Geotechnical Engineering Report - Pavilion Construction Vista Housin… · Geotechnical Engineering Report Montana Vista Apartments Silver City, New Mexico June 21, 2011 Terracon

Geotechnical Engineering Report

Montana Vista Apartments

SEC of Valley Vista Drive and 40th Street

Silver City, New Mexico

June 21, 2011

Terracon Project No. 68115036

Prepared for:

Western Regional Housing Authority

Silver City, New Mexico

Prepared by:

Terracon Consultants, Inc.

Las Cruces, New Mexico


Montana Vista Apartments ■ Silver City, New Mexico

June 21, 2011 ■ Terracon Project No. 68115036

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EXECUTIVE SUMMARY

This geotechnical executive summary should be used in conjunction with the entire report

for design and/or construction purposes. It should be recognized that specific details were not

included or fully developed in this section, and the report must be read in its entirety for a

comprehensive understanding of the items contained herein. The section titled General

Comments should be read for an understanding of the report limitations.

A geotechnical exploration has been performed for the Montana Vista Apartments to be located

at the southeast corner of Valley Vista Drive and 40th Street in Silver City, New Mexico. The

proposed project will include two separate 2 to 3 story apartment (1 to 3 bedrooms per unit)

structures and a laundry/office facility. Parking and drive areas are associated with the project.

Terracon’s geotechnical scope of work included the advancement of four test borings to

approximate depths ranging from 5 to 22 feet below existing site grades (bgs). Auger refusal

was encountered at depths of about 22, 13, and 6 feet in Borings B-1, B-2 and B-3,

respectively, due to suspected bedrock or cobble/boulder sized materials.

Based on the information obtained from our subsurface exploration, the site is suitable for

development of the proposed project. The following geotechnical considerations were

identified:

The site soils in the building areas on the west side of the project site generally

consisted of fill soils comprised of silty, clayey sand with varying amounts of gravel from

the surface to depths of about 10 to 12 feet in Borings B-1 and B-2. The upper fill soils

were underlain by sandy lean clay to the total explored depths of 20 feet bgs (Boring B-

1) and 13 feet bgs (Boring B-2). The fill extended from the ground surface to the total

explored depth of 6 feet bgs in Boring B-3 and 5 feet bgs in Boring B-4. Auger refusal

due to suspected bedrock or boulder sized materials was encountered in Borings B-1, B-

2 and B-3. The east side (sloping down about 5 to 10 feet below the west side of the

site) of the site generally consisted of exposed native soils, boulders and/or bedrock

outcrops. Groundwater was not encountered in the test borings at the time of drilling.

Due to the presence of fill soils on the site (west side), we recommend complete removal

the fill material (6 to 12 feet in thickness) and replacement with engineered fill. Standard

spread and continuous foundations bearing on engineered fill can be used for support of

the proposed structures. Engineered fill would not be required in areas of the site where

exposed native soils or bedrock is encountered (east side). The on-site fill soils and

native soils may be used as engineered fill if screened for large diameter materials and

debris, provided the soil meets the engineered fill specification contained in this report.




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Supplemental exploration and evaluation would be needed to further assess the fill if it is

desired to possibly support the standard spread footings on partial removal and

replacement.

Construction of floor slabs on the new engineered fill, compacted native soils or bedrock

is considered acceptable for the project.

Automobile parking areas – 3” AC over 4” ABC or 5” PCC over 8” Compacted Subgrade.

Heavy vehicle access and drives – 3-1/2” AC over 6” ABC or 6” PCC over 8” Compacted

Subgrade.

Earthwork on the project should be observed and evaluated by Terracon. The evaluation

of earthwork should include observation and testing of engineered fill, subgrade

preparation, foundation bearing soils, and other geotechnical conditions exposed during

construction




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TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY ....................................................................................................... i

1.0 INTRODUCTION ...................................................................................................... 1

2.0 PROJECT INFORMATION ....................................................................................... 1

2.1 Project Description ........................................................................................ 1

2.2 Site Location and Description ........................................................................ 2

3.0 SUBSURFACE CONDITIONS.................................................................................. 3

3.1 Typical Subsurface Profile ............................................................................. 3

3.2 Groundwater ................................................................................................. 3

4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION ............................... 4

4.1 Geotechnical Considerations......................................................................... 4

4.2 Earthwork ...................................................................................................... 5

4.2.1 Site Preparation ................................................................................. 5

4.2.2 Excavation ......................................................................................... 5

4.2.3 Subgrade Preparation ........................................................................ 6

4.2.4 Fill Materials and Placement .............................................................. 6

4.2.5 Compaction Requirements................................................................. 7

4.2.6 Grading and Drainage ........................................................................ 8

4.2.7 Slopes ............................................................................................... 8

4.2.8 Corrosion Potential ............................................................................ 9

4.3 Foundation Recommendations ...................................................................... 9

4.3.1 Design Recommendations ................................................................. 9

4.3.2 Lateral Earth Pressures ....................................................................10

4.4 Seismic Considerations ................................................................................10

4.5 Floor Slabs ...................................................................................................11

4.5.1 Design Recommendations ................................................................11

4.5.2 Construction Considerations .............................................................12

4.6 Pavements ...................................................................................................12

5.0 GENERAL COMMENTS .........................................................................................14

Exhibit No.

Appendix A – Field Exploration

Site Location Map and Boring Location Plan............................................. A-1 and A-2

Field Exploration Description ................................................................................. A-3

Boring Logs .............................................................................................. A-4 and A-8

General Notes ....................................................................................................... A-9

Unified Soil Classification System ........................................................................ A-10

Appendix B – Laboratory Testing

Laboratory Test Description ................................................................................... B-1

Laboratory Test Results ............................................................................ B-2 thru B-6


1

GEOTECHNICAL ENGINEERING REPORT

MONTANA VISTA APARTMENTS

SEC OF VALLEY VISTA DRIVE AND 40TH STREET

SILVER CITY, NEW MEXICO Terracon Project No. 68115036

June 21, 2011

1.0 INTRODUCTION

This report presents the results of our geotechnical engineering services performed for the

Montana Vista Apartments located at the southeast corner of Valley Vista Drive and 40th Street in

Silver City, New Mexico. Items addressed in this report are as follows:

subsurface soil/bedrock conditions groundwater conditions

earthwork/pavements foundation design and construction

seismic considerations floor slab design and construction

Our geotechnical engineering scope of work for this project included the advancement of four

test borings to approximate depths ranging from 5 to 22 feet below existing site grades (bgs).

