for 2 or 3 minutes. Level the surface of the sample and seat the loading cap with gentle pressure. Make sure that the ribs on the bottom of the loading cap are perpendicular to the shear direction.

120

8. TEST PROCEDURES The test can be run using the standard or the multi-stage procedure. a) Standard Procedure - Connect and adjust the shear force loading system so that no force is imposed on the

load measuring device. - Properly position and adjust the horizontal displacement measurement device used to

measure shear displacement. Obtain an initial reading or set the measurement device to indicate zero displacement.

- Place the normal force loading yoke into position and adjust it so that the loading bar is horizontal. Level the lever and adjust the yoke until it sits snugly against the ball bearing on the load transfer plate.

- Apply a small normal load to the specimen. Verify that all components of the loading system are seated and aligned. The top porous insert and load transfer plate must be aligned so that the movement of the load transfer plate into the shear box is not inhibited. Record the applied vertical load and horizontal load on the system. The normal stress applied to the specimen should be approximately 1 lbf/in2 (7 kPa).

- Attach and adjust the vertical displacement measurement device. Obtain initial readings for the vertical measurement device and the horizontal displacement measurement device.

- If the multi-stage procedure is required for the sample, fill the shear box with distilled water and keep it full for the duration of the test. Allow the sample to be submerged at least two hours before the test starts.

- Calculate and record the normal force required to achieve the desired normal stress or increment thereof. Apply the desired normal stress by adding the appropriate mass to the lever arm hanger.

- Apply the desired normal load or increments thereof to the specimen and begin recording the normal deformation readings against elapsed time. For all load increments, verify completion of primary consolidation before proceeding - equilibrium conditions can be observed by taking readings with time on the dial gauge on the top of the soil specimen.

- The total normal load on the sample equals the weight on the yoke including the weight of the yoke, plus the weight of the top half of the shear box, plus the weight of the loading cap, plus half the weight of the sample.

- Using a vernier or micrometer, measure the vertical distance between the top of the shear box and the straight edge of the loading cap to obtain the sample height and then the relative density of the test specimen at the designed normal load. Relative density is calculated by dividing the sample mass by its volume. Specimen volume is determined by measurements of the shear box lengths and diameter and of the measured thickness of the specimen.

- After primary consolidation is completed, remove the alignment screws or pins from the shear box. Open the gap between the shear box halves to approximately 0.039 in. (1.0 mm) using the gap screws. Back out the gap screws.

- Select the appropriate strain rate. For clean dense sands which drain quickly, a value of 10 min. may be used for reaching failure. For dense sands with more than 5 %

121

fines, a value of 60 min. may be used as the time for failure. The magnitude of displacement at failure can be assumed to range from 10 to 20 % of the sample length. As a guide, use a strain rate of about 0.04 inches (1 mm) / minute for coarse material, and 0.01 inch (0.25 mm) / minute for material containing more than 5 % fines. Refer to ASTM 3080 for more details on estimating the strain rate based on the primary consolidation time.

- Record the initial time, the vertical and horizontal displacements, and the normal and shear forces.

- Start the apparatus and initiate shear. - Take readings of the horizontal force and vertical displacement dials corresponding to

horizontal displacement increments of 0.004 in. (0.1 mm) up to a total displacement of 0.04 in. (1.0 mm). Reduce the reading frequency to a horizontal displacement increment of 0.08 in. (0.2 mm) up to a total displacement of 0.12 in. (3.0 mm of total displacement). Then reduce the frequency of readings to every 0.02 in. (0.5 mm) of horizontal displacement increment up to a total displacement of 0.2 in. (5.0 mm) of the specimen. Thereafter, read the instruments every 0.04 in. (1.0 mm) of horizontal displacement to the failure of the sample.

- After failure is reached, remove the sample from the shear box and determine the gravimetric water content (SOP 40) if the test was performed in unsaturated conditions.

- Calculate the following: a) Nominal shear stress acting on the specimen is:

τ = F/A where:

τ = Nominal shear stress at the moment of the reading (kPa, kg/cm2, lbs/cm2, etc.), F = Shear force at the moment of the reading (N, kg, lbs, etc.), A = Surface area of the sample (cm2, in2, etc.).

b) Normal stress acting on the specimen is:

n= N/A where:

n = Normal stress (lb/m2, kg/cm2, kPa, etc.), N = Normal vertical force acting on the specimen (N, kg, lbs, etc.), A = Initial surface area of the specimen (cm2, in2, etc.).

c) Horizontal displacement rate is: r = d / t

where: r = Horizontal displacement rate (mm/min.), d = Total displacement of the sample (mm), t = Time to complete the test (min.).

- Prime another sample and repeat the procedures for the next planned normal load. b) Multi-Stage Procedure

122

When the multi-stage procedure is required, the sample is submerged in distilled water and allowed to displace to the peak strength. After that, the sample is returned to the initial position and the same sample is used to test the shear strength for all loads planned. The multi-stage test should be performed as follows:

- Submerge the sample in distilled water and apply the lowest normal stress to the soil specimen. Wait until the consolidation phase is complete - equilibrium conditions can be observed by taking readings with time on the dial gauge on the top of the soil specimen.

- Once equilibrium is achieved, the specimen is ready for the application of the first shear force. As the shear force is applied, plot the data showing horizontal displacement versus shear stress. The first portion of the stress versus displacement should have a relatively straight line relationship. At some point, the displacement should start to increase as the specimen moves towards the point of failure. Care and judgment must be exercised in determining the point at which the displacement should be stopped.

