Geotechnical Investigation Bow Ridge Subdivision Phase 3

Geotechnical Investigation Bow Ridge Subdivision Phase 3 Cochrane, Alberta

FINAL

Prepared for: The Town of Cochrane 101 Ranchehouse Road Cochrane, Alberta

Prepared by: Stantec Consulting Ltd. Calgary, Alberta

PROJECT NO. 123310172 April 6, 2010

Geotechnical Investigation Bow Ridge Subdivision Phase 3 Final

E.1

Executive Summary

As requested by the Town of Cochrane, Stantec Consulting Ltd. (Stantec) has carried out a geotechnical investigation in Bow Ridge Subdivision Phase 3 in Cochrane, Alberta (see Figures 1 and 2, Appendix B). The purpose of the investigation is to determine the cause of differential movements of two (2) rows of gabion retaining walls within Phase 3, and to provide geotechnical recommendations for remedial measures from the geotechnical engineering perspective.

Field Work – Stantec advanced a total of twelve (12) boreholes along the retaining walls. Representative soil samples were collected at regular intervals. Standpipe piezometers and slope inclinometers were installed in all the boreholes to permit groundwater level and ground displacement monitoring. Groundwater level and ground displacement monitoring were carried out on a monthly basis between July 2009 and February 2010. In addition, a 3D laser survey was completed to measure and document the existing conditions of the retaining walls.

Existing Design Review – The original design of the retaining walls was reviewed. It is understood that a section of the retaining wall has been repaired with a “Retrofit Wall” design, and reconstructed with a “Rebuild Wall” design. Both Retrofit Wall and Rebuild Wall designs were also reviewed by Stantec. Stability analyses against both overturning and sliding of the retaining walls in all three (3) designs were completed. Based on the parameters provided in the designs, the Factor of Safety against both overturning and sliding appeared to be adequate. The Factor of Safety was recalculated based on recommendations provided in the Canadian Foundation Engineering Manual. The results indicated that all three (3) existing wall designs have inadequate Factors of Safety against sliding. In addition, Stantec is of the opinion that frost action of the clay fill material contributed to the differential movements of the retaining walls. Other factors such as poor quality of the base drainage gravel, undermining of the base of the retaining walls during construction, and migration of the subgrade soil into the gabion baskets may also have contributed to the differential movements.

Based on the results of the inclinometer monitoring, the maximum accumulated lateral displacements of the retaining walls during the measurement period were in the order of 8 mm. The measured displacements represent movements that occurred within the monitoring period only and do not represent total displacements experienced by the wall since construction. Based on the inclinometer results, we are of the opinion that failure planes do not exist within the measurement depths at the borehole locations, with the exception of borehole BH8. At borehole BH8, the inclinometer results indicate an impending bearing capacity failure in the soil below the retaining wall.

Conclusion – Based on the information provided and our observations during the field investigation, no signs of global instability were observed or reported within the subdivision outside of the immediate areas of the retaining walls. However continued localized movements or failure of the retaining walls should be expected.

Recommendation – Stantec is of the opinion that remediation of the existing retaining walls using the existing design will not be effective. It is recommended that the retaining walls be removed entirely and reconstructed using other alternate wall systems.

• The wall at and near borehole BH8 should be repaired or reconstructed as soon as possible.

• Continued monitoring at all borehole locations on a monthly basis should be carried out prior to repair or reconstruction to provide warning of potentially dangerous situations. The monitoring program should be reviewed annually.

• Homeowners need to be advised that downspouts should not discharge directly on to the gabion retaining walls.

• Construction of other retaining walls within backyards without proper geotechnical design is not recommended.


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Table of Contents

1 INTRODUCTION ......................................................................................................... 1

1.1 Site and Geology .......................................................................................... 1 1.2 Background .................................................................................................. 1

2 METHOD OF INVESTIGATION ................................................................................. 5

2.1 Field Investigation ........................................................................................ 5 2.2 Laboratory Testing....................................................................................... 5 2.3 Laser Survey Scan of Walls ........................................................................ 6 2.4 Slope Inclinometer Installation ................................................................... 7

3 RESULTS OF INVESTIGATION ................................................................................ 7

3.1 General .......................................................................................................... 7 3.2 Surficial Materials ........................................................................................ 7 3.3 Fill Materials ................................................................................................. 7

3.3.1 Clay ................................................................................................... 7

3.3.2 Gravel ................................................................................................ 8

3.4 Clay (CL-CH) ................................................................................................. 8 3.5 Sandy Silt (ML) and Silty Sand (SM) .......................................................... 8 3.6 Low Plastic Clay (CL)................................................................................... 9 3.7 Groundwater ................................................................................................. 9

4 DISCUSSION ............................................................................................................ 11

4.1 Original Wall ............................................................................................... 11 4.1.1 Design Data .................................................................................... 11

4.1.2 Stability Analyses ............................................................................ 12

4.1.3 Wall Construction ............................................................................ 13

4.2 Retrofit Wall ................................................................................................ 14 4.3 Rebuilt Wall ................................................................................................. 18 4.4 Slope Inclinometer Results ....................................................................... 20 4.5 Global Stability of the Subdivision and Local Stability of the Walls .... 21

5 RECOMMENDATIONS ............................................................................................. 24

6 CLOSURE ................................................................................................................. 25


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APPENDIX A STATMENT OF GENERAL CONDITIONS

APPENDIX B FIGURES

APPENDIX C BOREHOLE RECORDS

APPENDIX D LABORATORY TESTING

APPENDIX E SLOPE INCLINOMETER READINGS

APPENDIX F UNIFIED SOIL CLASSIFICATION SYSTEM

APPENDIX G EXAMPLES OF MSE WALLS FROM SIERRA

List of Tables

Table 3-1 Groundwater Levels July 2009 to September 2009 ................................ 10

Table 3-2 Groundwater Levels November 2009 to February 2010 ......................... 10

Table 4-1 Analysis Parameters based on Stantec Investigation – Original Wall Analyses ..................................................................................................... 12

Table 4-2 Calculated Factor of Safety (Original Wall) ............................................. 13

Table 4-3 Calculated Factor of Safety (Original Wall using ka = 1.0) ..................... 13

Table 4-4 Analysis Parameters based on Stantec Investigation – Retrofit Wall Analyses ..................................................................................................... 15

Table 4-5 Analysis Parameters based on Stantec Investigation – Rebuilt Wall Analyses ..................................................................................................... 18

List of Figures

Figure 1 Site Location Plan .................................................................... APPENDIX B

Figure 2 Site Plan .................................................................................... APPENDIX B

Figure 4-1 Original Wall Design Cross Sections ....................................................... 12

Figure 4-2 Retrofit Wall Design ................................................................................... 16

Figure 4-3 Cross Section at Borehole BH7 ................................................................ 17


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Figure 4-4 Rebuilt Wall Design.................................................................................... 19

Figure 4-5 Cross Sections through Rebuilt Wall....................................................... 20

List of Photos

Photo 1-1 Failure of stairway connecting Bow Ridge Link and Bow Ridge Close . 3

Photo 1-2 Support Column of Stairway ....................................................................... 3

Photo 1-3 Evidence of settlement at 10 Bow Ridge Close ........................................ 4

Photo 2-1 Typical laser scanned image ...................................................................... 6

Photo 4-1 Progressive Buckling of Fence ................................................................ 22


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1 INTRODUCTION Stantec Consulting Ltd. (Stantec), acting in accordance with the terms of reference provided by our proposal number 116599000.100.200, has carried out a geotechnical investigation in Bow Ridge Subdivision Phase 3 in Cochrane, Alberta. Specifically, Stantec was requested to investigate the stability of the two (2) rows of gabion retaining walls within Phase 3, and if necessary, to provide conceptual remedial recommendations to stabilize the walls. Authorization to proceed with the work was received from Mr. Mike Saley, P.Eng., Director of Planning and Engineering, from the Town of Cochrane on May 19, 2009.

The scope of the geotechnical investigation was carried out as indicated in the above mentioned proposal and as discussed within the text of this report. The scope of work for this investigation included the following:

• Coordinate and supervise underground utility locates

• Conduct site visits to observe differential movements of the gabion retaining walls

• Conduct a field drilling program to characterize the soil and groundwater conditions and assess their possible contribution to observed deformations and measured displacements of the gabion retaining walls

• Preparation of a report presenting the factual information obtained during this investigation and provide geotechnical recommendations for remedial measures from the geotechnical engineering perspective

1.1 Site and Geology

Bow Ridge Subdivision Phase 3 is located in SW¼ of Section 4, Township 26, Range 4, West of 5 Meridian in Cochrane, Alberta (Figure 1, Appendix B); herein referred to as the Site. The two subject gabion retaining walls are located on the back of the lots along Bow Ridge Link and Bow Ridge Drive (see Figure 2, Appendix B). For the purpose of this report, the walls located on the south and north are labeled as Retaining Wall A and B, respectively.

Based on published geological information1 and our experience in the area, it was expected that the Site would be located within a lacustrine deposit of silt and clay.

1.2 Background

The following documents were reviewed prior to completion of this report:

• Almor Engineering Associates Ltd. (Almor) report Retaining Wall Evaluation – Bow Ridge Phase 3 Subdivision, Cochrane, dated October 17, 2003

• McIntosh-Lalani Engineering Ltd. report Bow Ridge Gabion Basket Retaining Wall, dated September 12, 2003

• Almor report Foundation Considerations – Bow Ridge Phase 2 and 3, dated July 27, 2000

• Almor report Retaining Wall Recommendations – Bow Ridge Phase 3 Subdivision, dated March 15, 1999

1 Shetsen, I., 1987. Quaternary Geology, Southern Alberta, Alberta Research Council


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• Almor report Subsoil Investigation – Bow Ridge Subdivision, dated October, 1996

• Geo-Engineering (M.S.T.) Ltd. report Bow Ridge Developments – Report on Preliminary Slope Stability Assessment, dated June, 1994

Based on the information from the above listed documents, communication with the Town of Cochrane, and our observations, it is understood that the subject gabion retaining walls have undergone differential movements. We also understand that the east portion of Retaining Wall B has been repaired. Two (2) methods (referred to in this report as Retrofit Wall and Rebuilt Wall) were used to repair this section of the retaining wall.

Based on the results of our site visits, the observed distresses and conditions of the retaining walls and the surrounding structures are as follows:

• Gabion baskets were pushed out in various locations along the retaining wall.

• Ground subsidence was noted behind the retaining wall at several locations.

• Adjacent fences of the walkway connecting Bow Ridge Link and Bow Ridge Drive, at the toe of Retaining Wall B, showed progressively more buckling of the panels towards the toe of the wall.

• Fences at both the top and toe of the walls at several locations were observed to be leaning.

• Two (2) wood-framed stairways, located between Bow Ridge Close and Bow Ridge Link, and between Bow Ridge Link and Bow Ridge Drive, were damaged and the wood components were separated at various locations (see Photo 1-1).

• Water discharge from roof downspouts towards the back of the retaining walls were observed at some locations.

• Private retaining walls built in some backyards (behind the gabion walls) were observed.

• The support columns of the stairways were supposed to be founded on concrete piers. However, due to differential movements, the support columns were pushed away from the piers and were no longer bearing on the concrete piers (see Photo 1-2).

• Evidence of backyard subsidence was observed at 10 Bow Ridge Close behind the retaining wall adjacent to the stairways connecting Bow Ridge Link and Bow Ridge Close (see Photo 1-3, note the elevation difference on both sides of the red line).


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Photo 1-1 Failure of stairway connecting Bow Ridge Link and Bow Ridge Close

Photo 1-2 Support Column of Stairway


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Photo 1-3 Evidence of settlement at 10 Bow Ridge Close


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2 METHOD OF INVESTIGATION

2.1 Field Investigation

Prior to the start of the investigation, Stantec personnel made arrangements to verify the locations of underground utilities at and near the proposed borehole locations. The fieldwork for the investigation was carried out from June 4 to 18, 2009. Twelve (12) boreholes (numbered BH1 to BH12) were advanced using a track-mounted solid stem auger drill rig operated by Mobile Augers and Research Ltd. of Calgary, Alberta. The boreholes were advanced to depths ranging from 6.9 m to 9.9 m below existing grade. Borehole locations are shown on Figure 2, Appendix B.

The subsurface stratigraphy encountered in the boreholes was recorded by Stantec personnel as the boreholes were advanced. Representative samples of each stratum encountered were collected at close intervals during the performance of Standard Penetration Tests (SPTs) and from the auger flights. Pocket penetrometer tests were carried out on samples of cohesive soils to assist with the assessment of the shear strengths of the soils.

Standpipe piezometers were installed in all boreholes to permit groundwater level monitoring. The standpipe piezometers were monitored between July 2, 2009 and February 9, 2010. The groundwater levels are shown in Table 3-1 and Table 3-2 (see Section 3.7) and on the Borehole Records in Appendix C.

2.2 Laboratory Testing

All samples recovered were stored in moisture tight containers and were returned to our Calgary laboratory for detailed classification and testing. Laboratory testing was performed on selected samples. The results of the laboratory testing are provided on the Borehole Records in Appendix C, presented in Appendix D, or are discussed in Section 3 of this report. Symbols and terms used in the borehole records are included in Appendix C.

Laboratory testing was carried for the purposes of determining the classifications and strengths of the site soils accurately, in order to understand past behaviour and predict future behaviour of the soils. The tests carried out and the corresponding information of the tests are outlined below.

• Moisture Content – determination of the percentage of water to soil solids by weight

• Atterberg Limits – determination of the degree of plasticity of a soil through the determination of moisture contents at which the soil exhibits solid, plastic and liquid states

• Grain Size Analysis – determination of the percentages by weight of gravel, sand, silt/clay sized particles in a soil using sieves

Samples remaining after testing will be stored for a period of three (3) months after issuance of this report. Samples will be discarded after this period unless we are otherwise directed.


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2.3 Laser Survey Scan of Walls

To accurately measure and document the existing conditions of the retaining walls, state-of-the-art 3D laser scanning techniques were employed to produce 3D topographic visuals of the wall surface. 3D laser scanners collect approximately 50,000 points per second, gathering more data in less time than traditional surveying techniques, with higher accuracy and less inconvenience to the homeowners. Whereas conventional survey techniques allow for the walls to be documented and analyzed only at pre-defined locations, the volume of data using the laser scanner allows the entire walls to be analyzed. If deemed required, laser scanning also allows for ongoing monitoring of wall deformation by providing a fast, convenient way of comparing the current wall locations to measurements made previously. A typical laser scanned image is shown in Photo 2-1.

