B08_Attachment_4_Geotech_Report.pdf

Prepared for:

Bureau of Land Management

Prepared by:

North Wind Infrastructure & Technology, LLC

October 26, 2017

Geotechnical Report

Shoshone BLM Field Office Replacement (DO #30)

Shoshone, ID

ID/UT IDIQ Contract No. L14PC00105

NWI-070048.030-TR-001

Geotechnical Report

Shoshone BLM Field Office Replacement (DO #30)

May 25, 2021

Prepared for:

Bureau of Land Management Twin Falls District

Prepared by:

North Wind Infrastructure & Technology, LLC

1425 Higham Street Idaho Falls, Idaho 83402

Project No. 70048.030

CHANGE MANAGEMENT RECORD

Project No.: 70048.030

Report Number: 70048.030-TR-001

Report Name: Geotechnical Report

Shoshone BLM Field Office Replacement

(DO #30)

Bureau of Land Management Twin Falls District

Revision No. Date Description of Changes/Affected Pages 0 May 25, 2021 Base Document

Geotechnical Report for 070048.030 5 North Wind Infrastructure & Technology, LLC Shoshone, ID May 2021

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 ........................................................................................................................ 2-1

3. SUBSURFACE STRATIGRAPHY AND ENGINEERING LAYERING ..................................... 3-2

3.1 Summary of Field Investigation and Laboratory Testing ................................................... 3-2

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

3.2.1 Soil Survey Review ............................................................................................ 3-1

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

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

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

4.2.1 Bedrock ............................................................................................................... 4-2

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 ............................................................... 4-9

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

Geotechnical Report for 070048.030 6 North Wind Infrastructure & Technology, LLC

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

FIGURES

Figure 4-1. Effect of Wall Movement on Wall Pressures (from NAVFAC DM7.02) ............................... 4-3

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 .................................................................................... 4-4

Table 4-3. Light-Duty Flexible Pavement Section Design. ....................................................................... 4-6

Table 4-4. Heavy-Duty Flexible Pavement Section Design. ..................................................................... 4-6

Table 4-5. Rigid Pavement Section Design. .............................................................................................. 4-6

Table 4-6 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

Geotechnical Report for 070048.030 7 North Wind Infrastructure & Technology, 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

NWIT North Wind Infrastructure & Technology, LLC

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

PI plasticity index

SF square feet

USCS United Soil Classification System

USDA United States Department of Agriculture

USGS United States Geological Survey

UW Unit Weight

Geotechnical Report for 070048.030 1-1 North Wind Infrastructure & Technology, 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) Field Office Replacement located in Shoshone, 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. L14PC00105, DO #030. The objective of this investigation was to determine general soil conditions for use by the engineer to determine the preferred site layout and design of the proposed site improvements. The study was conducted in accordance with generally accepted geotechnical engineering practices. The report presents the results of this limited study.

1.1 Project Description

The existing Shoshone Field Office is an approximate 9,500 SF one-story building built in 1975, located on the approximate 6-acre Shoshone Administrative Site in the town of Shoshone, Idaho. The site is located on the southwest corner of Shoshone, ID and southwest of Lincoln County as shown in Plate A-1 Project Vicinity Map in Appendix A. The topography across the sites varies due to exposed basalt bedrock in the undeveloped areas within the property and as observed outside the boundaries. The elevations varied from approximately 3966 feet MSL to 3987 feet MSL as seen on Plate B-1 Exploration Location Map in Appendix B. The existing surface conditions consists primarily of asphalt concrete and sagebrush overlaying the exposed bedrock. At the time of the investigation conducted by NWIT, several support buildings, a landscape area, and a solar panel field, in addition to the existing BLM field office building were found within the site boundaries.