- The horizontal shear force is then reduced to zero and the two halves must be returned to the initial position corresponding to the beginning of the test.

- Apply the normal stress corresponding to the second stage. Following equilibrium, apply shear stress until the peak strength is attained again.

- The above procedure is repeated for each of the normal stresses until all load stages have been applied. Following the last stage, apply horizontal displacement up to the maximum conditions the apparatus can achieve.

9. DOCUMENTATION - PLOTS AND REPORTING Test sheets will be stored electronically in the Utah-maintained Molycorp database. See database for appropriate forms. The report shall include the following: - Sample identification, project, location and date of the test, and name of the person

completing the test. - Description of the type of shear device and shear box used in the test. - Description of sample type, that is, whether the specimen is undisturbed, remolded,

compacted, or otherwise prepared. - Description of sample characteristics such as: dry mass, initial void ratio, gravimetric

water content (SOP 40), dry unit weight, wet unit weight, and degree of saturation. - Initial thickness and diameter (width for square shear boxes). - Final gravimetric water content (SOP 40). - Normal stress, rate of deformation, shear displacement, and corresponding nominal

shear stress values and specimen thickness changes. - Plot of nominal shear stress versus percent relative lateral displacement for each

normal load used. - Plot of nominal shear stress at failure versus normal load. - Calculated friction angle and cohesion intercept.

123

- Departure from the procedure outlines, such as special loading sequences or special wetting requirements.

10. QUALITY ASSURANCE/QUALITY CONTROL All equipment will be calibrated for the equipment load-deformation characteristics when first placed in service or whenever parts are changed. ASTM Standard D 3080 (Appendix 1) gives detailed procedures for equipment calibration. A record of the date and results of each calibration will be permanently retained by each tester. Accuracy of readouts and dial indicators should be verified. Check the values of the weights set that will be used. When using a machine that is not automatic, the operator should calibrate the rate of the loading crank to obtain the desired displacement rate. It is important that the sample be continuously deformed at a constant rate which is strongly affected by the rotating loading crank. Where feasible, samples should be archived for future studies. 11. REFERENCES - ASTM D3080-98; Standard Test Method for direct shear test of soils under

consolidated drained conditions. - ASTM D854-02; Standard Test Method for specific gravity of soil solids by water

pycnometer. - HEADQUARTERS EM1110-2, 1986, Drained Direct Shear Test, Laboratory Soils

Testing-Engineer Manual, Department of the Army

124

APPENDIX I. METHOD FOR PREPARING AND RUNNING LABORATORY DIRECT SHEAR TESTS ON SATURATED SAMPLES 1.0 Related SOPs

• SOP 1 - Data management (including verification and validation) • SOP 2 - Sample management (including chain of custody) • SOP 4 - Taking photographs • SOP 5 - Sampling outcrops, rock piles, and drill core (solid) • SOP 6 - Drilling, logging and sampling of subsurface materials (solid) • SOP 9 - Test pit excavation, logging and sampling • SOP 35 - Volumetric Moisture Content • SOP 36 - Particle size analysis • SOP 40 - Gravimetric water content • SOP 64 - Portable Tensiometer • SOP 75 - Specific Gravity • SOP 82 - In-Situ Direct Shear Test

2.0 Equipment list

• Flat metal pan for drying samples • Tares for determining moisture content • Oven with capacity for maintaining 110 degrees F (~44 degrees C) overnight • No. 6 (3.36 mm, 0.132 in.) sieve with lid and pan • De-ionized water • Ziplock® bags, quartz size or smaller • Direct shear testing apparatus with a shear box at least 2” square • Optional “mold” the same size and shape as the shear box you have • Permanent marker pen (like a Sharpie™) • Metal utensil that has a flat surface perpendicular to the handle for compacting

sample • Metal or rubber spatula for transferring sample • Small portable tensiometer • Balance with 1000 gram capacity • Tools for moving sample material around such as spatulas or spoons

3.0 Procedure for preparing and running laboratory shear tests on specimens with moisture content 1.1 Calculate the water content associated with degree of saturation (S) of

80% (ωmax ) (Knowing soil wet density (γwet), field water content (ωf) and specific gravity (Gs) of soil, ωmax = S ((γwet / γ) + (γwet * ωf / γ) –(1/Gs ))

1.2 Pan/air dry sample overnight or until dry to the touch.

125

1.3 Perform sieve analysis on dry sample using No. 6 sieve (3.36 mm, 0.132 in.) for 2-inch shear box or 3/8-inch sieve for 4-inch shear box.

1.4 Eliminate particles retained on No. 6 sieve (3.36 mm, 0.132 in.) for 2-inch shear box or on 3/8-inch sieve for 4-inch shear box.

1.5 Mix the remaining material well by stirring it with a spatula. 1.6 Oven dry specimen 1.7 Take a mass of the material from the specimen equal to the dry in-situ

density multiplied by 80% of the volume of the shear box (V). 1.8 Add enough de-ionized water to sample to obtain water content of either

0%, 30%, 60%, or 90% of ωmax and mix it very thoroughly with the spatula.

1.9 Place the damp sample in two sealed Ziplock® bags. 1.10 Use a permanent marker to mark the inside of a mold fabricated similar to

the size of the shear box being used or mark the inside of the shear box itself with a line corresponding to 80% of the shear box volume with. The volume of sample used must remain constant and consistent for all samples.