Photo 2-1 Typical laser scanned image


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2.4 Slope Inclinometer Installation

Slope inclinometers were installed in all the boreholes for ground displacement monitoring. Inclinometer casings are heavy-walled PVC pipes with 2 sets of grooves at 90 degrees to each other (typically installed perpendicular and parallel to the face of the wall). These grooves allow the instrument to provide a three dimensional (x-y-z directions, i.e. parallel-perpendicular-depth) model of soil movements. The inclinometers were protected with flush-mounted road boxes. The slope inclinometers were monitored between July 2, 2009 and February 9, 2010. The results of the monitoring are presented in Appendix E and are discussed in the text of this report (see Section 4.4).

3 RESULTS OF INVESTIGATION

3.1 General

The subsurface conditions encountered in the boreholes are described in detail on the Borehole Records, with additional and supplementary information provided in this section. All soil descriptions and identifications during drilling were made in accordance with ASTM Standard D2488 (Visual Manual Procedure). The Borehole Records, along with an explanation of the symbols and terms used in their description, are provided in Appendix C.

In general, the observed stratigraphy consisted of topsoil or fill overlying clay, which extended to silt and sand deposits.

3.2 Surficial Materials

Topsoil was present at the surface in eight (8) of the twelve (12) boreholes (BH1, BH2, BH4, BH5, BH6, BH9, BH11, and BH12) and ranged in thickness from 200 mm to 300 mm. It should be noted that borehole BH3 was drilled through existing pavement; a 150 mm thick layer of asphalt and 350 mm thick layer of base gravel were encountered at the surface. Gravel surfacing (approximately 100 mm to 200 mm thick) was noted in boreholes BH7, BH8 and BH10.

3.3 Fill Materials

3.3.1 Clay

Clay fill was encountered beneath the asphalt pavement structure in borehole BH3, beneath the topsoil in boreholes BH4 and BH12, and beneath the gravel surfacing in boreholes BH7 and BH10. The clay fill extended to depths ranging from 1.4 m to 4.3 m below existing grade. It contained trace silt, sand, gravel, organics and rootlets. It should be noted that the fill was gravelly in boreholes BH7 and BH10. The fill was generally brown in color and damp to moist.

Results of the Atterberg Limits testing on a representative sample of the fill indicated a Liquid Limit of 49 and a Plasticity Index of 32. Based on the laboratory testing and following the Unified Soils Classification (USC) System2 as set forth in ASTM D2487, this material is classified as low to medium plastic clay (CL-CH). Moisture content of the fill ranged from 15% to 30%, with an average moisture content of 22%.

2 For reference purposes, detail of the USC System is included in Appendix F.


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Results of SPTs conducted in the clay fill indicated N-values3 between 3 and 10, with an average N-value of 6. Pocket penetrometer test within this stratum indicated an undrained shear strength of 144 kPa. In terms of relative consistency, based on Standard Penetration Test N-values and pocket penetrometer result, the fill may be described as firm to stiff.

3.3.2 Gravel

Gravel fill was encountered beneath surface gravel in borehole BH8 and beneath the clay fill in boreholes BH7 and BH10. The gravel fill extended to a depth of 3.8 m below existing grade in all three boreholes. It was clayey, contained trace silt and sand, and was generally brown in color and damp to moist.

A grain size analysis completed on a representative sample of this material indicated the following group percentages: 69% gravel; 4% sand; and 27% silt and clay size particles. Based on the laboratory testing and following the USC system, this material may be classified as clayey gravel (GC). Moisture content of the gravel fill ranged from 8% to 25%, with an average moisture content of 17%.

Results of SPTs indicated N-values of 4 and 5. In terms of relative density, based on Standard Penetration Test N-values, the gravel fill may be described as loose.

3.4 Clay (CL-CH)

Clay was encountered under the topsoil and fill in boreholes BH1 to BH6 and BH12. It extended to beyond the termination depths (6.9 m to 9.9 m below existing grade) in boreholes BH1 to BH4, and to depths ranging from 3.5 m to 7.3 m below existing grade in the remaining boreholes. The clay contained trace silt and gravel, was generally brown with grey mottling in color and damp to moist.

Results of the Atterberg Limits testing on four (4) representative samples of the clay indicated Liquid Limits ranging from 43 to 50 and Plasticity Indices ranging from 27 to 31. Based on the laboratory testing and following the USC system, this material is classified as medium to high plastic clay (CL-CH). Moisture contents of the clay samples were between 20% and 35%, with an average moisture content of 23%.

Results of SPTs conducted on the clay indicated N-values between 6 and 39, with an average N-value of 19. Pocket penetrometer tests within this stratum indicated undrained shear strength ranging from approximately 84 kPa to 120 kPa, with an average value of 106 kPa. In terms of relative consistency, based on Standard Penetration Test N-values and pocket penetrometer results, the clay may be described as firm to very stiff.

3.5 Sandy Silt (ML) and Silty Sand (SM)

Interbedded sandy silt and silty sand were logged beneath the clay and fill in boreholes BH5 to BH12. The silt and sand extended to a depth of 8.4 m below existing grade in boreholes BH8 and BH10, and beyond the termination depths in the remaining boreholes (6.9 m to 9.9 m below existing grade). The silt and sand was generally brown in color, interbedded with clay layers and dry to wet.

Grain size analyses were completed on two (2) representative samples of these materials. The results indicated that one sample had 33% sand and 67% fines (silt and clay size particles) and the second sample had 58% sand and 42% fines. Based on the laboratory testing and following the USC system, this material may be classified as sandy silt (ML) and silty sand (SM). Moisture contents ranged from 1% to 25%, with an average moisture content of 12%.

3 For reference purposes, determination of relative density and consistency based on N-values and undrained shear strengths are outlined in the Symbols and Terms Used on Borehole and Test Pit Records provided in Appendix C.


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Results of SPTs conducted on the silt and sand indicated N-values between 8 and 45, with an average N-value of 26. In terms of relative density, based on Standard Penetration Test N-values, the silt and sand may be described as loose to dense.

3.6 Low Plastic Clay (CL)

A low plastic clay layer was noted beneath the topsoil and medium to high plastic clay in boreholes BH5 and BH11, and beneath the silt and sand in boreholes BH8 and BH10. The low plastic clay extended to depths ranging from 2.1 m to 4.6 m below existing grade in boreholes BH5 and BH11, and beyond the termination depths ranging from 9.0 m to 9.1 m below existing grade in the remaining boreholes. The clay had trace silt, sand and gravel. It was generally brown in color and damp to moist.

Results of the Atterberg Limits testing on a representative sample of the clay indicated a Liquid Limit of 36 and a Plasticity Index of 20. Based on the laboratory testing and following the USC system, this material is classified as low plastic clay (CL). Moisture content of the clay ranged from 13% to 26%, with an average moisture content of 19%.

Results of SPTs conducted on the clay indicated N-values between 12 and 30, with an average N-value of 22. Pocket penetrometer test within this stratum indicated an undrained shear strength of 108 kPa. In terms of relative consistency, based on Standard Penetration Test N-values and pocket penetrometer result, the clay may be described as stiff to very stiff.

3.7 Groundwater

Groundwater levels within the standpipe piezometers were monitored from July 2, 2009 to February 9, 2010. The measured groundwater levels are presented in Table 3-1, Table 3-2, and on the Borehole Records in Appendix C. Groundwater levels vary from year to year and from season to season, and depend on many factors including surface and subsurface drainage, precipitation, and the hydrogeology of the area. Fluctuations in the groundwater levels should be anticipated. Additional groundwater monitoring may be conducted to confirm the measured groundwater levels. Groundwater levels in Alberta can typically experience fluctuation of up to 1 m with the peak groundwater levels generally occurring in June or July.


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Table 3-1 Groundwater Levels July 2009 to September 2009

Borehole Number

July 2, 2009 (m)

July 16, 2009 (m)

August 7, 2009 (m)

September 10, 2009(m)

BH1 2.2 0.8 0.4 1.3 BH2 Dry Dry Dry Dry BH3 6.1 3.6 2.9 3.8 BH4 6.1 4.9 4.4 4.3 BH5 Dry Dry Dry Dry BH6 6.7 6.6 6.4 6.3 BH7 Dry 6.1 6.3 6.6 BH8 Dry Dry Dry Dry BH9 Dry Dry Dry Dry

BH10 Dry Dry Dry Dry BH11 Dry Dry Dry Dry BH12 5.5 5.4 5.6 5.7

Table 3-2 Groundwater Levels November 2009 to February 2010

Borehole Number

November 4, 2009 (m)

December 3, 2009 (m)

January 12, 2010 (m)

February 9, 2010 (m)

BH1 1.5 1.6 1.8 1.8 BH2 Dry Dry Dry Dry BH3 3.4 4.1 4.9 4.8 BH4 5.4 4.3 4.6 4.4 BH5 Dry Dry Dry Dry BH6 6.6 6.6 6.7 6.7 BH7 6.6 6.9 Dry Dry BH8 Dry Dry Dry Dry BH9 Dry Dry Dry Dry

BH10 Dry Dry Dry Dry BH11 Dry Dry Dry Dry BH12 5.6 --- 6.0 5.7


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4 DISCUSSION Based on review of the information available and the results of our investigation, Stantec is of the opinion that the observed differential movements of the gabion retaining walls may be due to a combination of the following possible factors:

• Low factor of safety against sliding

• Poor construction method

• Post construction factors, such as excess water discharge towards the back of the walls, surcharge of the walls due to other retaining structures apparently constructed after the gabion walls were installed

Based on the available information, there are three (3) different types of gabion retaining walls: the original wall, the retrofit wall and the rebuilt wall. Each wall design is discussed in detail in the following sections.

4.1 Original Wall

4.1.1 Design Data

The original retaining walls included locations near boreholes BH1 to BH6 and BH12. Details of the original design were provided in the March 1999 Almor report. It should be noted that the design provided in the report was completed by G. Douglas Dey Engineering. A copy of the design cross section drawing is presented in Figure 4-1. The key geotechnical features of the design are summarized below:

• The offset of the gabion baskets was to range from 0.15 m to 0.30 m.

• A layer of drainage gravel was to be placed behind and beneath the retaining wall.

• Filter fabric was to be placed between the drainage gravel and gabion baskets.

• Clay material was identified as the backfill behind the retaining wall.

• The report stated “a wet unit wight (sic) of the soils of 2100 kg/m³ and a co-efficient of passive earth pressure (k) of 0.5” were used in the design. Although the report used the term passive earth pressure, it is assumed that the author was referring rather to the active earth pressure coefficient.


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Figure 4-1 Original Wall Design Cross Sections

4.1.2 Stability Analyses

Using the above design and soil parameters derived from the soils encountered during drilling (see Table 4-1) the factor of safety (FOS) against sliding and overturning of the retaining wall were analyzed at each borehole location. Active earth pressure coefficients (ka) ranging from 0.33 to 0.43 were used for the above analyses. A FOS of 1.5 against sliding is typically accepted as industry standard in retaining wall design. The results are presented in Table 4-2.

Table 4-1 Analysis Parameters based on Stantec Investigation – Original Wall Analyses

Parameter Value

Clay Fill Unit Weight (kN/m³) 18

Clay Fill Friction Angle, φ (°) 25°

Gabion Basket Unit Weight (kN/m³) 20.5

Friction Angle between Gabions and Clay Fill, δ (°) 17°

Friction Angle between Gabions and Base Drainage Gravel, δ (°) 25°

Back Slope, β (°) 6° to 10°


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Table 4-2 Calculated Factor of Safety (Original Wall)

Borehole Number

Calculated Factor of Safety Against Overturning Against Sliding

BH1 3.4 1.3

BH3 3.7 1.4

BH4 8.9 3.3

BH6 4.6 1.4

BH12 5.6 1.5

It should be noted that the Canadian Foundation Engineering Manual (CFEM), 4th Edition, Section 12.12.3.3 states that “Soils classified as CH, CL, MH, ML or OL, according to the USCS, are often subject to excessive frost action and swelling when used as wall backfill. Wall movement is likely to be excessive; the use of these materials should be avoided. Where they must be used, frost protection should be provided and an earth-pressure coefficient of 1.0 used in design.”

Since clay was used as the backfill material behind the retaining walls and excessive wall movements were observed, the comments from CFEM are considered to be applicable. As such, the FOS was recalculated using a ka of 1.0 as recommended in CFEM. The calculated FOS values are presented in Table 4-3. The calculations indicate that if the recommendations in CFEM are followed the original design has an inadequate FOS at most wall locations. It should be noted that an FOS less than 1.0 indicates a failure condition.

Table 4-3 Calculated Factor of Safety (Original Wall using ka = 1.0)

Borehole Number

Calculated Factor of Safety Against Overturning Against Sliding

BH1 1.9 0.7

BH3 1.5 0.5

BH4 4.5 1.6

BH6 2.0 0.6

BH12 2.1 0.6

4.1.3 Wall Construction

Based on our review of the design drawing and the results of our investigation, it appears that frost protection was not provided. Since gabion retaining walls contain numerous large void spaces between the rock fill in the baskets, frost penetration into the clay backfill is expected both vertically and horizontally. The results of the laboratory testing indicated that the average moisture content of the clay fill was 22%. As moisture content is defined by weight and that the weight of water is about half the weight of soil solids, approximately 44% of the clay mass by volume is water. Since water expands by 9% when it changes from water to ice, and assuming frost penetration depth of 1.5 m horizontally, lateral movements of the walls based on water freezing expansion alone could be in the order of 60 mm throughout each winter. The observed lateral movements of sections of the retaining walls appear to confirm this calculated magnitude of movements. If the walls do not move back entirely upon thawing, the lateral movements can be cumulative over several years.


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If the construction was not adequately supervised, it may have also contributed to the movement of the retaining wall. The Factor of Safety against sliding of the retaining wall is based on the friction between the gabion rocks and the drainage gravel layer beneath the base of the retaining walls. Poor quality or preparation of the base drainage gravel can reduce the FOS of the retaining walls. Poor preparation of the subgrade materials can cause longitudinal differential settlements of the retaining wall as observed.

