B08_Attachment_7_Geotechnical_Report.pdf

Prepared for:

Bureau of Land Management

Prepared by:

LBYD Federal, LLC

Geotechnical Report

Salmon Fire Center Site Investigation and Schematic Design Geotechnical Investigation (TO#17)

Salmon, ID

ID/UT IDIQ Contract No. 140L0622D0002

NWI-070117.017-TR-001

Geotechnical Report

Salmon Fire Center Site Investigation and Schematic Design Geotechnical Investigation (TO# 17)

March 15, 2024

Prepared for:

Prepared by:

LBYD Federal, LLC 1425 Higham Street

Idaho Falls, Idaho 83402

Project No. 70117.017

APPROVALS

Project No.: 70117.017

Report Number: 70117.017-TR-001

Report Name: Geotechnical Report

Salmon Fire Center Site Investigation and Schematic Design Geotechnical Investigation (TO# 17)

Date: March 15, 2024

Revision No.: 0

Approval by the responsible manager signifies that the document is complete, all required reviews are complete, and the document is released for use.

Originators:

Emily Evans, P.E. Date Civil/Geotechnical Project Manager

Independent Technical Reviewers:

Ben L. Carter, P.E. Date Principal Civil/Geotechnical Engineer Project Manager:

Ben L. Carter, P.E. Date Principal Civil/Geotechnical Engineer bcarter Idaho emily.evans Snapshot emily.evans Text Box 03/21/2024

CHANGE MANAGEMENT RECORD

Project No.: 70117.017

Report Number: 70117.017-TR-001

Report Name: Geotechnical Report

Salmon Fire Center Site Investigation and Schematic Design Geotechnical Investigation (TO# 17)

Revision No. Date Description of Changes/Affected Pages 0 March 15, 2024 Base Document

Salmon Fire Center v LBYD Federal, LLC Salmon, ID March 2024

CONTENTS

1. INTRODUCTION ........................................................................................................................... 1-1

1.1 Project Description ............................................................................................................. 1-1

1.2 Purpose and Scope .............................................................................................................. 1-1

1.3 Terms and Conditions / Warranties .................................................................................... 1-2

2. GENERAL DATA .......................................................................................................................... 2-1

2.1 Geologic Setting and Stratigraphy ...................................................................................... 2-1

2.2 General Geology ................................................................................................................. 2-1

2.3 Quaternary Fault and Seismic Design Criteria ................................................................... 2-1

2.4 Liquefaction ........................................................................................................................ 2-2

3. SUBSURFACE STRATIGRAPHY AND ENGINEERING LAYERING ..................................... 3-1

3.1 Summary of Field Investigation and Laboratory Testing ................................................... 3-1

3.2 Stratigraphy ........................................................................................................................ 3-1

3.2.1 Soil Survey Review ............................................................................................ 3-2

4. DISCUSSION AND RECOMMENDATIONS .............................................................................. 4-1

4.1 Slab-on-grade Considerations ............................................................................................ 4-1

4.2 Building Foundations ......................................................................................................... 4-1

4.3 Lateral Earth Pressure and Sliding Analyses ...................................................................... 4-2

4.4 Chemical Considerations .................................................................................................... 4-5

4.5 Roadway Design ................................................................................................................. 4-5

4.6 Site Preparation and Excavation Recommendations .......................................................... 4-6

4.6.1 Climate ................................................................................................................ 4-6

4.6.2 Demolition, Clearing and Grubbing ................................................................... 4-7

4.6.3 Excavations and Backfill .................................................................................... 4-7

4.6.4 Grading and Filling ............................................................................................. 4-8

4.6.5 Slope Stability and Erosion ................................................................................. 4-8

4.6.6 Drainage and Storm Water Collection ................................................................ 4-8

4.7 Structural Fill and Aggregate Recommendations ............................................................... 4-8

5. LIMITATIONS ............................................................................................................................... 5-1

Salmon Fire Center vi LBYD Federal, LLC

6. REFERENCES ................................................................................................................................ 6-1

FIGURES

Figure 4-1. Effect of Wall Movement on Wall Pressures (from NAVFAC DM-7.02) ............................. 4-2

TABLES

Table 2-1. ASCE 7 Seismic Design Parameters ........................................................................................ 2-1

Table 3-1. Laboratory Test Results. ........................................................................................................... 3-1

Table 4-1. Static Equivalent Fluid Pressure ............................................................................................... 4-3

Table 4-2. Typical Properties of Compacted Soils (from NAVFAC DM-7.02). ....................................... 4-3

Table 4-3. Ultimate friction factors between interface materials (NAVFAC DM 7.02) ........................... 4-4

Table 4-4. Flexible Pavement Section Design for Light-Duty. ................................................................. 4-5

Table 4-5. Flexible Pavement Section Design for Heavy-Duty ................................................................. 4-5

Table 4-6. Rigid Pavement Section Design for Light-Duty. ...................................................................... 4-6

Table 4-7. Rigid Pavement Section Design for Heavy-Duty. .................................................................... 4-6

Table 4-8 Structural Fill Specifications. .................................................................................................... 4-9

APPENDICES

Appendix A: Project Vicinity Map ........................................................................................................... A-1

Appendix B: Exploration Location Map ................................................................................................... B-1

Appendix C: Exploratory Boring Logs ..................................................................................................... C-1

Appendix D: Geologic Map ...................................................................................................................... D-1

Appendix E: Quaternary Fault Map .......................................................................................................... E-1

