ENCL F_Geotech Report.pdf

Preliminary Geotechnical Investigation Report Version: Draft

Twentynine Palms MCAGCC Project No. 09GE013

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TABLE OF CONTENTS

Section Page

1.0 INTRODUCTION

1.1 Project Description

1.2 Site Description

1.3 Purpose and Scope of Work

1.4 Previous Investigations

2.0 FIELD INVESTIGATION AND LABORATORY TESTING

2.1 Field Investigation

2.2 Soil Laboratory Analysis

3.0 GEOLOGIC SETTING

3.1 Regional Geology

3.2 Site Geology

3.2.1 Alluvial Deposits

3.3 Groundwater Conditions

3.4 Geologic Hazards

3.4.1 Tsunamis and Seiche Evaluation

3.4.2 Landsliding

3.4.3 Compressible and Expansive Soils

4.0 FAULTING AND SEISMOLOGICAL CONDITIONS

4.1 Faulting

4.1.1 Mesquite Lake Fault

5.0 CONCLUSIONS AND RECOMMENDATIONS

5.1 Site Preparation and Earthwork

5.1.1 Engineered Fill

5.1.2 Temporary Slopes and Shoring

5.2 Lateral Earth Pressures

5.2.1 Soil Engineering Design Parameters for Temporary and/or Permanent Structures

5.2.2 Allowable Bearing Pressure Values

5.3 Underground Utilities, Pipelines

5.4 Soil Corrosivity

5.5 Dewatering

5.5.1 Hydrostatic Pressures and Uplift

5.6 Permanent Slopes

5.7 Pavement Design

6.0 LIMITATIONS

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7.0 REFERENCES

TABLES

Table 1 Summary of Geotechnical Laboratory Test Results Table 2 Corrosion Test Results

FIGURES

Figure 1 Site Location Map Figure 2 Field Investigations Location and Geological Site Map Figure 3 Regional Geologic Map Figure 4 Regional Fault Map Figure 5 Local Fault Map Figure 6 Flood Hazard Map Figure 7 Preliminary Design of Rigid Pavement Figure 8 Preliminary Design of Flexible Pavement Figure 9 P-130 Cross Section

APPENDICES

Appendix A Exploratory Test-Pit Logs Appendix B Soils Laboratory Test Results Appendix C Sieve Analysis Test Results Plot Appendix D Pile Design Values and Specifications

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1.0 INTRODUCTION

RORE, Inc. (RORE) was contracted by RBF Consulting, Inc. (RBF) to conduct a preliminary geotechnical investigation for the proposed development of North Mainside Projects P-126, P-130, P-131, P-132, P-143, P-171per consultant agreement dated June 24, 2009. The scope of the proposed development includes the installation of a communication/utility vault (P- 126), a water storage tank and associated improvements (P-130), sewer improvements (P- 131), high temperature hot water and chilled water system (P-132), construction of new roads (P-143), and site work for construction, including grading, excavation, detention basins, and culverts (P-171). The findings from RORE’s geotechnical investigation will be used in requests for proposal (RFPs) issued by the Navy for design build projects.

1.1 Project Description

The Site vicinity and location maps are included in Figures 1 and 2, respectively. RORE understands that the proposed projects will consist of the following:

P- 126 - Communication/Utility Vault: The vault will traverse the north road, down each north-south road and along the middle road. The overall length is approximately 15,000 lineal feet.

P- 130 - Water Improvements and Storage Tank: A 4,500,000 gallon 150 feet diameter steel water storage tank and 20 inch gravity feed water line that will be placed in the north road from the existing tank/well site to a point near the proposed tank site.

P- 131 – Sewer Improvements: Includes the interior sewer lines and the improvements at the headworks to connect future development areas to the base sewer system.

P- 132 – HTHW / Chilled Water System: Includes the utility vaults and associated improvements for the High Temperature Hot Water and Chilled Water system construction.

P- 143 – Construct Roads Mainside: Includes the road work, associated grading, culvert crossings (pedestrian bridges), lighting, traffic signals, curbs, gutters, sidewalks and demolition of the existing tank trail. The heavily traveled roads (Gillespie, 11th & 13th) will have sections of concrete and asphalt that are designated as Industrial Collector roads, with a traffic index of 8.0. The other roads in the grid will only be constructed of asphalt and will be designated as Collectors with a traffic index of 7.0. The total linear feet of proposed roadway is approximately 17,000 feet.

P- 171 – Laydown Site work – North Mainside: This will facilitate the overall development of the area and allow construction to begin upon award of a construction contract. The work generally includes overall site grading, excavation, concrete-lined channels, detention basins, bridges/culverts and associated work.

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That includes the road work, associated grading, culvert crossings (pedestrian bridges), lighting, traffic signals, curbs, gutters, sidewalks and demolition of the existing tank trail.

No grading plans and/or structural design details had been developed at the time of our investigation.

Figure 2 provides a general layout of the proposed development.

1.2 Site Description

The proposed development consists of approximately 150 acres along the northeast side of the Mainside Area (Figure 2). The area is located south of 16th Street and north of 9th Street in the mostly undeveloped areas to the east of Del Valle Road.

The Mainside Area is located near the base of northwest trending mountains with the general topography sloping away from the mountains to the southwest. The elevations range approximately between 1,800 and 2,100 feet above mean sea level (msl).