Auger refusal was encountered at depths of about 22, 13, and 6 feet in Borings B-1, B-2 and

B-3, respectively, due to suspected bedrock or cobble/boulder sized materials.

Terracon reviewed an existing report prepared by Weber Engineering (dated December 2008)

that references 2 to 12 feet of fill were placed on the site derived from adjacent construction. The

information contained in this report was used to supplement the information generated for this

current study.

Logs of the borings along with a Site Location Map and Boring Location Plan (Exhibits A-1 and A-

2) are included in Appendix A of this report. The results of the laboratory testing performed on

soil samples obtained from the site during the field exploration are included in Appendix B of this

report. Descriptions of the field exploration and laboratory testing are included in their respective

appendices.

2.0 PROJECT INFORMATION

2.1 Project Description




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ITEM DESCRIPTION

Site layout Refer to the Site Location Map and Boring Location Plan (Exhibits

A-1 and A-2)

Structures

The proposed project will include two separate 2- to 3-story

apartment (1 to 3 bedrooms per unit) structures and a

laundry/office facility. Parking and drive areas are associated with

the project.

Building construction

The buildings will consist of wood frame bearing on exterior and

interior spot footings. The floor system is anticipated to be slab-on-

grade isolated from standard spread and continuous foundations.

Finished floor elevation

Finished floor elevation of the apartment structures is planned to

essentially match existing grades from the highest elevations on

the west side to the lowest elevation of the east side (step-down

construction).

Maximum loads

Columns: 50 kips maximum (assumed)

Walls: 2.0 klf maximum (assumed)

Slabs: 150 psf max (assumed)

Maximum allowable movement 1 inch

Maximum allowable differential

movement

½ inch over 40 feet for walls, ¾ inch over 40 feet for interior

columns (assumed)

Grading in building area Cuts and fills of about 5 feet may be required for grading purposes

Retaining walls 5 feet are anticipated

Cut and fill slopes 5 feet are anticipated

2.2 Site Location and Description

ITEM DESCRIPTION

Location Southeast corner of Valley Vista Drive and 40

th Street in Silver

City, New Mexico

Existing site features Vacant lot. The west side of the property contains fill soils with an

approximate maximum depth of about 12 feet.

Surrounding developments

North: 40th Street

East: Undeveloped

West: Valley Vista Drive

South: Undeveloped

Current ground cover Exposed subgrade soils, boulders and/or bedrock outcrops.

Sparsely vegetated with native grasses and small trees and

bushes.

Existing topography Estimated vertical relief on the order of about 15 to 20 feet across

the site from west to east.





3.0 SUBSURFACE CONDITIONS

3.1 Typical Subsurface Profile

Specific conditions encountered at the boring locations are indicated on the individual boring

logs. Stratification boundaries on the boring logs represent the approximate location of

changes in soil types; in-situ, the transition between materials may be gradual. Details for each

of the borings can be found on the boring logs included in Appendix A of this report. Based on

the results of the borings, subsurface conditions on the project site can be generalized as

follows:

Description Approximate Depth to

Bottom of Stratum (feet) Material Encountered Consistency/Density

Stratum 1 5 to 12

Fill Soils consisting of Silty,

Clayey Sand with varying

amounts Gravel

Medium Dense to

Very Dense

Stratum 2

20 (Boring B-1),

13 (Boring B-2)

Sandy Lean Clay Hard

Stratum 3 6 to 22 feet*

Bedrock (Shale and

Sandstone) or boulder sized

materials

Very Hard

*auger refusal at 6 to 22 feet below existing grade

Laboratory tests were conducted on selected soil samples and the test results are presented

in Appendix B. Laboratory test results indicate that the near surface fill soils exhibit low to

moderate compressibility potentials at in-situ moisture contents. The fill soils have a slight to

high tendency for hydro-compaction when elevated in moisture content. The fill soils do not

exhibit expansion under a surcharge load of 1,000 psf. Sample disturbance is likely

reflected in test results, since the field penetration resistance of the material is high (40).

3.2 Groundwater

Groundwater was not observed in the test borings at the time of field exploration. These

observations represent groundwater conditions at the time of the field exploration and may

not be indicative of other times, or at other locations. Groundwater conditions can change

with varying seasonal and weather conditions, and other factors.





4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION

4.1 Geotechnical Considerations

The fill soil placement at the site was not observed or tested by a geotechnical engineer. It

is possible that the fill soils contain construction debris, boulders and large diameter cobbles

and gravels. It is also likely that the previous slope was not benched prior to placement of

the fill to aid in the prevention of potential movement along the fill/native soil (or bedrock)

interface. The Standard Penetration Test (SPT) N-counts for the fill were relatively high.

However, the unknown fill placement techniques and suspected large diameter boulders

along with possible debris and the fill/soil interface issue present substantial risk of

movement to the structures if supported on standard spread and continuous foundations

bearing directly on the fill material.

Due to the presence of fill soils on portions of the site, standard spread and continuous

foundations (and floor slabs) bearing on engineered fill material can be used for support of

the proposed structures. The fill material (located on the west side of the site) should be

completely removed and replaced with engineered fill (6 to 12 feet). The fill material may be

re-used as engineered fill provided that the debris and large diameter cobbles or boulders

are removed from the stockpiles generated during the excavations and meet the

specifications outline in this report. Delineation of the horizontal and vertical extents of the

existing fill should be confirmed with supplemental exploration or during construction.