Salmon Fire Center vii LBYD Federal, LLC

ACRONYMS

AASHTO American Association of State Highway and Transportation Officials

ACI American Concrete Institute

ASTM American Society for Testing and Materials

BLM Bureau of Land Management

Bgs Below ground surface

CFR Code of Federal Regulations

FS Factors of Safety ft feet

IBC International Building Code

in. inch

MDD maximum dry density

MSL Mean Sea Level

NAVFAC DM Naval Facilities Engineering Command Design Manual

NSHMP National Seismic Hazard Mapping Project

OSHA Occupational Safety and Health Administration pcf pounds per cubic foot psf pounds per square foot

PI plasticity index

USCS United Soil Classification System

USDA United States Department of Agriculture

USGS United States Geological Survey

UW Unit Weight

Salmon Fire Center 1-1 LBYD Federal, LLC

1. INTRODUCTION

This report presents the findings, conclusions, and recommendations of a geotechnical investigation and analysis for the proposed Bureau of Land Management (BLM) Salmon Fire Center facility to be constructed Salmon campus in Salmon, ID. The findings, conclusions, and recommendations of this geotechnical report are based on surface and subsurface conditions encountered at the time of the field exploration. This also includes the project details presented to this office under the ID/UT IDIQ Contract No. 140L0622D0002, TO# 017. The objective of this investigation was to determine general soil conditions for use by the engineer and determine the preferred site layout and design of the proposed site improvements. The study was conducted in accordance with generally accepted geotechnical engineering practices. This report presents the results of this study.

1.1 Project Description

The project site is located just north of the existing buildings as shown in Plate A-1 Project Vicinity Map in Appendix A. The general topography across the site varies with a general downslope towards the northwest.

The western side of the facility will abut S. Challis Street, while the northern side will abut Cemetery Street.

The elevations vary slightly across the Subject property from approximately 3963 feet MSL to 3960 feet MSL. The existing surface conditions consists of gravel roads, fencing, trailers and containers, and undeveloped land. The trailers and containers are located within the site’s footprint along with some abandoned utilities.

The new site improvements in consideration consist primarily of the construction of one (1) ~12,595 square foot Fire Station and Cache building, one (1) 3,726 square foot 10-person Crew Quarters and site layout improvements including site access, grading, roadways, parking, storm water drainage, utilities, and security. The conceptual layout plan can be found in Plate A-2 Site Conceptual Layout. Site utilities including power, water, sanitary sewer, gas, and communications are anticipated to be extended to the facility from onsite utility infrastructure.

1.2 Purpose and Scope

The purpose of this investigation was to explore and evaluate the subsurface conditions at the project site, and to provide geotechnical engineering recommendations based upon our findings. Understanding of the project is based on a Scope of Work provided by BLM and a site visit performed on October 27, 2023.

The scope of this investigation included surface reconnaissance, subsurface exploration, analysis of field and laboratory data, research of pertinent geologic literature, and report preparation. This report provides conclusions and recommendations concerning the following:

• General subsurface site conditions and geology

• Seismic conditions

• Groundwater conditions

• Clearing and grubbing

• Site preparation and earthwork grading

• Subgrade preparation for slab-on-grade concrete

• Subgrade preparation for building foundations

• Site roadway/pavement design

• Lateral earth pressures and drainage recommendations for retaining structures

• Construction considerations including:

o Climate

Salmon Fire Center 1-2 LBYD Federal, LLC o Excavation and backfill o Slope stability and erosion protection o Drainage and storm water collection.

1.3 Terms and Conditions / Warranties

Geotechnical reports are written to provide test results, observations, and professional opinions regarding a specific site for a specific project. This report was prepared for the BLM. The contents of this report may not be relied upon by any other party without the expressed written permission of LBYD Federal and the written permission of the BLM. The report presents site conditions at the time of the investigation and for the aforementioned proposed development.

Each geotechnical report considers only the site boundaries and construction information presented at the time of the investigation. This geotechnical report cannot be used for an adjacent lot and modifications of construction plans (i.e. size, shape, location, weight, intended use). Doing so, nullifies the conclusions and recommendations contained in this report, unless indicated otherwise by the geotechnical engineer.

The site conditions which existed at the time of the geotechnical investigation can change. Conditions can only be reported at a particular time and place and no guarantee exists to ensure that recommendations will apply after natural or man-made changes occur. Examples of some possible changes include: floods, earthquakes, fluctuation of groundwater, construction activities on or next to site, demolition of existing structures, and the addition or removal of soil. The report should be updated prior to construction if a minimum of one year has elapsed from the issued date.

Our professional services were performed, our findings obtained, and our recommendations proposed in accordance with generally accepted engineering principles and practices. This warranty is in lieu of all other warranties either expressed or implied. Test findings and statements of professional opinion do not constitute a guarantee or warranty, expressed or implied.

Salmon Fire Center 2-1 LBYD Federal, LLC

2. GENERAL DATA

2.1 Geologic Setting and Stratigraphy

The site is located to the north of the USDA Forest Department building and BLM fire station and warehouse. The elevation varies slightly across the site with a mean elevation of 3962 feet MSL. The site is located south of Salmon, Idaho, to the south of Cemetery Street and the east of S. Challis Street. The terrace gravels upon which the site lies are composed of gravels from the ancestral Salmon River deposits.