Based on information shared with NWIT at the time of the completion of this report, the proposed new site improvements will consist of the demolition of the existing Shoshone Field Office and constructing the new one-story stick-frame building with an approximate footprint of ±13,000 SF at a new location within the site boundaries. The existing building is anticipated to be functional during the construction of the new building. The location of the proposed new building was not determined at the time of the completion of this report. In addition to the new building, parking lots will be added and modified as needed surrounding the new structure.

1.2 Purpose and Scope

The purpose of this investigation was to explore and evaluate the subsurface conditions where the proposed new improvements are anticipated to be completed. This report will provide geotechnical engineering recommendations based upon our findings for the construction of the new field office building and other site improvements. Understanding of the project is based on a Scope of Work provided by BLM and several site visits during the month of January and February of 2021. This report does not include any recommendations for areas not explored or within the vicinity of the support buildings as mentioned in the Project Description.

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

Geotechnical Report for 070048.030 1-2 North Wind Infrastructure & Technology, LLC

• Clearing and grubbing

• Site preparation and earthwork grading

• Subgrade preparation for slab-on-grade concrete

• Subgrade preparation for building foundations

• Site roadway design

• Lateral earth pressures and drainage recommendations for retaining structures

• Construction considerations including:

o Climate 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 North Wind Infrastructure & Technology (NWIT) 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.

Geotechnical Report for 070048.030 2-1 North Wind Infrastructure & Technology, LLC

2. GENERAL DATA

2.1 Geologic Setting and Stratigraphy

The site is located approximately 15 miles north of Jerome, ID and 20 miles north of Twin Falls, ID located north of the Snake River Canyon. As discussed, the elevations varied across the Subject property from 3966 feet MSL to 3987 feet MSL. In general, the Snake River Canyon is made up of historical Rhyolite and Basalt formations that expand north into the area where the project site is located. This canyon existed, prior to the Bonneville Flood. However, the flood increased the erosion of the canyon walls and floors to expose the native rock formations. Today, the canyon is over 480 feet deep with varying widths.

2.2 General Geology

The existing surface conditions consists of sagebrush, and exposed bedrock. The Idaho Geological Survey (IGS) Maps indicates that this area is composed of olivine tholeiite basalt from the Pleistocene and Pliocene era with some areas covered with 3-10 feet of loess. This description appeared to be generally consistent with the field exploration results. A geologic map showing the unit description can be seen in Plate D-1 Geologic Map in Appendix C.

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 tertiary faults is located less than 20 miles north, the Mormon Reservoir, Mount Bennet Hills, and the Moonstone Mountain Fault System. Quaternary faults consist of Danskin Mountain and Spring Creek Faults system within 50 miles north and west as shown on Plate E-1 Quaternary Fault Map. Based upon the soil properties and rock depth encountered during the field investigation, the site can be classified as Site Class C in accordance with Chapter 16 of the 2018 edition of the International Building Code (IBC). Seismic Design Parameters are shown in Table 2-1 for project site coordinates latitude: 42.932039 longitude: -114.41379 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 2018 IBC and were summarized in Table 2-1, which may be used for design purposes.

Geotechnical Report for 070048.030 2-1 North Wind Infrastructure & Technology, LLC

Table 2-1. ASCE 7 Seismic Design Parameters

ASCE 7 SEISMIC DESIGN PARAMETERS

Mapped spectral acceleration for short periods SS 0.176g

Mapped spectral acceleration for 1-second periods [from ASCE 7] S1 0.082g

Site coefficient Fa 1.3

Site coefficient Fv 1.5

Max considered earthquake spectral response acceleration for short periods SMS=FaSS 0.229g

Max considered earthquake spectral response acceleration for 1-second periods SM1=FvS1 0.124g

5% damped design spectral response acceleration at short periods SDS=2/3 SMS 0.152g

5% damped design spectral response acceleration at 1-second periods SD1=2/3 SM1 0.083g

Peak Ground Acceleration (%g) PGA 0.077g

Modified Peak Ground Acceleration (%g) PGAM 0.10g

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 silty coarse-grained soils, lack of groundwater, and shallow bedrock found during the field exploration indicate the potential for liquefaction to be low.

