Appendix_6_-_Geotech_Report_-_Beale_AFB_TLF.pdf

Geotechnical Engineering Report

PROPOSED TEMPORARY LODGING FACILITY

BEALE AIR FORCE BASE

YUBA COUNTY, CALIFORNIA

December 4, 2012 Terracon Project No. 80125009

Prepared for:

Lee & Sakahara Architects, Inc.

Las Vegas, Nevada

Prepared by:

Terracon Consultants, Inc.

Sacramento, California

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TABLE OF CONTENTS

Page

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

1.0 INTRODUCTION

2.0 SCOPE OF SERVICES

3.0 PROJECT INFORMATION

3.1 Project Description

3.2 Site Location and Description

4.0 SUBSURFACE CONDITIONS

4.1 Site Geology

4.2 Subsurface Soil Conditions

4.3 Groundwater

4.4 Liquefaction

4.5 Potential Fuel Oil Contamination

5.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION

5.1 Geotechnical Considerations

5.2 Earthwork

5.2.1 Site Preparation

5.2.2 Subgrade Preparation

5.2.3 Fill Materials and Placement

5.2.4 Compaction Recommendations

5.2.5 Grading and Drainage

5.2.6 Exterior Slab Design and Construction

5.2.7 Corrosion Potential

5.2.8 Earthwork Construction Considerations

5.3 Foundation Recommendations

5.3.1 Foundation Design Recommendations

5.3.2 Foundation Construction Considerations

5.4 CBC Seismic Design Criteria

5.5 Floor Slab

5.5.1 Floor Slab Design Recommendations

5.5.2 Floor Slab Construction Considerations

5.6 Lateral Earth Pressures

5.7 Pavements

5.7.1 Pavement Design Recommendations

5.7.2 Pavement Construction Considerations

5.8 Retention Basins

6.0 GENERAL COMMENTS

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TABLE OF CONTENTS (continued)

APPENDIX A – FIELD EXPLORATION

Exhibit A-1 Field Exploration Description Exhibit A-2 Vicinity and Boring Location Map Exhibit A-3 Project Site Layout Exhibits A-4 to A-11 Boring Logs

APPENDIX B – LABORATORY TESTING

Exhibit B-1 Laboratory Testing Description Exhibit B-2 Summary of Laboratory Results Exhibit B-3 Atterberg Limits Test Results Exhibit B-4 Unconfined Compression Test Results

APPENDIX C – SUPPORTING DOCUMENTS

Exhibit C-1 General Notes Exhibit C-2 Unified Soil Classification

APPENDIX D – ENVIRONMENTAL LABORATORY TESTING

Exhibit D-1 Total Petroleum Hydrocarbons Analytical Test Results

Temporary Lodging Facility Beale Air Force Base, Yuba County, California December 4, 2012 Terracon Project No.: 80125009

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EXECUTIVE SUMMARY

A geotechnical investigation has been completed for the proposed Temporary Lodging Facility located at Beale Air Force Base in Yuba County, California. Eight borings were completed for this evaluation. Seven borings were completed within the native areas which were covered with grasses and one boring (B-5) was completed in the center of the existing asphalt parking area.

The borings were extended to depths of about 11 to 21½ feet below the existing ground surface.

Based on the information obtained from our subsurface exploration, the site is suitable for design and construction of the proposed project. The geotechnical considerations identified included the following:

The near-surface soils encountered throughout the site generally consisted mostly of interbedded layers of silty clay with various amounts of sand and gravel, sandy lean clay, silt with sand, and sandy silt. Silty clayey sand was encountered in boring B-2. The surface materials in Boring B-5 consisted of approximately 3½ inches of asphalt concrete overlying 9½ inches of aggregate base.

The proposed structures may be supported by shallow spread footings bearing on a minimum of 10 inches of scarified, moisture conditioned, and compacted native soils.

The on-site surface and near surface materials are expected to exhibit “low” expansion potential when placed as engineered fill and subjected to light loading conditions such as those imposed by floor slabs. Floor slabs should be constructed over 6-inches of Class II Aggregate Base materials directly supported on at least 10 inches of scarified, moisture conditioned, and compacted native soils.

Asphalt pavement recommendations may be used for the project. Depending on anticipated traffic loading, pavement sections consisting of 3 to 4 inches of asphalt over 7 to 12 inches of Class II Aggregate Base may be used.

The 2010 California Building Code (CBC) Seismic Site Classification for this site is C.

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.

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 summary, 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.