2.2 General Geology

The existing surface conditions consists of existing vegetation, and gravel/soil roads. The Idaho Geological Survey (IGS) Maps indicates that this area is composed of gravel and fine-grained Holocene to Late Pleistocene sediments. The soils encountered, within the explored depth and locations, were consistent with this description. A geologic map showing the unit description can be seen in Plate D-1 Geologic Map in Appendix D.

2.3 Quaternary Fault and Seismic Design Criteria

According to the United States Geological Survey several active and inactive faults have been identified at various distances from the site. The closest group of faults is located less than 20 miles southeast, the Beaverhead fault system as shown on Quaternary Fault Map in Appendix E. Based upon the soil properties, site soils would be classified as Site Class C in accordance with Chapter 16 of the 2021 edition of the International Building Code (IBC). Seismic Design Parameters are shown in Table 2-1 for project site coordinates latitude: 45.163451 longitude: -113.892461 from the American Society of Civil Engineers (ASCE) ASCE 7 Hazards Tool (ASCE, online hazards tool). The report provides the short and one second period responses for the project site. The annual exceedance frequency was taken to be 2% in 50 years. All other seismic design parameters were developed from the 2016 IBC and were summarized in Table 2-1, which may be used for design purposes.

Table 2-1. ASCE 7 Seismic Design Parameters

ASCE 7 SEISMIC DESIGN PARAMETERS

Mapped spectral acceleration for short periods SS 0.484g

Mapped spectral acceleration for 1-second periods [from ASCE 7] S1 0.159g

Site coefficient Fa 1.3

Site coefficient Fv 1.5

Max considered earthquake spectral response acceleration for short periods SMS=FaSS 0.629g

Max considered earthquake spectral response acceleration for 1-second periods SM1=FvS1 0.238g

5% damped design spectral response acceleration at short periods SDS=2/3 SMS 0.419g

5% damped design spectral response acceleration at 1-second periods SD1=2/3 SM1 0.159g

Peak Ground Acceleration (%g) PGA 0.212g

Modified Peak Ground Acceleration (%g) PGAM 0.254g

Salmon Fire Center 2-2 LBYD Federal, LLC

2.4 Liquefaction

Research and historical data indicate that soil liquefaction generally occurs in saturated, relatively loose granular soil (primarily fine to medium-grained, clean sand deposits) during or after strong seismic ground shaking and is typified by a loss of shear strength in the affected soil layer, thereby causing the soil to behave as a liquid. The encountered fine-grained soils and clayey coarse-grained soils during the field exploration indicate the potential for liquefaction to be low.

Salmon Fire Center 3-1 LBYD Federal, LLC

3. SUBSURFACE STRATIGRAPHY AND ENGINEERING LAYERING

3.1 Summary of Field Investigation and Laboratory Testing

To characterize the subsurface conditions beneath the proposed improvement areas, a field exploration program was conducted on October 27, 2023. This field exploration consisted of twelve (12) exploratory borings down to a maximum depth of 21.5 feet below ground surface (bgs). The borings were completed with a truck-mounted drill rig and backfilled with bentonite chips and soil cuttings upon completion. The borings were completed using traditional hollow stem auger to maximum explored depth. Locations of the borings were determined to the nearest foot and are shown on Plate B-1 Exploration Location Map in Appendix B.

A LBYD Federal representative visually classified the materials encountered in the borings and maintained a log according to the Unified Soil Classification System (USCS). Representative bulk soil samples were obtained and preserved in plastic sample bags for possible laboratory testing.

Laboratory tests were performed on selected samples from the twelve (12) borings to determine some of the physical and engineering properties of the subsurface soils. The results of the laboratory testing are summarized in Table 3-1 Laboratory Test Results and on the boring logs included in Appendix C. All laboratory testing was conducted in accordance with generally accepted industry standards and appropriate American Society for Testing and Materials (ASTM) standards. The following soil tests were performed for this study:

Moisture Content (ASTM D2216) –Moisture tests were conducted on selected samples to measure the in-place moisture content of the subsurface materials. These properties provide information for evaluating the physical characteristics of the subsurface soils. Test results are shown on the borings logs in Appendix C.

Particle Size Analysis (Wet and Dry Sieve) and Fines Content (ASTM D422 and D1140) - Sieve analysis or fines content (minus No. 200 sieve) tests were conducted on selected samples to determine the soil particle size distribution. This information is useful for characterizing the soil type according to USCS and evaluate potential hazards. Test results are presented in Table 3-1 Laboratory Test Results and on the borings logs in Appendix C.

Table 3-1. Laboratory Test Results.

Boring

No.

Depth

(ft) USCS Soil

Type Grain Size Distribution Atterberg Limits

% Gravel % Sand % Fines LL PI

B-2 2-4’ SC 0 52.3 47.7 45 23

B-6 1-2.5’ CL 13 30.7 56.3 44 26

B-9 1.5-2’ SC 30 34.7 35.3 40 25

3.2 Stratigraphy

During our subsurface exploration program, we investigated the subsurface soils and evaluated soils conditions to maximum depths of about 21.5 feet bgs in 12 exploratory borings. From our collected data, we concluded that where explored, the soils consist predominantly of approximately 0 to 4+ feet of Sandy Clay with gravel underlain by Sandy Gravel layer to depths explored. A detailed description of the lithology across the site is shown on the Exploratory Boring Logs in Appendix C.