1.3 Purpose and Scope of Work

The objective of this preliminary geological/geotechnical investigation is to evaluate the subsurface soil conditions and to develop initial geotechnical engineering parameters for use in the RFPs for the design build contracts to complete the proposed developments.

RORE’s scope of work under this investigation included the advancement of 25 soil borings, completion of 12 exploratory test pits, collection of in-situ and bulk soil samples at or near the proposed developments, laboratory testing of selected soil samples, compilation and analysis of the data generated, and preparation of this report.

This report incorporates results of field and laboratory testing as required under the guidelines prepared by the California Geological Survey (CGS, 2004 and 2005). Both general and specific recommendations pertinent to suitable site development and road design, respectively, are provided. Construction guidelines related to the geotechnical aspects of the project are also addressed.

1.4 Previous Investigations

Previous site-specific geological and/or geotechnical investigations have not been performed at the Site. However, Construction Testing Engineering, Inc. (CTE), issued a geotechnical report dated February 20, 2009 that summarizes their findings, conclusions, and recommendations for the then proposed project sites 2A, 2B, 1C, 5, 6A, and 8 located within the developed Mainside area to the southwest of the proposed North Mainside development area. According to the exploratory test pit logs, poorly graded sands and silty-sand alluvium were encountered at all of the test pit locations (CTE, 2009).

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2.0 FIELD INVESTIGATION AND LABORATORY TESTING

RORE conducted a field investigation to evaluate the subsurface conditions at the Site in order to develop preliminary soil engineering parameters and to provide initial recommendations for road pavement design. The investigation activities included a field reconnaissance, subsurface exploration via soil borings and exploratory test pits, and soils laboratory testing as described in the following subsections of this report.

2.1 Field Investigation

Field investigations were conducted from July 30, 2009 to August 7, 2009. A total of twenty five soil borings were advanced to total depths that varied between approximately 6 and 27 feet bgs using a CME 75 or CME 750 all terrain hollow stem auger drill rigs. The exploratory test pits were advanced to total depths that varied between 4.5 and 7 feet bgs, using a John Deere 410 backhoe loader equipped with a 24-inch bucket.

Five soil borings (TB-1 through TB-5) were advanced in the area of the proposed water tank (P-130). The remaining twenty borings (B-1 through B-18, B-31, and B-32), were spread throughout the areas of the proposed communications/utility vault (P-126), sewer improvements (P-131), HTHW/chilled water systems (P-132), and laydown site work (P- 171). Twelve exploratory test pits (TP-19 through TP-30) were excavated along the alignment of the proposed roads (P-143). The locations of all borings and test pits are shown on Figure 2. The logs of the borings and exploratory test pits are included in Appendix A.

The borings and exploratory test pits were used primarily to evaluate the subsurface conditions and to obtain soil samples for subsequent soil laboratory testing. The State of California Licensed Professional Geologist directed the drilling and excavation operations, logged the test pits, and collected soil samples. Bulk and drive samples were collected at regular intervals and noted changes in lithology. The samples were transported to the soils laboratory for subsequent testing of physical, chemical, and mechanical properties.

Drive samples were collected from borings at regular intervals with a California split-spoon sampler (3-inch outside diameter and 2.5-inch inside diameter lined with 1-inch long brass rings). A 140-pound automatic-trip hammer with a 30-inch drop was used to drive the sampler. The number of blows required to drive the sampler the final 12 inches of an 18-inch drive was recorded in the soil data logs. The brass tubes were removed from the sampler and placed inside PVC tubes with plastic caps. In addition, bulk samples were collected in plastic bags, sealed with tape, and transported to the soils laboratory for subsequent testing. Both the borings and test pits were backfilled with soil cuttings upon completion of the logging.

The soils encountered were classified in accordance with ASTM designation D2488, “Standard Practice for Description and Identification of Soils” (Visual Manual Procedure).

The log prepared in the field was reviewed in the laboratory, and based on the review and

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2.1.1 Subsoil Conditions

As described in Section 2.1 a total of twenty-five shallow soil borings were drilled at different locations as described below. Additionally, a total of 12 test pits were excavated to a maximum depth of 7 feet bgs. The purpose of exploratory soil borings and test pits was to evaluate subsoil conditions, provide Unified Soil Classification System (USCS) descriptions, and obtain in-situ densities (a measure indicated by Standard Penetration Test (SPT) values) and moisture conditions.

P-130 – Water Improvement and Storage Tank

At the proposed foot print of the water storage tank, RORE drilled five soil borings (TB-1 thru TB-5) to explore subsoil conditions and its suitability for foundation of the proposed 4,500,000 gallon capacity water tank. All the five soil borings were drilled to a maximum depth of 6 to 10 feet, beyond which refusal was encountered. The near surface soil from 0 to 6 feet encountered was very dense, dry to moist, poorly graded and gravelly sand with little or no fines (SP-SM). The Standard Penetration Test values ranged between 66 blows per foot to 50 blows per 2 inch penetrations, which are indicative of relatively dense material. Since refusal was encountered in all the five soil borings, it is believed that dense and massive granitic rock materials underlay the alluvium encountered at the surface. It should be noted that a vertical difference in elevation of approximately 6 to 10 feet between soil borings was evident as shown in cross-sections AA and BB (Figure 9). The underlain hard formation material will be suitable foundation materials for the proposed water tank, provided the proposed foundation is laid on hard formational material and not on fill material.