Geotechnical Report for 070048.030 3-2 North Wind Infrastructure & Technology, 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 February 9, 2021, which consisted of six (6) exploratory borings down to a maximum depth of 15 feet below ground surface (bgs). The borings were completed with a truck-mounted drill rig and backfilled with cuttings upon completion. The borings were completed using traditional hollow stem auger and cored through the basalt 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 North Wind Infrastructure & Technology (NWIT) representative visually classified the materials encountered in the borings and maintained a log according to the Unified Soil Classification System (USCS). Representative bulk soil and rock core samples were obtained and preserved in plastic sample bags or boxes for observation and possible laboratory testing.

Laboratory tests were performed on selected samples to determine some of the physical and engineering properties of the subsurface soils. The results of the laboratory testing are presented on the boring logs shown 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. All test results are presented in Table 3-1 Laboratory Test Results and on the exploratory boring logs in Appendix C. The following laboratory 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.

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.

Atterberg Limits (ASTM D4318 and CT204) - Atterberg Limits tests were performed on selected samples of cohesive soils encountered at the site. Liquid Limit, Plastic Limit, and Plasticity Index are useful in the classification and characterization of the engineering properties of soil and help to evaluate the expansive characteristics of the soil and determine the USCS soil classification.

Unconfined Compression Test for Intact Rock – Unconfined Compression tests were conducted on selected rock core samples obtained from borings B-1 and B-4 within the upper ten (10) feet. The results are used to evaluate the condition and compressive strength of the existing rock.

Geotechnical Report for 070048.030 3-1 North Wind Infrastructure & Technology, LLC

Table 3-1. Laboratory Test Results.

Laboratory Test Results

Boring No.

Depth

(ft) USCS Soil Type

Grain Size Distribution Atterberg Limits

Gravel

Sand

Fines LL PI

B-1 1.0 ML – Sandy Silt 3.0 29.2 67.8 NP NP B-2 5.0 ML – Sandy Silt 5.0 31.0 64.0 NP NP B-4 0.0 SW-SM – Poorly Graded Sand with silt and gravel (Base Course)

33.0 59.7 7.3

B-5 2.5 ML – Sandy Silt 2.0 29.1 68.9 B-6 5.0 ML – Sandy Silt 7.0 28.2 64.8

3.2 Stratigraphy

From our collected data, we concluded that where explored, the soils consist predominantly of approximately 2 to 5 feet of Sandy Silt extending down to bedrock or basalt boulder depth. Bedrock depth was encountered at depths ranging from surface outcrop down to 10 feet. Due to the varying topography and bedrock outcrop observed across the site, the bedrock depth may be located at a depth greater than 10 feet in other areas not explored during out investigation. The existing surface conditions consisted of natural sagebrush and bedrock outcrop across the site. A detailed description of the lithology across the site is shown on the Exploratory Boring Logs in Appendix C.

No signs of groundwater were encountered during our field investigation. Groundwater levels, although unlikely, 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 or construction activities encroach into groundwater depths.

3.2.1 Soil Survey Review

A review of the United States Department of Agriculture (USDA) Natural Resource Conservation Service Soil Survey indicates the area where the site is located is primarily composed of the Starbuck-Sidlake- Rock outcrop complex with 2 to 15 percent slopes. USDA also described the bedrock depth from 0 to 60 inches. The findings from the exploratory program activities were consistent with the soil type determined by the Soil Survey.

Geotechnical Report for 070048.030 4-1 North Wind Infrastructure & Technology, 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 for the Subject Property based on the limited study.

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. Although no expansive soils were encountered at the explored locations, the design of all slabs-on-grade should account for 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 4.6. 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 or bearing on bedrock provided a cushion is prepared between the foundation and the bedrock as outlined on Section 4.2.1. Footings should be founded a minimum of 18 inches below lowest adjacent finished grade (exterior grade or building pad subgrade elevation, as applicable) for frost protection. Nevertheless, due to the presence of basalt boulders and bedrock in several locations, the proper site preparation may vary from:

• existing native undisturbed soils after being properly proof-rolled and approved by a qualified Geotechnical Engineer upon observation;

• properly prepared bedrock surface; or

• compacted structural fill placed above existing fill or bedrock.