Salmon Fire Center 3-2 LBYD Federal, LLC

Groundwater was encountered during our field exploration and was found to be between 1.6 to 4.8 feet below ground surface. Groundwater levels could change due to rainfall, snowmelt, irrigation, construction activities, or other factors. The evaluation of these factors would require long term monitoring and is beyond the scope of this study. The design engineer should take this into consideration if grading encroaches into groundwater depths. The contractor should also be prepared for dewatering of trenches and excavations as needed.

3.2.1 Soil Survey Review

A review of the United States Department of Agriculture (USDA) Natural Resource Conservation Service Soil Survey indicates the soils for the site to be primarily composed of Wimpey-Zeph-Ajax complex with 0 to 2 percent slopes and a minor area of the site is composed of Zeegee-Ajax complex with 0 to 2 percent slopes.

The findings from the exploratory program activities were consistent with the soil type determined by the Soil Survey.

Salmon Fire Center 4-1 LBYD Federal, LLC

4. DISCUSSION AND RECOMMENDATIONS

From a geotechnical engineering standpoint, it is the engineer’s opinion that the site is suitable for construction of the proposed site improvements, provided all the conclusions and recommendations presented in this report are incorporated into the design and construction. The following sections present the conclusions and recommendations based on this study. Due to the variation in topography across the site, it should be noted that the recommendations apply to the areas explored. Conditions may differ at areas not explored at the time of construction; therefore, LBYD Federal should be retained to provide additional guidance should it be necessary.

4.1 Slab-on-grade Considerations

Non-structural concrete interior slab-on-grade floors should be a minimum of four inches in thickness. Slab thickness and structural-reinforcing requirements within the slab should be determined by the design engineer. In order to control normal shrinkage and stress cracking in slabs, adequate reinforcement should be used together with sufficient control joints. Exterior finish grades should be at or below the floor subgrade level unless special drainage and waterproofing features are employed to reduce the potential for moisture migration under the slab. Due to the bearing soils susceptibility to movements from frost heave, the design of all slabs-on-grade should account for such potential movements.

Concrete flatwork should consist of at least 4 inches of properly compacted, free-draining granular fill beneath concrete slabs to provide uniform support and promote uniform curing during construction. Should fine-grained high plasticity soils be encountered during construction of the building pad, select engineering fill may be used to limit the movement from the expansive soils. A minimum of 6 inches of structural fill may be placed and properly compacted as outlined in Section 5.6. Prior to placing granular or structural fill, the exposed ground surface should be scarified (a minimum of 6 inches), moisture-conditioned, properly placed. and compacted to a minimum of 90 percent of the maximum dry density as per ASTM D1557. Refer to Table 4-6 for acceptable aggregate.

4.2 Building Foundations

The proposed structures can be supported on conventional continuous and isolated spread footings bearing on non-plastic native soil. Footings should be founded a minimum of 36 inches below lowest adjacent finished grade (exterior grade or building pad subgrade elevation, as applicable) for frost protection.

The selection of each system should be determined by the government with the guidance of the Geotechnical Engineer of Record (GEOR). For the design of footings bearing on approved undisturbed granular native soil, we recommend a net allowable bearing pressure of 2,500 psf if a minimum of 1 foot of properly compacted structural fill is used to reach final footing elevations. The bearing pressure is a net value, as the weight of the footing itself has already been accounted for and can be neglected as a load for design purposes. Furthermore, slab thickness and structural-reinforcing requirements within the footing should be determined by the design engineer.

Foundation elements can resist lateral loads with a combination of bottom friction and passive resistance.

An allowable coefficient of friction of 0.30 for undisturbed native silty sand, 0.40 for granular structural fill, or 0.70 for suitable bedrock between the base of the foundation elements and underlying material is recommended.

Salmon Fire Center 4-2 LBYD Federal, LLC

4.3 Lateral Earth Pressure and Sliding Analyses

Recommended lateral earth pressures are required for design of retaining structures including abutments, wing walls, and retaining walls. For this project, these pressures are estimated by applying recommended pressure coefficients to the estimated moist unit weight of proposed fill material to calculate an equivalent fluid pressure. If, during backfill operations, the top of the soil-retaining structure is restrained against lateral deflection, the at-rest equivalent fluid pressure should be used for design. If the top is allowed to deflect away from the soil mass, the active equivalent fluid pressure may be used for design. While, if the top deflects into the soil mass or if soils are used for passive resistance, the passive equivalent fluid pressure may be used for design. The deflections that would typically generate the active and passive pressures are less than 0.5 inches for active pressures and 1.5 inches for passive pressures. These deflections are calculated based on the NAVFAC DM-7.2 found on page DM-7.2-60, presented in Figure 4-1 below.

Figure 4-1. Effect of Wall Movement on Wall Pressures (from NAVFAC DM-7.02)

The coefficients and static lateral earth pressures recommended for design are listed in Table 4-1 for the general soil type identified on site, CL and SC-SM. These values are based on the correlated soil friction angles and bulk unit weights of typical compacted soils found in NAVFAC DM-7.02, Table 1, Page 7.2- 39, presented in this report as Table 4-1 Static Equivalent Fluid Pressures.