The differential movements of the retaining walls and the surrounding structures listed in Section 1.2 are most likely due to the lateral movement (sliding) of the retaining wall. As the retaining walls move laterally outward, the backfill behind the retaining walls settles to “fill up” the extra space created by the walls moving outward. Since the wood framed stairways were constructed adjacent to the retaining walls, the walls pushed the columns of the stairways outward, causing the columns off the support piers, and causing the damage observed. It should be noted that although the lower stairway structure connecting Bow Ridge Link and Bow Ridge Drive has not failed at this time, the same lateral movement of the retaining walls is observed and similar failure is considered likely. The timing of such failure is unknown but is inevitable.

Water discharge towards the back of the retaining walls either through natural runoff or excessive discharge from roof downspouts are expected to reduce the Factor of Safety of the retaining walls since water contributes to the swelling of the clay backfill and increased moisture content leading to larger lateral movements due to freezing.

Retaining walls built in the backyards may also surcharge the gabion retaining walls which, in turn, would also reduce the Factor of Safety against both sliding and overturning.

The slope inclinometer installed in borehole BH1 measured a maximum movement of 7 mm during the monitoring period. Groundwater depths at BH1 were measured at less than 1.0 m from the ground surface during the summer and at about 1.8 m from the ground surface over the winter months. These groundwater levels are significantly higher than those measured at other borehole locations. We are of the opinion that the shallow groundwater levels play a significant part in contributing to the outward movements of the wall at this location, as observed prior to and during the inclinometer monitoring period. Slope inclinometer results are further discussed in Section 4.4.

4.2 Retrofit Wall

It is understood that a section of Retaining Wall B was repaired previously using the Retrofit design provided in Almor’s October 17, 2003 report. The Retrofit Wall is located near BH7. According to the drawing, it appears that the Retrofit Wall design was intended to provide reinforcement to the original retaining wall without complete reconstruction. The key geotechnical features of the Retrofit Wall design as shown in Figure 4-2 are summarized below.

• Three (3) gabion baskets were installed at the back of the retaining wall, starting from the base and extended to 1.5 m below existing grade, with the width of the base increased from 1.5 m to 2.5 m.

• Two (2) concrete blocks were placed on the base gabion baskets.

• Clay material was used as backfill for the top 1.0 m behind the retaining wall.

• Gravel material was used as backfill beneath the clay backfill.

• Filter fabrics were placed between the gravel fill, clay fill and gabion baskets.


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The analysis of the design of the Retrofit Wall was done using the parameters provided in Table 4-4. The analyzed FOS against sliding and overturning of the Retrofit Wall design were 10.0 and 2.7, respectively, when a ka of 0.34 was used in the analysis. As stated in the previous section, CFEM recommends against using clay materials as backfill, and a ka of 1.0 be used for the analysis should clay be used as backfill. Should ka of 1.0 be used for the analysis, the FOS against sliding would be reduced significantly to 1.1. It should also be noted that frost protection was not included in the design; hence frost action of the clay backfill as discussed above is expected to have contributed to the lateral movement of the retaining wall at this location.

Table 4-4 Analysis Parameters based on Stantec Investigation – Retrofit Wall Analyses

Parameter Value


Gravel Fill Unit Weight (kN/m³) 20

Gravel Fill Friction Angle, φ (°) 35°



New Gabion Basket Unit Weight (kN/m³) 19.5


Friction Angle between Gabions and Gravel Fill, δ (°) 25°

Back Slope, β (°) 22°


16

Figure 4-2 Retrofit Wall Design

Stantec conducted a survey of the retaining wall at borehole BH7. The cross-section showed evidence of the influence of the frost action within the clay fill. According to the cross-section, the offset between the top and the middle gabion baskets was larger than the offset between the middle and the base gabion baskets. Our investigation identified that clay fill was used as the top part of the backfill and gravel backfill was used as the bottom part. The clay backfill in borehole BH7 extended to 1.4 m below existing grade, which is near the top of the base gabion basket. It is expected that expansion from the clay backfill due to frost action pushed the top and middle gabion baskets outward, while the gravel backfill did not. Hence, the observed offsets between the gabions are different.


17

Figure 4-3 Cross Section at Borehole BH7

In order to place the new gabion baskets behind the retaining wall, a vertical excavation into the subgrade soil would have been required. The field investigation indicated that the subgrade soil at this location consisted of silt and sand material. It is anticipated that sloughing of side walls of these materials would have occurred during excavation. Hence, it is likely that the original base gabion was undermined during construction. In addition, from a constructability perspective, it would have been difficult to backfill and compact the sloughed area while installing the gabion baskets. Therefore, it is possible that a gap would have existed between the gabion baskets and the subgrade soil.

According to the design drawing, there was no filter fabric between the gabion baskets and the subgrade soil. Since the subgrade soil was silt and sand materials, migration of the subgrade silt and sand into the gabion baskets is likely. Migration of the subgrade soil would cause the front portion of the retaining wall (the gabion baskets of the original design) to settle. Combined with the lateral movement due to frost expansion of the clay fill materials, the retaining wall would have a tendency to tilt forward, which is what was observed at this location.

In addition to visual observations, the slope inclinometer installed in borehole BH7 measured a maximum movement of 7 mm during the monitoring period. The result of the slope inclinometer matched closely with the hypothesized failure mechanism discussed above. Slope inclinometer results are further discussed in Section 4.4.

It is expected that the effects of water discharge behind the gabion walls and homeowner constructed walls would have the same negative effects to the FOS of the Retrofit Wall as discussed in Section 4.1.


18

4.3 Rebuilt Wall

It is understood that the original wall was completely removed and reconstructed near boreholes BH8 and BH10. Details of the Rebuilt Wall were also provided in the October 17, 2003 Almor report (see Figure 4-4). The key geotechnical features of the Rebuilt Wall design are summarized below.

• The configuration of the top three (3) gabion baskets was unchanged from the Original Wall design.

• A 2.5 m wide and 1.5 m high base gabion basket was added below the original wall and buried into the subgrade soil.

• Clay material was used as backfill for the top 1.0 m behind the retaining wall.

• Gravel material was used as backfill beneath the clay backfill.

• Filter fabric was placed between the gravel fill, clay fill and gabion baskets.

The analysis of the design of the Rebuilt Wall was carried out using the parameters provided in Table 4-5. The analyzed FOS against sliding and overturning of the Rebuilt Wall design were 2.7 and 1.2, respectively, if a ka of 0.57 was used in the analysis. As stated in the previous section, CFEM recommends against using clay materials as backfill and a ka of 1.0 be used for the analysis should clay be used. Should a ka of 1.0 be used for the analysis, the FOS against sliding would be reduced significantly to a value of 0.8, suggesting failure of the wall. It should also be noted that frost protection was not included in the design; hence frost action of the clay backfill as discussed above is expected to have contributed to the lateral movement of the retaining wall at this location.

Table 4-5 Analysis Parameters based on Stantec Investigation – Rebuilt Wall Analyses

Parameter Value


Gravel Fill Unit Weight (kN/m³) 25

Gravel Fill Friction Angle, φ (°) 20°



New Gabion Basket Unit Weight (kN/m³) 17


Friction Angle between Gabions and Gravel Fill, δ (°) 18°

Back Slope, β (°) 18°


19

Figure 4-4 Rebuilt Wall Design

Results of the survey at the Rebuilt Wall section (from boreholes BH8 to BH10) as shown in Figure 4-5 indicated similar offset conditions between the gabion baskets as evidenced in the Retrofit Design. The offset between the top and the middle gabion baskets was larger than the offset between the middle and the base gabion baskets, which is most likely due to the frost action within the clay backfill as discussed in the previous section.

It is expected that the effects of water discharge behind the gabion walls and homeowner constructed walls would have the same negative effects to the FOS of the Retrofit Wall as discussed in Section 4.2.


20

Figure 4-5 Cross Sections through Rebuilt Wall

4.4 Slope Inclinometer Results

The slope inclinometers installed in the boreholes were monitored between July 2, 2009 and February 9, 2010. Displacements along both perpendicular and parallel to the retaining wall directions were measured. The results of the monitoring are presented in graphical format, plotted as borehole depth versus accumulated displacement, in Appendix E. It should be noted that due to ice blockage in the road boxes, inclinometers measurements in boreholes BH1 and BH4 were not possible between December 2009 and February 2010. Some inclinometer measurements have been removed from the graphs due to measurement errors.


21

The inclinometer measurements indicated that the maximum accumulated lateral displacements of the retaining walls during the measurement period were in the order of 7 mm at borehole BH1 and 8 mm at borehole BH8. Measured displacements at the other borehole locations ranged from negligible to less than 8 mm. It should be pointed out that the measured displacements represent the movements that occurred within the monitoring period only. The measured displacements do not represent total displacements experienced by the wall since construction, as significant displacements were observed prior to commencement of monitoring. It is also difficult to predict the rates of future displacements at a particular location, as future displacement rates depend on many factors such as backfill materials, moisture content, frost penetration, and seepage conditions. As such factors are highly variable along the walls, displacements rates can be expected to be highly variable as well.

At borehole BH1, the inclinometer monitoring results indicated that the retaining wall is leaning forward at a gradual rate. It does not appear that a shear plane (failure plane) exists at this location. Based on the inclinometer results, we are of the opinion that failure planes do not exist within the measurement depths at the other borehole locations, with the exception of borehole BH8.

At borehole BH8, the inclinometer results indicated that the gabion blocks are moving independently of each other, but generally tilting backwards. The results further show that there are movements indicative of impending bearing capacity failure in the soil below the retaining wall. From January 12, 2010 to February 9, 2010, the incremental movement was measured to be about 2 mm. It is expected that this movement will continue until bearing capacity failure of the underlying soil.

4.5 Global Stability of the Subdivision and Local Stability of the Walls

Based on conversations with representatives of the Town of Cochrane, it is understood that there are concerns regarding the global stability of the entire Bow Ridge Subdivision. A study of the stability of the subdivision was not within Stantec’s scope of work and therefore the opinion offered below is a conditional one. The only definitive method of determining the potential for global instability would be to extend the geotechnical study to cover the subdivision as a whole. In this way, relevant geotechnical data could be gathered and a technical recommendation could be prepared. Stantec has only studied the stability conditions of the retaining walls and has not studied the global stability of the subdivision. However, we are of the opinion that there are no immediate signs of global instability observed or reported within the subdivision outside of the immediate areas of the retaining walls. Should there be global stability issues affecting the subdivision outside of the immediate areas of the retaining walls, we are of the opinion that some or all of the following distresses would be evident:

• Cracking or differential movements of asphalt pavements, concrete sidewalks, and other surface structures

• Damages to underground utilities

• Cracking and other distresses of houses

• Tension cracks within the subdivision outside of the areas immediately adjacent to the retaining walls

Should the above noted distresses be observed, Stantec should be contacted immediately to determine if a study of global instability of the subdivision is required.


22

The wooden fences adjacent to the walkway connecting Bow Ridge Link and Bow Ridge Drive have observed to have buckled (see Photo 4-1). The severity of buckling of the fence panels appears to be progressive (i.e. the panels buckle more near the slope and progressively less away from the slope). Stantec is of the opinion that the buckling is the result of the retaining wall moving laterally (forward) pushing on the soil underneath the walkway and the asphalt pavement. Typically the effect of the pushing would be expected to be quite localized and immediately in front of the wall. We are of the opinion that the reason why the effect of the pushing is observed a long distance from the wall at this location is due to the asphalt pavement. Since asphalt is a stiff material, it moves as a rigid unit thus essentially “transmits” the lateral movement of the wall a long distance from the wall, dissipating the total displacement gradually, thus causing progressively less buckling of the fence panels with increased distance from the wall. We are of the opinion that this progressive buckling observed is not a sign of global instability of the subdivision.

Photo 4-1 Progressive Buckling of Fence


23

As indicated in Section 4.4, we are of the opinion that shear planes do not exist behind the retaining wall with the exception of borehole BH8. Therefore, sudden shear type failure of the walls is not expected. As such, residential structures adjacent to the walls are considered to be safe. However, it should be expected that lateral displacements of the walls will continue. In time, localized failures of the walls can be expected. Such failures may include the collapse of localized gabion baskets, which may pose dangerous conditions to people and properties located immediately adjacent to the wall when the event occurs.

At borehole BH8 location, there are signs indicative of an impending bearing capacity failure. At the time of failure, it is expected that the wall will undergo excessive settlement and tilting, leading to rapid collapse of the wall. However, it is difficult to predict when the bearing capacity failure will occur.


24

5 RECOMMENDATIONS Based on our observations, investigation, and analysis, it is anticipated that observed distresses will continue to worsen, including the following conditions:

• The retaining walls will continue to move laterally (outward), pushing onto stairways, fences, decks, etc. where such structures are close by.

• As the retaining walls continue to move outward, the backfill soil behind the walls will continue to settle, and tension cracks will develop.

• Water will seep into the soils and accelerate the movement and settlement.

• The above mechanism will ultimately lead to localized failures of gabion baskets.

• Continued longitudinal differential settlements of the retaining walls will occur.

Based on the study presented herein, Stantec offers the following recommendations:

• Remediation of the existing retaining walls using the existing design will not be effective, as the original design has deficiencies as outlined above. Previous remediation incorporating the original wall has proven to be ineffective. It is, therefore, our opinion that the retaining walls should be removed entirely and reconstructed.

• Based on the existing soil and groundwater conditions, it is expected that Mechanically Stabilized Earth (MSE) walls (see Appendix G) or reinforced concrete walls will be the most suitable retaining structure types for the Site. Should it be decided to proceed with the replacement of the walls, the type of retaining structures and geotechnical recommendations for the detailed design of the walls can be provided.

• The wall at and near borehole BH8 should be repaired or reconstructed as soon as possible.

• Continued monitoring at all borehole locations on a monthly basis should be carried out prior to repair or reconstruction to provide warning of potentially dangerous situations. The monitoring program should be reviewed annually.

• Homeowners need to be advised that downspouts should not discharge directly on to the gabion retaining walls.

• Construction of other retaining walls within backyards without proper geotechnical design is not recommended.


25

6 CLOSURE This report has been prepared for the sole benefit of The Town of Cochrane and their agents, and may not be used by any third party without the express written consent of Stantec and The Town of Cochrane.

Any use which a third party makes of this report is the responsibility of such third party. Use of this report is subject to the Statement of General Conditions provided in Appendix A. It is the responsibility of the Town of Cochrane who is identified as “the Client” within the Statement of General Conditions, and its agents to review the conditions and to notify Stantec should any of these not be satisfied. The Statement of General Conditions addresses the following:

• Use of the report • Basis of the report • Standard of care • Interpretation of site conditions • Varying or unexpected site conditions • Planning, design or construction

We trust the above information meets with your present requirements. Should you have any questions or require further information, please contact us.