1.11 Compact the specimen in the mold or the shear box to the marked line in order to achieve the 80% of volume of the shear box and also to approximate the same dry density as in the field. Compact the material in stages instead of all at once. Put 1/3 of the material into the mold or shear box and compact it by pounding on it with a metal utensil that has a flat surface perpendicular to the handle while retaining the remainder of the material in the plastic bag to prevent moisture loss. Then add 1/3 more of the material and compact, finally adding the last third. Make sure the top of the compacted sample coincides with the line you drew on the inside of the mold or shear box. Perform loading and compacting of the sample quickly to prevent loss of moisture.

1.12 Use a small portable tensiometer at two different locations on the sample and measure the matric suction of the sample (in the shear box or the mold). Record the average of these two values as the matric suction of that sample.

1.13 Remove the soil from the mold or shear box and re-compact it in three layers in the shear box only as in step 1.11

1.14 Follow the procedure in the main part of this SOP to perform the direct shear test using a normal stress of 20 KPa. Normal stresses of 20, 60, and 100 KPa will then be used as in the main part of this SOP.

1.15 After the shear test is completed, remove the material from the shear box and place it in a Ziplock® bag. Follow SOP 40 procedure to find the final moisture content of the sample. Record the moisture content.

1.16 Repeat step 1.3 through 1.16 for the same moisture content for two shear tests with different normal stresses of 60 and 100 KPa.

1.17 Follow step 1.3 through 1.16 for different moisture content corresponding to the ωmax

1.18 Plot shear stress vs normal stress for the different water contents (for an example see Figure 1 below).

126

20 KPa 60 KPa 100 KPa

Shear Stress (KPa)

Normal Stress (KPa)

(Ua-Uw) = 0%, 30%, 60%, or 90% of ωmax Matric Suction

Figure 1. Shear stress plotted versus normal stress for the same sample at

three different moisture contents. Addition to this SOP is ASTM D 3080-98: Standard Test Method for Direct Shear Test of Soils under Consolidated Drained Condition.

.

127

Appendix 4. Dry and Wet Sieving Analysis

(a) New Mexico Tech Dry and Wet Sieving Analysis Results

Particle Size Distribution

0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

t

Sample A(dry)

Sample B(wet_dry)

COBBLES GRAVEL SAND

SILT CLAYBOULDERS

Coarse Fine Coarse Medium Fine

3/83 41.5 1 103/4 16 304050 60 200100

U.S. Standard Sieve Size

2 6

Figure 4-1. Gradation curve for sample MIN-SAN-0001 (Debris Flow).


0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

t

Sample A(dry)

Sample B(wet_dry)

COBBLES GRAVEL SAND

SILT CLAYBOULDERS


3/83 41.5 1 103/4 16 30 4050 60 200100U.S. Standard Sieve Size

2 6

Figure 4-2. Gradation curve for sample QPS-SAN-0001 (Alteration Scar).

128


0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

tSample A(dry)

Sample B(wet_dry)

COBBLES GRAVEL SAND

SILT CLAYBOULDERS


3/83 41.5 1 103/4 1 3 4 5 60 200100U.S. Standard Sieve Size

2 6

Figure 4-3. Gradation curve for sample SSW-SAN-0005 (Sugar Shack West).


0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

t

Sample A(dry)

Sample B(wet_dry)

COBBLES GRAVEL SAND

SILT CLAYBOULDERS


3/83 41.5 1 103/4 16 304050 60 200100U.S. Standard Sieve Size

2 6

Figure 4-4. Gradation curve for sample SPR-SAN-0001 (Spring Gulch).

129


0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

tSample A(dry)

Sample B(wet_dry)

COBBLES GRAVEL SAND

SILT CLAYBOULDERS

Coarse Fine Medium Fine

3/83 41.5 1 103/4 16 304050 60 200100


2 6

Coarse

Figure4-5. Gradation curve for sample SSW-SAN-0001 (Sugar Shack West).

130

(b) Golder Laboratory Wet Sieving Analysis Results


0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

t

COBBLES GRAVEL SAND SILT CLAY

BOULDERS


3/83 41.5 1 103/4 16 30 40 50 60 200100


2 6

(a)


0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

t


BOULDERS


3/83 41.5 1 103/4 16 30 40 50 60 200100


2 6

(b) Figure 4-6. Wet sieving analysis results of the samples collected from Debris Flow (MIN-SAN-0002), a) -1-inch field material, b) minus No. 4 sieve material.

131


0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

t


BOULDERS


3/83 41.5 1 103/4 16 30 40 50 60 200100


2 6

(a)


0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

t


BOULDERS


3/83 41.5 1 103/4 16 30 40 50 60 200100


2 6

(b) Figure 4-7. Wet sieving analysis results of the samples collected from Pit Alteration Scar (QPS-SAN-0002), a) -1-inch field material, b) minus No. 4 sieve material.

132


0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

t


BOULDERS


3/83 41.5 1 103/4 16 30 40 50 60 200100


2 6

(a)


0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

t


BOULDERS


3/83 41.5 1 103/4 16 30 40 50 60 200100


2 6

(b) Figure 4-8. Wet sieving analysis results of the samples from Sugar Shack West rock pile (SSW-SAN-0006), a) -1-inch field material, b) minus No. 4 sieve material.

133


0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

t


BOULDERS


3/83 41.5 1 103/4 16 30 40 50 60 200100


2 6

(a)


0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

t


BOULDERS


3/83 41.5 1 103/4 16 30 40 50 60 200100


2 6

(b) Figure 4-9. Wet sieving analysis results of the samples from Spring Gulch rock pile (SPR-SAN-0002), a) -1-inch field material, b) minus No. 4 sieve material.

