Attachment 3 Geotechnical Report.pdf

Prepared for:

Bureau of Land Management

Prepared by:

North Wind Resource Consulting, LLC

October 26, 2017

30130.103-TR-001

Geotechnical Report Bruneau Guard Station Bureau of Land Management Boise District Office Boise, ID

ID/UT IDIQ Contract No. L14PC00105

Geotechnical Report

Bruneau Guard Station Bureau of Land Management

Boise District Office

November 4, 2019

Prepared for:

Bureau of Land Management

Prepared by:

North Wind Resource Consulting, LLC

1425 Higham Street

Idaho Falls, Idaho 83402

Project No. 30130.103

APPROVALS

Project No.: 30130.103

Report Number: 30130.103-TR-001

Report Name: Geotechnical Report

Bureau of Land Management

Boise District Office

Date: November 4, 2019

Revision No.: 1

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

Originators:

Bryce Marsh Date

Civil Engineer

Independent Technical Reviewers:

Ben L. Carter, P.E. Date

Senior Geotechnical Engineer Project Manager:

Gary Mecham, P.E. Date

Engineering Manager

CHANGE MANAGEMENT RECORD

Project No.: 30130.103

Report Number: 30130.103-TR-001

Report Name: Geotechnical Report

Bureau of Land Management

REVISION

NO. DATE DESCRIPTION OF CHANGES/AFFECTED PAGES

0 October 25, 2019 Base Document

1 November 4, 2019 BLM comments/throughout document

30130.103 TR-001

Geotechnical Report v North Wind Resource Consulting, LLC

Bruneau Guard Station November 2019

CONTENTS

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

1.1 Project Description ............................................................................................................. 1-2

1.2 Purpose and Scope .............................................................................................................. 1-2

1.3 Terms and Conditions / Warranties .................................................................................... 1-3

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

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

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

2.3 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 Concrete Footing Considerations ....................................................................................... 4-1

4.3 Lateral Earth Pressure and Sliding Analyses ...................................................................... 4-1

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

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

4.6 Site Preparation and Excavation Recommendations .......................................................... 4-5

4.6.1 Climate ................................................................................................................ 4-5

4.6.2 Clearing and Grubbing ........................................................................................ 4-5

4.6.3 Excavations and Backfill .................................................................................... 4-6

4.6.4 Grading and Filling ............................................................................................. 4-7

4.6.5 Slope Stability and Erosion ................................................................................. 4-7

4.6.6 Drainage and Storm Water Collection ................................................................ 4-7

4.6.7 Septic System ...................................................................................................... 4-7

4.7 Structural Fill and Aggregate Recommendations ............................................................... 4-7

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

Geotechnical Report vi North Wind Resource Consulting, LLC

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

Geotechnical Report vii North Wind Resource Consulting, LLC

FIGURES

Figure 1-1: Subject Property Site Vicinity Map ........................................................................................ 1-1

Figure 1-2: BLM Conceptual Layout......................................................................................................... 1-2

Figure 2-1. Screen Shot of USGS Interactive Quaternary Fault Map. ....................................................... 2-2

Figure 4-1. Effect of Wall Movement on Wall Pressures (from NAVFAC DM7.02) ............................... 4-2

TABLES

Table 2-1. 2015 IBC Seismic Design Parameters ...................................................................................... 2-1

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

Table 3-2. Standard Penetration Test ......................................................................................................... 3-2

Table 4-1. Static Equivalent Fluid Pressure for ML .................................................................................. 4-2

Table 4-2. Static Equivalent Fluid Pressure for SM .................................................................................. 4-3

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

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

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

Table 4-6. Structural Fill Specifications. ................................................................................................... 4-8

APPENDICES

Appendix A: Bore Logs ............................................................................................................................ A-1

Appendix B: Bore Hole Locations ............................................................................................................ B-1

Geotechnical Report viii North Wind Resource Consulting, LLC

ACRONYMS AND ABBREVIATIONS

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

CBR California Bearing Ratio

CFR Code of Federal Regulations

FS Factors of Safety ft feet

IBC International Building Code

in. inch

LL liquid limit

NAVFAC DM Naval Facilities Engineering Command Design Manual

NSHMP National Seismic Hazard Mapping Project

NWRC North Wind Resource Consulting, LLC

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

PI plasticity index

TP test pit

USCS United Soil Classification System

USDA United States Department of Agriculture

USGS United States Geological Survey

UW Unit Weight

Geotechnical Report 1-1 North Wind Resource Consulting, LLC

1. INTRODUCTION

This report presents the findings, conclusions, and recommendations of a geotechnical investigation and analysis for a new Bruneau Guard Station for the Bureau of Land Management (BLM). The new Bruneau