Salmon Fire Center 4-3 LBYD Federal, LLC

Table 4-1. Static Equivalent Fluid Pressure Soil Type and Characteristics

Lateral Earth Pressure Case and Coefficient Equivalent Fluid Pressure

CL

φ‘ = 20o MDD= 110 pcf

At-rest case, Ko = 0.66 72 pcf (unsaturated)

Active case, Ka = 0.49 54 pcf (unsaturated)

Passive case, Kp = 2.04 224 pcf (unsaturated)

SC

φ‘ = 30o MDD= 120 pcf

At-rest case, Ko = 0.50 60 pcf (unsaturated)

Active case, Ka = 0.33 40 pcf (unsaturated)

Passive case, Kp = 3.00 360 pcf (unsaturated)

Table 4-2. Typical Properties of Compacted Soils (from NAVFAC DM-7.02).

Group Symbol Soil Type

R an ge o f M ax im um

D ry

U ni t W ei gh t, pc f

R an ge o f O pt im um

M oi st ur e, P er ce nt

Typical Values of

Compressio n

Typical Strength Characteristics

T yp ic al

C oe ff ic ie nt o f

Pe rm ea bi lit y, ft ./m in

R an ge o f C B

R V al ue s

R an ge o f S ub gr ad e M od ul us k

, l bs

/c u in

At 1.4 Tsf (20 psi)

At 3.6 Tsf (50 psi)

Cohesion (as compacted ) psf

Cohesion (saturate

d) psf β (E ff ec tiv e

St re ss

E nv el op e D eg re es

Tan φ

GW

Well graded clean gravels, gavel-sand mixtures.

125-135 11-8 0.3 0.6 0 0 >38 >0.79 5x10-2 40-80

GP

Poorly graded clean gravels, gravel-sand mix 115-125 14-11 0.4 0.9 0 0 >37 >0.74 10-1 30-60

GM

Silty gravels, poorly graded gravel-sand-silt.

120-135 12-8 0.5 1.1 *** *** >34 >0.67 >10-6 20-60

GC

Clayey gravels, poorly graded gravel-sand-clay.

115-130 14-9 0.7 1.6 *** *** >31 >0.60 >10-7 20-40

SW

Well graded clean sands, gravelly sands.

110-130 16-9 0.6 1.2 0 0 38 0.79 >10-3 20-40

SP

Poorly graded clean sands, sand-gravel mix.

100-120 21-12 0.8 1.4 0 0 37 0.74 >10-3 10-40

SM

Silty sands, poorly graded sand-silt mix.

110-125 16-11 0.8 1.6 1050 420 34 0.67 5x >10-5 10-40

SM-SC

Sand-silt clay mix with slightly plastic fines.

110-130 15-11 0.8 1.4 1050 300 33 0.66 2x >10-6 5-30

SC

Clayey sands, poorly graded sand-clay-mix.

105-125 19-11 1.1 2.2 1550 230 31 0.6 5x >10-7 5-20

ML Inorganic silts and clayey silts. 95-120 24-12 0.9 1.7 1400 190 32 0.62 >10-5 15 or less

ML-CL

Mixtures of inorganic silt and clay.

100-120 22-12 1 2.2 1350 460 32 0.62 5x >10-7 ***** ***

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CL

Inorganic clays of low to medium plasticity.

95-120 24-12 1.3 2.5 1800 270 28 0.54 >10-7 15 or less

50-

OL

Organic silts and silt-clays, low plasticity.

80-100 33-21 ****

* **** **** **** **** **** 5 or less 50-

MH Inorganic clayey silts, elastic silts. 70-95 40-24 2 3.8 1500 420 25 0.47 5x >10-7 10 or less 50-

CH Inorganic clays of high plasticity. 75-105 36-19 2.6 3.9 2150 230 19 0.35 >10-7 15 or less 50-

OH Organic clays and silty clays. 65-100 45-21 ****

* **** **** **** **** **** 5 or less

25-

Notes:

1. All properties are for condition of "Standard Proctor" maximum density, except values of k and CBR which are for "Modified Proctor" maximum density.

3. Compression values are for vertical loading with complete lateral confinement.

2. Typical Strength characteristics are for effective strength envelopes and are obtained from USBR data.

4. (>) indicates that typical property is greater than the value shown. (**) indicates insufficient data available for an estimate.

The equivalent fluid pressures were calculated using the Rankine theory to determine the friction angle for onsite soils to be used as backfill. This method assumes a vertical wall, the surfaces are straight planes and the resultant force on the wall act parallel to the backfill slope. The backfill soils may vary during design and therefore, the final lateral earth pressure should be evaluated to determine the appropriate friction angle.

Furthermore, retaining walls should be designed to prevent hydrostatic pressure by including weeping holes, or other methods to prevent the accumulation of water behind the wall.

In addition to the lateral earth pressures found in Table 4-2 Typical Properties of Compacted Soils, lateral surcharge loads from heavy equipment or storage materials should be considered for design of retaining structures. Lateral surcharge loads are in addition to the above coefficients. A lateral surcharge pressure coefficient of 0.45 acting uniformly over the entire below-grade soil-retaining structure should be used to estimate surcharge loads from heavy equipment operation and storage materials.

For sliding stability analyses, the frictional resistance of concrete footings or foundations placed against soils shall be calculated as µR, where R is the applied normal force delivered to the foundation soil/rock concurrent with the sliding force, and where µ, the coefficient of friction between concrete foundation and the foundation material is determined from Table 4-3.