134


0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

t


BOULDERS


3/83 41.5 1 103/4 16 30 40 50 60 200100


2 6

(a)


0102030405060708090

100

0.0010.010.11101001000Grain Size, mm

Perc

ent P

assi

ng b

y W

eigh

t


BOULDERS


3/83 41.5 1 103/4 16 30 40 50 60 200100


2 6

(b) Figure 4-10. Wet sieving analysis results of the samples from Sugar Shack West rock pile (SSW-SAN-0002), a) -1-inch field material, b) minus No. 4 sieve material.

135

Appendix 5. Shear Displacements, and Normal Displacement Plots for Dry, Moist,

and Wet Conditions

Shear Stress versus Shear Displacement and Normal Displacement versus Shear Displacement Graphs for both 12-Inch and 2.4-Inch Shear Boxes under Dry, Moist, and Wet Conditions (Golder)

0

100

0 10 20 30 40 50 60 70 80

SHEAR DISPLACEMENT (mm)

200

300

400

500

600

SHEA

R S

TRES

S (k

Pa)

MIN-SAN-0002(400kPa)MIN-SAN-0002(50kPa)QPS-SAN-0002(400kPa)QPS-SAN-0002(50kPa)SSW-SAN-0006(400kPa)SSW-SAN-0006(50kPa)SPR-SAN-0002(400kPa)SPR-SAN-0002(50kPa)SSW-SAN-0002(400kPa)SSW-SAN-0002(50kPa)

(a)

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 10 20 30 40 50 60 70 80


NO

RM

AL

DIS

PLA

CEM

ENT

(mm

)


(b)

136

1;τ = 1.0247x + 45.757R2 = 0.9956

2;τ = 1.123x + 18.364R2 = 0.9989

3;τ = 1.1129x + 12.009R2 = 0.986

4;τ = 1.2836x + 11.495R2 = 0.9989

5;τ = 1.0733x + 29.43R2 = 0.9983

0

100

200

300

400

500

600

0 50 100 150 200 250 300 350 400 450

Normal Stress (kPa)

Peak

She

ar S

tres

s (k

Pa)

1-MIN-SAN-00022-QPS-SAN-00023-SSW-SAN-00064-SPR-SAN-00025-SSW-SAN-0002

c)

Figure 5-1. a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot for 12-inch dry samples. Positive normal displacement shows contraction of the sample.

0

100

200

300

400

500

600

700

0 3 6 9 12 15


SHEA

R S

TRES

S (k

Pa)

QPS-SAN-0002(700kPa)

QPS-SAN-0002(50kPa)

SSW-SAN-0006(700kPa)

SSW-SAN-0006(50kPa)

SPR-SAN-0002(700kPa)

SPR-SAN-0002(50kPa)

SSW-SAN-0002(700kPa)

SSW-SAN-0002(50kPa)

(a)

137

-1.6

-1.2

-0.8

-0.4

0

0.4

0.8

1.2

1.6

0 3 6 9 12 15


NO

RM

AL

DIS

PLA

CEM

ENT

(mm

)


(b)

1;τ = 0.8171x + 32.183R2 = 0.9999

2;τ = 0.7943x + 54.366R2 = 0.9985

3;τ = 0.8145x + 30.302R2 = 0.9992

4;τ = 0.7911x + 33.896R2 = 0.9981

5;τ = 0.722x + 64.356R2 = 0.9928

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700 800

Normal Stress (kPa)

Peak

She

ar S

tres

s (k

Pa)


c)

Figure 5-2. a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot for 2.4-inch dry samples. Positive normal displacement shows contraction of the sample.

138

0

100

200

300

400

500

600

0 10 20 30 40 50 60 70 80

SHEA

R S

TRES

S (k

Pa)



(a)

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 10 20 30 40 50 60 70 80


NO

RM

AL

DIS

PLA

CEM

ENT

(mm

)


(b)

139

1;τ = 1.0198x + 33.29R2 = 0.9939

2;τ = 0.9964x + 35.505R2 = 0.9982

3;τ = 0.7469x + 41.28R2 = 0.99

4;τ = 1.1247x + 21.757R2 = 0.9969

5;τ = 0.949x + 37.093R2 = 0.9996

0

100

200

300

400

500

0 50 100 150 200 250 300 350 400 450

Normal Stress (kPa)

Peak

She

ar S

tres

s (k

Pa)


c)

Figure 5-3. a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot for 12-inch moist samples. Positive normal displacement shows contraction of the sample.

0

100

200

300

400

500

600

700

0 3 6 9 12 15


SHEA

R S

TRES

S (k

Pa)


(a)

140

-1.6

-1.2

-0.8

-0.4

0

0.4

0.8

1.2

1.6

0 3 6 9 12 15


NO

RM

AL

DIS

PLA

CEM

ENT

(mm

)


(b)

1;τ = 0.7915x + 29.267R2 = 0.9891

2;τ = 0.7075x + 39.054R2 = 0.9991

3;τ = 0.674x + 47.713R2 = 0.9888

4;τ = 0.8067x + 26.812R2 = 0.9983

5;τ = 0.7222x + 38.792R2 = 0.9882

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700 800

Normal Stress (kPa)

Peak

She

ar S

tres

s (k

Pa)


c)

Figure 5-4. a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot for 2.4-inch moist samples. Positive normal displacement shows contraction of the sample.