Supplemental exploration and evaluation would be needed to further assess the fill if it is

desired to possibly support the standard spread footings (and floor slabs) on partial removal

and replacement of these materials. However, even with the recommended construction

testing services, there is an inherent risk for the owner that compressible fill or unsuitable

material within or buried by the fill will not be discovered. This risk of unforeseen conditions

cannot be eliminated without completely removing the existing fill.

In areas of the site where fill is not encountered (east side), standard spread and continuous

foundations bearing on compacted native soils or bedrock could be used for support of the

structures. In these areas, floor slabs can be supported on prepared subgrade.

Support of pavements on existing fill can be considered, if the owner is willing to assume

risk of movement and potential increase in maintenance.

Geotechnical engineering recommendations for foundation systems and other earth

connected phases of the project are outlined below. The recommendations contained in this





report are based upon the results of field and laboratory testing (which are presented in

Appendices A and B), engineering analyses, and our current understanding of the proposed

project.

4.2 Earthwork

The following presents recommendations for site preparation, excavation, subgrade

preparation and placement of engineered fills on the project. The recommendations

presented for design and construction of earth supported elements including foundations

and slabs are contingent upon following the recommendations outlined in this section. All

grading for the structures should incorporate the limits of the proposed structure plus a

minimum pad blow-up of five feet beyond proposed perimeter building walls (where

applicable).

Earthwork on the project should be observed and evaluated by Terracon. The evaluation of

earthwork should include observation and testing of engineered fill, subgrade preparation,

foundation bearing soils, and other geotechnical conditions exposed during the construction

of the project.

4.2.1 Site Preparation

Strip and remove existing vegetation, boulders (if encountered) and other deleterious

materials from proposed building and pavement areas. Exposed surfaces should be free of

mounds and depressions which could prevent uniform compaction.

Stripped materials consisting of vegetation and organic materials should be wasted from the

site, or used to revegetate landscaped areas or exposed slopes after completion of grading

operations. If it is necessary to dispose of organic materials on-site, they should be placed

in non-structural areas, and in fill sections not exceeding 5 feet in height.

The site should be initially graded to create a relatively level surface to receive fill, and to

provide for a relatively uniform thickness of fill beneath the proposed building structures.

Although evidence of underground facilities such as septic tanks, cesspools, utilities and

basements was not observed during the site reconnaissance, such features could be

encountered during construction. If unexpected fills or underground facilities are

encountered, such features should be removed and the excavation thoroughly cleaned prior

to backfill placement and/or construction.

4.2.2 Excavation

It is anticipated that some excavations for the proposed construction can be accomplished

with conventional earthmoving equipment. Hard soils, boulders and cobbles may require





heavy duty equipment or additional effort to advance deep excavations, such as

underground utilities or finished grades substantially below existing grades.

On-site soils may pump or become unstable or unworkable at high water contents.

Workability may be improved by scarifying and drying. Overexcavation of wet zones and

replacement with granular materials may be necessary. Lightweight excavation equipment

may be required to reduce subgrade pumping.

Use of lime, fly ash, kiln dust, cement or geotextiles could also be considered as a

stabilization technique. Laboratory evaluation is recommended to determine the effect of

chemical stabilization on subgrade soils prior to construction.

4.2.3 Subgrade Preparation

Remove and replace existing fill as engineered fill. The existing fill should be screened for

large diameter rock and debris to meet specifications outlined in this report. Exposed areas

which will receive fill or be constructed upon, once properly cleared and benched where

necessary, should be scarified to a minimum depth of 10 inches, conditioned to near

optimum moisture content, and compacted. The above recommendation does not apply is

the excavation terminates at the bedrock surface.

Areas of loose soils may be encountered at foundation bearing depth after excavation is

completed. When such conditions exist beneath planned foundation areas, the subgrade

soils should be surficially compacted prior to placement of the foundation system. If

sufficient compaction cannot be achieved in-place, the loose soils should be removed and

replaced as engineered fill.

If fill is placed in areas of the site where slopes are steeper than 5:1 (horizontal:vertical), the

area should be benched to reduce the potential for slippage between existing slopes and

fills. Benches should be wide enough to accommodate compaction and earth moving

equipment, and to allow placement of horizontal lifts of fill.

Subgrade soils beneath exterior slabs should be scarified, moisture conditioned and

compacted to a minimum depth of 10 inches. The moisture content and compaction of

subgrade soils should be maintained until slab or pavement construction.

4.2.4 Fill Materials and Placement

All fill materials should be inorganic soils free of vegetation, debris, and fragments larger

than six inches in size. Pea gravel or other similar non-cementitious, poorly-graded

materials should not be used as fill or backfill without the prior approval of the geotechnical

engineer.





Clean on-site soils, approved imported materials, on-site screened soils or on-site clay soils

(if encountered) blended with granular material may be used as fill material for the following:

general site grading exterior slab areas

foundation areas foundation backfill

pavement areas

Imported, on-site, screened soils or blended soils for use as fill material within proposed

building areas should conform to low volume change materials as indicated in the following

specifications:

Percent Finer by Weight

Gradation (ASTM C 136)

6" ......................................................................................................... 100

3” .................................................................................................... 70-100

No. 4 Sieve ..................................................................................... 50-100

No. 200 Sieve ................................................................................ 50 max

Liquid Limit ....................................................................... 40 (max)

Plasticity Index .................................................................. 20 (max)

Maximum expansive potential (%)* ............................................ 1.0

*Measured on a sample compacted to approximately 95 percent of the ASTM D698

maximum dry density at about 3 percent below optimum water content. The sample

is confined under a 100 psf surcharge and submerged/inundated.

Engineered fill should be placed and compacted in horizontal lifts, using equipment and

procedures that will produce recommended moisture contents and densities throughout the

lift. Fill lifts should not exceed ten inches loose thickness.