Table 4-3. Ultimate friction factors between interface materials (NAVFAC DM 7.02)

Foundation Material Friction Factor, μ Clean sound rock 0.7 Clean gravel, gravel-sand mixtures, and coarse sand. 0.55 to 0.60 Clean fine to medium sand, silty medium to coarse sand and silty or clayey gravel. 0.45 to 0.55 Clean fine sand and silty or clayey fine to medium sand. 0.35 to 0.45 Fine sandy silt and non-plastic silt. 0.30 to 0.35 Very stiff and hard residual or pre-consolidated clay. 0.40 to 0.50 Medium stiff, stiff clay, and silty clay. 0.30 to 0.35

R = the applied normal force delivered to the foundation soil/rock concurrent with the sliding force

This frictional resistance, when combined with any reliable passive resistance due to shear keys or soil embedment, shall be sufficient to resist the total lateral design forces with a minimum FS of 1.5.

Salmon Fire Center 4-5 LBYD Federal, LLC

4.4 Chemical Considerations

Concrete durability requirements include exposure to naturally occurring chemicals in the soils. These chemical exposures include sulfates and chlorides. The geotechnical investigation on the project site did not include testing for chemical exposure. However, the USGS Soil Survey documented a corrosion rating of concrete and steel to be primarily low.

The reactivity of cement to sulfate and chloride concentrations in soils is an important factor for determining cement type. Based on ACI 318 Chapter 4, “Durability Requirements,” the sulfate and chloride values reported at the Subject Property from the soil survey are moderate. It is recommended to use ASTM C 150 Type I or II cement unless further documentation or testing indicates otherwise. Uncoated reinforcing steel or building steel should not be placed in direct contact with soil without having a protective coating.

4.5 Roadway Design

The parameters and assumptions used in the analysis of the proposed access roads and parking areas at the Subject Property are summarized below. The analyses for the roadway design were performed using the American Association of State Highway and Transportation Officials (AASHTO) pavement thickness design procedures.

For purposes of this report, a California Bearing Ratio (CBR) was assumed, for design of the pavement structure. This CBR was taken to be 6 for the soils classified as Clayey Sand soils encountered within the maximum explored depths of 21.5 feet bgs. Traffic flows for the proposed pavement areas were also assumed using conservative values. These values as well as a 25-year design life and 50% reliability, were used in determining a minimum required structural number. A flexible pavement section of asphalt concrete underlain by aggregate base is proposed for the connecting roads to and from each proposed building and parking lot areas. Two separate asphalt concrete pavement designs are proposed: light duty (parking lot) and heavy duty (connecting roads and parking for heavy loads). The asphalt concrete pavement section design was determined using AASHTO design procedures (GDPS 1993) and can be found in Table 4-4, Table 4-5 for light and heavy-duty asphalt concrete pavement. A rigid Portland cement concrete paving section with aggregate base course is given in Table 4-6, Table 4-7 for rigid pavement sections. The rigid concrete paving section is recommended in areas where large trucks, trailers, and heavy vehicle traffic will be maneuvering or parking.

Table 4-4. Flexible Pavement Section Design.

Traffic Min Subgrade CBR Asphalt Concrete

(in.)

Aggregate Base

(in)

Access Road/Maneuvering Areas 2 4 9

Table 4-5. Flexible Pavement Section Design for Heavy-Duty

Traffic Min Subgrade CBR Asphalt Concrete

(in.)

Aggregate Base

(in)

Ramp/Maneuvering Areas 6 5 16

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Table 4-6. Rigid Pavement Section Design for Light-Duty.

Traffic Min Subgrade CBR Concrete

(in.)

Aggregate Base

(in)

Access Road/Maneuvering Areas 2 6 6

Table 4-7. Rigid Pavement Section Design for Heavy-Duty.

Traffic Min Subgrade CBR Concrete

(in.)

Aggregate Base

(in)

Access Road/Maneuvering Areas 8 8 12

All subgrade, aggregate base, asphalt, and concrete materials shall conform to local and state requirements regarding gradation, oil content, and general mix design, placement and testing procedures. The pavement area subgrade shall be stripped of all organic materials, loose soils, etc., and any required cuts and fills required. A minimum of 12 inches of approved subgrade shall be scarified and compacted beneath the pavement sections. The subgrade shall be field verified to be native non-plastic soil, moisture conditioned and compacted to dry densities of greater than or equal to 95% of the maximum dry density per ASTM D 1557 test method.

Studies have indicated that a major factor in extending pavement life is to provide adequate drainage for both the pavement surface and subgrade. Care should be taken during the development of the grading plan to provide for good drainage. Landscaped and irrigated planters that are constructed adjacent to pavement shall have cut-off curbing constructed around them that extends a minimum of 4 inches into the subgrade soils. Similarly, where gravel area will infiltrate storm water into improved asphalt or concrete sections, it is recommended to have cut-off curbing constructed between the transition and extend a minimum of 4 inches into the subgrade soils. Thus, controlling storm water infiltration and extending the life and performance of the improved section.

Gravel parking lots may consider the use of geogrids to increase stability and decrease the thickness gravel where feasible. Permeable pavers may also be considered to increase the drainage ability of the upper layer in addition to increasing the stability of the pavement. The GEOR should be consulted if these alternatives are being considered for this project.

4.6 Site Preparation and Excavation Recommendations

4.6.1 Climate

If construction is to be conducted during the dry seasonal conditions, many problems related to soft soils may be avoided. However, lack of moisture during the dry season may cause problems with compaction of moisture sensitive soils and exposed soils. Low cohesion soils (i.e. gravels, sands, and silts) exposed in excavations may become dry, increasing the chances of sloughing or caving. Measures for these, as well as excess dust, should be considered as part of the overall health and safety management plan.