141

0

100

200

300

400

500

600

0 10 20 30 40 50 60 70 80


SHEA

R S

TRES

S (k

Pa)


(a)

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 10 20 30 40 50 60 70 80


NO

RM

AL

DIS

PLA

CEM

ENT

(mm

)


(b)

142

1;τ = 0.8452x + 12.888R2 = 0.9984

2;τ = 0.8905x + 20.776R2 = 0.9946

3;τ = 0.68x + 18R2 = 0.9925

4;τ = 0.877x + 43.636R2 = 0.9883

5;τ = 0.9202x + 13.71R2 = 0.9976

0

100

200

300

400

500

0 50 100 150 200 250 300 350 400 450

Normal Stress (kPa)

Peak

She

ar S

tres

s (k

Pa)


c)

Figure 5-5. a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot for 12-inch wet samples. Positive normal displacement shows contraction of the sample.

0

100

200

300

400

500

600

700

0 3 6 9 12 15


SHEA

R S

TRES

S (k

Pa)


(a)

143

144

-1.6

-1.2

-0.8

-0.4

0

0.4

0.8

1.2

1.6

0 3 6 9 12 15


NO

RM

AL

DIS

PLA

CEM

ENT

(mm

)


(b)

1;τ = 0.724x + 20.213R2 = 0.9973

2;τ = 0.6846x + 24.02R2 = 0.9983

3;τ = 0.5941x + 22.931R2 = 0.9932

4;τ = 0.6532x + 30.97R2 = 0.9843

5;τ = 0.7166x + 26.094R2 = 0.9978

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700 800

Normal Stress (kPa)

Peak

She

ar S

tres

s (k

Pa)


c)

Figure 5-6. a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot for 2.4-inch wet samples. Positive normal displacement shows contraction of the sample.

145

Shear Stress versus Shear Displacement, Normal Displacement versus Shear Displacement, Mohr-Coulomb Graphs for 2-inch Shear Box and dry samples using High Normal stress These tests were conducted at New Mexico Tech. MIN-SAN-0001

0

200

400

600

800

0 2 4 6 8 10 12Shear Displacement (mm)

Shea

r Str

ess

(kPa

)

Normal Stress = 53kPa




MIN-SAN-0001

-2

-1.2

-0.4

0.4

1.2

2

0 2 4 6

Shear Displacemen

Nor

mal

Dis

plac

emen

t (m

m)

Normal stress = 53kPa

Normal stress = 152kPaNormal stress = 403kPa

Normal stress = 702kPa

8 10 12

t (mm)

(a) (b)

τ = 0.8305x + 26.055R2 = 0.9992

τ = 0.8407x - 0.1227R2 = 0.9996

0

200

400

600

800

0 200 400 600 800Normal Load (kPa)

Pea

k S

hear

Stre

ss (k

Pa)

Friction angle Residual Friction angle

(c)

Figure 5-7. a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot, for Debris Flow samples. Positive normal displacement shows dilation of the sample.

QPS-SAN-0001

0

200

400

600

800


Shea

r Str

ess

(kPa

)



Normal Stress = 403kPaNormal Stress = 702 kPa

QPS-SAN-0001

-2

-1.2

-0.4

0.4

1.2

2

0 2 4 6 8 10 12


Nor

mal

Dis

plac

emen

t (m

m)

Normal stress = 53 kPaNormal stress = 152 kPaNormal stress = 403 kPaNormal stress = 702 kPa

(a) (b)

τ = 0.7923x + 33.406R2 = 0.9987

τ = 0.6747x + 29.18R2 = 0.995

0

200

400

600

800

0 200 400 600 800Normal Load (kPa)

Pea

k S

hear

Stre

ss (k

Pa)


(c) Figure 5-8 a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot, for Pit Alteration Scar samples. Positive normal displacement shows dilation of the sample.

146

SPR-SAN-0001

0

200

400

600

800


Shea

r Str

ess

(kPa

)Normal Stress = 53kPa




SPR-SAN-0001

-2

-1.2

-0.4

0.4

1.2

2

0 2 4 6 8 10 12


Nor

mal

Dis

plac

emen

t (m

m)

Normal stress = 53kPaNormal stress = 152kPaNormal stress = 403kPaNormal stress = 702kPa

(a) (b)

τ = 0.7843x + 26.596R2 = 0.9982

τ = 0.6792x + 32.388R2 = 0.9983

0

200

400

600

800

0 200 400 600 800Normal Load (kPa)

Pea

k S

hear

Stre

ss (k

Pa)


(c) Figure 5-9 a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot, for Spring Gulch samples. Positive normal displacement shows dilation of the sample.

147

148

SSW-SAN-0001

0

200

400

600

800


Shea

r Str

ess

(kPa

)



Normal Stress = 403kPaNormal Stress = 702kPa

SSW-SAN-0001

-2

-1.2

-0.4

0.4

1.2

2

0 2 4 6 8 10 12


Nor

mal

Dis

plac

emen

t (m

m)


(a) (b)

τ= 0.8876x + 17.668R2 = 0.9996

τ = 0.8328x + 6.7978R2 = 0.9998

0

200

400

600

800

0 200 400 600 800Normal Load (kPa)

Pea

k S

hear

Stre

ss (k

Pa)


(c) Figure 5-10 a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot, for Sugar Shack West samples. Positive normal displacement shows dilation of the sample.

149

SSW-SAN-0005

0

200

400

600

800


Shea

r Str

ess

(kPa

)Normal Stress = 53kPa


Normal Stress = 403kPaNormal Stress = 702kPa

SSW-SAN-0005

-2

-1.2

-0.4

0.4

1.2

2

0 2 4 6 8 10 12


Nor

mal

Dis

plac

emen

t (m

m)


(a) (b)

τ = 0.709x + 28.886R2 = 0.9972

τ = 0.7129x + 18.999R2 = 0.9975

0

200

400

600

800

0 200 400 600 800Normal Load (kPa)

Pea

k S

hear

Stre

ss (k

Pa)


(c) Figure 5-11 a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot, for Sugar Shack West samples. Positive normal displacement shows dilation of the sample.