Guard Station, located in Bruneau, Idaho, will be referred to as Subject Property, hereinafter. The Subject

Property is located in portion of the SE ¼ and NE ¼, SW ¼, Section 26, Township 6 South, Range 5 East of the Boise meridian. Refer to vicinity map in Figure 1.1, for more information. The project site encompasses approximately 14 acres which includes approximately 11 acres of development area for a new guard station. The findings, conclusions, and recommendations of this geotechnical report are based on surface and subsurface conditions encountered in the field and laboratory explorations. This also includes the project details presented to this office under the ID/UT IDIQ Contract No. L14PC00105, DO

#103. The objective of this investigation was to determine general soil conditions for use by the engineer for the design of the proposed guard station, in accordance with generally accepted geotechnical engineering practices. The report presents the results of this limited study.

Figure 1-1: Subject Property Site Vicinity Map

PROPOSED

GUARD STATION

Geotechnical Report 1-2 North Wind Resource Consulting, LLC

1.1 Project Description

The Subject Property is located approximately 2.5 miles southwest of Bruneau, Idaho, on Reniecke Road and lies within Owyhee County. Site vicinity characteristics include natural grasses and sagebrush on undeveloped land. Development was limited to the gravel road (Reniecke Road) and the only utility near the proposed development was telephone on the west side of Reniecke Road. Power is known to be located on Hot Creek Road near the existing Bruneau Guard Station.

The anticipated site improvements include the following new structures: fire station, crew quarters, Hotsy shed, cabana, landscape shed, and vault toilet. Associated site improvements will likely include asphaltic and concrete paving, fill stands, and fencing. Site utilities will likely include power, telephone, well water and sanitary wastewater piping for a subsurface wastewater disposal system. These improvements will encompass approximately three acres of the eleven-acre development. Refer to Figure 1-2 below for anticipated site improvements.

Figure 1-2: BLM Conceptual Layout

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 preliminary drawing provided by the BLM and a site visit performed on Wednesday

September 11, 2019. Refer to Figure 1-2 for conceptual drawing.

N

Geotechnical Report 1-3 North Wind Resource Consulting, LLC

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 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 NWRC, 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) 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 2-1 North Wind Resource Consulting, LLC

2. GENERAL DATA

2.1 Geologic Setting and Stratigraphy

The Subject Property is located on the south side of the Bruneau River and Hot Creek Road. More specifically, the Subject Property is located on the east side of Reniecke Road. The Subject Property consists of undeveloped BLM land with natural sagebrush and grasses. Vegetation is supported with native soils that appeared to be silts, sands and gravels. Furthermore, the existing Bruneau Guard station lies approximately 0.5 miles northwest of the proposed development, off of Hot Creek Road. Thus, the proposed concept is to develop the Subject Property to form a new Guard Station. Elevation at the site is approximately 2,500 feet. Drainage consists of percolation by site soils and overland flow to the northeast into the historical low points which are tributary to the Bruneau River. Similarly, the Bruneau

River is tributary to the Snake River which lies north of Bruneau.

Surficial gravelly sandy loam from unimproved surfaces was underlain by a silts, sands and mixed alluvium deposits from natural ground to approximately 16.5 ft. Sand to large coarse cobbles are known to lie within this mixed stratum.

2.2 General Geology

According to the Idaho Geologic Survey, the geologic map of the area indicates that most of the onsite soils are described as fluvial deposits from the historical Bruneau River drainage. These deposits can range in size from fine grained clays, silts and sands to coarse quartzite cobbles.

2.3 Seismic Design Criteria

According to the United State Geological Survey, (see Figure 2-1), several active faults have been identified within proximity to the site. Further, no indications of faulting were discovered during the limited field investigation. Based upon the soil properties, site soils would be classified as Site Class D in accordance with Chapter 16 of the 2015 edition of the International Building Code (IBC). The site latitude and longitude coordinates were used in the United States Geologic Survey (USGS) Unified

Hazard Tool (UHT) to determine 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 2015 IBC and were summarized in Table 2-1, which may be used for design purposes.