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GEOTECHNICAL ENGINEERING REPORT

PROPOSED TEMPORARY LODGING FACILITY

BEALE AIR FORCE BASE

YUBA COUNTY, CALIFORNIA

Terracon Project No. 80125009

December 4, 2012

1.0 INTRODUCTION

A geotechnical engineering report has been completed for the proposed temporary lodging facility at Beale Air Force Base located in Yuba County, California. Per a proposed boring plan prepared by Lee and Sakahara Architects, eight borings and two percolation tests were completed.

The borings were completed to depths of approximately 11 to 21½ feet below the existing ground surface throughout the site. The deeper borings were terminated at depths shallower than the proposed deepest target depth (30 feet) due to difficult drilling conditions encountered in the field.

The two percolation tests were performed at depths of about 3 and 5 feet below site grade in the northwestern area of the site. It is our understanding that the percolations tests were located on the proposed boring plan near proposed retention basins. Logs of the borings along with a Vicinity and Boring Location Map and site aerial photo are included in Appendix A of this report.

The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

Subsurface soil conditions Earthwork Groundwater conditions Seismic considerations Foundation design and construction Retention basin design Pavement design and construction Concrete slab design and construction

The project description, site conditions and our geotechnical conclusions and design recommendations are presented in the text of this report. Supporting data including field exploration procedures, detailed exploration logs, results of laboratory testing are presented as appendices.

2.0 SCOPE OF SERVICES

The authorized scope of services completed by Terracon for this project included a visual site reconnaissance, subsurface exploration, laboratory testing, geotechnical engineering analyses, and preparation of this report. This report was prepared in general accordance with our

Responsive Resourceful Reliable 2 proposal (P80120040) dated September 5, 2012 however, the number of borings and locations were adjusted due to site restricitons (vernal pools) at the time of our site exploration.

Eight borings were completed for this evaluation. At the time of our field investigation we were unable to perform explorations in areas of vernal pools with 50-foot offsets as required by the Air Force Base biologist. The vernal pools were generally located in the central, northern, and western areas of the site. Accordingly explorations were not performed within all proposed building footprints but were performed throughout the site where accessible. This scope change was discussed with and approved by Lee and Sakahara Architects.

3.0 PROJECT INFORMATION

3.1 Project Description

ITEM DESCRIPTION1

Proposed site layout Refer to Appendix A, Exhibit A-3: Project Site Layout.

Existing improvements

The site is mostly a vacant area with an asphalt paved parking area located in the southeastern area and a concrete/asphalt path meandering throughout the site.

Based on historical aerial photos, a structure appears to have existed to the north of the asphalt parking area in the past and appears to have been demolished prior to 2003. Based on a preliminary map of the site, above and/or underground storage tanks previously existed on the site mainly near the asphalt parking area.

Proposed Construction

The proposed construction includes four one-story, slab on grade structures for use as Temporary Lodging Facilities.

The complex will have an estimated gross area of about 50,000 square feet and will consist of a total of 34 two-bedroom units. Buildings will be supported on shallow foundation systems.

Building Construction The proposed building construction is anticipated to be light weight wood and/or steel construction with concrete slab-on-grade floors.

Finish floor elevation Not available at this time but assumed to be within 3 to 5 feet of existing grade.

Maximum loads (assumed) Column Load – 20 to 40 kips Continuous wall loads – 1 klf Maximum uniform floor slab load – 150 psf max

Grading Based on site topography cuts and fills on the order of 1 to 6 feet are anticipated to provide level building pads.

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ITEM DESCRIPTION1

Cut and fill slopes

Based on preliminary grading plans, cut slopes as much as 6 feet are expected for the retention basin in the northwestern area of the site. Fill slopes as much as 2 feet are expected for the building pad areas.

Parking Area The parking areas will consist of asphalt concrete pavement.

Free-standing retaining walls A free standing retaining wall less than 5 feet high is proposed along the northeastern edge of the project site.

Below grade areas None

Retention basins

An on-site retention basin will be incorporated into the project to collect storm water runoff. We understand that the retention basin will be located in the northern and/or western area of the site.

3.2 Site Location and Description

ITEM DESCRIPTION

Location The site is located to the northwest corner of the intersection of Robert Nicoletti Way and C Street at Beale Air Force Base.

Surrounding developments

The surrounding area consists of vacant land to the north and west and various structures to the south and east of the site which are associated with the Air Force Base. Additionally, Robert Nicoletti Way borders the site to the south and C Street borders the site to the east. Based on our observations and a preliminary map of the site, a ditch is located to the north and south of the site, a stream is located to the west, and swales and vernal pools were located throughout the site mainly to the west of the existing asphalt parking area.