4.2.5 Compaction Requirements

Recommended compaction and moisture content criteria for engineered fill materials are as

follows:

Material Type and Location

Per the Modified Proctor Test (ASTM D 1557)

Minimum

Compaction

Requirement (%)

Range of Moisture Contents

for Compaction

Minimum Maximum

Approved on-site or imported fill soils:

Beneath foundations: 95 -2% +2%





Material Type and Location

Per the Modified Proctor Test (ASTM D 1557)

Minimum

Compaction

Requirement (%)

Range of Moisture Contents

for Compaction

Minimum Maximum

Beneath slabs: 95 -2% +2%

Beneath pavements: 95 -2% +2%

Miscellaneous backfill 90 -3% +3%

4.2.6 Grading and Drainage

Positive drainage should be provided during construction and maintained throughout the life

of the project. Infiltration of water into utility trenches or foundation excavations should be

prevented during construction. Planters and other surface features which could retain water

in areas adjacent to the buildings should be sealed or eliminated. In areas where sidewalks

or paving do not immediately adjoin the structures, we recommend that protective slopes be

provided with a minimum grade of approximately five percent for at least 5 feet from

perimeter walls. Backfill against footings, exterior walls, and in utility and sprinkler line

trenches should be well compacted and free of all construction debris to reduce the

possibility of moisture infiltration. Water should not be allowed to pond within 20 feet of the

perimeter of the foundations.

Downspouts, roof drains or scuppers should discharge into splash blocks or extensions

when the ground surface beneath such features is not protected by exterior slabs or paving.

Sprinkler systems should not be installed within five feet of foundation walls. Landscaped

irrigation adjacent to the foundation systems should be minimized or eliminated.

4.2.7 Slopes

For permanent unprotected slopes in compacted fill areas the recommended maximum

configurations for on-site materials are as follows:

Maximum Slope

Material Horizontal:Vertical

Native Sands and Gravel Soils ..................................................................................... 3:1

The face of all slopes should be compacted to the minimum specification for fill

embankments. Alternately, fill slopes can be over-built and trimmed to compacted material.

If any slope in cut or fill will exceed 10 to 15 feet in height, the grading design should include

mid-height benches to intercept surface drainage and divert flow from the face of the

embankment.





4.2.8 Corrosion Potential

Results of soluble sulfate, chloride content, pH, and resistivity testing from the general site

area indicate that the soils should have a low corrosion potential to reinforcing steel and

buried metal structures. However, if metal structures are to be used, the corrosion potential

should be analyzed by the manufacturer and appropriate protection provided. Soluble

sulfate testing in the general area indicates that ASTM Type I/II Portland cement is suitable

for all concrete on and below grade. Foundation concrete should be designed in

accordance with the provisions of the ACI Design Manual, Section 318, Chapter 4.

4.3 Foundation Recommendations

The structures can be supported by standard spread and continuous foundations bearing on

engineered fill (west side) or compacted native soils and bedrock (east side). Design

recommendations for foundations for the proposed structures and related structural

elements are presented in the following paragraphs.

4.3.1 Design Recommendations

DESCRIPTION VALUE

Foundation Type Standard Spread and Continuous

Foundations

Structures Apartments

Bearing Material

West Side: Complete removal and

replacement of fill soils (6 to 12 feet in

thickness).

East Side: Minimum of 10 inches of scarified,

moisture conditioned, and compacted native

soils or engineered fill or bedrock.

Allowable Bearing Pressure 2,500 psf for spread and continuous

foundations

Minimum Embedment Depth Below Finished

Grade 24 inches

Total Estimated Settlement 1 inch

Estimated Differential Settlement ½ inch

Finished grade is defined as the lowest adjacent grade within five feet of the foundation.

The allowable foundation bearing pressures apply to dead loads plus design live load

conditions. The design bearing pressure may be increased by one-third when considering

total loads that include wind or seismic conditions. The weight of the foundation concrete

below grade may be neglected in dead load computations.





Foundations should be proportioned to reduce differential foundation movement.

Proportioning on the basis of equal total settlement is recommended. Additional foundation

movements could occur if water from any source infiltrates the foundation soils; therefore,

proper drainage should be provided in the final design and during construction.

Foundations should be reinforced as necessary to reduce the potential for distress caused

by differential foundation movement.

Foundation excavations and engineered fill placement should be observed by the

geotechnical engineer. If the soil conditions encountered differ significantly from those

presented in this report, supplemental recommendations will be required.

4.3.2 Lateral Earth Pressures

For soils above any free water surface, recommended equivalent fluid pressures for

unrestrained foundation elements when using on-site silty, clayey sand as backfill are:

Active ..................................................................................... 35 psf/ft

Passive ................................................................................ 375 psf/ft

Coefficient of base friction ........................................................... 0.40*

*The coefficient of base friction should be reduced to 0.35 when used in

conjunction with passive pressure.

Where the design includes restrained elements, the following equivalent fluid pressures are

recommended:

At rest .................................................................................... 55 psf/ft

The lateral earth pressures herein do not include any factor of safety and are not applicable

for submerged soils/hydrostatic loading. Additional recommendations may be necessary if

such conditions are to be included in the design.

Fill against foundations should be compacted to densities specified in the Earthwork section

of this report. Compaction of each lift adjacent to walls should be accomplished with

hand-operated tampers or other lightweight compactors. Overcompaction may cause

excessive lateral earth pressures which could result in wall movement.

4.4 Seismic Considerations

We have provided seismic design parameters according to the 2006 International Building





Code (IBC) for design and construction of the proposed structure. Selected site ground

motion parameters for the project have been determined in general accordance with the

IBC. The values provided are based on the subsurface exploration presented herein and

the USGS software for use in interpolating values.

