Attachment_3_-_Henry_Mountains_Geotechnical_Report.pdf

Prepared for:

Bureau of Land Management

Prepared by:

North Wind Infrastructure & Technology, LLC

October 26, 2017

70048.017-TR-001

Geotechnical Report Henry Mountains Field Station Replacement Bureau of Land Management Color Country District Hanksville, UT

ID/UT IDIQ Contract No. 140L0619D0008

Geotechnical Report Henry Mountains Field Station Replacement

Bureau of Land Management Color Country District

May 21, 2021

Prepared for:

Bureau of Land Management Color County District

Prepared by:

North Wind Infrastructure & Technology, LLC

1425 Higham Street Idaho Falls, Idaho 83402

Project No. 70048.017

CHANGE MANAGEMENT RECORD

Project No.: 70048.017

Report Number: 70048.017-TR-001

Report Name: Geotechnical Report

Henry Mountains Field Station Replacement Bureau of Land Management Color Country District

Revision No. Date Description of Changes/Affected Pages 0 May 21, 2021 Base Document

70048.017 TR-001

Geotechnical Report v North Wind Infrastructure & Technology, LLC Henry Mountains BLM Field Station Replacement 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 ........................................................................................................................ 2-2

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

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

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

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

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

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

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

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

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

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

4.5.1 Pavement Design for Untreated Subgrade .......................................................... 4-5

4.5.2 Pavement Design with Treated Subgrade ........................................................... 4-5

4.5.3 Additional Pavement Recommendations ............................................................ 4-6

4.6 Site Preparation and Excavation Recommendations .......................................................... 4-7

4.6.1 Climate ................................................................................................................ 4-7

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

4.7 Structural Fill and Aggregate Recommendations ............................................................... 4-9

Geotechnical Report vi North Wind Infrastructure & Technology, LLC

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

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

FIGURES

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

TABLES

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

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

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

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

Table 4-3. Flexible Pavement Section Design. .......................................................................................... 4-5

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

Table 4-5. Flexible 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: Test Pit Exploratory Logs .................................................................................................... C-1

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

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

Geotechnical Report vii North Wind Infrastructure & Technology, 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

Bgs Below ground surface

CBR California Bearing Ratio

CFR Code of Federal Regulations

FS Factors of Safety ft feet

IBC International Building Code

in. inch

LL liquid limit

MDD maximum dry density

MSL Mean Sea Level

NAVFAC DM Naval Facilities Engineering Command Design Manual

NLA National Lime Association

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

TP test pit

USCS United Soil Classification System

Geotechnical Report viii North Wind Infrastructure & Technology, LLC

USDA United States Department of Agriculture

USGS United States Geological Survey

UW Unit Weight

Geotechnical Report 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 developments for the Bureau of Land Management (BLM) Henry Mountains Field Station Replacement. 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. 140L0619D0008, DO #017. The objective of this investigation was to determine general soil conditions for use by the engineer for the design of the proposed site improvements in accordance with generally accepted geotechnical engineering practices. The report presents the results of this limited study.

1.1 Project Description

The site is located in Wayne County, 380 South 100 West in Hanksville, Utah as shown in Plate A-1 Project Vicinity Map in Appendix A. The project site is approximately 2.5 acres, relatively flat, and consists of one office building with a visitor center, one warehouse/shop building which are separated by a paved access and parking area. In addition, a storage shelter, two small outbuildings, one hazmat building, one historical mill, one public restroom, ware yard to store vehicles and equipment, parking, and landscaping are found within the project site area.

The new site improvements consist primarily of the construction of a new 3,310 square foot office building/visitor center, one 1,500 square foot warehouse/shop building, a 7-vehicle shelter, and other site features. Several structures are anticipated to be demolished upon the completion of the new office building including the existing visitor center, warehouse/shop, and two outbuildings. No final conceptual layout plan was determined at the time of this investigation.

1.2 Purpose and Scope

The purpose of this investigation was to explore and evaluate the subsurface conditions at the project site, and to provide geotechnical engineering recommendations based upon our findings. Understanding of the project is based on a Scope of Work provided by BLM and a site visit performed on September 17, 2020.

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.

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

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 2-1 North Wind Infrastructure & Technology, LLC

2. GENERAL DATA

2.1 Geologic Setting and Stratigraphy

The site is located approximately half a mile southwest of the city of Hanksville, Utah and on the east side of the South Pinto Hills which is part of a series of hills east of Capitol Reef National Park. The site topography site is relatively flat at an approximate elevation of 4,325 feet MSL with the surrounding ground composed of natural sagebrush and grasses. The Utah Geologic Maps indicates that this area is composed of surficial alluvium and colluvium deposits. This description appeared to be consistent with the field exploration results.