Wet weather conditions present problems with soft/wet soils and must be considered as part of the construction plan. During cooler and wetter times of year, fine-grained soils such as silts become unstable with increased moisture content. Also, vehicle traffic loading, especially heavy trucks, and construction equipment, will highlight poor soil conditions. Care shall be taken to minimize unnecessary vehicle traffic, especially during or after soils are wet or become saturated.

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Prior to placement of structural fill materials or concrete, frozen soils must either be allowed to thaw or be removed to depths of non-frozen soils. Frozen soils shall not be placed as structural fill until allowed to thaw and return to optimal moisture conditions.

4.6.2 Demolition, Clearing and Grubbing

The site should be cleared of any old pavement, debris, vegetation and organics, trees, brush, roots, irrigation lines, near surface debris, undocumented fills or disturbed soils, and other deleterious materials within the proposed development area. Removed fill soil and processed pavement material may be evaluated by the Geotechnical Engineer for possible reuse and placement as engineered fill. Undocumented fill and underlying native loose soils should be removed to native undisturbed soils. Other clean topsoil and disturbed soils can be stockpiled and placed as a final lift in landscaped areas only.

The grading contractor should be aware of any possible buried objects and underground utilities at the site which are to be removed or abandoned appropriately. Holes resulting from the removal of underground obstructions extending below the proposed finish grade should be cleared and backfilled with properly compacted engineered fill or other material approved by the Geotechnical Engineer. We recommend backfilling operations for any excavations to remove deleterious material be carried out under the observation of the Geotechnical Engineer.

Existing underground utilities, if present, may impact the project construction. Any such utilities will need to be protected during construction, avoided, properly abandoned and/or entirely removed from proposed building areas. In general, utility pipelines less than four inches in diameter to be abandoned may be left in place provided they will not be in close proximity to new foundation elements or interfere with new utilities.

Such pipes should be plugged at the ends with concrete or sand-cement slurry.

4.6.3 Excavations and Backfill

The existing site soils consisting of Sandy Clay (CL) and Clayey Sands (SC) can be excavated using conventional excavation equipment. These soils should be excavated as needed but should extend a minimum of 3 ft beyond the footprint, for over excavations and large cuts. Bedrock or coarse cobbles were found during the field exploration and are anticipated to be encountered in other areas not explored across the site area. The removal of bedrock or boulders required will vary across the site and should be determined by the project engineer for each proposed development areas.

Temporary shallow excavations that do not exceed 4 ft in depth may be constructed with side slopes approaching vertical, provided that proper moisture conditions are maintained. Below this depth or if trenches are allowed to dry out, the excavations may become unstable. Therefore, it is recommended that slopes be constructed in accordance with Occupational Safety and Health Administration (OSHA) regulations (29 Code of Federal Regulations [CFR], Section 1926, Subpart P). Based on these regulations, most of the onsite soils are classified as “Type C” soils and as such, excavations up to 20 ft in depth shall have a maximum slope of 1.5 foot horizontal to 1 foot vertical (1.5H:1V).

Flatter slopes and/or shoring might be required if loose, cohesionless soils are encountered along the slope face. Sloughing of granular soils could occur if soils are allowed to dry or are wetted during rain/snow periods. Sloping and benching for excavations greater than 20 ft deep shall be designed by a registered professional engineer.

Heavy construction equipment, building materials, excavated soils and vehicular traffic should not be allowed within 1/3 of the slope height from the top of any excavation without special consideration. In addition to heavy loads on slopes, other geological hazardous features should be evaluated. Some of these

Salmon Fire Center 4-8 LBYD Federal, LLC hazards include discontinuities in soil layers and collapsible clays. Collapsible clays are often found in loess materials and should be evaluated for stability and maintained with good drainage. During wet weather, earthen berms or other methods should be used to prevent runoff from entering excavations.

Backfill in the pipe zone (material within 6 in. below and 12 in. above the pipe) of underground utilities shall, as a minimum, consist of clean, granular materials free of clay and organic material, with 100% passing a 1-in. sieve and not more than 8% fines (passing a No. 200 sieve). See Table 4-6 for structural fill and trench fill material criteria. Trench zone backfill (material from pipe zone to subgrade) shall consist of structural fill materials placed in the structural areas (i.e., under foundation, roadways, paved areas, and other slabs) and native soils in non-structural areas. Soils used for backfilling should be uniformly moisture conditioned, placed, and compacted per the structural fill section criteria. Jetting and flooding shall not be permitted for compaction of backfill. Poor compaction in utility trench backfill may cause excess settlements or unstable soils, resulting in damage to overlying structures, pavements, and slabs.

4.6.4 Grading and Filling

After clearing and grubbing operations and any excavation cuts have been completed the subgrade soils shall be scarified a minimum of 12 in., moisture conditioned, and compacted to dry densities of 95% of the maximum dry densities obtained by the Standard Test Methods for Laboratory Compaction Characteristics of Soil, using the Standard Effort per ASTM D 698. The soil should be moisture conditioned to within 2% (plus or minus) of the optimum moisture content obtained in the same test. Structural fill placed on the pads and in pavement areas should be non-expansive and placed following ASTM D1557. Other areas such as landscape or non-structural section can follow ASTM D698 using onsite materials where applicable.