CONTERMINOUS 48 STATES-2003 NEHRP SEISMIC DESIGN PROVISIONS

LATITUDE: 32.802 LONGITUDE: -108.263

Spectral Response Accelerations SMs and SM1 SMs = FaSs and SM1 = FvS1

Site Class C - Fa = 1.2, Fv = 1.7

Period (sec) Sa (g)

0.2 0.326 (SMs, Site Class C)

1.0 0.138 (SM1, Site Class C)

SDs = 2/3 x SMs and SD1 = 2/3 x SM1

Site Class C - Fa = 1.2 ,Fv = 1.7

Period (sec) Sa (g)

0.2 0.218 (SDs, Site Class C)

1.0 0.092 (SD1, Site Class C)

4.5 Floor Slabs

4.5.1 Design Recommendations

DESCRIPTION VALUE

Interior floor system Slab-on-grade concrete.

Floor slab support

West Side: Engineered fill soils placed and compacted in

accordance with Earthwork section of this report following

complete removal of on-site fill soils.

East Side: Compacted native soils or bedrock.

Modulus of subgrade reaction 150 pounds per square inch per inch (psi/in)

Construction of floor slabs compacted fills composed of approved soils, native soils or

bedrock is considered acceptable for the project.

In areas of exposed concrete, control joints should be saw cut into the slab after concrete

placement in accordance with ACI Design Manual, Section 302.1R-37 8.3.12 (tooled control

joints are not recommended). Additionally, dowels should be placed at the location of





proposed construction joints. To control the width of cracking (should it occur) continuous

slab reinforcement should be considered in exposed concrete slabs.

Positive separations and/or isolation joints should be provided between slabs and all

foundations, columns or utility lines to allow independent movement. Interior trench backfill

placed beneath slabs should be compacted in accordance with recommendations outlined in

the Earthwork section of this report. Other design and construction considerations, as

outlined in the ACI Design Manual, Section 302.1R are recommended.

4.5.2 Construction Considerations

Engineered fill (following complete replacement of the on-site fill soils on the west side of the

site), compacted native soils or bedrock (east side) is recommended below slabs-on-grade.

The engineered fill (if applicable) should extend horizontally a minimum distance of 5 feet

beyond the outside edge of perimeter footings. Some differential movement of a slab-on-

grade floor system is possible should the subgrade soils become elevated in moisture

content. Such movements are anticipated to be within general tolerance for normal slab-on-

grade construction. To reduce potential slab movements, the subgrade soils should be

prepared as outlined in the Earthwork section of this report.

4.6 Pavements

Due to the existing fill on-site, there is a potential for increased maintenance. If the owner is

not willing to assume the risk of movement due to the presence of existing fill, these

materials should be completely removed and replaced as engineered fill. If some movement

can be tolerated, the pavement can be supported on prepared subgrade. If movement

needs to be reduced, consideration should be given to partial removal and replacement of

the existing fill. We are available to discuss potential options.

The new pavement sections are based on a laboratory correlated R-value for the silty,

clayey sand soil conditions generally consistent with those encountered in the soil borings.

Design of pavements for the project have been based on the procedures outlined in the

Design of Hot Mix Asphalt Pavements by the National Asphalt Pavement Association

(NAPA) and ACI for PCC pavement. Assumed traffic criteria used for pavement thickness

design includes single 18-kip equivalent standard axle loads (ESAL's) of 36,000 for planned

auto parking areas and 70,000 for heavy vehicle access and drives. Actual design traffic

loading should be verified. Reevaluation of the recommended pavement sections may be

necessary if the actual traffic varies from the assumed criteria outlined above.

Recommended alternatives for flexible and rigid pavements, summarized for each traffic

area, are as follows:





Traffic Area Alternative

Recommended Pavement Section Thickness (inches)

Asphalt

Concrete

Surface

Portland

Cement

Concrete

Aggregate

Base

Course

Total

Automobile

Parking Areas

A 3 --- 4 7

B --- 5 --- 5

Heavy Vehicle

Access and

Drives

A 3-1/2 --- 6 9-1/2

B --- 6 --- 6

Each alternative should be investigated with respect to current material availability and

economic conditions. Rigid concrete pavement, a minimum of 6 inches in thickness, is

recommended at the location of dumpsters where trash trucks will park and load or areas of

anticipated heavy vehicle loads.

Concrete construction and placement for the parking and drive areas (i.e. curb and gutter,

drainage ditches, etc.) should be in accordance with the New Mexico Department of

Transportation guidelines.

Aggregate base course should be placed in lifts not exceeding six inches and should be

compacted to a minimum of 95% Modified Proctor Density (ASTM D1557).

Asphaltic concrete mix designs should be submitted prior to construction to verify their

adequacy. Asphalt material should be placed in maximum 3-inch lifts and should be

compacted to a minimum of 93% Maximum Theoretical Density (AASHTO T-209).

Future performance of pavements constructed at this site will be dependent upon several

factors, including maintaining stable moisture content of the subgrade soils, conditioning of

the existing fill and providing for a planned program of preventative maintenance.

Recommendations for pavement construction presented depend upon compliance with

recommended material specifications. To assess compliance, observation and testing

should be performed under the direction of the geotechnical engineer.

Pavement design methods are intended to provide structural sections with adequate

thickness over a particular subgrade such that wheel loads are reduced to a level the

subgrade can support. The support characteristics of the subgrade for pavement design do

not account for settlement induced movements of subgrade such as the soils encountered

on this project. Thus, the pavement may be adequate from a structural standpoint, yet still

experience cracking and deformation due to settlement related movement of the subgrade.





It is, therefore, important to minimize moisture changes in the subgrade to reduce

settlement.

Future performance of pavements constructed on the fill and native soils at this site will be

dependent upon several factors, including:

nature of the existing fill materials

depth/thickness of existing fill materials

maintaining stable moisture content of the subgrade soils.

providing for a planned program of preventative maintenance.

Pavements could crack in the future primarily because of settlement or expansion of the

soils when subjected to an increase in moisture content to the subgrade. The cracking,

while not desirable, does not necessarily constitute structural failure of the pavement.