Yours truly,

STANTEC CONSULTING LTD.

Signed By Edwin Choy Signed By Charles Kwok

Edwin C.H. Choy, M.Sc., P.Eng. Charles C.K. Kwok, M.Sc., P.Eng. Geotechnical Engineer Senior Principal Senior Geotechnical Engineer Tel: (403) 781-5472 Tel: (403) 781-4135 Fax: (403) 716-7922 Fax: (403) 716-7922 [email protected] [email protected]

APEGGA Permit No. P258 V:\1233\active\123310172\bow_ridge_subdivision\Report\R06_Fnl_Geo_Apr 05-10 Bow Ridge.docx


APPENDIX A Statement of General Conditions


USE OF THIS REPORT: This report has been prepared for the sole benefit of the Client or its agent and may not be used by any third party without the express written consent of Stantec and the Client. Any use which a third party makes of this report is the responsibility of such third party.

BASIS OF THE REPORT: The information, opinions, and/or recommendations made in this report are in accordance with Stantec’s present understanding of the site specific project as described by the Client. The applicability of these is restricted to the site conditions encountered at the time of the investigation or study. If the proposed site specific project differs or is modified from what is described in this report or if the site conditions are altered, this report is no longer valid unless Stantec is requested by the Client to review and revise the report to reflect the differing or modified project specifics and/or the altered site conditions.

STANDARD OF CARE: Preparation of this report, and all associated work, was carried out in accordance with the normally accepted standard of care in the state or province of execution for the specific professional service provided to the Client. No other warranty is made.

INTERPRETATION OF SITE CONDITIONS: Soil, rock, or other material descriptions, and statements regarding their condition, made in this report are based on site conditions encountered by Stantec at the time of the work and at the specific testing and/or sampling locations. Classifications and statements of condition have been made in accordance with normally accepted practices which are judgmental in nature; no specific description should be considered exact, but rather reflective of the anticipated material behaviour. Extrapolation of in situ conditions can only be made to some limited extent beyond the sampling or test points. The extent depends on variability of the soil, rock and groundwater conditions as influenced by geological processes, construction activity, and site use.

VARYING OR UNEXPECTED CONDITIONS: Should any site or subsurface conditions be encountered that are different from those described in this report or encountered at the test locations, Stantec must be notified immediately to assess if the varying or unexpected conditions are substantial and if reassessments of the report conclusions or recommendations are required. Stantec will not be responsible to any party for damages incurred as a result of failing to notify Stantec that differing site or sub-surface conditions are present upon becoming aware of such conditions.

PLANNING, DESIGN, OR CONSTRUCTION: Development or design plans and specifications should be reviewed by Stantec, sufficiently ahead of initiating the next project stage (property acquisition, tender, construction, etc), to confirm that this report completely addresses the elaborated project specifics and that the contents of this report have been properly interpreted. Specialty quality assurance services (field observations and testing) during construction are a necessary part of the evaluation of sub-subsurface conditions and site preparation works. Site work relating to the recommendations included in this report should only be carried out in the presence of a qualified geotechnical engineer; Stantec cannot be responsible for site work carried out without being present.


APPENDIX B Figures

EK V:\1233\active\123310172\bow_ridge_subdivision\Drawings\cad\Figure_1_0.mxdDate: February 16, 2010

Project Number 123310172

0 500 1,000 1,500m

Client/Project

TOWN OF COCHRANEGEOTECHNICAL INVESTIGATIONBOW RIDGE SUBDIVISION PHASE 3, COCHRANE, AB

Figure No.

Title

1.0

SITE LOCATION PLAN200 - 325 25th St. SE Calgary, AB T2A 7H8

This map is not intended to replace a survey by a licensed Surveyor. Stantec does not certify the accuracy of the data. This map is for reference only and should not be used for construction.

SITE

1:40000

SITE

Ã

22


APPENDIX C Borehole Records

SYMBOLS AND TERMS USED ON BOREHOLE AND TEST PIT RECORDS – MARCH 2009 Page 1 of 3

SYMBOLS AND TERMS USED ON BOREHOLE AND TEST PIT RECORDS SOIL DESCRIPTION

Terminology describing common soil genesis:

Topsoil - mixture of soil and humus capable of supporting vegetative growth

Peat - mixture of visible and invisible fragments of decayed organic matter

Till - unstratified glacial deposit which may range from clay to boulders

Fill - material below the surface identified as placed by humans (excluding buried services)

Terminology describing soil structure:

Desiccated - having visible signs of weathering by oxidization of clay minerals, shrinkage cracks, etc.

Fissured - having cracks, and hence a blocky structure

Varved - composed of regular alternating layers of silt and clay

Stratified - composed of alternating successions of different soil types, e.g. silt and sand

Layer - > 75 mm in thickness

Seam - 2 mm to 75 mm in thickness

Parting - < 2 mm in thickness

Terminology describing soil types: The classification of soil types are made on the basis of grain size and plasticity in accordance with the Unified Soil Classification System (USCS) (ASTM D 2487 or D 2488). The classification excludes particles larger than 76 mm (3 inches). The USCS provides a group symbol (e.g. SM) and group name (e.g. silty sand) for identification.

Terminology describing cobbles, boulders, and non-matrix materials (organic matter or debris): Terminology describing materials outside the USCS, (e.g. particles larger than 76 mm, visible organic matter, construction debris) is based upon the proportion of these materials present:

Trace, or occasional Less than 10%

Some 10-20%

Frequent > 20%

Terminology describing compactness of cohesionless soils: The standard terminology to describe cohesionless soils includes compactness (formerly "relative density"), as determined by the Standard Penetration Test N-Value (also known as N-Index). A relationship between compactness condition and N-Value is shown in the following table.

Compactness Condition SPT N-Value

Very Loose <4

Loose 4-10

Compact 10-30

Dense 30-50

Very Dense >50

Terminology describing consistency of cohesive soils: The standard terminology to describe cohesive soils includes the consistency, which is based on undrained shear strength as measured by in situ vane tests, penetrometer tests, or unconfined compression tests.

Consistency Undrained Shear Strength

kips/sq.ft. kPa

Very Soft <0.25 <12.5

Soft 0.25 - 0.5 12.5 - 25

Firm 0.5 - 1.0 25 - 50

Stiff 1.0 - 2.0 50 – 100

Very Stiff 2.0 - 4.0 100 - 200

Hard >4.0 >200


ROCK DESCRIPTION

Terminology describing rock quality:

RQD Rock Mass Quality

0-25 Very Poor

25-50 Poor

50-75 Fair

75-90 Good

90-100 Excellent

Rock quality classification is based on a modified core recovery percentage (RQD) in which all pieces of sound core over 100 mm long are counted as recovery. The smaller pieces are considered to be due to close shearing, jointing, faulting, or weathering in the rock mass and are not counted. RQD was originally intended to be done on NW core; however, it can be used on different core sizes if the bulk of the fractures caused by drilling stresses are easily distinguishable from in situ fractures. The terminology describing rock mass quality based on RQD is subjective and is underlain by the presumption that sound strong rock is of higher engineering value than fractured weak rock.

Terminology describing rock mass:

Spacing (mm) Joint Classification Bedding, Laminations, Bands

> 6000 Extremely Wide -

2000-6000 Very Wide Very Thick

600-2000 Wide Thick

200-600 Moderate Medium

60-200 Close Thin

20-60 Very Close Very Thin

<20 Extremely Close Laminated

<6 - Thinly Laminated

Terminology describing rock strength:

Strength Classification Unconfined Compressive Strength (MPa)

Extremely Weak < 1

Very Weak 1 – 5

Weak 5 – 25

Medium Strong 25 – 50

Strong 50 – 100

Very Strong 100 – 250

Extremely Strong > 250

Terminology describing rock weathering:

Term Description

Fresh No visible signs of rock weathering. Slight discolouration along major discontinuities

Slightly Weathered Discolouration indicates weathering of rock on discontinuity surfaces. All the rock material may be discoloured.

Moderately Weathered Less than half the rock is decomposed and/or disintegrated into soil.

Highly Weathered More than half the rock is decomposed and/or disintegrated into soil.

Completely Weathered All the rock material is decomposed and/or disintegrated into soil. The original mass structure is still largely intact.


STRATA PLOT

Strata plots symbolize the soil or bedrock description. They are combinations of the following basic symbols. The dimensions within the strata symbols are not indicative of the particle size, layer thickness, etc.

Boulders Cobbles Gravel

Sand Silt Clay Organics Asphalt Concrete Fill Igneous Bedrock

Meta-morphic Bedrock

Sedi-mentary Bedrock

SAMPLE TYPE

SS Split spoon sample (obtained by performing

the Standard Penetration Test)

ST Shelby tube or thin wall tube

DP Direct-Push sample (small diameter tube

sampler hydraulically advanced)

PS Piston sample

BS Bulk sample

WS Wash sample

HQ, NQ, BQ, etc. Rock core samples obtained with the use of

standard size diamond coring bits.

RECOVERY For soil samples, the recovery is recorded as the length of the soil sample recovered. For rock core, recovery is defined as the total cumulative length of all core recovered in the core barrel divided by the length drilled and is recorded as a percentage on a per run basis.

N-VALUE Numbers in this column are the field results of the Standard Penetration Test: the number of blows of a 140 pound (64 kg) hammer falling 30 inches (760 mm), required to drive a 2 inch (50.8 mm) O.D. split spoon sampler one foot (305 mm) into the soil. For split spoon samples where insufficient penetration was achieved and N-values cannot be presented, the number of blows are reported over sampler penetration in millimetres (e.g. 50/75). Some design methods make use of N value corrected for various factors such as overburden pressure, energy ratio, borehole diameter, etc. No corrections have been applied to the N-values presented on the log.

DYNAMIC CONE PENETRATION TEST (DCPT) Dynamic cone penetration tests are performed using a standard 60 degree apex cone connected to A size drill rods with the same standard fall height and weight as the Standard Penetration Test. The DCPT value is the number of blows of the hammer required to drive the cone one foot (305 mm) into the soil. The DCPT is used as a probe to assess soil variability.

OTHER TESTS

S Sieve analysis

H Hydrometer analysis

k Laboratory permeability

γ Unit weight

Gs Specific gravity of soil particles

CD Consolidated drained triaxial

CU Consolidated undrained triaxial with pore pressure measurements

UU Unconsolidated undrained triaxial

DS Direct Shear

C Consolidation

Qu Unconfined compression

Ip Point Load Index (Ip on Borehole Record equals Ip(50) in which the index is corrected to a reference diameter of 50 mm)

WATER LEVEL MEASUREMENT

measured in standpipe, piezometer, or well

inferred

Single packer permeability test; test interval from depth shown to bottom of borehole

Double packer permeability test; test interval as indicated

Falling head permeability test using casing

Falling head permeability test using well point or piezometer

9

300

450

450

450

450

400

11

12

13

TOPSOIL

39

24

25

27

Very stiff brown CLAY(CL-CH)- with light brown and greymottling, trace silt and gravel,damp to moist

- greyish brown below 7.3 m

- brown, trace claystonefragments below 8.4 m

End of Borehole (9.9 m)Borehole dry and open uponcompletion25 mm standpipe hand slottedfrom 3.8 m to 6.9 mAnnulus backfilled with sandand cuttingsBentonite seal at surface

8

10

12

3

4

5

6

7

SS 22

BSSS

BS

SS

BS

SS

BS

BS

BS

SS

BS

SS

10 20 30 40 50 60 70 80 90

DATES (mm/dd/yy): BORING

1

W

22

L

N-V

ALU

E

1052130CLIENT150 mm

TYPE

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OR

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(m)

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2.2 m (7/2/09)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Bow Ridge, Cochrane, AB BH SIZE

STR

ATA

PLO

T

mm

6/4/09

BH1

WATER CONTENT & ATTERBERG LIMITSPocket Penetrometer kPaSTANDARD PENETRATION TEST, BLOWS/0.3m

UNDRAINED SHEAR STRENGTH - kPa

Sep 28 2009 10:23:22

BOREHOLE RECORD

App'd__________

PW W

50 100 150 200

17

400

350

200 19

17

TOPSOILVery stiff brown CLAY(CL-CH)- with light brown and greymottling, trace silt, damp tomoist


BS

BS

SS

BS

SS

SS

4

5

6

7

8

2

1

BS

3

BS

10 20 30 40 50 60 70 80 90


1

OR

RQ

D %

ELEV

ATI

ON

(m)

NU

MB

ER

REC

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RY

1

Dry (7/2/09)

N-V

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0

1

2

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7

8

9

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WATER LEVEL

150 mmLOCATION

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)

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1052130

SOIL DESCRIPTION

BH SIZE

STR

ATA

PLO

T

TYPE

mm

6/8/09

BH2

Bow Ridge, Cochrane, ABCLIENT

PW W

50 100 150 200

Sep 28 2009 10:23:28App'd__________

BOREHOLE RECORD

WATER CONTENT & ATTERBERG LIMITSL


W

STANDARD PENETRATION TEST, BLOWS/0.3mPocket Penetrometer kPa

250

400

450

75

450 15

24

ASPHALTFILL: gravel, trace cobblesFILL: brown clay- trace to some gravel, trace siltand sand, damp to moist

Stiff brown CLAY (CL-CH)- with light brown and greymottling, trace silt and gravel,damp to moist


7

11

11

1

2

3

4

5

6

7

8

9

10

BS

BS

SS

BS

SS

BS

SS

BS

ST

SS

BS

10 20 30 40 50 60 70 80 90


1

N-V

ALU

E


NU

MB

ER

- trace sand lenses andclaystone fragmentsbelow 8.7 m

150 mm

TYPE

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0

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SOIL DESCRIPTION

CLIENT

STR

ATA

PLO

T

mm

6/4/09

BH3

Bow Ridge, Cochrane, ABEL

EVA

TIO

N(m

)

BH SIZE

App'd__________Sep 28 2009 10:23:34

BOREHOLE RECORD



WPW W

50 100 150 200

150

350

400

350

300

300

9

11

12

13

TOPSOIL

10

13

18

FILL: brown clay- trace silt, organics androotlets, damp

Stiff brown CLAY (CL-CH)- with light brown and greymottling, trace silt, gravel andoxides, damp to moist