Current ground cover Native vegetation and grasses, and asphalt concrete.

Existing topography The topography in the area generally consists of gently rolling hills with about 5 to 6 feet of relief across the site.

4.0 SUBSURFACE CONDITIONS

A description of our field exploration is presented in Appendix A. Laboratory tests were conducted on selected soil samples obtained during our exploration. A description of the laboratory testing is presented in Appendix B.

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4.1 Site Geology

Beale Air Force Base lies near the interface of the Great Valley and Sierra Nevada geomorphic provinces. The Great Valley geomorphic province is an alluvial plain about 50 miles wide and 400 miles long and is characterized by a trough in which sediments have been deposited almost continuously since the Jurassic Period. The Sierra Nevada geomorphic province is located to the east of the Great Valley province and is a tilted fault block nearly 400 miles. Its western slope disappears under the sediments of the Great Valley province. According to geologic maps of the Chico Quadrangle, the site area is generally characterized by alluvial deposits of the Riverbank and Laguna Formations. The Riverbank Formation generally contains fine grained soils capped with coarse sand and the Laguna Formation generally contains gravel, sand, and silt.

4.2 Subsurface Soil Conditions

Seven borings were completed within the native areas which were covered with grasses and one boring (B-5) was completed in the center of the existing asphalt parking area. The borings were extended to depths of about 11 to 21½ feet below the existing ground surface. The near-surface soils encountered throughout the site generally consisted mostly of interbedded layers of silty clay with various amounts of sand and gravel, sandy lean clay, silt with sand, and sandy silt.

Silty clayey sand was encountered in boring B-2. Approximately 3½ inches of asphalt concrete overlying 9½ inches of aggregate base and 4½ inches of lean clay was encountered in Boring B-5 which was completed within the existing asphalt concrete pavement area.

Laboratory tests were conducted on selected soil samples and the test results are presented in Appendix B. Laboratory test results indicate that the subsoils at shallow depths have low to medium plasticity and exhibit a low swell potential when saturated.

Soil descriptions presented in this report are based on the subsurface conditions encountered at specific exploration locations. Variations in subsurface conditions may exist between the exploration locations. Refer to the boring logs in Appendix A for a detailed description of the subsurface conditions encountered at the locations of the explorations completed for this project. Stratification boundaries on the logs represent the approximate locations of changes in soil types; in-situ, the transition between materials may be gradual.

4.3 Groundwater

The borings were monitored during drilling for the presence and level of groundwater.

Groundwater was not encountered in our borings. Based on available regional groundwater mapping and well data, the depth to groundwater in the site area is expected to be in the range of 40 to 60 feet below site grade. Groundwater conditions should be expected to fluctuate due to changes in season, precipitation patterns, site utilization, on-site or off-site irrigation activities, and other on- and off-site factors.

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4.4 Liquefaction

Liquefaction is a mode of ground failure that results from the generation of high pore water pressures during earthquake ground shaking, causing loss of shear strength. Liquefaction is typically a hazard where loose sandy soils exist below groundwater. The California Geologic Survey (CGS) has designated certain areas within California as potential liquefaction hazard zones. These are areas considered at a risk of liquefaction-related ground failure during a seismic event, based upon mapped surficial deposits and the presence of a relatively shallow water table. The project site is not mapped for potential liquefaction hazard by the CGS.

In the event liquefiable soils are present below the maximum depth of exploration, the consequences of one-dimensional settlement may be largely mitigated by the presence of a thick non-liquefied layer above the liquefied soils (Ishihara 1985, Naesgaard et al. 1998, Bouckovalas and Dakoulas 2007). It is our opinion that the presence of non-liquefied layer in the upper soils may act as a bridging layer that redistributes stresses and therefore results in more uniform ground surface settlement.

Based on the subsurface conditions, depth of groundwater, blow counts of soils, and the presence of non-liquefiable soils encountered in our soil borings to a maximum depth of 21½ feet, we conclude that the potential for liquefaction at the site is low. Other geologic hazards related to liquefaction, such as lateral spreading, are therefore also considered low.