150

Shear Stress versus Shear Displacement and Normal Displacement versus Shear Displacement Graphs for 2-inch Shear Box and dry samples using low normal stress and conducted at NMT.

MIN-SAN-0001-1

-1

-0.6

-0.2

0.2

0.6

1

1.4

1.8


Nor

mal

Dis

plac

emen

t (m

m)


MIN-SAN-0001-1

0

40

80

120

160

200


Shea

r str

ess

(kPa

)

Normal stress = 52kPaNormal stress = 82kPaNormal stress = 120kPaNormal stress =150kPa

(a) (b)

τ = 0.9088x + 31.417R2 = 0.9853

τ = 0.9092x + 0.939R2 = 0.9885

0

50

100

150

200

0 40 80 120 160Normal Load (kPa)

She

ar s

treng

th (k

Pa)


(c) Figure 5-12. a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot, for Debris Flow samples Positive normal displacement shows dilation of the sample.

QPS-SAN-0001-1

0

40

80

120

160

200


Shea

r str

ess

(kPa

)


QPS-SAN-0001-1

-1

-0.6

-0.2

0.2

0.6

1

1.4

1.8


Nor

mal

Dis

plac

emen

t (m

m)


(a) (b)

τ = 0.8524x + 25.343R2 = 0.9767

τ= 0.6907x + 12.807R2 = 0.9676

0

50

100

150

200


She

ar s

treng

th (k

Pa)

Friction angle Residual Friction angle (c) Figure 5-13 a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot, for Pit Alteration Scar samples. Positive normal displacement shows dilation of the sample.

151

SPR-SAN-0001-1

0

40

80

120

160

200


Shea

r str

ess

(kPa

)

Normal stress =150kPaNormal stress = 120kPaNormal stress = 82kPaNormal stress = 52kPa

SPR-SAN-0001-1

-1

-0.6

-0.2

0.2

0.6

1

1.4

1.8


Nor

mal

Dis

plac

emen

t (m

m)


(a) (b)

τ = 0.9315x + 26.333R2 = 0.9539

τ = 0.8485x + 7.1496R2 = 0.9954

0

50

100

150

200


She

ar s

treng

th (k

Pa)

Friction angle Residual Friction angle (c) Figure 5-14 a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot, for Spring Gulch samples. Positive normal displacement shows dilation of the sample.

152

153

SSW-SAN-0001-1

0

40

80

120

160

200


Shea

r str

ess

(kPa

)


SSW-SAN-0001-1

-1

-0.6

-0.2

0.2

0.6

1

1.4

1.8


Nor

mal

Dis

plac

emen

t (m

m)


(a) (b)

τ = 1.0596x + 17.849R2 = 0.9895

τ = 0.7456x + 12.316R2 = 0.9928

0

50

100

150

200


She

ar s

treng

th (k

Pa)

Friction angle Residual Friction angle (c) Figure 5-15 a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot, for Sugar Shack West samples. Positive normal displacement shows dilation of the sample.

SSW-SAN-0005-1

0

40

80

120

160

200


Shea

r str

ess

(kPa

)


SSW-SAN-0005-1

-1

-0.6

-0.2

0.2

0.6

1

1.4

1.8


Nor

mal

Dis

plac

emen

t (m

m)


(a) (b)

τ = 0.852x + 32.144R2 = 0.9983

τ = 0.9047x + 1.6386R2 = 0.9929

0

50

100

150

200


She

ar s

treng

th (k

Pa)

Friction angle Residual Friction angle (c) Figure 5-16 a) Shear stress vs. shear displacement, b) normal displacement vs. shear displacement, c) Mohr Coulomb plot, for Sugar Shack West samples. Positive normal displacement shows dilation of the sample.

154

155

Non-Linear Coulomb Failure Envelopes for the 12-Inch and 2.4-Inch Direct Shear Tests Samples, under Dry, Moist and Wet Conditions (Golder)

1;y=3.9826x0.7888

2 ;y=1.9817x0.9109

3 ;y = 2.3969x0.8688

5;y=3.4847x0.808

4;y=2.2382x0.9063

0

100

200

300

400

500

600

700

0 50 100 150 200 250 300 350 400 450

NORMAL STRESS (kPa)

PEA

K S

HEA

R S

TRES

S (k

Pa)

1-MIN-SAN-0002_12INCH DRY_GOLDER TEST2-QPS-SAN-0002_12INCH DRY_GOLDER TEST3-SSW-SAN-0006_12INCH DRY_GOLDER TEST4-SPR-SAN-0002_12INCH DRY_GOLDER TEST5-SSW-SAN-0002_12INCH DRY_GOLDER TEST

(a)

1;y=2.8454x0.8114

3;y=2.3201x0.8448

4;y=2.9626x0.8013

5;y=4.7484x0.7282

2;y=6.142x0.6896

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700

NORMAL STRESS (kPa)

PEA

K S

HEA

R S

TRES

S (k

Pa)

1-MIN-SAN-0002_2.4INCH DRY_GOLDER TEST2-QPS-SAN-0002_2.4INCH DRY_GOLDER TEST3-SSW-SAN-0006_2.4INCH DRY_GOLDER TEST4-SPR-SAN-0002_2.4INCH DRY_GOLDER TEST5-SSW-SAN-0002_2.4INCH DRY_GOLDER TEST

(b) Figure 5-17. Curve failure envelope for a) 12-inch and b) 2.4-inch dry samples.