- trace coal and claystonefragments below 6.6 m


25

8

10

12

3

4

5

6

7

SS

BSSS

BS

SS

BS

SS

BS

BS

BS

SS

BS

16SS

10 20 30 40 50 60 70 80 90


1

W

13

L

N-V

ALU

E

1052130CLIENT150 mm

TYPE

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REC

OVE

RY

1

6.1 m (7/2/09)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Bow Ridge, Cochrane, AB BH SIZE

STR

ATA

PLO

T

mm

6/10/09

BH4

WATER CONTENT & ATTERBERG LIMITS



App'd__________Sep 28 2009 10:23:39

BOREHOLE RECORD

50 100 150 200

WPW

400

400

250

450

350

Stiff brown CLAY (CL-CH)- with light brown and greymottling, trace silt and gravel,damp to moist

Very stiff brown CLAY (CL)- silty, trace sand, damp

Dense brown silty SAND (SM)- dry to damp

- 0.5 m thick layer of clayat 6.3 m

- moist to wet below 6.9 mEnd of Borehole (7.3 m)Borehole dry and open uponcompletion25 mm standpipe hand slottedfrom 3.0 m to 6.9 mAnnulus backfilled with sandand cuttingsBentonite seal at surface

27

34

TOPSOIL

11

14

22

BS

3

2

4

5

6

7

8

9

10

1SS

BS

SS

BS

SS

BS

SS

SS

BS

10 20 30 40 50 60 70 80 90


1

N-V

ALU

EO

R R

QD

%

ELEV

ATI

ON

(m)

NU

MB

ER L

Dry (7/2/09)

REC

OVE

RY

TYPE

Page of


WATER LEVEL

1052130CLIENT

LOCATION

DATUM

MO

NIT

OR

WEL

L/

DEP

TH(m

)

PIEZ

OM

ETER

SAMPLES

STR

ATA

PLO

T

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

SOIL DESCRIPTION

BH SIZE 150 mm

1

mm

6/10/09

BH5

Bow Ridge, Cochrane, AB

W

App'd__________Sep 28 2009 10:23:43

BOREHOLE RECORD

P W

STANDARD PENETRATION TEST, BLOWS/0.3m

WATER CONTENT & ATTERBERG LIMITSW

50 100 150 200

Pocket Penetrometer kPa


100

200

450

400

350

400

10

12

Firm to stiff brown CLAY(CL-CH)- with grey mottling, trace siltand gravel, damp to moist

6

14

14

32

TOPSOIL

- silty, damp below 6.6 m

Compact brown sandy SILT(ML)- trace gravel, dry to damp- interbedded with clay layersbelow 8.2 m


9

11

1

2

3

4

5

6

7

8

BS

SS

BS

SS

BS

SS

BS

SS

SS

28SS

BS

BS

10 20 30 40 50 60 70 80 90


1

N-V

ALU

E


OR

RQ

D %

15

L

1052130150 mm

TYPE

Page of


WATER LEVEL

LOCATION

DATUM

MO

NIT

OR

WEL

L/

DEP

TH(m

)

PIEZ

OM

ETER

SAMPLES

ELEV

ATI

ON

(m)

NU

MB

ER

REC

OVE

RY

1

6.7 m (7/2/09)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

CLIENT

BH SIZE

STR

ATA

PLO

T

mm

6/17/09

BH6

Bow Ridge, Cochrane, AB

SOIL DESCRIPTION

App'd__________Sep 28 2009 10:23:47

BOREHOLE RECORD



W


PW

50 100 150 200

W

5

25

250

200

250

23

3

28

45

FILL: 40 mm gravelFILL: brown gravelly clay- trace silt and sand, damp tomoistFILL: brown gravel- trace to some clay, trace siltand sand, damp to moist

Compact brown silty SAND(SM)- damp

End of Borehole (7.9 m) due toauger refusalSlough to 3.4 mBorehole dry upon completion25 mm standpipe hand slottedfrom 3.0 m to 6.1 mAnnulus backfilled with sandand cuttingsBentonite seal at surface

SS

BSSSBS

25

SS

5

6

7

SS

2

SS

4

3

1

ELEV

ATI

ON

(m)

1

N-V

ALU

EO

R R

QD

%

10 20 30 40 50 60 70 80 90

NU

MB

ER

REC

OVE

RY

1

Dry (7/2/09)DATES (mm/dd/yy): BORING

BH SIZE

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15


WATER LEVEL

1052130

TYPE

LOCATION

DATUM

MO

NIT

OR

WEL

L/

DEP

TH(m

)

PIEZ

OM

ETER

SAMPLES

BH7

STR

ATA

PLO

T

mm

Page of

6/16/09

SOIL DESCRIPTION


150 mm

50 100 150 200

W


App'd__________Sep 28 2009 10:23:51

BOREHOLE RECORD

WP LWATER CONTENT & ATTERBERG LIMITSPocket Penetrometer kPaSTANDARD PENETRATION TEST, BLOWS/0.3m

W

0

0

50

100

175

50Very stiff brown CLAY (CL)- trace silt, sand and gravel,damp to moistEnd of Borehole (9.1 m) due toauger refusalSlough to 3.4 mBorehole dry upon completion25 mm standpipe hand slottedfrom 3.0 m to 6.1 mAnnulus backfilled with sandand cuttingsBentonite seal at surface

FILL: 40 mm gravel

Loose to compact brown siltySAND (SM)- interbedded with clay layers,trace clay, damp

FILL: brown clayey gravel- trace silt and sand, moist 5

4

8

20

27

30

BSSS

6

12

3

5

7

8

9

4

BS

SS

BS

SS

SS

SS

SS

10 20 30 40 50 60 70 80 90


1

N-V

ALU

EO

R R

QD

%

ELEV

ATI

ON

(m)

NU

MB

ER

REC

OVE

RY

1

Dry (7/2/09)

TYPE

Page of


WATER LEVEL

150 mmLOCATION

DATUM

MO

NIT

OR

WEL

L/

DEP

TH(m

)

PIEZ

OM

ETER

SAMPLES

1052130

mm0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

SOIL DESCRIPTION

BH SIZE6/12/09

BH8


STR

ATA

PLO

T

BOREHOLE RECORD

PW W

50 100 150 200

App'd__________Sep 28 2009 10:23:55


LWATER CONTENT & ATTERBERG LIMITS

W



350

350

400

350


- moist to wet below 5.3 m

13

25

28

31

TOPSOILCompact brown silty SAND(SM)- damp- interbedded with clay layersbelow 0.8 m BS

5

BS 12

4

6

7

8

9

3

SS

BS

SS

BS

SS

BS

SS

10 20 30 40 50 60 70 80 90


1

N-V

ALU

EO

R R

QD

%

ELEV

ATI

ON

(m)

NU

MB

ER

REC

OVE

RY

1

Dry (7/2/09)

Page of


WATER LEVEL

150 mmLOCATION

DATUM

MO

NIT

OR

WEL

L/

DEP

TH(m

)

PIEZ

OM

ETER

SAMPLES

1052130

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

SOIL DESCRIPTION

BH SIZE

STR

ATA

PLO

T

TYPE

mm

6/11/09

BH9


PW

App'd__________Sep 28 2009 10:23:58

BOREHOLE RECORD

50 100 150 200

W LWWATER CONTENT & ATTERBERG LIMITS


Pocket Penetrometer kPaSTANDARD PENETRATION TEST, BLOWS/0.3m

4

5

29

28

17

24

FILL: brown gravel- trace to some clay, trace siltand sand, damp to moist

FILL: 40 mm gravel

App'd__________Sep 28 2009 10:24:35

BOREHOLE RECORD

150

Compact brown silty SAND(SM)- interbedded with clay layers,dry to damp

Very stiff brown CLAY (CL)- trace to some gravel, trace silt,sand and coal, damp to moistEnd of Borehole (9.0 m) due toauger refusalSlough to 3.4 mBorehole dry upon completion25 mm standpipe hand slottedfrom 3.0 m to 6.1 mAnnulus backfilled with sandand cuttingsBentonite seal at surface

FILL: brown gravelly clay- trace silt and sand, damp tomoist

SS

SS

SS

SS

SS

SS 6

0

0

0

100

150

1

2

3

4

5

1

N-V

ALU

EO

R R

QD

%

ELEV

ATI

ON

(m)

REC

OVE

RY

1

Dry (7/2/09)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

SOIL DESCRIPTION

NU

MB

ER

10 20 30 40 50 60 70 80 90


BH SIZE

Stantec Consulting Ltd.

WATER LEVEL

1052130

Page of

TYPE

LOCATION

DATUM

MO

NIT

OR

WEL

L/

DEP

TH(m

)

PIEZ

OM

ETER

SAMPLES

STR

ATA

PLO

T

mm

PROJECT No.

BH10


150 mm6/16/09

PW W

50 100 150 200




WL

200

300

400

450


24

29

24

TOPSOILStiff brown CLAY (CL)- with light brown mottling,trace silt, damp to moist- silty, trace gravel, seepagebelow 1.2 mCompact brown SILT andSAND (ML-SM)- dry to damp

- interbedded with clay layersbelow 4.8 m- trace clay, moist to wetbelow 5.2 m

12SSBS

7

123

4

BS

6

8

9

5

SS

BS

SS

BS

SS

BS

N-V

ALU

E

10 20 30 40 50 60 70 80 90


1

OR

RQ

D %

ELEV

ATI

ON

(m)

NU

MB

ER

REC

OVE

RY

1

TYPE

Page of


WATER LEVEL Dry (7/2/09)LOCATION

DATUM

MO

NIT

OR

WEL

L/

DEP

TH(m

)

PIEZ

OM

ETER

SAMPLES

1052130

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

SOIL DESCRIPTION

BH SIZE

STR

ATA

PLO

T

mm

150 mm6/11/09

BH11


W W

50 100 150 200

App'd__________Sep 28 2009 10:24:39

BOREHOLE RECORD

P WLWATER CONTENT & ATTERBERG LIMITS


Pocket Penetrometer kPaSTANDARD PENETRATION TEST, BLOWS/0.3m

75

450

400

450

450

350

9

11

12

39

4

17

17

TOPSOILFILL: brown clay- silty, trace sand, gravel androotlets, moistStiff brown CLAY (CL-CH)- with grey mottling, trace siltand gravel, damp to moist

- interbedded with silt seams,trace oxides below 6.9 mCompact to dense brown siltySAND (SM)- dry to damp


8

10

1

2

3

4

5

6

7

SS

SS

BS

SS

BS

SS

BS

BS

15

BS

SS

BS

SS

10 20 30 40 50 60 70 80 90


1

N-V

ALU

E


OR

RQ

D %

10

1052130CLIENT150 mm

TYPE

Page of


WATER LEVEL

Bow Ridge, Cochrane, ABLOCATION

DATUM

MO

NIT

OR

WEL

L/

DEP

TH(m

)

PIEZ

OM

ETER

SAMPLES

ELEV

ATI

ON

(m)

NU

MB

ER

REC

OVE

RY

1

5.5 m (7/2/09)

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

BH SIZE

STR

ATA

PLO

T

mm

6/18/09

BH12

SOIL DESCRIPTION

BOREHOLE RECORD

App'd__________Sep 28 2009 10:24:43


W


P

50 100 150 200

WW


APPENDIX D Laboratory Testing

OFFICE LABORATORYGrain Size

AnalysisASTM C136, ASTM C117 orCSA A23.3-2A, CSA A23.2-5A

--07/09/09

SAMPLE DESCRIPTION: Silty Sand (SM)

Sieve Sample Specifications(mm) % Passing Lower Upper0.63 1000.315 99.90.16 99.30.08 41.6

Form MAT.003B, Rev. 3, 2009/04/20

SOURCE:TESTED BY:

DATE SAMPLED:

Canada T2P 1H7

DATE RECEIVED:DATE TESTED:

BS7BH5S.Evans

Client:Project Name:

Project No:

Stantec Consulting Ltd.Bow Ridge Retaining Wall

805 - 8th Avenue SW

Suite 300Calgary, Alberta

10830 - 46th Street SE

SAMPLE No:

Calgary, Alberta1052130.02

Tel: (403) 253-7876

Fax: (403) 253-0021

Tel: (403) 269-5150

Fax: (403) 269-5245

Canada T2C 1G4

0

10

20

30

40

50

60

70

80

90

100

0.010.11

Perc

ent P

assi

ng

Sieve Size (mm)

% Passing Upper Limit Lower Limit

Reporting of these test results constitutes a testing service only. Engineering interpretation or evaluation of the test results is provided only on written request. The data presented above is for the sole use of the client stipulated above. Stantec is not responsible, nor can be held liable, for the use of this report by any other party, with or without the knowledge of Stantec.

COMMENTS:

Reviewed By: __________________

One Team. Infinite Solutions.