2.2 General Geology

As discussed, the Utah Geological Map with soil unit descriptions of the area characterizes the soils as alluvium and colluvium deposits indicating most of the soils around the site originating from stream, river, and channel deposits. The soils encountered within the explored depth and locations were consistent with this description. A geologic map showing the unit description can be seen in Plate D-1 Geologic Map in Appendix C.

2.3 Quaternary Fault and Seismic Design Criteria

According to the United States Geological Survey several active faults have been identified at various distances from the site (USGS, web quaternary faults map). The closest of these are Thousand Lake Fault, Needle Fault Zone, and the Bright Angel Fault System approximately 40 to 45 miles east, west and southeast of the site as shown on Plate E-1 Quaternary Fault Map. 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 2018 edition of the International Building Code (IBC). Seismic Design Parameters are shown in Table 2-1 for project site coordinates latitude:

38.366517 longitude: -110.71762 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.

Table 2-1. ASCE 7 Seismic Design Parameters

ASCE 7 SEISMIC DESIGN PARAMETERS

Mapped spectral acceleration for short periods SS 0.318g

Mapped spectral acceleration for 1-second periods [from ASCE 7] S1 0.094g

Site coefficient Fa 1.546

Site coefficient Fv 2.4

Max considered earthquake spectral response acceleration for short periods SMS=FaSS 0.491g

Max considered earthquake spectral response acceleration for 1-second periods SM1=FvS1 0.226g

5% damped design spectral response acceleration at short periods SDS=2/3 SMS 0.328g

Geotechnical Report 3-2 North Wind Infrastructure & Technology, LLC

5% damped design spectral response acceleration at 1-second periods SD1=2/3 SM1 0.151g

Peak Ground Acceleration (%g) PGA 0.173g

Modified Peak Ground Acceleration (%g) PGAM 0.252g

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 found during the field exploration and lack of groundwater indicate the potential for liquefaction to be low.

Nevertheless, a full evaluation for liquefaction-induced settlement potential is out of this scope. Typically, a minimum exploration down to at least 50 feet to determine the groundwater elevations is needed.

3. SUBSURFACE STRATIGRAPHY AND ENGINEERING LAYERING

3.1 Summary of Field Investigation and Laboratory Testing

In order to characterize the subsurface conditions beneath the proposed improvement areas, a field exploration program was conducted on October 1, 2020, which consisted of four (4) exploratory test pits down to a maximum depth of 7 feet below existing ground surface (bgs). The test pits were excavated with a rubber-tired backhoe and backfilled upon completion. Locations of the test pits were determined to the nearest foot. The locations 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 test pits and maintained a log according to the Unified Soil Classification System (USCS). Representative bulk soil samples were obtained and preserved in plastic sample bags for possible laboratory testing.

Laboratory tests were performed on selected samples to determine some of the physical and engineering properties of the subsurface soils. The results of the laboratory testing are either presented on the test pit logs, and/or are included in Appendix C. All laboratory testing was conducted in accordance with generally accepted industry standards and appropriate American Society for Testing and Materials (ASTM) standards. The following soil tests were performed for this study:

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

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. Test results are presented in Appendix C, and on the test pit logs.

Geotechnical Report 3-3 North Wind Infrastructure & Technology, LLC

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

Table 3-1. Laboratory Test Results.

Laboratory Test Results

Test Pit No. Depth (ft) USCS Soil Type Grain Size Distribution Atterberg Limits % Gravel % Sand % Fines LL PI

TP-1 0.5 SP-SM 45 45.3 9.7

1.0 CH 0 21.4 78.6 68 49

2.0 CL 0 31.5 68.2

TP-2 3.0 SM 0 82.4 17.6

TP-4 2.0 CH 0 22.2 77.8 59 42

3.2 Stratigraphy

During our subsurface exploration program, we investigated the subsurface soils and evaluated soils conditions to maximum depths of about 7 feet bgs in four (4) test pits. From our collected data, we concluded that where explored, the areas of the proposed new construction are underlain predominantly by approximately 10 inches of Silty GRAVEL roadbase on paving areas overlaying 1-2 feet of Sandy Lean CLAY to Fat CLAY to approximately 2-3 feet bgs. This clay layer overlays a more granular layer classified as Silty SAND with small amount of clay pockets extending down to a maximum explored depth of 7 feet bgs. Existing surface conditions consisted of approximately 3.5 inches of asphalt concrete in paving areas and grass and/or topsoil in non-paved areas. A detailed description of the stratigraphy across the site is shown on the Test Pit Exploratory 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 encroaches 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 of the Subject Property, indicates one predominate onsite soil type: Billings silt loam. The composition of Billings silt loam varies from silt loam to silty clay loam extending down to 5 feet bgs and a slope varying from 0 to 4 percent. The findings from the exploratory program activities were consistent with the soil type determined by the Soil Survey.