The performance of all pavements can be enhanced by minimizing excess moisture which

can reach the subgrade soils. The following recommendations should be considered at

minimum:

site grading at a minimum 2 percent grade away from the pavements.

the subgrade and the pavement surface have a minimum 1/4 inch per foot slope to

promote proper surface drainage.

consider appropriate edge drainage and pavement underdrain systems.

install pavement drainage surrounding areas anticipated for frequent wetting (e.g.,

garden centers, wash racks).

install joint sealant and seal cracks immediately.

compaction of any utility trenches for landscaped areas to the same criteria as the

pavement subgrade.

seal all landscaped areas in or adjacent to pavements to minimize or prevent

moisture migration to subgrade soils.

place compacted, low permeability backfill against the exterior side of curb and

gutter.

place curb, gutter and/or sidewalk directly on subgrade soils without the use of base

course materials.

5.0 GENERAL COMMENTS

Terracon should be retained to review the final design plans and specifications so

comments can be made regarding interpretation and implementation of our geotechnical





recommendations in the design and specifications. Terracon also should be retained to

provide observation and testing services during grading, excavation, foundation construction

and other earth-related construction phases of the project.

The analysis and recommendations presented in this report are based upon the data

obtained from the borings performed at the indicated locations and from other information

discussed in this report. This report does not reflect variations that may occur between

borings, across the site, or due to the modifying effects of construction or weather. The

nature and extent of such variations may not become evident until during or after

construction. If variations appear, we should be immediately notified so that further

evaluation and supplemental recommendations can be provided.

The scope of services for this project does not include either specifically or by implication

any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or

identification or prevention of pollutants, hazardous materials or conditions. If the owner is

concerned about the potential for such contamination or pollution, other studies should be

undertaken.

This report has been prepared for the exclusive use of our client for specific application to

the project discussed and has been prepared in accordance with generally accepted

geotechnical engineering practices. No warranties, either express or implied, are intended

or made. Site safety, excavation support, and dewatering requirements are the

responsibility of others. In the event that changes in the nature, design, or location of the

project as outlined in this report are planned, the conclusions and recommendations

contained in this report shall not be considered valid unless Terracon reviews the changes

and either verifies or modifies the conclusions of this report in writing.

APPENDIX A

FIELD EXPLORATION

MONTANA VISTA APARTMENTS SEC OF VALLEY VISTA DR AND 40

TH STREET

SILVER CITY, NEW MEXICO

SITE LOCATION MAP

Project Mngr: DC

Drawn By:

Checked By:

Approved By:

JM

DC

DC

Project No. 68115036

Scale

File No.

Date:

Not to scale

Site Vicinity

6/21/11

1640 Hickory Loop, Suite 105

Las Cruces, New Mexico 88005

575.527.1700 Fax: 575.527.1092

FIG No.

A-1

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES.

Source: USGS 7.5-Minute Topographic Map “Silver City, New Mexico, United States 1996”

N

PROJECT

LOCATION

EAST 40TH

ST.

VALLEY VISTA DR.

MONTANA VISTA APARTMENTS SEC OF VALLEY VISTA DR AND 40

TH STREET

SILVER CITY, NEW MEXICO

BORING LOCATION PLAN

Project Mngr: JDC

Drawn By:

Checked By:

Approved By:

JM

DC

DC

Project No. 68115036

Scale

File No.

Date:

Not to Scale

Boring Location

6/7/11


Las Cruces, New Mexico 88005

575.527.1700 Fax: 575.527.1092

FIG No.

A-2

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES.

Approximate Boring Location

B-1

Source: Integrated Design Architecture

B-3

N

B-2

B-3

B-4

Approximate extent limit of fill material




Reliable ■ Responsive ■ Convenient ■ Innovative Exhibit A-3

Field Exploration Description

A total of four test borings were drilled at the site on June 3, 2011. The borings were drilled

to depths ranging from about 5 to 22 feet below the ground surface at the approximate

locations shown on the attached Site Location Map and Boring Location Plan, Exhibit A-1

and A-2, respectively. Auger refusal was encountered at depths of about 22, 13 and 6 feet

bgs in Borings B-1, B-2 and B-3, respectively. The test borings were located as follows:

Borings Location Depth (feet)

B-1, B-2 and B-3 Building Footprints 6, 13, and 22

B-4 Parking and Drive Areas 5

The test borings were advanced with a truck-mounted CME-75 drill rig utilizing 8-inch

diameter hollow-stem augers.

The borings were located in the field using aerial photos, on-site corner stakes and using the

proposed site plan. The accuracy of boring locations should only be assumed to the level

implied by the method used.

Lithologic logs of each boring were recorded by the field geologist during the drilling

operations. At selected intervals, samples of the subsurface materials were taken by driving

split-spoon or ring-barrel samplers. Bulk samples of subsurface materials were also

obtained.

Penetration resistance measurements were obtained by driving the split-spoon and ring-

barrel samplers into the subsurface materials with a 140-pound automatic hammer falling 30

inches. The penetration resistance value is a useful index in estimating the consistency or

relative density of materials encountered.

A CME automatic SPT hammer was used to advance the split-barrel sampler in the borings

performed on this site. The effect of the automatic hammer's efficiency has been

considered in the interpretation and analysis of the subsurface information for this report.

Groundwater conditions were evaluated in the borings at the time of site exploration.

GENERAL NOTES

DRILLING & SAMPLING SYMBOLS:

SS: Split Spoon - 1-3/8" I.D., 2" O.D., unless otherwise noted HS: Hollow Stem Auger

ST: Thin-Walled Tube - 2" O.D., 3” O.D. unless otherwise noted PA: Power Auger

RS: Ring Sampler - 2.42" I.D., 3" O.D., unless otherwise noted HA: Hand Auger

DB: Diamond Bit Coring - 4", N, B RB: Rock Bit

BS: Bulk Sample or Auger Sample WB: Wash Boring or Mud Rotary

The number of blows required to advance a standard 2-inch O.D. split-spoon sampler (SS) the last 12 inches of the total 18-inch penetration with a 140-pound hammer falling 30 inches is considered the “Standard Penetration” or “N-value”. For 3” O.D. ring samplers (RS) the penetration value is reported as the number of blows required to advance the sampler 12 inches using a 140-pound hammer falling 30 inches, reported as “blows per foot,” and is not considered equivalent to the “Standard Penetration” or “N-value”.