--07/10/09

SAMPLE DESCRIPTION: Sandy Silt (ML)

Sieve Sample Specifications(mm) % Passing Lower Upper0.630 100.00.315 99.90.160 99.60.080 66.6

Form MAT.003B, Rev. 3, 2009/04/20

SOURCE:TESTED BY:

DATE SAMPLED:

Canada T2P 1H7


BS10BH6K.Asgarpour


Project No:


805 - 8th Avenue SW



SAMPLE No:


Tel: (403) 253-7876

Fax: (403) 253-0021

Tel: (403) 269-5150

Fax: (403) 269-5245

Canada T2C 1G4

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

0.0100.1001.000

Perc

ent P

assi

ng

Sieve Size (mm)



COMMENTS:

Reviewed By: __________________




--07/09/09

SAMPLE DESCRIPTION: Clayey Gravel (GC)

Sieve Sample Specifications(mm) % Passing Lower Upper40.0 10025.0 58.420.0 39.116.0 35.612.5 32.310.0 31.85.0 30.62.5 30.01.25 29.60.630 29.30.315 28.90.160 28.40.080 26.8

Form MAT.003B, Rev. 3, 2009/04/20

SOURCE:TESTED BY:

DATE SAMPLED:

Canada T2P 1H7


BS3BH8S.Evans


Project No:


805 - 8th Avenue SW



SAMPLE No:


Tel: (403) 253-7876

Fax: (403) 253-0021

Tel: (403) 269-5150

Fax: (403) 269-5245

Canada T2C 1G4

0

10

20

30

40

50

60

70

80

90

100

0.00.11.010.0

Perc

ent P

assi

ng

Sieve Size (mm)



COMMENTS:

Reviewed By: __________________



APPENDIX E Slope Inclinometer Readings

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m

)Borehole BH1 ‐ Depth vs Displacement (Perpendicular to the Retaining Wall)

10‐Aug‐09

10‐Sep‐09

4 Nov 09O

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10

Cumulative Displacement (mm)

4‐Nov‐09

3‐Dec‐09IN OUT

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m

)Borehole BH1 ‐ Depth vs Displacement

(Parallel to the Retaining Wall)

10‐Aug‐09

10‐Sep‐09

4 Nov 09LEFT F i W llRIGHT F i W ll

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


4‐Nov‐09

3‐Dec‐09LEFT ‐ Facing WallRIGHT ‐ Facing Wall

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m


10‐Aug‐09

10‐Sep‐09

4‐Nov‐09

3 Dec 09O

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


3‐Dec‐09

12‐Jan‐10

9‐Feb‐10

IN OUT

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m



10‐Aug‐09

10‐Sep‐09

4‐Nov‐09

3 Dec 09LEFT F i W llRIGHT F i W ll

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


3‐Dec‐09

12‐Jan‐10

9‐Feb‐10

LEFT ‐ Facing WallRIGHT ‐ Facing Wall

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m


4‐Nov‐09

3‐Dec‐09

12 Jan 10O

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


12‐Jan‐10

9‐Feb‐10IN OUT

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m



4‐Nov‐09

3‐Dec‐09

12 Jan 10LEFT F i W llRIGHT F i W ll

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


12‐Jan‐10

9‐Feb‐10LEFT ‐ Facing WallRIGHT ‐ Facing Wall

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m


10‐Aug‐09

10‐Sep‐09O

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


4‐Nov‐09IN OUT

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m



10‐Aug‐09

10 Sep 09LEFT F i W llRIGHT F i W ll

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


10‐Sep‐09LEFT ‐ Facing WallRIGHT ‐ Facing Wall

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m


10‐Aug‐09

10‐Sep‐09

4‐Nov‐09

3 Dec 09O

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


3‐Dec‐09

12‐Jan‐10

9‐Feb‐10

IN OUT

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m



10‐Aug‐09

10‐Sep‐09

4‐Nov‐09


‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


3‐Dec‐09

12‐Jan‐10

9‐Feb‐10


‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m


10‐Sep‐09

4‐Nov‐09

3‐Dec‐09O

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


12‐Jan‐10

9‐Feb‐10

IN OUT

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m



10‐Sep‐09

4‐Nov‐09

3‐Dec‐09LEFT F i W llRIGHT F i W ll

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


12‐Jan‐10

9‐Feb‐10


‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m


10‐Sep‐09

4‐Nov‐09

3‐Dec‐09O

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


12‐Jan‐10

9‐Feb‐10

IN OUT

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m



10‐Sep‐09

4‐Nov‐09


‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


12‐Jan‐10

9‐Feb‐10


‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m


10‐Sep‐09

4‐Nov‐09

12 Jan 10O

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


12‐Jan‐10

9‐Feb‐10IN OUT

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m



10‐Sep‐09

4‐Nov‐09

12 Jan 10LEFT F i W llRIGHT F i W ll

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


12‐Jan‐10

9‐Feb‐10LEFT ‐ Facing WallRIGHT ‐ Facing Wall

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m


10‐Aug‐09

10‐Sep‐09

4‐Nov‐09

3 Dec 09O

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


3‐Dec‐09

12‐Jan‐10

9‐Feb‐10

IN OUT

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m



10‐Sep‐09

4‐Nov‐09


‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


12‐Jan‐10

9‐Feb‐10


‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m


10‐Sep‐09

4‐Nov‐09

3 Dec 09O

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


3‐Dec‐09

12‐Jan‐10IN OUT

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m



10‐Sep‐09

4‐Nov‐09


‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


3‐Dec‐09

12‐Jan‐10LEFT ‐ Facing WallRIGHT ‐ Facing Wall

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m


10‐Sep‐09

4‐Nov‐09

3‐Dec‐09O

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


12‐Jan‐10

9‐Feb‐10

IN OUT

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m



10‐Sep‐09

4‐Nov‐09


‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


12‐Jan‐10

9‐Feb‐10


‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m


10‐Aug‐09

10‐Sep‐09

4‐Nov‐09

3 Dec 09O

‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


3‐Dec‐09

12‐Jan‐10

9‐Feb‐10

IN OUT

‐6

‐5

‐4

‐3

‐2

‐1

Dep

th (m



10‐Sep‐09

4‐Nov‐09


‐10

‐9

‐8

‐7

‐10 ‐8 ‐6 ‐4 ‐2 0 2 4 6 8 10


12‐Jan‐10

9‐Feb‐10



APPENDIX F Unified Soil Classification System

Unified Soil Classification System -- GEOTECHNICAL ENGINEERING-1997 -- Prof. G.P. Raymond.© 9

Figure 1. Textural classification system found inappropriate forengineering use.

Figure 2. Ranges for coarseparticle sizing.

UNIFIED SOIL CLASSIFICATION SYSTEM1. INTRODUCTION

Most soils are a heterogeneous accumulation of mineral grains notcemented together. However, the term `soil' or èarth', as used byengineers, includes virtually every type of uncemented or partiallycemented inorganic and organic material found in the ground. Only hardrock which remains firm after exposure is wholly excluded.

In order for engineers, both in the field and in the office, to be able to`speak the same language' with respect to soils, a standard method ofidentifying and classifying soils regarding their engineeringcharacteristics rather than agricultural or geological or othercharacteristics is needed. A system of describing the soil (identification)and placing it into a category or group (classification) which has distinctengineering properties enables engineers to exchange information and toprofit by one another's experiences. Borehole logs of soil profileexplorations containing adequate descriptions and soil classifications(often from field identification) can be used in making preliminaryestimates to determine the extent of additional field investigation neededfor (a) final design, (b) planning an economical testing program, and (c)extending test results to additional explorations. For final design ofimportant structures, however, visual soil classification must besupplemented by laboratory tests to determine performancecharacteristics of the soil, such as permeability, shearing strength, andcompressibility, under expected field conditions. Knowledge of soilclassification, including typical engineering properties of soils of thevarious groups, is especially valuable to the engineer engaged inprospecting for earth materials or investigating foundations forstructures. Initially much work was concentrated on grain sizerelationships as illustrated by the U.S. Bureau of Public Roadsclassification system shown in Figure 1 (Rose, 1924), however this wasfound insufficient for engineering use.

In 1952, the Bureau of Reclamation and the Corps of Engineers, withProfessor A. Casagrande as consultant, reached agreement on amodification of Professor Casagrande's airfield classification, which theynamed the Ùnified Soil Classification System' or ÙSCS' (Casagrande,1948). Today (1996) the classification of soils is still base on the USCSit is more extensive and is periodically updated by the American Societyfor Testing Materials (ASTM) via their two Standards ASTM-D2457 andASTM-D2488. The system takes into account the engineering propertiesof soils: it is descriptive and easy to associate with actual soils, and it

has the flexibility of being adaptable both to the field and to thelaboratory. Probably its greatest advantage is that a soil can be classifiedreadily by visual and manual examination without the necessity forlaboratory testing. The Unified Classification System is based on thesizes of the particles, the amounts of the various sizes, and thecharacteristics of the very fine grains. This method of classification ofsoils is recommended for use by the Canadian Foundation EngineeringManual and is described in the following text and summarized in Table1.

2. SOIL COMPONENTS

(A) Size

(i) GeneralParticles larger than 76 mm (3 inches) are excluded from the Unified

Soil Classification System. However, the amount of such oversizedmaterial may be of great importance in the selection of sources forembankment material: hence borehole logs of explorations alwayscontain information on quantity and size of particles larger than 76 mm(3 inches). Within the size range of the system (i.e. less than 76 mm)there are two major engineering performance divisions. (A third divisionis used for highly organic material, i.e. Peat):(a) Coarse grained soils have 50% by weight of their particles greaterthan the No. 200 sieve size (0.075 mm), approximately the smallest sizevisible by the unaided human eye.(b) Fine grained soils have 50% by weight of their particles less than theNo. 200 sieve size (0.075 mm) and thus no individual particle should bevisible by the unaided human eye.(c) Organic material (Symbol Pt): - Organic soils composed of morethan 50% organic material by weight are known as Peat.

(ii) Coarse Grained FractionThe coarse grain fraction is further divided into two soil types again

based on sizing. These two types form part of the initial identificationregarding engineering performance classification. For brevity they aregiven an identification symbol. The soil types and their symbol are -

(a) Gravel (Symbol G) whichidentifies a coarse grained soilwhere 50% by weight of only thatfraction of the soil retained on theNo. 200 sieve (0.074 mm) is largerthan the No. 4 sieve size (4.75 mmor about 3/16 inch).

Size Subdivision: In order to aidthe identification of particle sizesgravel has two particle sizesubdivisions as shown on Figure 2and as given by:-

Coarse gravel -- 76 mm (3 inch)to 19 mm (3/4 inch),

Fine Gravel -- 19 mm (3/4 inch) to 4.75 mm (No. 4 sieve).There are no symbol identifications for size.

(b) Sand (Symbol S) which identifies a coarse grained soil where 50%by weight of only that fraction of the soil retained on the No. 200 sieve(0.075 mm) is smaller than the No. 4 sieve size (4.75 mm).

Size Subdivision: In order to aid the identification of particle sizessand has three particle size subdivisions as shown on Figure 2 and asgiven by:-

Coarse sand -- No. 4 (4.75 mm) to No. 10 sieves (2.00 mm),Medium sand -- No. 10 (2.00 mm) to No. 40 sieves (0.425 mm),Fine sand -- No. 40 (0.425 mm) to No. 200 sieves (0.074 mm).

There are no symbol identifications for size.


Figure 3. Definitionrequirements for soil to beclassified as well graded.

Grading/Fines Subdivision -- In actual fact the engineeringbehaviour of the coarse grained soil is more dependent on whether it isclean or not (less than 5% by weight of fines being clean and more than12% by weight of fines being dirty). If clean, the gradation influencesperformance and, if dirty, the fines influence performance. Thus in theUnified Soil Classification System gravels and sands are subdivided forclassification purposes into (these subdivisions are defined under theheading of grading):-(i) Well Graded (Symbol _W) clean fraction,(ii) Poorly Graded (Symbol _P) clean fraction,(iii) Silt (Symbol _M) behaviour of fines of dirty fraction, and(iv) Clay (Symbol _C) behaviour of fines of dirty fraction.Note: Silt and Clay are also primary classification types for describingfine grained soils. Their definitions are given later.

Extension -- Burmister (1951) proposed as an extension of the USCSthat the proportions of the minor fractions may be identified by addingin small letters (percentages are by weight).(i) a for ànd' representing 35 to 50%(ii) s for `some' representing 20 to 35%(iii) l for `little' representing 10 to 20%(iv) t for `trace' representing 0 to 10%Thus a well graded sand with 5% gravel sizes would be SWtG. ASTMD2488 uses the terms: Trace < 5%, Few for 5% to 10%; Little for 15%to 25%; Some for 30% to 45%; and Mostly for 50% to 100%. Inaddition Burmister suggested the size fractions in quantities larger thanthe 10% are recommended as being identified as(i) c where coarse sizes constitute more than 10%(ii) m where medium sizes constitute more than 10%(iii) f where fine sizes constitute more than 10%so that, where all three sand sizes are each present in quantities greaterthan 10% of the total, the identification would be ̀ cmfS' placed after themain classification type (i.e. Swtg cmfS).

These suggestions require little extra effort to include and may beuseful.

(iii) Fine Grained Fraction, or FinesThe fine grained fraction of the soil sample is that portion smaller than

the No. 200 (0.074 mm) sieve size. In the Unified Soil ClassificationSystem fines are not subdivided by sizing but by behaviour. The fines,if of inorganic origin, are of two types (these types are further describedlater under the heading relating to moisture):(a) SILT (Symbol M for the Swedish word Mo), and(b) CLAY (Symbol C).Older classification systems define clay as those particles smaller than0.006 mm (6 microns) as seen on Figure 1 (some use 0.002 mm) anddefine silt as fines larger than clay sizes. However, it is a mistaken ideathat the typical engineering characteristics of silt and clay correspond toparticular grain sizes. Natural deposits of rock flour that exhibit all theproperties of silt and none of clay may consist entirely of grains smallerthan 0.006 mm. On the other hand, typical clays may consist mainly ofparticles larger than 0.006 mm, but containing small quantities ofextremely fine colloidal-sized particles. Thus in the Unified SoilClassification System, no size distinction is made between silt and clay,but rather, they are differentiated by their behaviour, and are furthersubdivided according to the amount of water required to make them actplastically or to flow as a semi liquid.

(iv) Organic Material (Symbol O)Organic material is often a component of soil, but in the Unified Soil

Classification System it has no specific grain size. It is distinguished bythe composition of its particles rather than by their sizes which rangefrom colloidal-sized particles of molecular dimensions to fibrous piecesof partly decomposed vegetable matter several inches in length.Subdivision of organic soils is the same as for silt or clay. Organic soilscomposed of more than 50% organic material by weight are known asPeat (Symbol Pt). A useful classification system for peat (given at the

end of this section) is due to Von Post (1922).

(B) GradationThe amounts of the various sizes of grains present in a soil can be

determined in the laboratory by means of sieving for the coarse grainsand sedimentation (wet mechanical analysis) for the fines. Thelaboratory results are presented in the form of a cumulative grain-sizecurve as shown in Figure 3. For soils consisting mainly of coarse grains,the grain-size distribution reveals something of the physical propertiesof the material. On the other hand, grain size is much less significant forsoils containing a preponderance of fine grains. In the Unified SoilClassification System two gradings for coarse soils free of fines (lessthan 12% by weight) are used. They are:

(a) Well Graded (Symbol _W) --Good representation of all particlesizes from largest to smallest

(b) Poorly Graded (Symbol _P)which includes: UniformGradation -- Most particles aboutthe same size, or Skip Gradation --Absence of one or moreintermediate sizes.Note that a dual classification isgiven if the fines are between 5%and 12%.

In the field, soil is estimated tobe well graded or poorly graded byvisual examination. For laboratorypurposes, the type of gradation canbe determined by the use of criteriabased on the range of sizes byweight and on the shape of thegrain-size curve. The measure ofsize range is called the coefficient of uniformity, Cu, which is the ratioof the 60 percent finer than size (D60) to the 10 percent finer than size(D10). The shape of the grain-size curve is given by the coefficient ofcurvature, Cc, which is the ratio of the square of the 30 percent finerthan size (D30) to the product (D60) (D10). The definitions useddistinguish between well and poorly graded Gravel or Sand and areshown in Figure 3.

