Geotechnical Engineering Report

Transcription

1 Montana Vista Apartments SEC of Valley Vista Drive and 40 th Street Silver City, New Mexico June 21, 2011 Terracon Project No Prepared for: Western Regional Housing Authority Silver City, New Mexico Prepared by: Terracon Consultants, Inc. Las Cruces, New Mexico

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3 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 40 th 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. i

4 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 ii

5 TABLE OF CONTENTS Page EXECUTIVE SUMMARY... i 1.0 INTRODUCTION PROJECT INFORMATION Project Description Site Location and Description SUBSURFACE CONDITIONS Typical Subsurface Profile Groundwater RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION Geotechnical Considerations Earthwork Site Preparation Excavation Subgrade Preparation Fill Materials and Placement Compaction Requirements Grading and Drainage Slopes Corrosion Potential Foundation Recommendations Design Recommendations Lateral Earth Pressures Seismic Considerations Floor Slabs Design Recommendations Construction Considerations Pavements 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

6 GEOTECHNICAL ENGINEERING REPORT MONTANA VISTA APARTMENTS SEC OF VALLEY VISTA DRIVE AND 40 TH STREET SILVER CITY, NEW MEXICO Terracon Project No June 21, 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 40 th 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 1

7 Site layout Structures ITEM Building construction Finished floor elevation Maximum loads Maximum allowable movement Maximum allowable differential movement Grading in building area Retaining walls Cut and fill slopes DESCRIPTION Refer to the Site Location Map and Boring Location Plan (Exhibits A-1 and A-2) 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. The buildings will consist of wood frame bearing on exterior and interior spot footings. The floor system is anticipated to be slab-ongrade isolated from standard spread and continuous foundations. 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). Columns: 50 kips maximum (assumed) Walls: 2.0 klf maximum (assumed) Slabs: 150 psf max (assumed) 1 inch ½ inch over 40 feet for walls, ¾ inch over 40 feet for interior columns (assumed) Cuts and fills of about 5 feet may be required for grading purposes 5 feet are anticipated 5 feet are anticipated 2.2 Site Location and Description ITEM Location Existing site features Surrounding developments Current ground cover Existing topography DESCRIPTION Southeast corner of Valley Vista Drive and 40 th Street in Silver City, New Mexico Vacant lot. The west side of the property contains fill soils with an approximate maximum depth of about 12 feet. North: 40 th Street East: Undeveloped West: Valley Vista Drive South: Undeveloped Exposed subgrade soils, boulders and/or bedrock outcrops. Sparsely vegetated with native grasses and small trees and bushes. Estimated vertical relief on the order of about 15 to 20 feet across the site from west to east. 2

8 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) Stratum 1 5 to 12 Material Encountered Fill Soils consisting of Silty, Clayey Sand with varying amounts Gravel Consistency/Density 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. 3

9 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 4

10 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 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 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 5

11 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 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 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. 6

12 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" No. 4 Sieve No. 200 Sieve max Liquid Limit (max) Plasticity Index (max) Maximum expansive potential (%)* *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 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% 7

13 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% 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 Slopes For permanent unprotected slopes in compacted fill areas the recommended maximum configurations for on-site materials are as follows: Material Maximum Slope 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. 8

14 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 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 Design Recommendations Foundation Type Structures Bearing Material DESCRIPTION Allowable Bearing Pressure Minimum Embedment Depth Below Finished Grade Total Estimated Settlement Estimated Differential Settlement VALUE Standard Spread and Continuous Foundations Apartments 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. 2,500 psf for spread and continuous foundations 24 inches 1 inch 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. 9

15 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 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 psf/ft Passive psf/ft Coefficient of base friction * *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 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 10

16 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: LONGITUDE: Spectral Response Accelerations SMs and SM1 SMs = FaSs and SM1 = FvS1 Period (sec) Site Class C - Fa = 1.2, Fv = 1.7 Sa (g) (SMs, Site Class C) (SM1, Site Class C) Period (sec) SDs = 2/3 x SMs and SD1 = 2/3 x SM1 Site Class C - Fa = 1.2,Fv = 1.7 Sa (g) (SDs, Site Class C) (SD1, Site Class C) 4.5 Floor Slabs Design Recommendations DESCRIPTION Interior floor system Floor slab support Slab-on-grade concrete. VALUE West Side: Engineered fill soils placed and compacted in accordance with Earthwork section of this report following complete removal of on-site fill soils. Modulus of subgrade reaction East Side: Compacted native soils or bedrock. 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 (tooled control joints are not recommended). Additionally, dowels should be placed at the location of 11

17 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 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-ongrade 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-ongrade 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: 12