4.5 Potential Fuel Oil Contamination

It is our understanding that above and below ground fuel oil storage tanks previously existed on site in the area of the existing asphalt pavement. Boring B-5 was completed within the existing asphalt pavement area and the samples collected from this test hole were field screened with a photo-ionization detector (PID). A PID is a hand-held, battery-operated detector which measures volatile organic compounds in air. The maximum concentration measured by the PID during our field screening was 5.8 parts per million vapor. Additionally, no visual or olfactory evidence of fuel oil was present in that boring. All of our samples obtained from boring B-5 were transported to and analyzed by a State-approved laboratory for Total Petroleum Hydrocarbons as referenced to Oil (C22-C40+) to provide an indication as to the presence of residual fuel oil contamination. All samples tested contained less than the laboratory reporting limit of 10 mg/kg.

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5.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION

5.1 Geotechnical Considerations

The site appears suitable for the proposed Temporary Lodging Facility based upon geotechnical conditions encountered in the test borings. The proposed structures may be supported on spread foundations.

Shallow foundations and floor slabs should bear on a minimum of 10 inches of scarified, moisture conditioned, and compacted native soils. On site soils with low expansion potential can be used as engineered fill for this project.

Geotechnical engineering recommendations for foundations, floor slabs, pavements 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.

5.2 Earthwork

The following presents recommendations for site preparation, excavation, subgrade preparation and placement of engineered fills on the project. The recommendations presented are for the design and construction of earth supported elements including, foundations, slabs, and pavements are contingent upon following the recommendations outlined in this section. All grading for each structure should incorporate the limits of the proposed structures plus a minimum lateral distance of at least 8 inches per foot of over-excavation.

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.

5.2.1 Site Preparation

Strip and remove pavements and other deleterious materials from proposed building areas.

This should include the removal of all existing asphalt concrete, aggregate base, and any fill materials that may exist within the areas of the proposed construction. Exposed surfaces should be free of mounds and depressions which could prevent uniform compaction. All materials derived from the removal of existing pavements and other deleterious materials should be removed from the site and not be allowed for use as on-site fill.

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Evidence of underground utilities were observed during the site reconnaissance, such features and any other underground facilities should be removed from the footprint of the proposed building areas and the excavation thoroughly cleaned prior to backfill placement and/or construction.

5.2.2 Subgrade Preparation

Foundations and floor slabs should bear on a minimum of 10 inches of scarified, moisture conditioned, and compacted native soils. The moisture conditioning is an attempt to pre-swell the soils to help limit the potential for post construction heave and cracking of overlying slabs.

The native soil should be moisture conditioned and compacted as specified in Section 5.2.4.

Subgrade soils beneath exterior slabs and pavements should be scarified, moisture conditioned, and compacted to a minimum depth of ten inches. The moisture content and compaction of subgrade soils should be maintained until slab or pavement construction.

Exposed areas which will receive fill, once properly cleared and benched where necessary, should be scarified to a minimum depth of 10 inches, moisture conditioned, and compacted per the compaction requirements in Section 5.2.4.

5.2.3 Fill Materials and Placement

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

Approved imported materials or onsite materials with low expansive potential may be used as fill material for the following:

general site grading foundation backfill foundation areas exterior slab areas interior floor slab areas

Imported soils for use as fill material within proposed building and structure areas should conform to low volume change materials as indicated as follows:

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Percent Finer by Weight Gradation (ASTM C 136)

3” No. 4 Sieve ..................................................................................... 50-100 No. 200 Sieve ................................................................................. 20 - 50

Liquid Limit ....................................................................... 30 (max) Plasticity Index ................................................................. 15 (max) Maximum expansive index* .............................................. 20 (max)

*ASTM D 4829

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 in loose thickness.

5.2.4 Compaction Recommendations

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

Beneath floor slabs & foundations:

Upper 12 inches

Depth greater than 12 inches

0%

+4%

Beneath pavement section materials:

Upper 12 inches

Depth greater than 12 inches

Utility trenches:

Landscape areas

Structural and pavement areas (upper 12 inches) Structural and pavement areas (depth greater than 12 inches)

+4%

Aggregate base (beneath pavements)1 95 0% +4%

1. All materials and placement methods should conform to the current Caltrans Standard Specifications

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5.2.5 Grading and Drainage

Positive drainage should be provided during construction and maintained throughout the life of the buildings. Infiltration of water into utility trenches or foundation excavations should be prevented during construction. 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. We recommend a minimum horizontal setback distance of 10 feet from the perimeter of any building and the high-water elevation of the nearest storm-water retention.

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 5 feet of foundation walls. Landscaped irrigation adjacent to the foundation system should be minimized or eliminated.

5.2.6 Exterior Slab Design and Construction

Compacted subgrade composed of on-site clayey soils will expand with increasing moisture content; therefore, exterior concrete slabs may heave, resulting in cracking or vertical offsets.