(C) ShapeThe shape of the particles is not a direct part of the Unified

Classification System but nevertheless has an important influence on thephysical properties of a soil (e.g. cubical shaped particles generallyinterlock better than plate-like particles, and as previously presentedroundness effects void ratio). The following shapes are most commonand are a useful addition.(i) Bulky or Equidimensional Grains -- These may be furtherdescribed as rounded, sub-rounded, subangular, and angular as illustratedin Figure 4. The coarse-grained components of a soil are usually of thebulky type, consisting chiefly of the minerals quartz and feldspar. Theinterlocking ability of angular cubic particles is many times greater thanrounded or subrounded particles such that mainline railway ballast isrequired to be from a quarried source (i.e. crushed rock).(ii) Flat or Flaky grains, also called plate-like particles -- These arepresent in appreciable quantities in many fine-grained soils and havewidth/thickness ratios > 3. Mica and some clay minerals have this shape,which is mainly responsible for their high compressibility.(iii) Elongated Grains -- These are long needle shaped particles andhave length to width ratios > 3.Length, Width and thickness are measured between two parallel plates.Length and thickness are maximum and minimum possible distancebetween two surface points measured by the two plates.


Figure 4. Typical description of bulky or equidimensionalgrains. Figure 5. Liquid limit device.

Figure 6. The plasticity chart.

(D) Soil MoistureThe effect of soil moisture on the fines forms a major part of the

Unified Soil Classification System. A typical soil mass has threeconstituents - soil grains, air and water. In soils consisting largely of finegrains, the amount of water present in the voids has a pronounced effecton the soil properties. Three main states of soils consistency arerecognizable --Liquid state in which the soil is either in suspension or has the nature ofa viscous fluid.Plastic state in which the soil can be rapidly deformed or mouldedwithout elastic rebound, change of volume, cracking, or crumbling.Solid state in which the soil will crack when deformed or will exhibitelastic rebound.(i) Consistency Limits

In describing these soil states it is customary to consider only thefraction of soil smaller than the No. 40 sieve (0.425 mm) size. For thisfraction the water content in percentage of dry weight at which the soilpasses from the liquid state into the plastic state is called the `liquidlimit' (LL or wL) and is recorded as a whole number. A deviceillustrated in Figure 5 which causes the soil to flow under certainconditions (25 drops of the cup through 10 mm) is used in the laboratoryto determine the liquid limit. In practice the 25 blow moisture content isoften determined from a single test result using the equation

LL ' wL ' m/c Blows25

0.1

(1)

Similarly, the water content of the soil at the boundary between theplastic state and the solid state is called the ̀ plastic limit' (PL or wP) andis recorded as a whole number. The laboratory test consists ofrepeatedly rolling threads of the soil to 3 mm (1/8 inch) in diameter untilthey crumble, and then determining the water content. The differencebetween the liquid limit and the plastic limit corresponds to the range ofwater contents within which the soil is plastic. This difference of watercontent is called the `plasticity index' (PI or Ip). Highly plastic soilshave high PI values. In a non-plastic soil the plastic limit and the liquidlimit are the same (and the PI equals 0) or the liquid limit test isimpossible to perform.

These limits of consistency, which are called ̀ Atterberg limits' aftera Swedish scientist, are used in the Unified Soil Classification System asthe basis for laboratory differentiation between materials of appreciableplasticity (clays) and slightly plastic or non-plastic materials (silts). Theyare also used to subdivide the silts, clays and organic materials into thosewith

(a) Low (_L) liquid limit, and (b) High (_H) liquid limits(c) Intermediate ? (an intermediate range is sometimes used, LL =

30-50).These divisions are shown in Figure 6. By definition a clay soil haslimits which plot above the "A" line shown on Figure 6 and silts plotbelow the "A" line with the exceptions shown in the range liquid limit10-30 and plastic limit less than 7.

With sufficient experience a soils engineer may acquire the ability toestimate the Atterberg limits of a soil. Such an estimation may befacilitated by three simple hand tests which have been found adequate forfield identification and classification of fine soils. These three testsdetermine whether the fine-grained fraction of a soil is silty or clayey,without requiring estimation of Atterberg limits. These hand tests, whichare part of the field procedure in the Unified Soil Classification System,are -

Dilatancy (reaction to shaking)Dry strength (crushing characteristics)Toughness (consistency near plastic limit)

These tests are described in the next section. There use is given below:


Soil Dry Strength Dilatancy Toughness

MLMHCLCH

None to LowLow to MediumMedium to High

High to Very High

Slow to RapidNone to SlowNone to Slow

None

Low. Cannot form threadLow to Medium

MediumHigh

Reaction Visual Response

LowMedium

High

No visible change.Water appears slowly on shaking and disappearsslowly on squeezing.Water appears quickly on shaking and disappearsquickly on squeezing.

Strength Visual Response of Dry Specimen

NoneLowMediumHighVery High

Crubles with handling.Crubles with light finger pressure. Breaks with considerable finger pressure. Requires thumb pressure to break.Cannot be broken with thumb pressure.

Toughness Response to Rolling 3 mm diameter thread.

LowMediumHigh

Slight pressure required to roll at PL.Medium pressure required to roll at PL.High pressure required to roll at PL.

3. FIELD IDENTIFICATION TESTSThe procedures for field identification of the fine grained fraction are

performed on the minus No. 40 sieve (0.425 mm) size particles,approximately 1/64 in. For field classification purposes, sieving orscreening is not intended, simply remove by hand the coarse particlesthat interfere with the tests.

(A) DilatancyDilatancy or reaction to shaking: -- After removing particles larger

than No. 40 sieve (0.425 mm) size, prepare a pat of moist soil with avolume of about two cubic cm (one-half inch). Add enough water, ifnecessary to make the soil soft but not sticky. Place the pat in the openpalm of one hand and shake horizontally, striking vigorously against theother hand several times. A positive reaction consists of the appearanceof water on the surface of the pat which changes to a livery consistencyand becomes glossy. When the sample is squeezed between the fingers,the water and gloss disappear from the surface, the pat stiffens, andfinally it cracks or crumbles. The rapidity of appearance of water duringshaking and of its disappearance during squeezing assist in identifyingthe character of the fines in a soil.

Very fine clean sands give the quickest and most distinct reactionwhereas a plastic clay has no reaction. Inorganic silts, such as a typicalrock flour, show a moderately quick reaction. Typical criteria forclassification is:

(B) Dry StrengthDry strength or crushing characteristics: -- After removing particles

larger than a No. 40 sieve (0.425 mm) size, mould a pat of soil to theconsistency of putty, adding water if necessary. Allow the pat to drycompletely by oven, sun, or air drying, and then test its strength bybreaking and crumbling between the fingers. This strength is a measureof the character and quantity of the colloidal fraction contained in thesoil. The dry strength increases with increasing plasticity.

High dry strength is characteristics for clays of high plasticity indexwhich by deduction must also have a high liquid limit and thus must bein the CH group or high range of the CL group. A low dry strengthindicates low plasticity index and thus a silt. Silty fine sands and siltshave about the same slight dry strength, but can be distinguished by thefeel after powdering the dried specimen. Fine sand feels gritty whereasa typical silt has the smooth feel of flour. Typical criteria forclassification is:

(C) ToughnessToughness or consistency near plastic limit: -- After removing

particles larger than the No. 40 sieve (0.425 mm) size, a specimen of soilabout two cubic cm (one-half inch) volume in size is moulded to theconsistency of putty. If too dry, water must be added and if sticky, thespecimen should be spread out in a thin layer and allowed to lose somemoisture by evaporation. Then the specimen is rolled out by hand on asmooth surface or between the palms into a thread about 3 mm (one-eighth inch) in diameter. The thread is then folded and then rerolledrepeatedly. During this manipulation the moisture content is graduallyreduced and the specimen stiffens, finally loses its plasticity, andcrumbles when the plastic limit is reached.

After the thread crumbles, the pieces should be lumped together anda slight kneading action continued until the lump crumbles.

The tougher the thread near the plastic limit and the stiffer the lumpwhen it finally crumbles, the more potent is the colloidal clay fraction inthe soil. Weakness of the thread at the plastic limit and quick loss ofcohesion of the lump below the plastic limit indicate either inorganic clayof low plasticity, or materials such as kaolin-type clays and organic siltswhich occur below the A-line.

Highly organic clays have a very weak and spongy feel at the plasticlimit. Typical criteria for classification is:

4. CLASSIFICATION OF SOILS (see Table 1).

(A) GeneralSoils in nature seldom exist separately as a gravel, sand, silt, clay, or

organic matter, but are usually found as mixtures with varyingproportions of these components. The Unified Soil ClassificationSystem is based on recognition of the type and predominance of theconstituents, considering grain size, gradation, plasticity andcompressibility. As already described it divides soils into three majordivisions - coarse-grained soils, fine-grained soils, and highly organic(peaty) soils. In the field, identification is accomplished by visualexamination for the coarse grains and by a few simple hand tests for thefine-grained soils or fraction. In the laboratory, the grain-size curve andthe Atterberg limits can be used. The peaty soils (Pt) are readilyidentified by colour, odour, spongy feel, and fibrous texture and are notfurther sub-divided in the classification.

(B) Field ClassificationA representative sample of soil (excluding particles larger than 76 mm

or 3 inches) is first classified as coarse grained or fine grained byestimating whether 50 percent, by weight, of the particles can be seenindividually by the naked eye. Soils containing more than 50 percent ofparticles that can be seen are coarse-grained soils, soils containing morethan 50 percent of particles smaller than the eye can see are fine-grainedsoils. If the soil is predominantly coarse grained, it is then identified asbeing a gravel or a sand by estimating whether 50 percent or more of the


Figure 7. Guide for field soil textural classification using unifiedsystem.

fraction of coarse grains are larger or smaller than the No. 4 sieve (4.75mm) size (about 1/4 inch).

If the soil is a gravel, it is next identified as being `clean' andcontaining little or no fines (by definition less than 5 percent by weight),or `dirty' and containing an appreciable amount of fines (by definitionmore than 12 percent by weight). For clean gravels, final classificationis made by estimating the gradation, the well-graded gravels belong tothe GW group, and uniform or well sorted (not to be confused with wellgraded) and skip-graded gravels belong to the GP group. Dirty gravelsare of two types - those with non-plastic (silty) fines, GM, and those withplastic (clayey) fines, GC. The determination of whether the fines aresilty or clayey is made by the three manual (i.e. by hand) tests for fine-grained soils.

If a soil is a sand, the same steps and criteria are used as for thegravels in order to determine whether the soil is a well-graded clean sand(SW), poorly graded clean sand (SP), sand with silty fines (SM), or sandwith clayey fines (SC).

If a material is predominantly (more than 50 percent by weight) finegrained, it is classified into one or six groups (ML, CL, OL, MH, CH,OH) by estimating its dilatancy (reaction to shaking), dry strength(crushing characteristics), and toughness (consistency near plastic limit),and by identifying it as being organic or inorganic.

Soils that are typical of the various groups are readily classified by theforegoing procedures. However, many natural soils will have propertycharacteristics of two groups because they are close to the borderlinebetween the groups, either in percentages of the various sizes or inplasticity characteristics. For this substantial number of soils, boundaryclassifications are used, that is, the two group symbols most nearlydescribing the soil are connected by a hyphen, such as GW-GC.

If the percentages of gravel and sand sizes in a coarse-grained soil arenearly equal, the classification procedure is to assume that the soil is agravel, and then continue in the chart until the final soil group, say GC,is reached. Since we could have assumed that the soil is a sand, thecorrect field classification is GC-SC, because the criteria for the graveland sand subgroups are identical. Similarly, within the gravel or sandgroupings, boundary classifications such as GW-GP, GM-GC, GW-GM,SW-SP, SM-SC, and SW-SM can occur.

Proper boundary classification of a soil near the borderline betweencoarse-grained and fine-grained soils is accomplished by classifying itfirst as a coarse-grained soil and then as a fine-grained soil. Suchclassifications as SM-ML and SC-CL are common.

Within the fine-grained division, boundary classifications can occurbetween low liquid limit soils and high liquid limit soils as well asbetween silty and clayey materials in the same range of liquid limits. Forexample, we may have ML-MH, CL-CH, OL-OH and ML-CL, ML-OL,CL-OL, MH-CH, MH-OH, CH-OH soils. A guide for a texturalclassification of soils is shown in Figure 7. The textural properties canbe supplemented by manually performed tests already presented for fieldclassification purposes.

(C) Laboratory ClassificationAlthough most classifications of soils will be done visually and by the

manually performed tests, the Unified Soil Classification Systemprovides a precise delineation of the soil groups by mechanical analysesand Atterberg limits tests in the laboratory. Laboratory classifications areoften performed on representative samples of soils which are beingsubjected to extensive testing for strength, compressibility, andpermeability. They also can be used to advantage in training the fieldclassifier of soils to improve his ability to estimate percentages anddegrees of plasticity.

The grain-size curve is used to classify the soil as being coarsegrained or fine grained, and if coarse grained, into gravel or sand by size,using the 50 percent criterion. Within the gravel or sand groupings, soilscontaining less than 5 percent finer than the No. 200 sieve (0.074 mm)size are considered `clean' and are then classified as well graded orpoorly graded by their coefficients of uniformity and curvature. In orderfor a clean gravel to be well graded (GW), it must have both a coefficient

of uniformity (Cu) greater than 4 and a coefficient of curvature (Cc)between 1 and 3 (see Figure 3) - otherwise, it must be classified as apoorly graded gravel (GP). A clean sand, having both a Cu greater than6 and a Cc between 1 and 3, is in the SW group - otherwise, it is a poorlygraded sand (SP).

`Dirty' gravels or sands are those containing more than 12 percent offines, and they are classified as silty (GM or SM) or clayey (GC or SC)by results of their Atterberg limits tests as plotted on the plasticity chartshown. Silty fines are those which have a plasticity index (PI) less than4 or which plot below the À' line. Clayey fines are those which have aPI greater than 7 and which plot above the À' line.