Table 2-1. 2015 IBC Seismic Design Parameters

2015 INTERNATIONAL BUILDING CODE SEISMIC DESIGN PARAMETERS

Mapped spectral acceleration for short periods [from UHT] SS 0.252g

Mapped spectral acceleration for 1-second periods [from UHT] S1 0.076g

Site coefficient [from Table 1613.3.3 (1)] Fa 1.598

Site coefficient [from Table 1613.3.3 (2)] Fv 2.4

Max considered earthquake spectral response acceleration for short periods SMS=FaSS 0.403g

Max considered earthquake spectral response acceleration for 1-second periods

SM1=FvS1 0.182g

5% damped design spectral response acceleration at short periods SDS=2/3 SMS 0.269g

5% damped design spectral response acceleration at 1-second periods SD1=2/3 SM1 0.121g

Peak Ground Acceleration (PGA) (%g) 0.113g

Geotechnical Report 2-2 North Wind Resource Consulting, LLC

Figure 2-1. Screen Shot of USGS Interactive Quaternary Fault Map.

2.4 Liquefaction

Liquefaction is a phenomenon where saturated, relatively loose, granular soils lose their bearing strength during ground shaking (usually caused by seismic events). Poorly drained soils are most suspectable to this process of soils behaving like fluids. The liquefaction potential at the site would be considered low for unsaturated soil and increases with saturated, poorly drained soil. This potential is based on the absence of groundwater found in liquefiable soils and the potential for adequate ground accelerations to induce liquefaction.

Project Site

Owyhee Mountains Fault System (typ)

Geotechnical Report 3-1 North Wind Resource Consulting, LLC

3. SUBSURFACE STRATIGRAPHY AND ENGINEERING LAYERING

3.1 Summary of Field Investigation and Laboratory Testing

The field exploration conducted at the site consisted of drilling nine bore holes to maximum depths of approximately 16.5 feet below the existing ground surface. The bore holes were drilled with a truck mounted boom that utilized a nominal eight-inch hollow stem auger and a two-inch diameter split spoon sampler for the Standard Penetration Test (SPT). The locations of the bore holes are identified in

Appendix B. The bore holes were located in the field by sighting from existing features on the site;

hence, accuracy of bore holes shown should be considered approximate. The site surficial and subsurface investigation was conducted on September 17, 2019 by North Wind’s Bryce Marsh.

A log of each bore hole was maintained by visually classifying soils encountered according to the Unified

Soil Classification System (USCS). In-situ and representative bulk soil samples were obtained and preserved in plastic sample bags for possible laboratory testing. Soil conditions encountered are presented on the bore hole logs found in Appendix A. Pictures were taken of site features and bore hole location to document the general location.

Laboratory tests were performed on selected representative samples to aid in soil classification and to estimate the engineering properties of the native soils. The testing program consisted of six sieve analyses and two Atterberg limits tests. Results of the laboratory tests are shown partially on the logs of each test pit and are summarized in the Laboratory Test Results Table 3-1, below. All laboratory testing was conducted in accordance with generally accepted industry standards and appropriate American Society for

Testing and Materials (ASTM) standards.

Table 3-1. Laboratory Test Results.

Laboratory Test Results

Bore Hole No. Depth (ft) USCS Soil Type Grain Size Distribution Atterberg Limits

% Gravel % Sand % Fines LL PI

B-1 2.5 ML – Sandy Silt 6 42.7 51.3 Non-Plastic

B-2 5 ML – Sandy Silt with Gravel 17 32.4 50.6 N/A

B-3 7.5 SM – Silty Sand with Gravel 49 36.4 14.6 Non-Plastic

B-4 5 SM – Silty Sand 5 52.4 42.6 N/A

B-7 2.5 SM- Silty Sand with Gravel 23 34.8 42.2 N/A

B-9 5 SM – Silty Sand with Gravel 37 38.4 24.6 N/A

3.2 Stratigraphy

Visual classification of each soil stratum encountered according to ASTM D2488 (Visual Manual