P- 171 – Laydown Site work – North Mainside

RORE drilled soil borings B-15 through B-18 and B-32 at the proposed detention basins area, and these exploratory soil borings drilled to a depth ranging between 16 and 26 feet bgs. The soil borings were encountered with alluvium deposits that consistently ranged in soil classification from dense to very dense poorly moist graded sands with some fine (SP) to silty sands (SM). The range of SPT values were from 16 to 81 blows/foot, but at some locations the SPT value was 90/10 inch, which is an indication that subsoil condition is generally dense to very dense; moist and lithology is uniform in this area of investigation.

P- 126 - Communication/Utility Vault P- 131 – Sewer Improvements P- 132 – HTHW / Chilled Water System P- 143 – Construct Roads Mainside

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At all the above proposed areas of planned improvements, several soil borings (B-1 through B-14) and test pits (TP-19 through TP-30) were drilled and excavated, respectively, to evaluate subsoil conditions. At all these locations subsoil conditions encountered was relatively uniform and consistent with other soil borings data described earlier. The depth of soil borings (B-01 through B-14) ranged between 16.5 feet to 27 feet bgs, and subsoil encountered was alluvium under USCS soil classification of well graded, to poorly graded sand with fine (SP-SM). The only exception was at B-01, where at 22 feet bgs, inorganic very dense silt, moist with very fine sand (ML) was encountered. The SPT values were in the range of 11 blows per foot to 100 blows per10 inches, which is dense to very dense sand.

2.2 Soil Laboratory Analysis

The samples collected during the field program were returned to the soils laboratory operated by Construction Testing and Engineering of Escondido, California for visual examination and testing. Soil laboratory analysis for Corrosion Potential was conducted at General Analytical Laboratories in San Diego, CA. The soil samples were selected for laboratory analysis based on field observations of changes in lithology and other parameters. The soils laboratory testing program consisted of the following:

In-situ moisture content and dry density (ASTM D2216 and D2937), Modified Proctor/Maximum Density (ASTM D1557), Sieve Analysis (ASTM D422, D1140), Atterberg Limits/Plasticity Index (ASTM D4318), Direct Shear (ASTM D3080), R-Value Test (ASTM D 2844 CA- 301), Corrosion Potential (Cal DOT 417, 422, 532 and 643)

The in-situ strength, cohesiveness, if any, was estimated using shear strength values, sieve analysis and moisture/density data. A complete laboratory report is provided in Appendix B and laboratory test data are summarized below in Table 1 and Table 2.

2.2.1 Sieve Analysis

The grain-size distribution of selected soil samples were analyzed according to ASTM test method D1140-92. The grain-size distribution curves are provided in Appendix B and it relates to visual soil classification made by field personnel.

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2.2.2 Atterberg Limits test

Several cohesive soil samples were sent to the laboratory for classification using liquid limit and plastic limit (Atterberg limit) test. The results are presented in Table 1, which indicate that all of the soil samples analyzed were non-plastic.

2.2.3 In-situ Dry Density and Moisture Content

The in-situ density and moisture content of representative, relatively undisturbed soil samples were obtained using ASTM test method D-2216. The moisture content and dry density test results are summarized in Table 1 above and it can be noted that in-situ moisture content generally ranged between 0.9% to 6.7%, an indication that in-situ soil moisture is almost dry, which is anticipated under desert environmental conditions at 29 Palms area.

The in-situ dry density measurement also ranged between 97 pcf to 124 pcf. A large portion of soil samples tested indicated an in-situ density of greater than 105 pcf, which is a reflection of greater SPT blow counts recorded during drilling activities. This test data is a demonstration of dense alluvial soils encountered at the surface, which will be considered a suitable foundation and/or base course material under properly re-compacted conditions.

2.2.4 Maximum dry density and optimum moisture conditions

Modified Proctor (compaction) tests were conducted at a testing laboratory to evaluate maximum dry density and optimum moisture content values. This data is presented in Table 1 and indicates that if subsoil conditions are properly re-compacted, it can serve as good foundation materials and/or base course materials. The reported maximum dry density and optimum moisture content ranged between 111 pcf and 5.5% and 127 pcf and 9%, respectively.

2.2.5 Direct Shear Test

Direct shear tests were conducted per ASTM test method D-3080 on selected soil samples and results are presented in Table 1. In almost all the soil samples tested, angle of internal friction ( ) was greater than 30 degrees and highest value reported was 46 degrees.

Some soil samples tested indicated apparent cohesion values of 180 psf to 430 psf, which is attributed to presence of fines and silts found in subsoil during drilling activities.

2.2.6 R-Value test

The R-value test per California Test 301 method measures the response of a compacted sample of soil or aggregate to vertically applied pressure under specific conditions. The R-value of the material is in a state of saturation such that water will be exuded from the compacted test specimen when a 16.8 KN load is applied. Since it is not always possible to prepare a test specimen that will exude water at the specified load, it is necessary to test a series of specimens prepared at different moisture contents. R-value is used in pavement design, with the thickness of each layer below and expected level of traffic loading, expressed on Traffic Index (TI).

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A total of fourteen R-value tests were conducted on selected soil samples, and particularly the soil samples collected from test pits (TP-19 through TP-30), which were excavated along the proposed road alignment. The R-value report ranged from 73 to 80, which are considered relatively high and very well suitable for subgrade material under both rigid and flexible pavement conditions. Two sets of rigid and flexible pavement conditions were designed using TI values provided by RBF.