WATER LEVEL MEASUREMENT SYMBOLS:

WL: Water Level WS: While Sampling N/E: Not Encountered

WCI: Wet Cave in WD: While Drilling

DCI: Dry Cave in BCR: Before Casing Removal

AB: After Boring ACR: After Casing Removal

Water levels indicated on the boring logs are the levels measured in the borings at the times indicated. Groundwater levels at other times and other locations across the site could vary. In pervious soils, the indicated levels may reflect the location of groundwater. In low permeability soils, the accurate determination of groundwater levels may not be possible with only short-term observations.

DESCRIPTIVE SOIL CLASSIFICATION: Soil classification is based on the Unified Soil Classification System. Coarse Grained Soils

have more than 50% of their dry weight retained on a #200 sieve; their principal descriptors are: boulders, cobbles, gravel or sand. Fine Grained Soils have less than 50% of their dry weight retained on a #200 sieve; they are principally described as clays if they are plastic, and silts if they are slightly plastic or non-plastic. Major constituents may be added as modifiers and minor constituents may be added according to the relative proportions based on grain size. In addition to gradation, coarse-grained soils are defined on the basis of their in-place relative density and fine-grained soils on the basis of their consistency.

CONSISTENCY OF FINE-GRAINED SOILS RELATIVE DENSITY OF COARSE-GRAINED SOILS

Unconfined

Compressive Strength, Qu, psf

Standard Penetration or N-value (SS)

Blows/Ft.

Consistency

Standard Penetration or N-value (SS)

Blows/Ft.

Ring Sampler (RS) Blows/Ft.

Relative Density

< 500 0 - 1 Very Soft 0 – 3 0-6 Very Loose 500 – 1,000 2 - 4 Soft 4 – 9 7-18 Loose 1,000 – 2,000 2,000 4 - 8 Medium Stiff 10 – 29 19-58 Medium Dense 2,000 – 4,000 4,000 8 -15 Stiff 30 – 50 59-98 Dense 4,000 – 8,000 15 - 30 Very Stiff ≥ 50 ≥ 99 Very Dense

8,000+ ≥ 30 Hard

RELATIVE PROPORTIONS OF SAND AND GRAVEL GRAIN SIZE TERMINOLOGY

Descriptive Term(s) of other constituents

Percent of Dry Weight

Major Component of Sample

Particle Size

Trace < 15 Boulders Over 12 in. (300mm) With 15 – 29 Cobbles 12 in. to 3 in. (300mm to 75 mm)

Modifier > 30 Gravel 3 in. to #4 sieve (75mm to 4.75 mm)

RELATIVE PROPORTIONS OF FINES Sand

Silt or Clay #4 to #200 sieve (4.75mm to 0.075mm)

Passing #200 Sieve (0.075mm)

Descriptive Term(s) of other constituents

Percent of Dry Weight

PLASTICITY DESCRIPTION

Term Plasticity Index

Trace With

Modifier

< 5 5 – 12 > 12

Non-plastic

Low Medium

High

0 1-10 11-30 > 30

Rev 04/10

Form 111—6/98

UNIFIED SOIL CLASSIFICATION SYSTEM

Criteria for Assigning Group Symbols and Group Names Using Laboratory TestsA Soil Classification

Group Symbol

Group NameB

Coarse Grained Soils

More than 50% retained

on No. 200 sieve

Gravels More than 50% of coarse fraction retained on No. 4 sieve

Clean Gravels Less than 5% finesC

Cu 4 and 1 Cc 3E GW Well-graded gravelF

Cu 4 and/or 1 Cc 3E GP Poorly graded gravelF

Gravels with Fines More than 12% finesC

Fines classify as ML or MH GM Silty gravelF,G, H

Fines classify as CL or CH GC Clayey gravelF,G,H

Sands 50% or more of coarse fraction passes No. 4 sieve

Clean Sands Less than 5% finesD

Cu 6 and 1 Cc 3E SW Well-graded sandI

Cu 6 and/or 1 Cc 3E SP Poorly graded sandI

Sands with Fines More than 12% finesD

Fines classify as ML or MH SM Silty sandG,H,I

Fines Classify as CL or CH SC Clayey sandG,H,I

Fine-Grained Soils 50% or more passes the No. 200 sieve

Silts and Clays Liquid limit less than 50

inorganic PI 7 and plots on or above “A” lineJ CL Lean clayK,L,M

PI 4 or plots below “A” lineJ ML SiltK,L,M

organic Liquid limit - oven dried 0.75 OL

Organic clayK,L,M,N

Liquid limit - not dried Organic siltK,L,M,O

Silts and Clays Liquid limit 50 or more

inorganic PI plots on or above “A” line CH Fat clayK,L,M

PI plots below “A” line MH Elastic SiltK,L,M

organic Liquid limit - oven dried 0.75 OH

Organic clayK,L,M,P

Liquid limit - not dried Organic siltK,L,M,Q

Highly organic soils Primarily organic matter, dark in color, and organic odor PT Peat

A Based on the material passing the 3-in. (75-mm) sieve

B If field sample contained cobbles or boulders, or both, add “with cobbles or boulders, or both” to group name.

C Gravels with 5 to 12% fines require dual symbols: GW-GM well-graded gravel with silt, GW-GC well-graded gravel with clay, GP-GM poorly graded gravel with silt, GP-GC poorly graded gravel with clay.