1;y = 2.565x0.8597

2;y = 3.3557x0.8081

3;y = 3.5387x0.7602

5;y = 4.4004x0.7515

4;y = 2.0322x0.9094

0

100

200

300

400

500

600

700

0 50 100 150 200 250 300 350 400 450

NORMAL STRESS (kPa)

PEA

K S

HEA

R S

TRES

S (k

Pa)

1-MIN-SAN-0002_12INCH MOIST_GOLDER TEST2-QPS-SAN-0002_12INCH MOIST_GOLDER TEST3-SSW-SAN-0006_12INCH MOIST_GOLDER TEST4-SPR-SAN-0002_12INCH MOIST_GOLDER TEST5-SSW-SAN-0002_12INCH MOIST_GOLDER TEST

(a)

1 ;y = 1.6993x0.8923

2; y = 3.5449x0.7575

3; y = 3.6806x0.7505

4; y = 1.7999x0.8844

5;y = 2.4743x0.8217

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700

NORMAL STRESS (kPa)

PEA

K S

HEA

R S

TRES

S (k

Pa)

1-MIN-SAN-0002_2.4INCH MOIST_GOLDER TEST2-QPS-SAN-0002_2.4INCH MOIST_GOLDER TEST3-SSW-SAN-0006_2.4INCH MOIST_GOLDER TEST4-SPR-SAN-0002_2.4INCH MOIST_GOLDER TEST5-SSW-SAN-0002_2.4INCH MOIST_GOLDER TEST

(b) Figure 5-18. Curve failure envelope for a) 12-inch and b) 2.4-inch moist samples.

156

157

1; y = 1.9532x0.8601

2; y = 1.672x0.9057

3; y = 1.2555x0.9115

5; y = 2.358x0.8405

4; y = 3.4259x0.7918

0

100

200

300

400

500

600

700

0 50 100 150 200 250 300 350 400 450

NORMAL STRESS (kPa)

PEA

K S

HEA

R S

TRES

S (k

Pa)

1-MIN-SAN-0002_12INCH WET_GOLDER TEST2-QPS-SAN-0002_12INCH WET_GOLDER TEST 3-SSW-SAN-0006_12INCH WET_GOLDER TEST

4-SPR-SAN-0002_12INCH WET_GOLDER TEST 5-SSW-SAN-0002_12INCH WET_GOLDER TEST

(a)

1;y = 1.657x0.8763

2; y = 1.6533x0.872

3;y = 1.3234x0.8873

4; y = 1.5662x0.8794

5; y = 1.6826x0.8775

0

100

200

300

400

500

600

0 100 200 300 400 500 600 700

NORMAL STRESS (kPa)

PEA

K S

HEA

R S

TRES

S (k

Pa)

1-MIN-SAN-0002_2.4INCH WET_GOLDER TEST2-QPS-SAN-0002_2.4INCH WET_GOLDER TEST3-SSW-SAN-0006_2.4INCH WET_GOLDER TEST4-SPR-SAN-0002_2.4INCH WET_GOLDER TEST5-SSW-SAN-0002_2.4INCH WET_GOLDER TEST

(b) Figure 5-19. Curve failure envelope for a) 12-inch and b) 2.4-inch wet samples.

Non-Linear Coulomb Failure Envelopes for 2-Inch Direct Shear Tests Samples under Dry Conditions (NMT)

1;y = 2.4189x0.8376

R2 = 0.998

2;y = 3.1464x0.7905

R2 = 0.9959

3;y = 2.5552x0.8065

R2 = 0.9968

4;y = 2.5371x0.8211

R2 = 0.997

5;y = 2.0025x0.8743

R2 = 0.9978

0

100

200

300

400

500

600

700

0 100 200 300 400 500 600 700 800

NORMAL STRESS (kPa)

PEA

K S

HEA

R S

TRES

S (k

Pa)

1-MIN-SAN-0001(DRY_NMT TEST)2-QPS-SAN-0001(DRY_NMT TEST)3-SSW-SAN-0005(DRY_NMT TEST)4-SPR-SAN-0001(DRY_NMT TEST)5-SSW-SAN-0001(DRY_NMT TEST)

Figure 5-20. Curve failure envelope for 2-inch dry samples.

158

Appendix 6. Golder Associates Triaxial Test Results CIU1, CIU2, CIU3, CIU4 are indicating Consolidated Undrained tests using confining pressures of 38, 131.9, 276.5, 678 kPa, respectively.

MIN-SAN-0002

0

50

100

150

200

250

300

0 2 4 6 8 10 12 14 16 18 20

Axial Strain (%)

Dev

iato

r Str

ess

(kPa

) CIU 1CIU 2CIU 3CIU 4

MIN-SAN-0002

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 2 4 6 8 10 12 14 16 18 20

Axial Strain (%)

stre

ss ra

tio

CIU 1CIU 2CIU 3CIU 4

MIN-SAN-0002

0

100

200

300

400

500

600

0 2 4 6 8 10 12 14 16 18 20

Axial Strain (%)

Exce

ss P

ore

Pres

sure

(kPa

)


Figure 6-1.Deviator stress (q = (σ´1 - σ´3)/2), stress ratio (q/p' MAX) and excess pore pressure versus axial strain for MIN-SAN-0002 sample.