Coarse-grained soils containing between 5 and 12 percent of fines areborderline cases between the clean and dirty gravels or sands (GW, GP,SW, SP, and GM, GC, SM, SC). Similarly, borderline cases may occurin dirty gravels and dirty sands where the PI is between 4 and 7 (GM-GC, SM-SC). It is theoretically possible, therefore, to have a borderlinecase of a borderline case - but this is not permitted, and the rule forcorrect classifications is to favour the non-plastic one. For example, agravel with 10 percent fines, a Cu of 20, a Cc of 2.0, and a PI of 6 wouldbe classified GW-GM rather than GW-GC.

Once a soil is determined to be fine grained by the grain-size curve,its classification into one of the six groups is done by the results ofAtterberg limits tests as plotted on the plasticity chart, with attentionbeing given to the organic content. Inorganic fine-grained soils with PIgreater than 7 and above the À' line are CL or CH, depending onwhether their liquid limits are below 50 percent or above 50 percentrespectively. Similarly, inorganic fine-grained soils with PI less than 4or below the À' line are ML or MH, depending on whether their liquidlimits are below or above 50 percent, respectively. Fine-grained soilswhich fall above the À' line but which have a plasticity index between4 and 7 are classified ML-CL.

Soils which plot below the À' line that are definitely organic areclassified as OL if they have liquid limits less than 50 and as OH if theliquid limit is above 50. Organic silts and clays are usually distinguishedfrom inorganic silts and clays which have the same position on theplasticity chart, by odour and colour. However, when the organiccontent is doubtful the material can be oven dried, remixed with water,and retested for liquid limit. The plasticity of fine-grained organic soilsis greatly reduced on oven drying, due to irreversible changes in theorganic colloids. Oven drying also affects the liquid limit of inorganicsoils, but to a much smaller degree. A reduction in liquid limit after ovendrying to a value less than three-fourths of the liquid limit before ovendrying is positive identification of organic soils.

5. ENGINEERING CHARACTERISTICS OF SOILCOMPONENTS

Some of the main engineering properties of the various soil types aregiven in summary form in Table 2 and typical safe bearing pressures and


Figure 8. Safe Bearing Stresses developed for highway andairport design (PCA, 1956).

Figure 9. Compressibility-Liquid Limit relationship forremoulded soils (Skempton, 1944).

California Bearing Ratios (CBR) as used in main class highways andairport design are shown in Figure 8. These may be consideredsomewhat conservative for use with railroads whose support need not beas rigid. A fifty percent increase in scale values is suggested for use withrailway track support subgrades

.(A) Gravel and SandBoth of the coarse-grained components of soil (gravel and sand) have

essentially the same engineering properties, differing mainly in degree.The division of gravel and sand sizes by the No. 4 sieve (4.75 mm) isarbitrary and does not correspond to a sharp change in properties. Well-graded, compacted gravels, or sands are stable materials. The coarse-grained soils when devoid of fines are pervious, easy to compact, littleaffected by moisture, and not subject to frost action. Although grainshape and gradation as well as size affect these properties, for the sameamount of fines gravels are generally more pervious, more stable, andless affected by water or frost than are sands. Similarly angular particlesresult in stronger strengths than rounded particles.

As a sand becomes finer and more uniform, it approaches thecharacteristics of silt with corresponding decrease in permeability andreduction in stability in the presence of water. Very fine, uniform sandsare difficult to distinguish visually from silt. However, dried sandexhibits no cohesion (does not hold together) and feels gritty in contrastto the very slight cohesion and smooth feel of dried silt.

(B) Silt and ClayEven small amounts of fines may have important effects on

engineering properties of the soils in which they are found. As little as12 percent of particles smaller than the No. 200 sieve (0.074 mm) size in

sand and gravel may make the soil virtually impervious, especially whenthe coarse grains are well graded. Also, serious frost heaving in well-graded sands and gravels may be caused by less than 12 percent of fines.Typically 6% fines at the surface results in some frost heave. Theallowable amount increases with depth.

Soils containing large quantities of silt and clay are the mosttroublesome to the engineer. These materials exhibit marked changes inphysical properties with change of water content. A hard, dry clay, forexample, may be suitable as a foundation for heavy loads so long as itremains dry, but may turn into a quagmire when wet. Many of the finesoils shrink on drying and expand on wetting, which may adverselyeffect structures founded on them or constructed on them. Even whenmoisture content does not change, the properties of fine soils may varyconsiderably between their natural condition in the ground and their stateafter being disturbed. Deposits of fine particles which have beensubjected to loading in geologic time frequently have a structure whichgives the material unique properties in the undisturbed state. When thesoil is excavated for use as a construction material or when the naturaldeposit is disturbed by driving piles, for example, the soil structure isdestroyed and the properties of the soil are changed radically.

Silts are different from clays in many important respects, but becauseof their similarity in appearance, they often have been mistaken one forthe other sometimes with unfortunate results. Dry, powdered silt andclay are indistinguishable, but they are easily identified by theirbehaviour in the presence of water. The importance of the recognitionof the difference in behaviour of fines as being silt or clay is an essentialpart of the Unified Soil Classification System.

(i) SiltsSilts are the non-plastic fines. They are inherently unstable in the

presence of water and have a tendency to become ̀ quick' when saturated.Silts are fairly impervious, difficult to compact, and are highlysusceptible to frost heaving. Silt masses undergo change of volume withchange of shape (the property of dilatancy) in contrast to clays whichretain their volume with change of shape (the property of plasticity).Thus silts, at the same liquid limit, have relatively low plasticitycompared with clays. In terms of the classification chart (Figure 6) theyplot below the ̀ A' line. The dilatancy property of silts, together with the`quick' reaction to vibration, affords a means of identifying typical silt inthe loose wet state. When dry, silt can be pulverized easily under fingerpressure (has very slight dry strength), and will have a smooth feelbetween the fingers in contrast to the grittiness of fine sand.

Silts differ among themselves in size and shape of grains which arereflected mainly in the property of compressibility. For similarconditions of previous loading, the higher liquid limit of a silt the morecompressible it is. This is also true for clays and a general pattern ofresults for remould fine grained soils is shown in Figure 9 demonstratingthis point. The liquid limit of a typical bulky-grained inorganic silt isabout 30, while highly micaceous or diatomaceous silts (so-calledèlastic' silts) consisting mainly of flaky grains, may have liquid limits ashigh as 100. The differences in quickness and dilatancy properties afforda means of distinguishing in the field between silts of low liquid limit


Figure 10. Relationship suggested by Bjerrum (1954) betweenundrained strength and plasticity Index.

Figure 11. Typical activity relationship for three natural soils(Skempton, 1953).

and those of high liquid limit.

(ii) ClaysClays are the plastic fines. Thus they plot above the À' line on the

plasticity chart (Figure 6). They have low resistance to deformationwhen wet, but they dry to hard cohesive masses. Clays are virtuallyimpervious, difficult to compact when wet, and impossible to drain byordinary means. Large expansion and contraction with changes in watercontent are characteristics of clays. The small size, flat shape, andmineral composition of clay particles combine to produce a material thatis both compressible and plastic. The higher the liquid limit of a clay, themore compressible it will be when compared at equal conditions ofprevious loading (Figure 9), hence, in the Unified Soil ClassificationSystem, the liquid limit is used to distinguish between clays of highcompressibility (symbol H) and those of low compressibility (symbol L).{Note:- The low range is sometimes subdivided into low (L) andintermediate (I).} Differences in plasticity of clays are reflected by theirplasticity indexes.

Since the plastic limit of a soil is rarely less than 15 the range of theplasticity index (PI = LL - PL) for a clay at any given liquid limit is smallsince they must plot above the ̀ A' line on Figure 6. Thus clays are oftenreferred to as low or high plasticity clays rather than low or highcompressible clays. In general the higher the liquid limit and thus theplasticity index the more cohesive is the clay at the same overburdenconsolidation pressure, as seen in Figure 10 for Norwegian soft(normally consolidated) clays. Field differentiation among clays isaccomplished by the toughness test in which the moist soil is mouldedand rolled into threads until crumbling occurs and by the dry strength testwhich measures the resistance of the clay to breaking and pulverizing.With a little experience in performing these tests, the clays of lowcompressibility and also low plasticity, `lean' clays (symbol _L), can bereadily distinguished from the highly compressible and also highlyplastic `fat' clays (symbol _H). {Since the plastic index is less than theliquid limit low or high compressibility for clays also means low or highplasticity. This however is not true for silts. The subdivision L or Hrefers to compressibility (Liquid Limit see Figure 9) and not plasticity.This point is often misquoted.}

(iii) Organic MatterOrganic matter in the form of partly decomposed vegetation is the

primary constituent of peaty soils. Varying amounts of finely dividedvegetable matter are found in plastic and non-plastic sediments, and oftenaffect their properties sufficiently to influence their classification. Thuswe have organic silts and silt-clays of low plasticity and organic clays ofmedium to high plasticity. Even small amounts of organic material incolloidal form in a clay will result in an appreciable increase in liquidlimit of the material without increasing its plasticity index. Organic soils

are dark grey or black in colour, and usually have a characteristic odourof decay. Organic clays feel spongy in the plastic range as compared toinorganic clays. The tendency for soils high in organic content to createvoids by decay or to change the physical characteristics of a soil massthrough chemical alteration makes them undesirable for engineering use.Soils containing even moderate amounts of organic matter aresignificantly more compressible and less stable than inorganic soils,hence they are less desirable for engineering use.

6. ACTIVITYAlthough not part of the classification of soils Skempton (1953) has

defined the Àctivity' of a soil as the ratio of the Plasticity Index to thepercentage by weight of the soil smaller than the 2 micrometre. Theresults that accommodated Skempton's definition are illustrated in Figure11 and were done on clays that were basicly 100% passing the 75 µmsieve. The value of obtaining the activity of the fines fraction is that highactivity is generally but not always associated with swelling soils.

7. VON POST CLASSIFICATION OF PEATVon Post's main classification of peat is for degree of decomposition

or "Humidification" symbol H.Secondary subdivisions are for "Relative Moisture", symbol B;

"Number of Fibres", symbol F; "Number of Root Threads", symbol R;and "Quantity of Wood" symbol V.

These classifications are given below (see after references):

8. REFERENCESASTM D-2487, "Classification of soils for engineering purposes",

American Society for Testing Materials. (TA401.A5S).ASTM D-2488, "Description and identification of soils (visual-

manual procedure)", American Society for Testing Materials.(TA401.A5S).

Bjerrum, L. (1954), "Geotechnical properties of Norwegian marineclays". Geotechnique, Vol. 4, pp. 49-69. (TA1.G3).

Burmister, D.M., 1951, "Identification and Classification of Soils".Symposium on Identification and Classification of Soils, SpecialTechnical Publication No. 113, American Society for Testing Materials,


Classification of Degree of Decomposition of Peat

H1 Completely unhumified and muck-free peat; upon pressingin the hand, gives off only colorless, clear water.

H2 Almost completely unhumified and muck-free peat; uponpressing, gives off almost clear but yellow-brown water.

H3 Little humified and little muck-containing peat; uponpressing, gives off distinctly turbid water, no peatsubstances pass between the fingers and the residue is notmushy.

H4 Poorly humified or some muck-containing peat; uponpressing, gives off strongly turbid water. The residue issomewhat mushy.

H5 Peat partially humified or with considerable muck-content.The plant remains are recognizable but not distinct. Uponpressing, some of the substance passes between the fingerstogether with mucky water. The residue in the hand isstronglv m1lshv

H6 Peat partially humified or with considerable muck-content.The plant remains are not distinct. Upon pressing, at themost, one third of the peat passes between the fingers. Theresidue is strongly mushy but the plant residue stands outmore distinctly than in the unpressed peat.

H7 Peat quite well humified or with considerablemuck-content, in which much of the plant remains can stillbe seen. Upon pressinR, about half of the peat passesbetween the fingers. If water separates it is soupy and verydark in color.

H8 Peat weIl humified or with considerable muck-content. Theplant remains are not recognizable. Upon pressing, abouttwo-thirds of the peat passes between the fingers. If itgives off water at alln it is soupy. The remains consistmainlY of more resistant root fibres, etc.

H9 Peat, very well humified or muck-like in which hardly anyplant remains are apparent. Upon pressing, nearly all of thepeat passes between the fingers like a homogeneous mush.

H10 Peat completely humified or muck-like in which no plantremains are apparent. Upon pressing all of the peat passesbetween the fingers.

Secondary Classification for Peat

B. RelativeMoisture:

B1 Air dryB2 Somewhat dryB3 Normal moistureB4 WetB5 Very wet

F. Number ofFibres:

F1 No fibresF2 Few fibresF3 Plenty of fibresF4 Mainly fibres

R. Number ofRoot Threads:

R1 No root threadsR2 Few root threadsR3 Plenty of root threadsR4 Root threads forming main part of peat

V. Quantity ofWood:

V1 No wood remainderV2 Few wood remaindersV3 Plenty wood remaindersV4 Very many wood remainders

pp. 3-24. (TA710.A5)Casagrande, A., 1948, "Classification and Identification of Soils".

Transactions of the American Society of Civil Engineers, Volume 113,pp. 901-991. (TA1.A5t)

Helenelund, K.V. (1968), "Compression, Tension and Beam Tests onFibrous Peat". Proceedings of the Third International Peat Congress,Quebec, Canada, pp. 136-142. (TN837.I58)

"Peat Testing Manual", (1979). Technical Memorandum 125,National Research Council of Canada, Ed. Com. Day, J.H., Rennie, P.J.,Stanek, W, and Raymond G.P. (Chairman). (TA710.A1N27).

Portland Cement Association (1956), "PCA soil primer". Portland Cement Association, Chicago, IL. 86p.

Rose, A.C. (1924), "Practical field tests for subgrade soils". PublicRoads, Vol. 5, pp. 10-15. (TE23.A4).

Skempton, A.W., 1944, "Notes on the compressibility of clays".Quart. J. Geol. Soc., London, C, pp. 119-135. (QE1.G345).

Skempton, A.W., 1953, "The colloidal activity of clays". Proc. 3rdInternational Conference on Soil Mechanics and FoundationEngineering, Vol. 1, pp. 57-61. (TA710.I6t)

Von Post, L. (1922) "Sveriges geologiska undersökningstorvinventering och några av dess hittills vunna resultat" Sv.Mosskulturför", Tidskr, 1:1-27.



Geotechnical Investigation : Examples of MSE Walls from Sierra April 6, 2010

APPENDIX G Examples of MSE Walls from Sierra

Documents

Geotechnical Investigation Bow Ridge Subdivision Phase 3