18 Traffic Area Automobile Parking Areas Heavy Vehicle Access and Drives Alternative Recommended Pavement Section Thickness (inches) Asphalt Concrete Surface Portland Cement Concrete Aggregate Base Course Total A B A 3-1/ /2 B 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. 13

19 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 14

20 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. 15

21 APPENDIX A FIELD EXPLORATION

22 EAST 40 TH ST. VALLEY VISTA DR. PROJECT LOCATION Source: USGS 7.5-Minute Topographic Map Silver City, New Mexico, United States 1996 N DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES. Project Mngr: DC Drawn By: JM Checked By: DC Approved By: DC Project No Scale Not to scale File No. Site Vicinity Date: 6/21/ Hickory Loop, Suite 105 Las Cruces, New Mexico Fax: SITE LOCATION MAP MONTANA VISTA APARTMENTS SEC OF VALLEY VISTA DR AND 40 TH STREET SILVER CITY, NEW MEXICO FIG No. A-1

23 B-4 B-1 B-2 B-3 B-3 Approximate Boring Location Approximate extent limit of fill material N Source: Integrated Design Architecture DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES. Project Mngr: Drawn By: Checked By: Approved By: JDC JM DC DC Project No Scale Not to Scale File No. Boring Location Date: 6/7/ Hickory Loop, Suite 105 Las Cruces, New Mexico Fax: BORING LOCATION PLAN MONTANA VISTA APARTMENTS SEC OF VALLEY VISTA DR AND 40 TH STREET SILVER CITY, NEW MEXICO FIG No. A-2

24 Field Exploration Description A total of four test borings were drilled at the site on June 3, 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 ringbarrel 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. Exhibit A-3

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29 GENERAL NOTES DRILLING & SAMPLING SYMBOLS: SS: Split Spoon /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 " 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 < Very Soft Very Loose 500 1, Soft Loose 1,000 2, Medium Stiff Medium Dense 2,000 4, Stiff Dense 4,000 8, Very Stiff Very Dense 8, Hard RELATIVE PROPORTIONS OF SAND AND GRAVEL Descriptive Term(s) of other constituents Percent of Dry Weight Major Component of Sample GRAIN SIZE TERMINOLOGY Particle Size Trace < 15 Boulders Over 12 in. (300mm) With 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 Descriptive Term(s) of other constituents Percent of Dry Weight Sand Silt or Clay #4 to #200 sieve (4.75mm to 0.075mm) Passing #200 Sieve (0.075mm) PLASTICITY DESCRIPTION Term Plasticity Index Trace With Modifier < > 12 Non-plastic Low Medium High > 30 Rev 04/10

30 Coarse Grained Soils More than 50% retained on No. 200 sieve Fine-Grained Soils 50% or more passes the No. 200 sieve UNIFIED SOIL CLASSIFICATION SYSTEM Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests A Gravels More than 50% of coarse fraction retained on No. 4 sieve Sands 50% or more of coarse fraction passes No. 4 sieve Silts and Clays Liquid limit less than 50 Silts and Clays Liquid limit 50 or more Clean Gravels Less than 5% fines C Gravels with Fines More than 12% fines C Clean Sands Less than 5% fines D Sands with Fines More than 12% fines D Group Symbol Soil Classification Group Name B Cu 4 and 1 Cc 3 E GW Well-graded gravel F Cu 4 and/or 1 Cc 3 E GP Poorly graded gravel F Fines classify as ML or MH GM Silty gravel F,G, H Fines classify as CL or CH GC Clayey gravel F,G,H Cu 6 and 1 Cc 3 E SW Well-graded sand I Cu 6 and/or 1 Cc 3 E SP Poorly graded sand I Fines classify as ML or MH SM Silty sand G,H,I Fines Classify as CL or CH SC Clayey sand G,H,I inorganic PI 7 and plots on or above A line J CL Lean clay K,L,M organic PI 4 or plots below A line J ML Silt K,L,M Liquid limit - oven dried Liquid limit - not dried 0.75 OL Organic clay K,L,M,N Organic silt K,L,M,O inorganic PI plots on or above A line CH Fat clay K,L,M organic PI plots below A line MH Elastic Silt K,L,M Liquid limit - oven dried Liquid limit - not dried 0.75 OH Highly organic soils Primarily organic matter, dark in color, and organic odor PT Peat Organic clay K,L,M,P Organic silt K,L,M,Q 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 (D30) Cu = D 60/D 10 Cc = D10 x D 2 60 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. H If 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. Form 111 6/98