The selection of each system should be determined by the project manager. For the design of footings bearing on approved undisturbed granular native soil, we recommend a net allowable bearing pressure of 2,000 psf or 2,500 psf if a minimum of 2 feet of properly compacted structural fill is used to reach final footing elevations. If footings will be resting on competent, approved and properly prepared bedrock, a designed net allowable bearing pressure of 8,000 psf may be used. 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.

Geotechnical Report for 070048.030 4-2 North Wind Infrastructure & Technology, LLC

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 sandy silt, 0.4 for granular structural fill, or 0.7 for suitable bedrock between the base of the foundation elements and underlying material is recommended.

4.2.1 Bedrock

Based upon an anticipated depth of foundations being at least 32 inches for frost protection, the bedrock encountered at shallow depths and the topography features significant slopes, it appears that encountering bedrock should be expected at depths shallower than the footing depths at several site improvement locations. The amount of bedrock removal required will be dependent upon the final floor elevation selected for the new building. Since the site improvements are spread across the site, each location should be evaluated individually to determine the preferred foundation system based on the final floor elevation in relation to the bedrock depth.

In general, where bedrock is present at or above the proposed foundation bearing depth, foundations could bear directly on the bedrock surface provided suitable soil-to-bedrock transition zones and/or structural control joints are included in the structural design of the foundations. The final finished floor elevation will determine whether bedrock over-excavation and constructing a soil cushion below the foundations will be most practical. This should be compared to having foundations bearing directly on rock along with transition zones for locations where rock removal is not required. Rock removal and construction of a soil cushion will reduce the risk of differential settlement of adjacent footings or continuous footings that bear on dissimilar materials (i.e., soil and bedrock). It is recommended that foundation support material bear or an approved material stratum and thicknesses as determined by the geotechnical engineer.

In addition, structural fill may be needed to fill voids caused from the removal of basalt boulders to reach footing depth. Should this be needed, it should be properly placed and compacted to 95% maximum dry density as per ASTM D-1557. If relatively limited bedrock removal is required for construction of the proposed building foundations (i.e., approximately less than 1 to 2 feet in depth and over approximately 30 percent of exterior footings and slab areas), it is anticipated that shallow bedrock removal could be possible using mechanical methods, such as a hydraulic hoe-ram. However, basalt is a somewhat medium to hard rock and the use of a hoe-ram may prove to be inefficient. If so, the need for systematic drilling and blasting could be required. Although not required, additional exploration and collection of rock cores may be performed to further evaluate the bedrock depth across the site.

Due to the site topography, it may be prudent to raise the proposed finished elevations to avoid or significantly minimize bedrock excavation for the structures. Similarly, depending upon the final pavement type, layout, and grades, bedrock removal may be required to accommodate the new pavement support system. Other related subsurface structures, such as drainage features could locally be affected by bedrock depending upon their required subgrade depths. Final grading design should consider the cost of importing fill to achieve new grades as opposed to cutting into bedrock.

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

Geotechnical Report for 070048.030 4-3 North Wind Infrastructure & Technology, LLC 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 in. for active pressures and 1.5 in. for passive pressures. These deflections are calculated based on the NAVFAC DM7.2 found on page DM7.2-60, presented in Figure 4-1 below.

Figure 4-1. Effect of Wall Movement on Wall Pressures (from NAVFAC DM7.02)

The coefficients and static lateral earth pressures recommended for design are listed in Table 4-1 Static Equivalent Fluid Pressures for the general soil type identified at the site as Sandy Silt, ML. These values are based on the correlated soil friction angles and bulk unit weights of typical compacted soils found in NAVFAC DM7.2, Table 1, Page 7.2-39, presented in this report as Table 4-2 Typical Properties of Compacted Soils.