D Sands with 5 to 12% fines require dual symbols: SW-SM well-graded sand with silt, SW-SC well-graded sand with clay, SP-SM poorly graded sand with silt, SP-SC poorly graded sand with clay

E Cu = D60/D10 Cc =

6010

2

30

DxD

)(D

F If soil contains 15% sand, add “with sand” to group name.

G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM.

HIf fines are organic, add “with organic fines” to group name.

I If soil contains 15% gravel, add “with gravel” to group name.

J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay.

K If soil contains 15 to 29% plus No. 200, add “with sand” or “with gravel,” whichever is predominant.

L If soil contains 30% plus No. 200 predominantly sand, add “sandy” to group name.

M If soil contains 30% plus No. 200, predominantly gravel,

add “gravelly” to group name. N PI 4 and plots on or above “A” line.

O PI 4 or plots below “A” line.

P PI plots on or above “A” line.

Q PI plots below “A” line.

APPENDIX B

LABORATORY TESTING





Exhibit B-1

Laboratory Testing

Samples retrieved during the field exploration were taken to the laboratory for further

observation by the project geotechnical engineer and were classified in accordance with the

Unified Soil Classification System (USCS) described in Appendix A. At that time, the field

descriptions were confirmed or modified as necessary and an applicable laboratory testing

program was formulated to determine engineering properties of the subsurface materials.

Laboratory tests were conducted on selected soil samples and the test results are presented

in this appendix. The laboratory test results were used for the geotechnical engineering

analyses, and the development of foundation and earthwork recommendations. Laboratory

tests were performed in general accordance with the applicable ASTM, local or other

accepted standards.

Selected soil samples obtained from the site were tested for the following engineering

properties:

Consolidation In-situ Water Content

Sieve Analysis In-situ Dry Density

Atterberg Limits

.

Sieve Size 1 1/2" 3/4" 3/8" #4 #10 #40 #100 #200

% Passing (Cumulative) 100% 93% 90% 78% 54% 35% 26% 19.9%

Specification

% GRAVEL = 22% D85 = 7.1 D15 =

% SAND = 58% D60 = 2.5 D10 =

% SILT & CLAY = 20% D50 = 1.5 CU =

D30 = 0.2 CC =

Sample Date: 6/3/2011

Project No.: 68115036

Project Name: Montana Vista Apartments-Silver City

Report Date: 6/21/2011

Sample Location: B1 at 2.5'

Liquid Limit: 25 5

USCS Classification: SC-SM

Material Description: Silty, Clayey Sand with Gravel

Reviewed By:

Dan Cosper, P.E.

TEST SUMMARY

(575) 527-1700

TERRACON


Las Cruces, NM 88005

Plasticity Index:

GRAIN SIZE - mm

GRAIN SIZE DISTRIBUTION GRAPH

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.0010.010.11101001000

PE

RC

EN

T F

INE

R

6 in

.

1.5

in

.

#4

#200

.

Sieve Size 1 1/2" 3/4" 3/8" #4 #10 #40 #100 #200


Specification

% GRAVEL = 2% D85 = 1.2 D15 =

% SAND = 45% D60 = 0.1 D10 =

% SILT & CLAY = 53% D50 = CU =

D30 = CC =





Sample Location: B1 at 15'

Liquid Limit: 32 14

USCS Classification: CL

Material Description: Sandy Lean Clay

Reviewed By:

Dan Cosper, P.E.

TEST SUMMARY

(575) 527-1700

TERRACON



Plasticity Index:

GRAIN SIZE - mm


0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.0010.010.11101001000

PE

RC

EN

T F

INE

R

6 in

.

1.5

in

.

#4

#200

.

Sieve Size 1 1/2" 3/4" 3/8" #4 #10 #40 #100 #200


Specification

% GRAVEL = 3% D85 = 1.2 D15 =

% SAND = 28% D60 = D10 =

% SILT & CLAY = 69% D50 = CU =

D30 = CC =





Sample Location: B2 at 10'

Liquid Limit: 32 13

USCS Classification: CL

Material Description: Sandy Lean Clay With Gravel

Reviewed By:

Dan Cosper, P.E.

TEST SUMMARY

(575) 527-1700

TERRACON



Plasticity Index:

GRAIN SIZE - mm


0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.0010.010.11101001000

PE

RC

EN

T F

INE

R

6 in

.

1.5

in

.

#4

#200

.

Sieve Size 1 1/2" 3/4" 3/8" #4 #10 #40 #100 #200


Specification

% GRAVEL = 30% D85 = 15.9 D15 =

% SAND = 46% D60 = 1.6 D10 =

% SILT & CLAY = 24% D50 = 0.4 CU =

D30 = 0.1 CC =





Sample Location: B4 at 0-5'

Liquid Limit: 24 6

USCS Classification: SC-SM

Material Description: Silty, Clayey Sand with Gravel

Reviewed By:

Dan Cosper, P.E.

TEST SUMMARY

(575) 527-1700

TERRACON



Plasticity Index:

GRAIN SIZE - mm


0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.0010.010.11101001000

PE

RC

EN

T F

INE

R

6 in

.

1.5

in

.

#4

#200

MONTANA VISTA APARTMENTS

SILVER CITY, NEW MEXICOTERRACON


LAS CRUCES, NEW MEXICO 88005

(575) 527-1700

fax (575) 527-1092

ELL

SWELL/CONSOLIDATION CHART

-2

-1

0

DA

TIO

N /

SW

E

water added

6

-5

-4

-3

EN

T C

ON

SO

LID

-7

-6

10 100 1000 10000

PE

RC

E

STRESS POUNDS PER SQUARE FOOT

BORING B-2 @ 2.5'

CLAYEY SAND

USCS Classification:

SC

DRY DENSITY= 103 lbs/ft3

MOISTURE CONTENT= 7.1%

[email protected]'.xls PROJECT NO. 68115036

Documents

Geotechnical Engineering Report - Pavilion Construction Vista Housin… · Geotechnical Engineering Report Montana Vista Apartments Silver City, New Mexico June 21, 2011 Terracon