Procedure) was made at the time of the field exploration. The soil lithology encountered in the field varied from bore hole to bore hole. Generally, the stratigraphy consisted of both coarse and fine grained soil stratums, across bore holes one through seven. The typical fine-grained soil group was identified as an ML. The typical coarse-grained soil group was identified as an SM. The soil classification varied with depth and primarily changed as a function of the grain size distribution. Overall, bore holes one through seven were explored from existing ground surface to depths of 16.5’. The soil contained the following characteristics: moisture content was dry to moist and consistent and blow counts taken at depths of 2.5, 5, 10 and 15 feet, with respect to depth. Bore holes eight and nine were drilled in the existing Reniecke

Road and consisted of an SM Silty Sandy with Gravel. These bore holes were explored from existing ground surface to 6.5’. Here, the soil stratum was brown, medium dense and consistently dry to moist but not saturated. Blow counts were taken at depths of 2.5 and 5 feet. Refer to Table 3-2 for SPT results.

Geotechnical Report 3-2 North Wind Resource Consulting, LLC

It is noteworthy to indicate that two split spoon samples were retrieved without recovery of soil. These locations, B-3 at 2.5 feet and B-7 at 15 feet, resulted in the scenario where the drive shoe lied directed on coarse gravel. Thus, no soil sample recovery at these locations. A more detailed description of the soils encountered can be found in the bore logs found in Appendix A. These logs show subsurface conditions at the time and location of the field investigation and may not be representative of subsurface conditions at other locations and times.

Table 3-2. Standard Penetration Test SPT Results

Bore Hole

No.

Blow Counts at Depth (ft)

2.5 5 10 15

B-1 11 18 22 30

B-2 28 22 23 30 1B-3 21 21 19 28

B-4 29 20 32 23

B-5 26 23 32 33

B-6 17 36 27 43 2B-7 10 21 44 52

B-8 9 20 N/A

B-9 18 45 N/A 1B-3 No recovery at 2.5’

2B-7 No recovery at 15’

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 encroaches into groundwater depths.

3.2.1 Soil Survey Review

A review of the United States Department of Agriculture (USDA) Soil Conservation Service, Soil Survey of the Subject Property, indicates one predominate onsite soil type: Loray-Dors complex. Specific soil characteristics of this soil type can be found below.

• Loray-Dors complex, 8 to 20 percent slopes – This soil occurs from mixed alluvium and fan skirt outflows of the historical Bruneau River drainage. This complex contains two predominate soils types, gravelly sandy loam and a fine sandy loam. Both soil descriptions describe the water table water to be more than 80 inches in depth. The soil is well drained and can contain calcium carbonate and dissolved sodium content.

Geotechnical Report 4-1 North Wind Resource Consulting, 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 proposed site.

4.1 Slab-on-grade Considerations

Prior to constructing concrete floor slabs, curb and gutter, valley gutter or other slabs, the upper 12 inches of native soil may serve as subgrade and shall be reworked as follows. The upper 12 inches of native soil shall be scarified, moisture conditioned, and compacted. Scarification and compaction of native soils are required for slabs to be placed directly on sub-base material. Thus, a minimum of 4 inches of structural fill should be placed as sub-base material, on top of the reworked subgrade, and beneath the slab-on-grade. Refer to Table 5 for acceptable aggregate.

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.

4.2 Concrete Footing Considerations

Prior to constructing concrete foundations including strip or spread foundations, the upper 12 inches of native soil may serve as subgrade and shall be reworked as follows. The upper 12 inches of native soil shall be scarified, moisture conditioned, and compacted. Scarification and compaction of native soils are required for foundations to be placed directly on sub-base material. Thus, a minimum of 6 inches of structural fill should be placed as sub-base material, on top of the reworked subgrade, and beneath the foundation. Refer to Table 5 for acceptable aggregate.

Bearing capacities for these foundations shall not exceed 2,500 psf. Due to the bearing soils susceptibility to movements from frost heave, the design of all foundations should account for minimum frost depth.

Furthermore, slab thickness and structural-reinforcing requirements within the footing should be determined by the design engineer.

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 at the top, 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 in. for active pressures and 1.5 in. for passive pressures. These deflections are calculated based on Figure 1 of the NAVFAC DM7.2 found on page DM7.2-60, presented in Figure 4-1 below.

Geotechnical Report 4-2 North Wind Resource Consulting, LLC

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 and

Table 4-2 for the two general soil types identified, ML and SM. 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.