The potential for damage would be greatest where exterior slabs are constructed adjacent to the building or other structural elements. To reduce the potential for damage caused by movement, we recommend:

exterior slabs should be supported directly on subgrade fill (not ABC) with no, or very low expansion potential;

strict moisture-density control during placement of subgrade fills;

maintain proper subgrade moisture until placement of slabs;

placement of effective control joints on relatively close centers and isolation joints between slabs and other structural elements;

provision for adequate drainage in areas adjoining the slabs;

use of designs which allow vertical movement between the exterior slabs and adjoining structural elements.

5.2.7 Corrosion Potential

Results of soluble sulfate testing indicate a soluble sulfate content of 19 ppm. Accordingly, ASTM Type I/II Portland cement is suitable for all concrete on and below grade. Foundation concrete should be designed for low sulfate exposure in accordance with the provisions of the ACI Design Manual, Section 318, Chapter 4.

Laboratory test results indicate the on-site soils have a pH of 7.2, a minimum resistivity of 1,197 ohm-centimeters, and a chloride content of 4 ppm, as shown on the attached Summary of Laboratory Results sheet. These values should be used to determine potential corrosive

Responsive Resourceful Reliable 10 characteristics of the on-site soils with respect to contact with the various underground materials that will be used for project construction.

Refer to Appendix B for the complete results of the various corrosivity testing conducted on the site soils in conjunction with this geotechnical exploration.

5.2.8 Earthwork Construction Considerations

At the time of our study, moisture contents of the surface and near-surface native soils and fill materials ranged from about 11 percent to 20 percent. Based on these moisture contents, some moisture conditioning will likely be needed for the project. The soils may need to be dried by aeration during dry weather conditions, or an additive, such as cement or kiln dust, may be needed to stabilize the soil. Subgrade conditions may require a rock protective mat covering of exposed subgrades in order to limit disturbance of the site soils as well as provide a stable base for the ground improvement contractor’s equipment.

Although the exposed subgrades are anticipated to be relatively stable upon initial exposure, on site clayey soils may pump and unstable subgrade conditions could develop during general construction operations, particularly if the soils are wetted and/or subjected to repetitive construction traffic. The use of light construction equipment would aid in reducing subgrade disturbance. The use of remotely operated equipment, such as a backhoe, would be beneficial to perform cuts and reduce subgrade disturbance. Should unstable subgrade conditions develop stabilization measures will need to be employed.

Upon completion of filling and grading, care should be taken to maintain the subgrade moisture content prior to construction of floor slabs and pavements. Construction traffic over the completed subgrade should be avoided to the extent practical. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. If the subgrade should become desiccated, saturated, or disturbed, the affected material should be removed or these materials should be scarified, moisture conditioned, and recompacted prior to floor slab and pavement construction.

We anticipate that site grading for concrete foundations, slab construction and utility trenches can be performed with conventional earthmoving equipment. Excavations penetrating the hard cohesive materials may require the use of specialized heavy-duty equipment to facilitate breakup and removal. The contractor is responsible for designing and constructing stable, temporary excavations (including utility trenches) as required to maintain stability of both the excavation sides and bottom. Excavations should be sloped or shored in the interest of safety following local and federal regulations, including current OSHA excavation and trench safety standards.

The geotechnical engineer should be retained during the construction phase of the project to observe earthwork and to perform necessary tests and observations during subgrade

Responsive Resourceful Reliable 11 preparation; proof-rolling; placement and compaction of controlled compacted fills; backfilling of excavations to the completed subgrade.

We recommend that the earthwork portion of this project be completed during extended periods of dry weather if possible. If earthwork is completed during the wet season (typically November through May) it may be necessary to take extra precautionary measures to protect subgrade soils. Wet season earthwork may require additional mitigative measures beyond that which would be expected during the drier summer and fall months. This could include diversion of surface runoff around exposed soils and draining of ponded water on the site. Once subgrades are established, it may be necessary to protect the exposed subgrade soils from construction traffic.

If unstable subgrade conditions develop during construction, suitable methods of stabilization will be dependent upon factors such as schedule, weather, size of area to be stabilized, and the nature of the instability. If soil stabilization is needed, Terracon should be consulted to evaluate the situation as needed.

5.3 Foundation Recommendations

The proposed structure can be supported by a shallow, spread footing foundation system bearing on a minimum of 10 inches of scarified, moisture conditioned, and compacted native soils. Design recommendations for foundations for the proposed structures and related structural elements are presented in the following subsections.