Geotechnical Report 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 proposed site.

4.1 Slab-on-grade Considerations

Non-structural concrete interior slab-on-grade floors should be a minimum of four inches in thickness.

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

Concrete flatwork should consist of at least 4 inches of properly compacted, free-draining granular fill beneath concrete slabs to provide uniform support and promote uniform curing during construction. Due to the existence of fine-grained high plasticity soils, select engineering fill may be used to limit the movement from the expansive soils. A minimum of 6 inches of structural fill may be placed and properly compacted as outlined in Section 5.6. Prior to placing 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 5 for acceptable aggregate.

4.2 Building Foundations

The proposed structure can be supported on conventional continuous and isolated spread footings bearing on undisturbed stiff non plastic native soil or properly compacted fill. 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. If unsuitable soils are encountered at footing elevation, the excavation should be extended deeper to suitable soils. Based on the field exploration, the low and high plasticity clay soils are found primarily within the upper 3-4 feet bgs. Footings may also bear on properly compacted structural fill extended down to suitable soils. Over-excavation for compacted backfill placement below footings should extend laterally beyond all edges of the footings at least 8 inches per foot of over-excavation depth, below footing base elevation. The over-excavation should then be backfilled up to the footing base elevation with granular material placed in lifts 8 inches or less in loose thickness and compacted to at least 95 percent of the material's modified effort maximum dry density (ASTM D-1557). Refer to Table 5 for acceptable aggregate.

For the design of footings bearing on approved undisturbed granular native soil or engineered fill, we recommend a net allowable bearing pressure of 2,000 psf. If anticipated footing elevation is located within the existing clay layer, the soil shall be over excavated down to more granular soils and replaced with approved structural fill. The bearing pressure is a net value, as the weight of the footing itself has already be 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 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 lean CLAY or 0.40 for granular structural fill between the base of the foundation elements and underlying material is recommended.

4.3 Lateral Earth Pressure and Sliding Analyses

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

Geotechnical Report 4-3 North Wind Infrastructure & Technology, LLC

The coefficients and static lateral earth pressures recommended for design are listed in Table 4-1 for the general soil type identified on the Subject Property, CL. 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 4-1 Static Equivalent Fluid Pressures.

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

CL

φ‘ = 28o

MDD= 110 pcf

At-rest case, Ko = 0.69 69 pcf (unsaturated)

Active case, Ka = 0.53 53 pcf (unsaturated)

Passive case, Kp = 1.89 189 pcf (unsaturated)

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

Group Symbol Soil Type

R an ge o f M ax im um

D ry U ni t W ei gh t, pc f

R an ge o f O pt im um

M oi st ur e, P er ce nt

Typical Values of

Compression Typical Strength Characteristics

Ty pi ca l C oe ff ic ie nt o f Pe rm ea bi lit y, ft

./m in

R an ge o f C B

R V al ue s

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

, l bs

/c u in

At 1.4 Tsf (20 psi)

At 3.6 Tsf (50 psi)

Cohesion (as compacted) psf

Cohesion (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 ***** ***

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

CL

Inorganic clays of low to medium plasticity.

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

50-

OL

Organic silts and silt-clays, low plasticity.

80-100 33-21 ****

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

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

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

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

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

25-

Notes:

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

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

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

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

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

For sliding stability analyses, the frictional resistance of concrete footings or foundations placed against soils shall be calculated as µR, where:

µ = coefficient of friction between concrete and rock, 0.7, granular soils (i.e. aggregate base), 0.6, and fine soils (i.e. CL), 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 corrosion rating of concrete and steel to be high.

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.

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

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.

Due to the existence of high plasticity clay soils, pavement recommendations have been broken down into three options. These options should be considered in the determination of subgrade preparation for the flexible pavement. The alternatives are as follows:

• the removal of the upper 12” of high-plasticity soil and replace with approved fill.

• treatment of the upper 6 inches the high-plasticity clay subgrade layer.

• a combination of both to remove/treat the upper 6” of expansive soils.

4.5.1 Pavement Design for Untreated Subgrade

For this option, a minimum of 12 inches of the high-plasticity subgrade shall be over excavated and replaced with approved structural fill beneath the pavement sections. No specific California Bearing Ratio (CBR) or resilient modulus tests were performed for this project to evaluate the support characteristics of the subgrade; therefore, a CBR was assumed, for design of the pavement structure. This CBR was taken to be 2 due to the existing expansive soils classified as lean to fat CLAY soils encountered within the upper 3-4 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 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 4-3. Flexible Pavement Section Design.