Table 4-1. Static Equivalent Fluid Pressure for ML

Soil Type and Characteristics Lateral Earth Pressure Case and Coefficient Equivalent Fluid Pressure

ML

‘ = 32o

MDD = 110 pcf

At-rest case, Ko = 0.47 52 pcf (unsaturated)

Active case, Ka = 0.31 34 pcf (unsaturated)

Passive case, Kp = 3.25 358 pcf (unsaturated)

Geotechnical Report 4-3 North Wind Resource Consulting, LLC

Table 4-2. Static Equivalent Fluid Pressure for SM

Soil Type and Characteristics Lateral Earth Pressure Case and Coefficient Equivalent Fluid Pressure

SM

‘ = 34o

MDD = 118 pcf

At-rest case, Ko = 0.44 52 pcf (unsaturated)

Active case, Ka = 0.28 33 pcf (unsaturated)

Passive case, Kp = 3.54 417 pcf (unsaturated)

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

Group Symbol

Soil Type

Range of Maximum Dry Unit Weight, pcf

Range of Optimum Moisture, Percent

Typical Values of Compression

Typical Strength Characteristics

Typical Coefficient of Permeability, ft./min.

Range of

CBR

Values

Range of Subgrad e Modulus k, lbs/cu in.

At 1.4 tsf

(20psi)

At 3.6 tsf

(50psi)

Cohesion (as compacte

d) psf

Cohesion (saturated

) psf

(Effective

Stress Envelope Degrees)

Tan

GW

Well graded clean gravels, gavel-sand mixtures.

125-135 11-8 0.3 0.6 0 0 >38 >0.79 5x10-2 40-80 300-500

GP

Poorly graded clean gravels, gravel-sand mix 115-125 14-11 0.4 0.9 0 0 >37 >0.74 10-1 30-60 250-400

GM

Silty gravels, poorly graded gravel-sand-silt.

120-135 12-8 0.5 1.1 ***** ***** >34 >0.67 >10-6 20-60 100-400

GC

Clayey gravels, poorly graded gravel-sand-clay.

115-130 14-9 0.7 1.6 ***** ***** >31 >0.60 >10-7 20-40 100-300

SW

Well graded clean sands, gravelly sands.

110-130 16-9 0.6 1.2 0 0 38 0.79 >10-3 20-40 200-300

SP

Poorly graded clean sands, sand-gravel mix.

100-120 21-12 0.8 1.4 0 0 37 0.74 >10-3 10-40 200-300

SM

Silty sands, poorly graded sand-silt mix.

110-125 16-11 0.8 1.6 1050 420 34 0.67 5x >10-5 10-40 100-300

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 5-30 100-300

SC

Clayey sands, poorly graded sand-clay-mix.

105-125 19-11 1.1 2.2 1550 230 31 0.6 5x >10-7 5-20 100-300

ML

Inorganic silts and clayey silts.

95-120 24-12 0.9 1.7 1400 190 32 0.62 >10-5

15 or less

100-200

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

50-200

OL

Organic silts and silt-clays, low plasticity.

80-100 33-21 ***** ***** ***** ***** *****

***** 5 or less 50-100

MH

Inorganic clayey silts, elastic silts.

70-95 40-24 2 3.8 1500 420 25 0.47 5x >10-7

10 or less

50-100

CH

Inorganic clays of high plasticity.

75-105 36-19 2.6 3.9 2150 230 19 0.35 >10-7

15 or less

50-150

OH

Organic clays and silty clays.

65-100 45-21 ***** ***** ***** ***** *****

***** 5 or less 25-100

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.

In addition to the lateral earth pressures found in Table 4-1 and Table 4-2, 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:

Geotechnical Report 4-4 North Wind Resource Consulting, LLC µ = coefficient of friction between concrete and rock, 0.7, granular soils (i.e. aggregate base), 0.6, and fine soils (i.e. ML/SM), 0.25. (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 corrosion rating of concrete and steel to be moderate.

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. We recommend the use of 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 8. 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 and aggregate sub-base is proposed. The pavement section design determined using AASHTO design procedures (GDPS 1993) can be found in Table 4-3. 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.

Table 4-4. Flexible Pavement Section Design.

Traffic Min Subgrade

CBR

Asphalt

Concrete

Aggregate

Base

Aggregate

Sub-Base

(Pit-Run)

Access Road/Maneuvering

Areas 8 4 in. 4 in. 12 in.

Parking 8 3 in. 4 in. 8 in.