2.2.7 Soil Corrosivity Analysis

In order to evaluate soil corrosivity, a set of seven bulk soil samples collected from drilling/excavation activities were sent to General Analytical Laboratories, San Diego to conduct the following tests: conductivity, resistivity, pH, sulfate and chloride test methods.

The test results are presented in Table 2 and discussed in Section 5.3.

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3.0 GEOLOGIC SETTING

3.1 Regional Geology

Geologically, the Site is located within the Mojave Desert geomorphic province of southern California (CDMG, 2002). The Mojave is a broad interior region of isolated mountain ranges separated by expanses of desert plains. It has an interior enclosed drainage and many playas. There are two important fault trends that control topography a prominent NW-SE trend and a secondary east-west trend (apparent alignment with Transverse Ranges is significant). The Mojave province is wedged in a sharp angle between the Garlock Fault (southern boundary Sierra Nevada) and the San Andreas Fault, where it bends east from its northwest trend. The northern boundary of the Mojave is separated from the prominent Basin and Range by the eastern extension of the Garlock Fault (CDMG, 2002).

3.2 Site Geology

Topographically, the elevations range approximately between 1,800 and 2,100 feet above mean sea level (msl). The area is located at the base of the Bullion Mountains with the area slope moderately to southwest away from the mountains. Drainage in the area follows multiple dry wash channels generally running east to west. The exploratory test pits and borings advanced at the Site encountered alluvial deposits which extended beyond the maximum explored depth of 27 feet (bgs).

3.2.1 Alluvial Deposits

Alluvial deposits were encountered in all 25 soil borings and twelve exploratory test pits.

The encountered deposits predominantly consist of poorly graded sand (SP) and silty sand (SM), which are described as medium dense to dense, dry to moist, brown to reddish-brown, containing trace to moderate amounts of gravel.

3.3 Groundwater Conditions

No groundwater was encountered in any of the soil borings or exploratory test pits that were advanced during the investigation. Based on our knowledge of the area and available data, the depth to groundwater is expected to be greater than 50 feet bgs. Therefore, groundwater is neither expected to be a factor nor a constraint with respect to the planned improvements to the area.

3.4 Geologic Hazards

From our investigation, it appears that geologic hazards at the site are primarily limited to those caused by strong shaking from earthquake generated ground motions. A discussion of earthquake hazards is presented in Section 4 of this report.

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3.4.1 Tsunamis and Seiche Evaluation

Due to site elevation and distance from the Pacific Ocean, the site is not considered to be subject to tsunamis. Based on the absence of large bodies of water in the area, impacts from seiche are not expected.

3.4.2 Landsliding

From our investigation the potential for landsliding in the vicinity of the site is considered very low. No features typically associated with landsliding were noted during the site investigations. Based on historical data review, no evidence of landslides was found to have occurred within the vicinity of the site.

3.4.3 Compressible and Expansive Soils

Soils encountered during the investigation consist of sands with low amounts of silt with low compressibility characteristics relative to post construction overburden. Soils identified with some silt/clay content were collected from borings B-4, B-7, B-11, B-31, and TB-4, and test pits TP-29 and TP-30. The samples were analyzed for Atterberg Limits an indication of expansion properties in soil. All samples were determined to be non-plastic, which indicates the soil is non-expansive or has a very low expansion potential.

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4.0 FAULTING AND SEISMOLOGICAL CONDITIONS

4.1 Faulting

Based on our review of readily-available geologic literature, the subject site is approximately 1 mile northeast of the active Mesquite Lake Fault (a generally northwest-southeast trending fault).

An active fault is defined by the California Geologic Survey as a “sufficiently active and well defined fault” that has exhibited surface displacement within the Holocene time (approximately the last 11,000 years). A potentially active fault is defined by the State of California as a fault with a history of movement within Pleistocene time (between 11,000 and 1.6 million years ago). Any fault proven not to have moved within the last 1.6 million years is considered inactive. The definition of active faults is used in delineating Earthquake Fault Zones as mandated by the Alquist-Priolo Special Studies Zones Act of 1972 and revised in 1994 and 1997 as the Alquist-Priolo Earthquake Fault Zoning Act and Earthquake Fault Hazard Zones. The intent of this act is to require fault investigations on sites located within Earthquake Fault Hazard Zones to preclude new construction of certain habitable structures across the trace of active faults. Based on review of available literature, the site is not located within an Alquist-Priolo Earthquake Fault Zone. Based on our investigation, no evidence of active faulting is present on site.

4.1.1 Mesquite Lake Fault

The Mesquite Lake Fault is a northwest-southeast trending right lateral strike-slip fault.

The fault is located approximately 1 mile west of the subject site, and runs sub-parallel to Del Valle Road. The most recent surface rupture along the fault trace occurred 12,000 to 17,000 years ago (SCEC.ORG).

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5.0 CONCLUSIONS AND RECOMMENDATIONS

The Proposed development area of approximately 150 acres along the northeast side of the main area (Figure 2) includes:

P- 130 - Water Improvements and Storage Tank (TB-1 through TB-5)

P- 171 – Laydown Site work – North Mainside (B-15 through B-18 and B-32)

P- 126 - Communication/Utility Vault (TP-19, TP-22, TP-24, TP-26, TP-28 and B-5, B- 9, B-11, and B-14)

P- 131 – Sewer Improvements

P- 143 – Construct Roads Mainside (TP-20, TP-23, TP-25, and B-10)

P- 132 – HTHW / Chilled Water System (B-2 and TP-21)

In almost all of the above-referenced proposed developments, RORE’s preliminary geotechnical investigation using shallow soil borings and test pit excavations at the maximum depth of drilling and/or excavation, identified a consistent dense to very dense, dry to moist, alluvium soil that consists of poorly graded sands and gravelly sand with little or no fines (SP-SM). Both field and laboratory data classified underlain soil as SP-SM, which will serve as a foundation material and/or base course materials.