5.3.1 Foundation Design Recommendations

DESCRIPTION VALUE

Foundation Type Conventional shallow spread footings

Bearing Material A minimum of 10 inches of scarified, moisture conditioned, and compacted native soils

Allowable Bearing Pressure 2,500 psf

Minimum Dimensions Columns: 24 inches, Walls: 18 inches

Minimum Embedment Depth Below Finished Grade1 24 inches

Total Estimated Static Settlement2 Less than 1 inch

Estimated Differential Static Settlement2 Less than ½ inch over 40 feet

1. To reduce effects of seasonal moisture variations in subgrade soils and to provide firm uniform base to support foundation loads.

2. The foundation settlement will depend upon the variations within the subsurface soil profile, the structural loading conditions, the embedment depth of the footings, the thickness of compacted fill, and the quality of the earthwork operations.

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Finished grade is defined as the lowest adjacent grade within five feet of the foundation for perimeter (or exterior) footings and finished floor level for interior footings.

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.

Total and differential settlements should not exceed predicted values, provided that:

foundations are constructed as recommended, and essentially no changes occur in water contents of foundation soils.

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.

Footings and foundations should be reinforced as necessary to reduce the potential for distress caused by differential foundation movement. The use of joints at openings, or other discontinuities, in masonry walls is recommended.

Foundation excavations and bearing soils 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.

5.3.2 Foundation Construction Considerations

The base of all foundation excavations should be free of water, loose soil, and gravel prior to placing concrete. Concrete should be placed soon after excavating and placement of engineered fill to reduce bearing soil disturbance. Should the soils at bearing level become excessively dry, disturbed, or saturated, the affected soil should be removed prior to placing concrete. In addition, as previously described unsuitable soils should be completely removed from any proposed construction areas prior to construction. We recommend that Terracon be retained to observe and test the soil foundation bearing materials.

5.4 CBC Seismic Design Criteria

The table below presents seismic design criteria for the subject project site. The values are based on data provided by the 2002 USGS National Seismic Hazard Mapping Project and are for use with the 2010 California Building Code.

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Description Value 2010 California Building Code Site Classification (CBC) 1 C2

Site Latitude 39.11801°

Site Longitude -121.39738o

Ss Spectral Acceleration for a Short Period 0.442g

S1 Spectral Acceleration for a 1-Second Period 0.204g

Fa Site Coefficient for a Short Period 1.200

Fv Site Coefficient for a 1-Second Period 1.596

1. Note: In general accordance with the 2010 California Building Code, Table 1613.5.2. CBC Site Class is based on the average characteristics of the upper 100 feet of the subsurface profile.

2. Note: The 2010 California Building Code (CBC) requires a site soil profile determination extending to a depth of 100 feet for seismic site classification. The current scope does not include the required 100 foot soil profile determination. Borings extended to a maximum depth of 21½ feet, and this seismic site class definition considers that hard soil continues below the maximum depth of the subsurface exploration. Additional exploration to deeper depths would be required to confirm the conditions below the current depth of exploration.

5.5 Floor Slab

5.5.1 Floor Slab Design Recommendations

DESCRIPTION VALUE

Interior floor system Slab-on-grade concrete

Floor slab support1 At least ten (10) inches of scarified, moisture conditioned, and compacted native soils (this is in addition to the base material)

Base 6-inches of crushed gravel or Aggregate Base

Modulus of subgrade reaction

150 pounds per square inch per inch (psi/in) (The modulus was obtained based on our experience with similar subgrade conditions and structural fill.) This value is for a small load area (1 sq. ft. or less) such as for forklift wheel loads or point loads and should be adjusted for large loaded areas.

1. Upon completion of grading operations in the building area, the recommended subgrade moisture content and density should be maintained to construction of the building floor slabs.

A vapor retarder should be considered beneath interior slabs that will be covered with moisture sensitive or impervious coverings, or when the slab will support equipment sensitive to moisture.

The slab designer and slab contractor should refer to ACI 302 and ACI 360 for procedures and cautions regarding the use and placement of a vapor barrier. The aggregate base should be compacted in accordance to the Section 5.2.4 of this report.

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

Responsive Resourceful Reliable 14 joints are not recommended). 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.

5.5.2 Floor Slab Construction Considerations

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.

On most project sites, the site grading is generally accomplished early in the construction phase.

However as construction proceeds, the subgrade may be disturbed due to utility excavations, construction traffic, desiccation, rainfall, etc. As a result, the floor slab subgrade may not be suitable for placement of base rock and concrete and corrective action will be required.