31 APPENDIX B LABORATORY TESTING

32 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 Exhibit B-1

33 GRAIN SIZE DISTRIBUTION. GRAPH 6 in. 1.5 in. #4 # % 90% 80% 70% PERCENT FINER 60% 50% 40% 30% 20% 10% 0% GRAIN SIZE - mm TEST SUMMARY 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% D 85 = 7.1 D 15 = % SAND = 58% D 60 = 2.5 D 10 = % SILT & CLAY = 20% D 50 = 1.5 C U = D 30 = 0.2 C C = Sample Date: 6/3/2011 Project No.: Project Name: Montana Vista Apartments-Silver City Report Date: 6/21/2011 Sample Location: B1 at 2.5' Liquid Limit: 25 Plasticity Index: 5 USCS Classification: SC-SM Material Description: Silty, Clayey Sand with Gravel Reviewed By: Dan Cosper, P.E. TERRACON 1640 Hickory Loop, Suite 105 Las Cruces, NM (575)

34 GRAIN SIZE DISTRIBUTION. GRAPH 6 in. 1.5 in. #4 # % 90% 80% 70% PERCENT FINER 60% 50% 40% 30% 20% 10% 0% GRAIN SIZE - mm TEST SUMMARY Sieve Size 1 1/2" 3/4" 3/8" #4 #10 #40 #100 #200 % Passing (Cumulative) 100% 100% 100% 98% 90% 75% 62% 52.7% Specification % GRAVEL = 2% D 85 = 1.2 D 15 = % SAND = 45% D 60 = 0.1 D 10 = % SILT & CLAY = 53% D 50 = C U = D 30 = C C = Sample Date: 6/3/2011 Project No.: Project Name: Montana Vista Apartments-Silver City Report Date: 6/21/2011 Sample Location: B1 at 15' Liquid Limit: 32 Plasticity Index: 14 USCS Classification: CL Material Description: Sandy Lean Clay Reviewed By: Dan Cosper, P.E. TERRACON 1640 Hickory Loop, Suite 105 Las Cruces, NM (575)

35 GRAIN SIZE DISTRIBUTION. GRAPH 6 in. 1.5 in. #4 # % 90% 80% 70% PERCENT FINER 60% 50% 40% 30% 20% 10% 0% GRAIN SIZE - mm TEST SUMMARY Sieve Size 1 1/2" 3/4" 3/8" #4 #10 #40 #100 #200 % Passing (Cumulative) 100% 100% 100% 97% 89% 79% 76% 69.1% Specification % GRAVEL = 3% D 85 = 1.2 D 15 = % SAND = 28% D 60 = D 10 = % SILT & CLAY = 69% D 50 = C U = D 30 = C C = Sample Date: 6/3/2011 Project No.: Project Name: Montana Vista Apartments-Silver City Report Date: 6/21/2011 Sample Location: B2 at 10' Liquid Limit: 32 Plasticity Index: 13 USCS Classification: CL Material Description: Sandy Lean Clay With Gravel Reviewed By: Dan Cosper, P.E. TERRACON 1640 Hickory Loop, Suite 105 Las Cruces, NM (575)

36 GRAIN SIZE DISTRIBUTION. GRAPH 6 in. 1.5 in. #4 # % 90% 80% 70% PERCENT FINER 60% 50% 40% 30% 20% 10% 0% GRAIN SIZE - mm TEST SUMMARY Sieve Size 1 1/2" 3/4" 3/8" #4 #10 #40 #100 #200 % Passing (Cumulative) 100% 87% 80% 70% 61% 52% 34% 24.4% Specification % GRAVEL = 30% D 85 = 15.9 D 15 = % SAND = 46% D 60 = 1.6 D 10 = % SILT & CLAY = 24% D 50 = 0.4 C U = D 30 = 0.1 C C = Sample Date: 6/3/2011 Project No.: Project Name: Montana Vista Apartments-Silver City Report Date: 6/21/2011 Sample Location: B4 at 0-5' Liquid Limit: 24 Plasticity Index: 6 USCS Classification: SC-SM Material Description: Silty, Clayey Sand with Gravel Reviewed By: Dan Cosper, P.E. TERRACON 1640 Hickory Loop, Suite 105 Las Cruces, NM (575)

37 MONTANA VISTA APARTMENTS SILVER CITY, NEW MEXICO TERRACON 1640 Hickory Loop, Suite 105 LAS CRUCES, NEW MEXICO (575) fax (575) PERCE ENT CONSOLID DATION / SWE ELL SWELL/CONSOLIDATION CHART water added STRESS POUNDS PER SQUARE FOOT BORING 2.5' CLAYEY SAND USCS Classification: SC DRY DENSITY= 103 lbs/ft3 MOISTURE CONTENT= 7.1% CONSOL-B-2@2.5'.xls PROJECT NO