Table 4-1. Static Equivalent Fluid Pressure Soil Type and Characteristics Lateral Earth Pressure Case and Coefficient Equivalent Fluid Pressure

ML

φ‘ = 30o MDD= 110 pcf

At-rest case, Ko = 0.69 55 pcf (unsaturated) Active case, Ka = 0.33 37 pcf (unsaturated) Passive case, Kp = 3.0 330 pcf (unsaturated)

Geotechnical Report for 070048.030 4-4 North Wind Infrastructure & Technology, LLC

Table 4-2. Typical Properties of Compacted Soils

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

Compression Typical Strength Characteristics

Ty pi ca l C oe ff ic ie nt of P er m 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 (saturated) psf β (E ff ec tiv e

St re ss

En ve lo pe

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 ***** ***

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.

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

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

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

Geotechnical Report for 070048.030 4-5 North Wind Infrastructure & Technology, LLC

In addition to the lateral earth pressures found in Table 4-1 Static Equivalent Fluid Pressures, 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:

µ = coefficient of friction between concrete and rock, 0.7, granular soils (i.e. aggregate base), 0.6, and fine soils (i.e. ML), 0.30. (NAVFAC DM-7.2, page 7.2-63, Table 1)

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.

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 low corrosion classification rating for corrosion of concrete and steel.

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 following roadway design for the proposed access roads and parking areas was prepared with parameters and assumptions based on anticipated traffic for similar BLM sites. 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 8 for the soils classified as Sandy Silt soils encountered within the maximum explored depths of 15 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. The flexible pavement section design for light-duty and heavy-duty traffic can be found in Table 4-3 and Table 4-4, respectively, as determined using AASHTO design procedures (GDPS 1993). Also, a rigid Portland cement concrete paving section with aggregate base course is given in Table 4-4. The rigid concrete paving section is recommended in areas where large trucks, trailers and heavy vehicle traffic will be maneuvering or parking.

Geotechnical Report for 070048.030 4-6 North Wind Infrastructure & Technology, LLC

Table 4-3. Light-Duty Flexible Pavement Section Design.

Traffic Min Subgrade CBR Asphalt Concrete

(in.)

Aggregate Base

(in) Access Road/Maneuvering Areas 8 4 8

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

Traffic Min Subgrade CBR Asphalt Concrete (in.)

Aggregate Base (in)

Access Road/Maneuvering Areas 8 6 12

Table 4-5. Rigid Pavement Section Design.

Traffic Min Subgrade CBR Asphalt Concrete (in.)

Aggregate Base (in)

Access Road/Maneuvering Areas 8 5 10

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 698 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 in. 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 in. into the subgrade soils. Thus, controlling storm water infiltration and extending the life and performance of the improved section.

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 Silt (ML) can be excavated using conventional excavation equipment. These soils should be excavated as needed but should extend a minimum of 3 ft horizontally 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 should be determined by the project engineer for each proposed development areas. In general, it may be possible to raise the finished floor elevations to eliminate or reduce the amount of ripping or blasting of bedrock as discussed in Section 4.2.1.

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.

Geotechnical Report for 070048.030 4-8 North Wind Infrastructure & Technology, LLC

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 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 backfill 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 per ASTM D 698 Standard Test Methods for Laboratory Compaction Characteristics of Soil using the Standard Effort. The soil should be moisture conditioned to within 2% (plus or minus) of the optimum moisture content obtained in the same test. Fill placed on the pads and in pavement areas should be non-expansive and placed as structural fill.

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.

Geotechnical Report for 070048.030 4-9 North Wind Infrastructure & Technology, LLC

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 soils encountered during the field exploration are not suitable to be used as structural. If granular materials 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 Silt to Sandy Silt 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 4-6 Structural Fill Specifications.

Table 4-6 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…