Particular attention should be paid to high traffic areas that were rutted and disturbed earlier and to areas where backfilled trenches are located. Areas where unsuitable conditions are located should be repaired by removing and replacing the affected material with properly compacted fill.

All floor slab subgrade areas should be moisture conditioned and properly compacted to the recommendations in this report immediately prior to placement of the base rock and concrete.

5.6 Lateral Earth Pressures

The lateral earth pressure recommendations herein are applicable to the design of rigid retaining walls subject to slight rotation, such as cantilever, or gravity type concrete walls. These recommendations are not applicable to the design of geogrid-reinforced-backfill walls.

Recommendations covering these types of wall systems are beyond the scope of services for this assignment; however, we would be available to develop recommendations for the design of such wall systems upon request.

For on-site soils above any free water surface, recommended equivalent fluid pressures for unrestrained foundation elements are:

ITEM VALUE1,2

Active Case 45 psf/ft

Passive Case 300 psf/ft

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ITEM VALUE1,2

At-Rest Case 70 psf/ft

Surcharge Pressure 0.41*(Surcharge)

Adhesion 1,000 psf 1 The values are based on the on-site engineered fill materials used as backfill.

2 Earth pressures should be increased by 35 percent for a slope of 2H:1V behind wall. Earth pressures increase exponentially for back slopes steeper than 2H:1V.

3Based on return period of 475 years and calculated using USGS 2002 deaggregations.

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.

Total lateral earth pressures acting on the wall during a seismic event will likely include the static force and the dynamic increment. This dynamic increment should be applied to the wall as an inverted triangular pressure over the entire wall height and is added to the static earth pressures. The dynamic lateral earth pressure increment at the top of the wall (for a 0.11g peak ground acceleration calculated based on a return period of 475 years using USGS 2002 deaggregations) is 10H (in units of pounds per square foot (psf), where H (in units of feet) is the height of the soil behind the wall.

Surcharge pressure for uniform pressure acting at the back of the wall should be applied to the wall as a uniform pressure over the entire wall height and is added to the static earth pressures.

Other surcharge loads should be considered where they are located within a horizontal distance behind the wall equal to 1.5 times the height of the wall. Surcharge stresses due to point loads, line loads, and those of limited extent, such as compaction equipment, should be evaluated using elastic theory.

Fill against foundation and retaining walls 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.

Adequate drainage should be provided behind the below-grade walls to collect water from irrigation, landscaping, surface runoff, or other sources, to achieve a free-draining backfill condition. The wall back drain should consist of Class 2 permeable materials that are placed behind the entire wall height to within 18 inches of ground surface at the top of the wall. As a minimum, the width of Class 2 permeable materials behind the wall should be two feet. Water collected by the back drain should be directed to an appropriate outlet, such as weep holes or perforated pipes, for disposal.

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5.7 Pavements

The pavement areas for this project may be supported by native subgrade soils prepared in accordance with Section 5.2.2 or by structural fill material placed and compacted as outlined in the Earthwork section of this report.

5.7.1 Pavement Design Recommendations

Based on our previous experience with similar developments we assumed traffic indices (TI’s) ranging from 4 to 6 will be applicable for the proposed parking areas. Pavement sections presented below were calculated based on a R-value of 5 using Caltrans design procedures. R-value testing should be completed prior to pavement construction to verify the design value.

This service could be provided by Terracon upon request.

Traffic Index1 ESALs3

Minimum Recommended Pavement Section Thickness (inches)2

Asphalt Concrete Surface Aggregate Base Course

4 1,100 3 7

5 7,200 3 10

6 33,000 4 12

1. The traffic index (TI) is a measure of traffic wheel loading frequency and intensity of anticipated traffic. For comparison, TI’s of between 4 and 5 are often suitable for design of automobile parking areas, TI’s of between 5 and 6 are commonly used for design of fire truck access lanes and areas subject to channelized flow with light delivery trucks, and TI’s greater than 6 are common for design of pavements supporting light to moderate bus and truck traffic.

2. All materials should meet the requirements as outlined in the Caltrans Standard Specifications

3. Based on TI=9(ESALs/106)0.119

These pavement sections are considered minimum sections based on the expected traffic and the existing subgrade conditions; however, they are expected to function with periodic maintenance and overlays if good drainage is provided and maintained.