4.6.5 Slope Stability and Erosion

Stability of permanent cut and fill slopes is dependent upon shear strength, unit weight and moisture content of soils, and slope angle. Cut and fill slopes at the Site should be stable at inclinations of up to 1.5 horizontal to 1 vertical. However, it is recommended that a 3 horizontal to 1 vertical slope be used for all final site slopes. It is recommended that permanent slopes be flatter whenever feasible. Slope performance will be primarily affected by surface runoff. Therefore, it is recommended that drainage be directed to flow away from slope faces by interceptor ditches or other means. Slope faces should further be protected from direct rain impact and melting snow by permanent erosion control measures, such as riprap, geosynthetics, and/or vegetation.

4.6.6 Drainage and Storm Water Collection

Special care should be taken to ensure adequate drainage is provided throughout the life of the improvements. Final elevations at the site should be planned so that drainage is diverted away from all foundations and roadway/pavement sections. Drainage grading should be sloped and maintained to carry surface water away from bearing soils and off the site. Earthen and exposed exterior subgrade soils should slope away from the structure a minimum of 5 percent for a distance of 10 feet beyond the perimeter, to the maximum extent feasible. Impervious site improvements shall slope away a minimum of 1 percent or more, to the maximum extent feasible. Storm water collection facilities may be constructed and should be routed away from all bearing soils and subsurface septic systems.

4.7 Structural Fill and Aggregate Recommendations

Granular structural fill will be required beneath any over excavated shallow foundations including improved concrete and asphalt sections and areas adjacent to retaining wall structures. The onsite surface soils encountered during the field exploration are not suitable to be used as structural fill. If granular materials

Salmon Fire Center 4-9 LBYD Federal, LLC are found on the site, laboratory testing for these soils should be performed to confirm that they are within the granular structural fill specifications established in this Section. Onsite native soils classified as Sandy Clay can be used as general fill for landscape areas or general site grading. All imported fill should be reviewed and approved by the Geotechnical Engineer prior to placement. See Section 3 for additional information on subsurface soil strata and characteristics. All structural fill shall meet the specifications outlined in Table 4-8 Structural Fill Specifications.

Table 4-8 Structural Fill Specifications.

Structural Fill Product

Allowable Use Material Specifications

Sieve Size

Passing

Granular Structural Fill Foundation, heavily loaded floor over-excavation Wall backfill

Soil classified as GP, GP-GM, GW, SP, SP-SM according to the United Soil Classification System (USCS), and meeting the gradation provided.

Soil consisting of inert earth materials with <3% organics or other deleterious substances (wood, metal, plastic, waste, etc.)

4 in. 100

3 in. 90-100

No. 4 30-60

No. 200 <10

Utility Trench Bedding Soil may not contain particles larger than 1 in. in median diameter and must meet the required gradation with a maximum PI of 6.

1 in. 100

No. 10 0-50

No. 40 0-30

No. 200 0-15

Aggregate Base Course Over-excavations Foundation and slab support General structural fill

Soil may not contain particles larger than 1 in.

in median diameter and must meet the required gradation

1 in. 100

¾ in. 90-100

No. 4 40-65

No. 8 30-50

No. 200 3-9

General Structural Fill Lightly loaded floor slab and pavement

Soil classified as SM, GM or granular structural fill according to the USCS and meeting the gradation.

Soil consisting of inert earth materials with <3% organics or other deleterious substances (wood, metal, plastic, waste, etc.)

3 in. 100

No. 200 <50

General Fill General site grading

Soils classified as SP, SM, ML, CL with a liquid limit < 40% and a plasticity index < 22. Soil consisting of inert earth materials with <3% organics or other deleterious substances (wood, metal, plastic, waste, etc.).

3 in. 100

All fill materials shall be placed in maximum 8-in. thick loose material lifts. Each lift shall be moisture conditioned to near optimum moisture content and compacted to a minimum of 95% of ASTM D 698 Standard Proctor. The maximum loose-lift thickness is based on using large, 5-ton, smooth-drum vibratory rollers and should be reduced when smaller or lighter compaction equipment is used.

Granular structural fill material with significant gravel content (>30% retained on the ¾” sieve) may be used as granular structural fill material if it meets the above criteria but cannot be tested for density.

Compaction method with these characteristics shall be determined by the contractor. The Geotechnical Engineer shall approve all compaction methods and will be retained to monitor compaction efforts during construction.

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5. LIMITATIONS

The recommendations of this report are based on field explorations, laboratory tests, and the engineer’s understanding of the proposed construction. If the proposed construction is modified or re-sited, or if subsurface conditions are found to differ from those found in this report, the conclusions and recommendations of this report shall be considered invalid, unless changes and/or conditions are reviewed and modified or approved in writing.

The conclusions and recommendations of this report are based on the site conditions as they existed at the time of the field exploration. It is assumed that the subsurface soils encountered in the bore holes are representative of the subsurface conditions throughout the site.

The engineer’s professional services were performed, findings obtained, and recommendations proposed in accordance with generally accepted engineering principles and practices. This warranty is in lieu of all other warranties either expressed or implied. Test findings and statements of professional opinion do not constitute a guarantee or warranty, expressed or implied.

The scope of services did not include any environmental assessment or investigation for presence or absence of wetlands, hazardous or toxic materials in the soils, surface water, groundwater or air, on or below or around this site. The use of information contained in this report for bidding purposes shall be at the contractor’s option and risk.

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6. REFERENCES

29 CFR 1926, Subpart P, 2002, Title 29, “Labor,” Part 1926, “Safety and Health Regulations for Construction,” Subpart P, “Excavations,” Code of Federal…