The planned construction activities will have the following geotechnical engineering considerations:

Stability of open trench sidewalls (in the case of box culvert construction) and temporary slopes and its potential impact to existing structures, if any

Impacts of groundwater dewatering and its seasonal conditions at the time of construction

Treatment of loose bedding soils when they occur within open trench excavations

Compaction of the trench backfill material

Thickness of pavement to accommodate planned traffic load

Based on the results of our preliminary subsurface explanations and from a geotechnical perspective, it is RORE’s opinion that the site is suitable for the proposed development, provided the recommendations included in this report are incorporated into the design and construction plans and specifications of the project site.

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As described in Section 2.1.1 at the proposed water storage tank (P-130), the subsoil conditions encountered at near surface soil (0 to 6 feet bgs) was dense, dry to moist, poorly graded sand and gravelly sand with little to no fines and is alluvium. However, refusal was encountered at 6 feet bgs or below. Since refusal was encountered in all the five soil borings, it is believed that dense and massive conglomerate rock materials underline the alluvium encountered at the surface. Therefore, considering the load bearing capacity of this conglomerate rock material, the design engineer should consider installing the planned water storage tank on this conglomerate rock material.

5.1 Site Preparation and Earthwork

RORE understands that grading plans for the proposed construction are not available at this time. We have tentatively estimated that maximum cuts and fill would not generally exceed approximately a few feet in thickness. Site preparation and grading should be performed under the observation of a qualified geotechnical engineer. Conclusions and recommendations given below are consistent with geotechnical conditions indicated at the property and should be incorporated into final plans and implemented during the construction phase.

Based on our evaluation of existing conditions, RORE recommends that the near-surface materials be excavated and replaced by material or engineered fill as summarized in the following paragraphs:

Areas of the site containing vegetation should be cleared and grubbed to remove organic matter. All vegetative matter, or other unsuitable materials, should be disposed off-site or be used in landscaped areas.

Near-surface materials up to an approximate depth of 2 to 4 feet should be excavated and replaced by a mat of engineered fill soils under the proposed structures. The Project Geotechnical Engineer should confirm this by observation and proof rolling as directed in the field during construction.

Building column and wall shallow foundations shall extend a minimum of 1 to 2 feet into competent dense sand (SP-SM). In order to meet uniform stiffness under the entire building footprint and to limit the amount of total and differential foundation settlements, shallow foundation material that is used should be relatively uniform in thickness.

Slabs on grade and structural mat foundations should be supported on a mat of engineered fill consisting of select non-expansive granular soils. Minimum thickness of this mat of engineered fill should be at least 2 feet under structural mats and shallow spread footings. It is recommended that this mat of engineered fill be of uniform thickness. Where zones of variable thickness of engineered fill are planned, a smooth and gradual transition should be designed in order to minimize differential settlements. It is recommended that over-excavation be performed as necessary under foundations to limit average rate of change of fill thickness under the

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Structural fill may include either select import soils or excavated materials, provided these soils meet all specifications for structural fill soils (provided in the following paragraphs), and are compacted to at least 95 percent of the maximum dry density, and moisture-conditioned to at least 2 percent above optimum moisture content, in accordance to ASTM D1557.

5.1.1 Engineered Fill

5.1.1.1 Structural Fill

On-site soils placed and compacted as fill under proposed structures supported by structural mats and shallow spread footings should consist of granular materials having a liquid limit (LL) less than 30, a plasticity index (PI) less than 15 (per ASTM D4318); a fines fraction (percent passing No. 200 sieve, per ASTM D422 and D1140) less than 30 percent; and an expansion index (EI, per ASTM D4829) less than 20. Structural fills should not contain particles greater than 4 inches in the maximum dimension, and should contain less than 15 percent particles greater than 2.5 inch.

All structural fill materials shall be compacted to a dry density of at least 95 percent of the maximum dry density and moisture-conditioned to at least 2 percent above optimum moisture content, as determined by ASTM D1557 test method. All fills shall be compacted in lifts no thicker than 6 inches (measured in lose state).

On-site near-surface soils include sand (SP-SM). It should be noted that all near surface soils tested for plasticity index per Atterberg limit test were found to be non plastic. Therefore, existing near-surface soils would meet material requirements to be used as structural fill.

5.1.1.2 General Fill

General fill shall be compacted to a dry density of at least 90 percent of the maximum dry density and moisture-conditioned to at least 2 percent above optimum moisture content, as determined by ASTM D1557 test method. All general fills shall be compacted in lifts no thicker than 8 inches (measured in lose state).

Actual depth of over-excavation will be determined in the field by the Project Geotechnical Engineer. If lose, soft, potentially expansive, or otherwise unsatisfactory soils are encountered at the bottom of the excavation, the excavation should be carried further into dense sand. The exposed soils at the bottom of the excavation should be probed and tested to the satisfaction of the Project Geotechnical Engineer. The limits of the over-excavation should extend horizontally beyond the footing areas to a minimum distance of 10 feet.