We recommend that reinforced concrete pads be provided for truck pad areas and in front of and beneath trash receptacles. The trash collection trucks should be parked on the rigid concrete pavement when the trash receptacles are lifted. The concrete pads should be a minimum of 5 inches thick and properly reinforced. Thickened edges should be used along outside edges of concrete pavements. Edge thickness should be at least 2 inches thicker than concrete pavement thickness and taper to the actual concrete pavement thickness 36 inches inward from the edge. Integral curbs may be used in lieu of thickened edges.

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5.7.2 Pavement Construction Considerations

Materials and construction of pavements for the project should be in accordance with the requirements and specifications of the latest edition of Caltrans Standard Specifications.

On most project sites, the site grading is generally accomplished early in the construction phase. However, as construction proceeds, the subgrades may become disturbed due to utility excavations, construction traffic, rainfall, etc. As a result, the pavement subgrade may not be suitable for placement of aggregate base and pavement.

We recommend the area underlying the pavement be rough graded and proof-rolled prior to placement of aggregate base material. Particular attention should be paid to high traffic areas and utility trenches that were backfilled. Areas where disturbance has occurred and materials are unsuitable should be removed and replaced with compacted structural fill.

The aggregate base should be uniformly moisture-conditioned and compacted to a minimum of 95 percent relative compaction (modified proctor) in accordance with this report. Base course or pavement materials should not be placed when the surface is wet. Surface drainage should be provided away from the edge of paved areas to minimize lateral moisture transmission into the subgrade.

Minimizing subgrade saturation is an important factor in maintaining subgrade strength. Water allowed to pond on or adjacent to pavements could saturate the subgrade and cause premature pavement deterioration. The pavement should be sloped to provide rapid surface drainage, and positive surface drainage should be maintained away from the edge of the paved areas. Design alternatives which could reduce the risk of subgrade saturation and improve long-term pavement performance include crowning the pavement subgrades to drain toward the edges, rather than to the center of the pavement areas; and installing surface drains next to any areas where surface water could pond. Properly designed and constructed subsurface drainage will reduce the time subgrade soils are saturated and can also improve subgrade strength and performance. In areas where there will be irrigation adjacent to pavements, we recommend the owner consider installing perimeter drains for the pavements.

Preventative maintenance should be planned and provided for through an on-going pavement management program in order to enhance future pavement performance. Preventative maintenance activities are intended to slow the rate of pavement deterioration, and to preserve the pavement investment.

5.8 Retention Basins

Two (2) percolation tests were performed during our field investigation at depths ranging from between about 3 to 5 feet below the existing ground surface. The approximate locations of the test holes are shown on Exhibit A-2.

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The percolation tests were performed by maintaining a head of water approximately 2 to 3 feet above the bottom of the test holes. The water level in each test hole was recorded and reestablished in approximate 30-minute intervals for four (4) hours. The last 60-minute readings were then used to calculate the percolation rate in gallons per square foot per day (gfd) and inches per hour (in/hr). The estimated percolation rates at each test location are as follows:

Percolation Test Depth (ft.)

Percolation Rate (gal/sq ft/day)

Percolation Rate (in/hr)

5 18 1.2

3 11 0.7

The field test results are not intended to be design rates. They represent the results of our tests at the depths and locations indicated. The design rate should be determined by applying an appropriate factor of safety.

There are many factors that influence storm water disposal. Clear water was used in our tests, whereas actual storm water will likely include oil residue, silt, organic matter, and other deleterious material. Variations in soil conditions within the basin will also likely affect percolation characteristics.

Depending on the depth of the basins, the design percolation rates for the basin sides should be further reviewed. Over time, very little percolation should be assumed through basin bottoms due to silting and organic matter build-up unless a vigorous plan is followed to maintain the basins by frequent cleaning and discing to reduce silt build-up. Our representatives should be allowed to observe the soils exposed during construction of the basins in order to evaluate if the design rates used are appropriate for the actual soils encountered.

6.0 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 should also be retained to provide observation and testing services during grading, excavation 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 explorations, across the site, or due to the modifying effects of construction or weather. The nature and extent of

Responsive Resourceful Reliable 19 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

Exhibit A-1

Field Exploration Description

Our field exploration for this project included performing eight (8) test borings and two (2) percolation tests on October 18 and 19, 2012. The approximate exploration locations are shown on Vicinity and Boring Location Map, Exhibit A-2. Exploration locations were located in the filed using the existing site features shown on an aerial photo. The exploration locations should only be considered accurate to the degree implied by the means and methods used to define them.

Boring Procedures

The test borings were advanced with a truck-mounted B-53 drill rig which each utilized 8-inch outside diameter (O.D.) hollow-stem augers…