159

QPS-SAN-0002

0

50

100

150

200

250

300

350

0 2 4 6 8 10 12 14 16 18 20

Axial Strain (%)

Dev

iato

r Str

ess

(kPa

) CUI 1CIU 2CIU 3CIU 4

QPS-SAN-0002

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 2 4 6 8 10 12 14 16 18 20

Axial Strain (%)

Stre

ss ra

tio CUI 1

CIU 2

CIU 3

CIU 4

QPS-SAN-0002

0

100

200

300

400

500

600

0 2 4 6 8 10 12 14 16 18 20

Axial Strain (%)

Exce

ss P

ore

Pres

sure

(kPa

)


Figure 6-2. Deviator stress (q = (σ´1 - σ´3)/2), stress ratio (q/p' MAX) and excess pore pressure versus axial strain for QPS-SAN-0002 sample.

160

SSW-SAN-0006

0

50

100

150

200

250

300

0 2 4 6 8 10 12 14 16 18 20

Axial Strain (%)

Dev

iato

r Str

ess

(kPa

)


SSW-SAN-0006

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 2 4 6 8 10 12 14 16 18 2

Axial Strain (%)

Stre

ss ra

tio

0


SSW-SAN-0006

0

100

200

300

400

500

600

0 2 4 6 8 10 12 14 16 18 20

Axial Strain (%)

Exec

ess

Pore

Pre

ssur

e (k

Pa)


Figure 6-3. Deviator stress (q = (σ´1 - σ´3)/2), stress ratio (q/p' MAX) and excess pore pressure versus axial strain for SSW-SAN-0006 sample.

161

SPR-SAN-0002

0

50

100

150

200

250

300

0 2 4 6 8 10 12 14 16 18 20

Axial Strain (%)

Dev

iato

r Str

ess

(kPa

) CIU 1CIU 2CIU 3CIU 4

SPR-SAN-0002

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 2 4 6 8 10 12 14 16 18 20

Axial Strain (%)

Stre

ss ra

tio


SPR-SAN-0002

0

100

200

300

400

500

600

0 2 4 6 8 10 12 14 16 18 20

Axial Strain (%)

Exce

ss P

ore

Pres

sure

(kPa

) CUI 1CUI 2CIU 3CIU 4

Figure 6-4. Deviator stress (q = (σ´1 - σ´3)/2), stress ratio (q/p' MAX) and excess pore pressure versus axial strain for SPR-SAN-0002 sample.

162

SSW-SAN-0002

0

50

100

150

200

250

300

0 2 4 6 8 10 12 14 16 18 20

Axial Strain (%)

Dev

iato

r Str

ess

(kPa

)


SSW-SAN-0002

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 2 4 6 8 10 12 14 16 18 2

Axial Strain (%)

Stre

ss ra

tio

0


SSW-SAN-0002

0

100

200

300

400

500

600

0 5 10 15 20 25

Axial Strain (%)

Exce

ss P

ore

Pres

sure

(kPa

) CIU 1CIU2CIU 3CIU 4

Figure 6-5. Deviator stress (q = (σ´1 - σ´3)/2), stress ratio (q/p' MAX) and excess pore pressure versus axial strain for SSW-SAN-0002 sample.

163

b) Mohr Circle Plots

Figure 6-6. The Mohr circles and failure envelope for MIN-SAN-0002 Sample

164

Figure 6-7. The Mohr circles and failure envelope for QPS-SAN-0002 Sample

165

Figure 6-8. The Mohr circles and failure envelope for SSW-SAN-0006 Sample

166

Figure 6-9. The Mohr circles and failure envelope for SPR-SAN-0002 Sample

167

Figure 6-10. The Mohr circles and failure envelope for SSW-SAN-0002 Sample

168

c) Best Fit Plots

MIN-SAN-0002

y = 4.4545x + 14.402R2 = 0.8953

0

100

200

300

400

500

600

700

0 20 40 60 80 100 120 140σ3´ (kPa)

σ1´(

kPa)

Figure 6-11. Best Fit Plots using effective confining pressures for MIN-SAN-0002 Sample

QPS-SAN-0002

y = 4.6912x + 34.062R2 = 0.9988

0

100

200

300

400

500

600

700

800

0 20 40 60 80 100 120 140 160σ3´ (kPa)

σ 1´ (

kPa)

Figure 6-12. Best Fit Plots using effective confining pressures for QPS-SAN-0002 Sample

169

SSW-SAN-0006

y = 4.4694x + 45.537R2 = 0.9895

0

100

200

300

400

500

600

700

0 20 40 60 80 100 120 140 160σ3´ (kPa)

σ 1´ (

kPa)

Figure 6-13. Best Fit Plots using effective confining pressures for SSW-SAN-0006 Sample

SPR-SAN-0002

y = 5.3431x + 26.803R2 = 0.9993

0

100

200

300

400

500

600

700

0 20 40 60 80 100 120 140σ3´ (kPa)

σ 1´ (

kPa)

Figure 6-14. Best Fit Plots using effective confining pressures for SPR-SAN-0002 Sample.

170

171

SSW-SAN-0002

y = 4.9338x + 23.708R2 = 0.9544

0

100

200

300

400

500

600

700

800

0 20 40 60 80 100 120 140σ3´ (kPa)

σ 1´ (

kPa)

Figure 6-15. The best fit failure envelope for sample SSW-SAN-0002 Sample

Documents

GEOTECHNICAL EVALUATION OF QUESTA MINE MATERIAL, … · 2009-04-28 · GEOTECHNICAL EVALUATION OF QUESTA MINE MATERIAL, TAOS COUNTY, NEW MEXICO . by . ... showed that rock fragments