Exposed subgrade soils should be scarified to a minimum depth of 8 inches, moisture-conditioned to at least 2 percent above optimum moisture content and compacted to at least 90 percent of the maximum dry density, in accordance with ASTM D1557. In addition, a

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Local pockets of deeper over-excavation (deeper than 5 feet) should be filled with structural fill soils, or three-sack cement-sand slurry grout or lean concrete, as determined by the Project Geotechnical Engineer in the field.

5.1.2 Temporary Slopes and Shoring

For sewer/water main installation, techniques will require suitable design of temporary slopes and shoring. RORE recommends that temporary excavations that are deeper than 5 feet should be either properly shored or sloped back to 1:1 (horizontal to vertical) or flatter. Excavations deeper than 20 feet should be evaluated on a case-by-case basis by the geotechnical engineer in the field. It should be the responsibility of the Contractor to maintain safe and stable excavation slopes in accordance with all safety regulations, including OSHA.

Shoring techniques may be used in lieu of inclined temporary slopes when vertical open construction excavations are required. Shoring techniques should effectively allow planned structure and provide protection for the workmen and nearby structures/improvements. Shoring design should be provided by a California registered civil engineer who is retained by the Contractor; the design, however, should be reviewed and approved by the project geotechnical engineer prior to the actual initiation of the project.

Open excavations should be continuously inspected by the project geotechnical consultant to help ensure safe working conditions with specific regards to sidewall stability. Particular attention should be given to the stability of temporary excavations, dewatering, safety of the construction area and field crews, and use of appropriate shoring and open excavation protection technique.

Additionally, construction above the project sewer/water main alignment is expected to expose dense alluvium sand (SP-SM). RORE recommends that in-situ alluvium material can be re-compacted to serve as a bedding material. The design specifications should include thickness of bedding material and its compaction requirements based on the anticipated traffic load on the pipeline alignment.

5.2 Lateral Earth Pressures

Recommendations regarding lateral earth pressures are provided below.

5.2.1 Soil Engineering Design Parameters for Temporary and/or Permanent Structures

Temporary and/or permanent retaining walls, or other subterranean walls, should be designed to resist the lateral pressures imposed by the surrounding soils and surcharge loads. RORE recommends using soil design values as follows.

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Soil dry density = 121 pcf.

Design active soil pressure for retaining structures = 30 pcf [Equivalent Fluid Pressure (EFP)], level backfill, cantilever, unrestrained walls.

Design at-rest soil pressure for retaining structures =45 pcf (EFP), non-yielding, restrained walls.

Design allowable passive soil pressure for retaining surfaces = 300 pcf (EFP), level surface at the toe.

Design allowable coefficient of friction for concrete on compacted fills = 0.30.

Modulus of Subgrade Reaction = 210 lbs per cubic inch (derived from NAVFAC Design Manual 7.02)

Notes:

Because larger movements must take place before maximum passive resistance can be developed, a minimum safety factor of two is recommended for sliding stability where structures and improvements are planned on top of the wall (not applicable for temporary shoring structures).

When combining passive pressure and frictional resistance, should be reduced by one third.

All earth pressure values presented herein are based on data from drained direct shear test values.

5.2.2 Allowable Bearing Pressure Values

Based on native engineered fill, RORE recommends allowable bearing capacity value of 3,000 psf. The allowable bearing values may be increased by one-third for loads of short duration, including wind and seismic forces. .

5.3 Underground Utilities, Pipelines

For the purpose of presenting design recommendations for pipe trench excavation and backfill, the following terminology is used in this report.

Pipe Zone - The pipe zone includes the full width of the trench from the bottom of the trench to a horizontal level about 12 inches above the top of the pipe along the entire pipeline alignment.

Above-Pipe Zone - The above-pipe zone is the full width of the trench above the pipe zone to ground surface.

Based on the results of our investigation, it appears the on-site soils in their in-situ condition along pipeline alignments will provide adequate bearing capacity to support the buried pipelines. Typically, the pressure imposed by the pipelines is less than the

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RORE, Inc. 16 overburden pressure at the pipeline invert levels; therefore, bearing capacity and settlement do not appear to be a design factor.

Subgrade Preparation: Pipes should be supported on firm material. Disturbed or lose materials at the bottom of the trenches should be compacted in situ to 90 percent relative compaction (ASTM D1557) or be removed to expose competent soils prior to placement of bedding material. After excavation is completed, subgrade soils should be scarified and compacted to 90 percent of the maximum dry density in accordance with ASTM D1557.

Pipe Bedding: It is recommended that the pipes be bedded on select sand meeting the requirements of the section below to provide relatively uniform and firm support.

Pipe-Zone Trench Backfill: Backfill to be placed in the pipe zone should consist of select sand that conforms to the gradation requirements as listed in the Table below. In addition, the select sand should have a minimum Sand Equivalent (SE) of 30, as determined by the California Test Method 217 or applicable ASTM standard test procedure.

Select Pipe-Zone Backfill Sand Gradation

U.S. Standard Sieve

(ASTM E11)

Select Sand (Percent passing by dry weight)

3/8 inch 100

No. 4 75-100

No. 40 10-50

No. 100 5-20

No. 200 0-10

Above-Pipe Zone Trench Backfill: The Site subsurface materials generated from trench excavation are considered suitable to be used as backfill in the above-pipe zone, provided that the backfill is free of vegetation, debris, organic materials, expansive soils and deleterious materials and particles greater than 3 inches in their largest dimension.