Geotechnical Report 4-5 North Wind Resource Consulting, LLC

Table 4-5. Rigid Pavement Section Design.

Traffic Min Subgrade

CBR

Portland

Cement

Concrete

Aggregate

Base

Aggregate

Sub-Base

(Pit-Run)

Access Road/Maneuvering

Areas 10 6 in. 4 in. 8 in.

Parking 10 6 in. 4 in. 0 in.

All subgrade, sub-base (pit-run), 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 made in accordance with Section 4.5. A minimum of 12 inches of subgrade shall be scarified and compacted beneath the pavement sections. The subgrade shall be field verified to be native 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, areas 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 extent a minimum of 4” 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.

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 Clearing and Grubbing

The excavation boundaries should be initially cleared of all vegetation, trees, brush, roots, irrigation lines, near surface debris, organic soils, deleterious materials, and undocumented fills or disturbed soils. All vegetation and debris materials should be removed from the site. Undocumented fill and underlying

Geotechnical Report 4-6 North Wind Resource Consulting, LLC native loose soils should be removed to native undisturbed soils. Other clean top soils and disturbed soils can be stockpiled and placed as a final lift in landscaped areas only.

It is recommended to remove all buried structures (i.e., foundations, pipes, abandoned utilities, or duct banks) and clean loose soils and debris from excavations. Further, over-excavate a minimum of 2 ft vertically and horizontally, below removed structures or bedrock whichever is encountered first. Voids resulting from removed structures shall be properly backfilled and compacted during grading operations.

Voids occurring under the removed structures shall be backfilled with structural fill.

4.6.3 Excavations and Backfill

The site soils (ML and SM) 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. Solid rock was not identified during excavation. However, coarse cobbles are known to existing within the project vicinity.

4.6.3.1 Soil Excavations and Backfill

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 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 4-5 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.

Geotechnical Report 4-7 North Wind Resource Consulting, LLC

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. 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 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. 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. Storm water collection facilities may be constructed and should be routed away from all bearing soils and subsurface septic systems.

4.6.7 Septic System

Native on site soils were evaluated with the use the United Stated Department of Agriculture’s soil textural classification group and site specific sieve analyses. The soils were classified as Silt Loam (B-2) and Sandy Loam (B-1). These classification groups can be used to determine application rates for use of a subsurface sewage disposal system. It is recommended to utilize the most recent Technical Guidance

Manual for Individual and Subsurface Sewage Disposal Systems published by the Idaho Department of

Environmental Quality for site specific evaluations and design characteristics.

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 native ML and SM soils were not an acceptable granular structural fill material that was encountered during our field investigation. If granular materials are found on the site, then laboratory testing for these soils should be performed to confirm that they are within the granular structural fill specifications established in this

Section.

The layers of subsurface material located in the soil strata are not acceptable as granular structural fill material. However, native SM soils are acceptable as fill beneath pavements and lightly loaded floor slabs. Also, native ML and SM soils are suitable for general fill. Overall, there were no naturally

Geotechnical Report 4-8 North Wind Resource Consulting, LLC occurring utility trench bedding or aggregate base course materials encountered during the site investigation, therefore, they will need to be imported.

See Section 3 for additional information on subsurface soil strata and characteristics. All structural fill shall meet the specifications outlined in Table 5-1.

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.

<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.

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.

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.

<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. This coarse fill material will need to have a method developed by the contractor based on means and methods of compaction and material characteristics. The Geotechnical Engineer shall approve all compaction methods and will be retained to monitor compaction efforts during construction.

Geotechnical Report 5-1 North Wind Resource Consulting, LLC

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 present 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.

Geotechnical Report 6-1 North Wind Resource Consulting, LLC

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 Regulations, Office of the Federal

Register.

AASHTO, GDPS, 1993, “AASHTO Guide for Design of Pavement Structures,” American Association of

State Highway and Transportation Officials, Washington, D.C., 1993.

ACI 302.1R-04, “Guide for Concrete Floor and Slab Construction,” American Concrete Institute, Farmington Hills, MI, 2004.

ACI 318-14, “Building Code Requirements for Structural Concrete and Commentary,” American

Concrete Institute, Farmington Hills, MI, 2014.

ASTM C150 / C150M-12, “Standard Specification for Portland Cement,” ASTM International, West

Conshohocken, PA, 2012.

ASTM D698-12, “Standard Test Methods…