Traffic Min Subgrade CBR Asphalt Concrete

(in.)

Aggregate Base

(in) Access Road/Maneuvering Areas 2 5 12

Table 4-4. Rigid Pavement Section Design.

Traffic Min Subgrade CBR Asphalt Concrete (in.)

Aggregate Base

Access Road/Maneuvering Areas 2 6 12

4.5.2 Pavement Design with Treated Subgrade

This option requires the top 6 inches of finished subgrade soils directly beneath the pavements to be chemically treated. The chemical treatment is intended to improve the strength of the soil layer and decrease expansion potential from moisture intrusion. Table 4-4 lists the pavement component thicknesses that may be used as a guide.

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

Table 4-5. Flexible Pavement Section Design.

Traffic Min Subgrade CBR Asphalt Concrete

(in.)

Treated Base

(in) Aggregate Base

Access Road/Maneuvering Areas 9 4 6 6

We anticipate that the pavement subgrade will generally consist of on-site high plasticity clay soils. The pavement subgrade should be treated with lime as recommended by the National Lime Association (NLA). Based on the classification test results, we recommend that approximately 7 to 9 percent lime by dry weight be used for estimating and planning. The percentages are given as application by dry weight and are typically equivalent to about 35 to 45 pounds of lime per square yard per 6-inch depth. The actual quantity of lime should be determined at the time of construction based on lime determination tests conducted using bulk samples of the subgrade soils. The pulverization, mixing, and curing of the lime treated subgrade is of particular importance for the on-site clay soils. The subgrade should be compacted to a minimum of 95 percent of the Standard Effort (ASTM D698) maximum dry density at a moisture content between optimum and 4 percent wet of the optimum moisture content.

Furthermore, care must be taken when performing lime stabilization on soil containing high amounts of sulfate. As outlined in this report, the USGS Web Soil Survey indicated this area to have high amounts of sulfate. In general, soils with organic contents in excess of one percent may be difficult to lime stabilize or may require uneconomical quantities of lime to achieve the desired results. As a general rule of thumb, if the total soluble sulfate level is greater than about 0.3% in a ten to one water to soil solution, then additional precautions to guard against sulfate reactions, such as swell tests, may be warranted (Little, 1997). If this option is considered, a chemical test of the existing soils should be conducted to assess the suitability of lime stabilization.

4.5.3 Additional Pavement Recommendations

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. 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. Due to the existence of expansive soils, a sheepsfoot roller may be needed to meet the compaction requirements

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.

The pavement design methods described above are intended to provide structural sections with adequate thickness over a particular subgrade such that wheel loads are reduced to a level the subgrade can support.

The support characteristics of the subgrade for pavement design do not account for shrink/swell movements of an expansive clay subgrade such as the soils encountered at this site. Thus, the pavement may be adequate from a structural standpoint, yet still experience cracking and deformation due to shrink/swell related movement of the subgrade. Post-construction subgrade movements and some

Geotechnical Report 4-7 North Wind Infrastructure & Technology, LLC cracking of pavements are not uncommon for clay subgrade conditions such as those observed at this site.

Reducing moisture changes in the subgrade is important to reduce shrink/swell movements. Although chemical treatment will help to reduce such movement/cracking, this movement/cracking cannot be economically eliminated. Furthermore, due to the

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 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 lean CLAY (CL) to fat CLAY (CH) and Silty SAND (SM) can be excavated using conventional excavation equipment. These soils should be excavated as needed but

Geotechnical Report 4-8 North Wind Infrastructure & Technology, LLC should extend a minimum of 3 ft beyond the footprint, for over excavations and large cuts. Bedrock or coarse cobbles were not found during the field exploration, neither are they shown on the web soil survey of the subject property. Should these be encountered during the site preparation, the Geotechnical Engineer should be contacted.

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.

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

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

4.7 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 lean to fat CLAY can be used as general fill for landscape areas or general site grading. All imported fill should be reviewed and approved by the Geotechnical Engineer prior to placement. See Section 3 for additional information on subsurface soil strata and characteristics. All structural fill shall meet the specifications outlined in Table 4-6 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 in. in median diameter and must meet the required gradation with a maximum PI of 6.

1 in. 100 No. 10 0-50 No. 40 0-30

No. 200 0-15

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

Soil may not contain particles larger than 1 in.

in median diameter and must meet the required gradation

1 in. 100 ¾ in. 90-100 No.