Trench Backfill Placement and Compaction Requirements: Backfill should be placed on each side of the pipe simultaneously to avoid unbalanced loads on the pipe. All backfill should be moisture-conditioned to, or slightly above, optimum moisture content, placed in lifts not exceeding 6 inches in lose thickness, and compacted to at least 90 percent of the maximum dry density in the pipe zone and above-pipe zone. The maximum density and optimum moisture content for each material used should be determined in accordance with ASTM Method D1557. During backfill of excavations, the fill should be properly benched into slopes as it is placed in lifts. Light weight compactors should be used near piping so that imposed loads are not excessive. Trench backfill should not be jetted or flooded.

5.4 Soil Corrosivity

Corrosion potential characteristics of on-site soils were evaluated to minimize the potential for: a) corrosion to underground metallic structures, and b) degradation of concrete

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RORE, Inc. 17 structures due to the presence of soluble sulfates in soils.

The potential for soil corrosion of metal and aggression to concrete structures was assessed by performing tests of water-soluble sulfates and chlorides in soils, as well as pH and electrical resistivity. In general, soluble sulfate concentrations greater than about 150 ppm and lower than about 1,000 ppm generally indicate that Type II Portland cement, instead of Type I, is needed to minimize the potential for aggression of sulfate soils to concrete.

Soluble chloride concentrations less than seawater (approximately 18,000 ppm) generally indicate low potential for aggressiveness of chloride soils to concrete, and is not considered a problem (Schiff, 1975). However, soluble chlorides and sulfates can prevent formation of protective types of corrosion products, and soluble chlorides in excess of 100 ppm are corrosive to steel.

Electrical resistivity tests are also generally used as a measure of soil resistance to the flow of corrosion currents. Corrosion currents are generally high in low resistivity soils. The electrical resistivity of a soil decreases primarily with an increase in its chemical and moisture contents. A commonly accepted correlation between electrical resistivity and corrosivity for buried ferrous metals is presented below.

Electrical Resistivity (Ohms/cm) Corrosion Potential

Less than 1,000 Severe 1,000 to 2,000 Corrosive 2,000 to 10,000 Moderate Greater than 10,000 Mild

Corrosion potential tests (consisting of pH, resistivity, soluble sulfates and soluble chlorides) were performed on seven bulk samples from approximately 5 feet of depth. The chemical test results at these locations indicated water-soluble sulfate concentrations in soils of approximately 26 and 54 parts per million (ppm), respectively, and water-soluble chloride concentrations ranging from 13 to 37 ppm. At these sample locations, electrical resistivity tests in the laboratory indicated values of 4,950 to 8,790 ohm-cm; pH units were approximate 7.07 and 9.13, respectively (Table 2).

Based on these tests, on-site soils are classified as mildly to moderately corrosive to underground metal structures. Should metal corrosion be a concern, further field resistivity tests should be performed to evaluate the soil profile. At a minimum, any buried metal piping and components should be protected with suitable coatings, wrappings, or seals. A corrosion consultant should be retained if a more detailed evaluation or a protection system is desired.

Where concrete will be exposed to sulfate-containing solutions, it shall comply with the provisions included in following table from Section 1904.3.1 of the IBC (2003).

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RORE, Inc. 18

TABLE 1904.3 OF IBC 2003

REQUIREMENTS FOR CONCRETE EXPOSED TO SULFATE CONTAINING SOLUTIONS

5.5 Dewatering

Groundwater was not encountered during our field exploration in July and August 2009 to a maximum depth of 27 feet bgs drilled. Therefore, construction dewatering should not be an issue during dry months. However, if the construction activities are planned during the rainy season (November through March), the contractor should be prepared for dewatering conditions, as appropriate. Consequently, dewatering may be necessary to complete open trench excavations and backfill operations along the impacted portions of the building foundation. The extent of dewatering at the site, if required, will depend primarily on seasonal conditions and actual levels at the time of construction. In this case, a detailed dewatering plan and procedures should be designed and implemented by a qualified contractor based on the actual groundwater conditions encountered.

In general, groundwater should be lowered to a minimum of one foot below the bottom of the excavation. If necessary, a dewatering program (plan) should be developed by the project contractor to complete trenching, installations, and construction of the structure.

Any dewatering technique such as gravel-trench or well-point methods, which could effectively lower water levels to specified depths, is acceptable, provided it is reviewed and approved by the project geotechnical consultant. Minor seeps during the rainy season may develop within the open excavation walls but may not grossly impact the overall sidewall stability. However, dewatering may improve stability of these construction slopes and should be implemented as warranted.

SULFATE

EXPOSURE

WATER

SOLUABLE

SULFATE (SO4)

IN SOIL,

PERCENT BY

WEIGHT

SULFATE

(SO4) IN

WATER

(ppm)

CEMENT TYPE

MAXIMUM WATER-

CEMENTITIOUS MATERIALS

RATIO BY WEIGHT,

NORMAL-WEIGHT

AGGREGATE CONCRETEa

MINIMUM f'e'

NORMAL-WEIGHT

AND LIGHTWEIGHT

AGGREGATE

CONCRETE (psi)a

ASTM

C 150

ASTM

C 595

ASTM

C 1157

Negligible 0.00 - 0.10 0 - 150 - - - - -

Moderate 0.10 - 0.20

150 -

1,500 II

II, IP (MS), IS

(MS), P (MS), I

(PM)(MS), I

(SM)(MS) MS 0.50 4,000

Severe 0.20 - 2.00

1,500 -

10,000 V - HS 0.45 4,500

Very

Severe Over 2.00

Over

10,000

V plus pozzolanc -

HS plus pozzoland 0.45 4,500

FOR SI: 1 pound per square inch = 0.00689 Mpa

a. A lower water-cementitious materials ratio or higher strength may be required for low permeability or for protection against corrosion of embedded items or freezing or thawing.

b. Seawater.

c. Pozzolan that has been determined by test or service record to improve sulfate resistance when used in concrete containing Type V cement.

d. Pozzolan that has been determined by test or service record to improve sulfate resistance when used in concrete containing Type HS blended cement.

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RORE, Inc. 19

Although minor sloughing of the temporary slope face should be anticipated, it should not impact the overall stability of the construction slope. Placing heavy construction equipment and materials within a distance equal to the height of the construction slope measured from the top of the temporary bank should be avoided. Also stockpiling of excavated soil or construction materials within the specified zone should not be allowed.

Water should not be allowed to run over the top of the temporary cut bank during construction.

5.5.1 Hydrostatic Pressures and Uplift

As mentioned earlier, the groundwater was not encountered during the site investigation.

However, if encountered, groundwater may affect excavation. Perched groundwater may possibly be encountered during construction as a result of seasonal variations (such as during and after rainy seasons). For preliminary planning purposes, RORE suggests that for “cantilever” shoring (“active” earth pressure condition) and level backfill, a minimum uniform lateral pressure of 30H pounds per square foot (psf) above the water table be used for temporary shoring design and level backfill, where H is the excavation depth measured in feet.

We recommend that, if perched groundwater is encountered, the uniform lateral pressure due to soil be at least 15H psf plus the hydrostatic pressure. For “restrained” shoring (“at-rest” earth pressure condition) and level backfill, we recommend to using a uniform lateral pressure of at least 45H psf above the water table.

For 2:1 (H: V) sloping backfill, the above recommended earth pressures should be increased by 30 percent. In addition, for “cantilever” shoring (“active” conditions), 35 percent of adjacent areal surface loads that may occur during construction should be added to the above recommended lateral pressures for shoring design. Conversely, for “restrained” shoring (“at-rest” conditions), 50 percent of adjacent surface loads that may occur during construction should be added to the above recommended lateral pressures for shoring design.

5.6 Permanent Slopes

Until final grading plans are developed, we have assumed permanent cut slopes of up to 10 feet in height or less and no steeper than 2:1 (horizontal to vertical), which are anticipated to occur within surficial soils at retention basin areas.. Engineered fill slopes are anticipated to be up to 10 feet in height and no steeper than 2:1 (H:V). For these assumed slope conditions, we consider slope instability not to be considered a concern. Higher cut or fill slopes should be evaluated on a case-by-case basis by the geotechnical engineer once preliminary grading plans have been developed.

5.7 Pavement Design

Pavement thickness design depends on the strength of construction materials as well as on the loading and repetition of truck traffic. Truck traffic loading and repetition should be carefully considered before choosing Traffic Indices (TI) and corresponding pavement sections.

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A total of fourteen R value tests were conducted from soil samples collected at soil boring locations and test pit areas. Almost all the R values obtained were from the proposed road alignment area and/or existing road ways. The minimum and maximum R values obtained were 73 and 80, respectively. Based on our experience with similar soils in the general vicinity of the subject site, we have assumed an R-value of 76 for preliminary pavement section design. The preliminary pavement design followed procedures laid in California Highway Design Manual under desert conditions. However, since an evaluation of the characteristics of the actual soils at pavement subgrade can only be provided at the completion of grading, the following pavement sections should be used for planning purposes only. Final pavement designs should be evaluated after R-value tests have been performed on the actual subgrade material.

Two set of preliminary design values are as listed below. One is for rigid pavement (i.e., Jointed Plain Concrete Pavement (JPCP) the other is flexible pavement using Hot Mix Asphalt (HMA). The Table below presents our recommendations for pavement sections for TI values of 7 to 8. Traffic indices of 7 and 8 correspond to Military Operational Vehicles and automobiles at MCAGCC 29 Palms area. The pavement design is recommended based on a limited evaluation of R-values of the on-site soils along the proposed service road alignment and standard pavement design procedures.

A schematic cross section of pavement design proposed is presented in Figures 7 and 8.

Recommended Rigid Pavement Sections

Recommended Flexible Pavement

Traffic Index 7.0 8.0

Hot Mixed Asphalt (inches) 6 6

Aggregate Base (inches) 12 12

Subbase (inches) 24 24

The subgrade soils for the proposed driveway should be scarified to a minimum depth of 12 inches, moisture-conditioned to approximately 0 to 2 percent above optimum and re-compacted to at least 95% of the maximum dry density per ASTM D1557. The aggregate base should also be compacted to a minimum of 95% relative compaction (ASTM 1557) and

Traffic Index 7.0 8.0

Jointed Plain Concrete (inches) 9 9

Hot Mix Asphalt ( inches) 1 1

Lean Cement Concrete (inches) 4.5 4.5

Subbase (inches) 24 24

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RORE, Inc. 21 should be in conformance with the materials criteria as set forth in Section 26 of the current Caltrans Standard Specifications.

The aggregate base may also…