Little Sahara Geotech Report.pdf

Prepared for:

Bureau of Land Management

Prepared by:

North Wind Resource Consulting, LLC

October 26, 2017

70048.007-TR-001

Geotechnical Report Little Sahara Visitor Center Bureau of Land Management West Desert District Eureka, UT

ID/UT IDIQ Contract No. 140L0619D0008

Geotechnical Report Little Sahara Visitor Center

Bureau of Land Management West Desert District

Eureka, UT

October 20, 2020

Prepared for:

Bureau of Land Management West Desert District Office

Eureka, UT

Prepared by:

North Wind Resource Consulting, LLC 1425 Higham Street

Idaho Falls, Idaho 83402

Project No. 70048.007

CHANGE MANAGEMENT RECORD

Project No.: 70048.007

Report Number: 70048.007-TR-001

Report Name: Geotechnical Report Little Sahara Visitor Center Bureau of Land Management West Desert District Office Eureka, UT

REVISION

NO. DATE DESCRIPTION OF CHANGES/AFFECTED PAGES

0 October 20, 2020 Base Document

70048.007 TR-001

Geotechnical Report v North Wind Resource Consulting, LLC Little Sahara Visitor Center October 2020

CONTENTS

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

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

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 ..................................... 3-2

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

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

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

4.6.2 Demolition, Clearing and Grubbing ................................................................... 4-6

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 ............................................................... 4-8

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

Geotechnical Report vi North Wind Resource Consulting, LLC Little Sahara Visitor Center October 2020

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

Geotechnical Report vii North Wind Resource Consulting, LLC Little Sahara Visitor Center October 2020

FIGURES

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

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

Figure 2-1. Quaternary Fault Map (USGS, web quaternary faults map). .................................................. 2-2

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 for CL ................................................................................... 4-3

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

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

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

Table 4-5. Structural Fill Specifications. ................................................................................................... 4-8

APPENDICES

Appendix A: Test Pit Logs ....................................................................................................................... A-1

Appendix B: Test Pit Locations ................................................................................................................ B-1

Geotechnical Report viii North Wind Resource Consulting, LLC Little Sahara Visitor Center October 2020

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

MDD maximum dry density

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 Little Sahara Visitor Center October 2020

1. INTRODUCTION

This report presents the findings, conclusions, and recommendations of a geotechnical investigation and analysis for the proposed Little Sahara Visitor Center for the Bureau of Land Management (BLM). The new visitor center, located approximately 20 miles southwest of Eureka, Utah, will be referred to as Subject Property, hereinafter. The Subject Property is located in Lot 4, Section 4, Township 13 South, Range 4 West of the Salt Lake meridian. Refer to vicinity map in Figure 1.1, for more information. The project site encompasses approximately 13 acres of development area within which a new visitor center will be built. 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 #007.

The objective of this investigation was to determine general soil conditions for use by the engineer for the design of the proposed visitor center, 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.

1.1 Project Description

The Subject Property is located approximately 20 miles southwest of Eureka, Utah, at 27020 W Sand Mountain Road and lies within Juab County. Site vicinity characteristics include natural grasses and

Geotechnical Report 1-2 North Wind Resource Consulting, LLC sagebrush on undeveloped land. Previous development at the site includes an existing visitor center, warehouse, bunkhouses, fire garage, RV pads, storm sewer, sanitary sewer, water, electricity and gas.

The anticipated site improvements include construction of a new single-story visitor center. Associated site improvements will likely include asphaltic and concrete paving, and fencing. Site utilities will likely include power, telephone, water, storm water, and sanitary wastewater piping for a subsurface wastewater disposal system. These improvements will encompass approximately an acre of the 13-acre site. Refer to Figure 1-2 below for more site details.

Figure 1-2: 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 concept provided by the BLM and a site visit performed on Monday May 18, 2020. Refer to Figure 1-2 for conceptual drawing.

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

Geotechnical Report 1-3 North Wind Resource Consulting, LLC

• 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 approximately 20 miles southwest of Eureka, Utah. More specifically, the Subject Property is located at 27020 W Sand Mountain Road and lies within Juab County. The Subject Property is located northeast of the Sand Dunes which are located west of the Tintic Valley and the East Tintic Mountains. The surrounding ground is vegetated with natural sagebrush and grasses. Vegetation is supported with native soils that appeared to be silts and clays. Elevation at the site is approximately 5,240 feet. Drainage consists of percolation by site soils and overland flow to the southwest toward the sand dunes.

2.2 General Geology

On the internet, the Utah Geological Survey has a geologic map with soil unit descriptions of the area.

The map characterizes the soils as alluvium and indicates that most of the soils around the site come from stream, river, and channel deposits consisting of clay- to cobble-size, poorly sorted, crudely stratified, and generally undissected detrital material. They are commonly less than a few meters thick but locally may reach 10 m. Locally soils may include alluvial fan deposits and stream terrace deposits. These soils overlie Lake Bonneville shoreline features (UGS, web soil unit map). The soils encountered during the field exploration were consistent with this description.

2.3 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). Figure 2-1 shows the identified faults that are closest to the site. The closest of these, East Tinte Mountains Faults, are approximately 10 miles east of 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 2018 edition of the International Building Code (IBC). Seismic Design Parameters are shown in Table 2-1 for project site coordinates latitude: 39.72 longitude: -112.30 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 0.52g Mapped spectral acceleration for 1-second periods [from ASCE 7] S1 0.182g Site coefficient Fa 1.384 Site coefficient Fv 2.236 Max considered earthquake spectral response acceleration for short periods SMS=FaSS 0.72g Max considered earthquake spectral response acceleration for 1-second periods

SM1=FvS1 0.407g

5% damped design spectral response acceleration at short periods SDS=2/3 SMS 0.48g 5% damped design spectral response acceleration at 1-second periods SD1=2/3 SM1 0.272g Peak Ground Acceleration (PGA) (%g) 0.226g

Geotechnical Report 3-2 North Wind Resource Consulting, LLC

Figure 2-1. Quaternary Fault Map (USGS, web quaternary faults map).

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

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 effort was conducted on May 18, 2020, which consisted of two (2) exploratory test pits down to a maximum depth of 10 feet below existing ground surface (bgs). The test pits were excavated with a rubber-tired backhoe (JCB 3CX) and backfilled upon completion. Locations of the test pits were determined to the nearest foot using a hand-held GPS unit. The locations are shown on the Test Pit Location Map in Appendix B.

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A 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 representative samples to aid in soil classification and to estimate the engineering properties of the native soils. The testing program consisted of two (2) moisture content (ASTM D2216) two (2) sieve analyses (ASTM C136) and two (2) Atterberg limits tests (ASTM D4318). 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. Test pit logs with descriptions of the various materials encountered in each test pit and select laboratory test results are included in Appendix A.

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

TP-1 3.5 CL – Lean Clay with Sand 0 20.2 79.8 39 20 TP-2 6.5 CL – Lean Clay 0 11.4 88.6 27 18

3.2 Stratigraphy

Visual classification of each soil stratum encountered at the time of the field exploration was completed according to ASTM D2488. The soil lithology encountered in the field was consistent between both test pits with slight variations. Generally, the stratigraphy for both test pits consisted of low-plasticity lean CLAY (CL) with varying degrees of sand extending down to a maximum exploratory depth of 10 feet bgs.

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: Linoyer very fine sandy loam. Specific soil characteristics of this soil type can be found below.

Linoyer very fine sandy loam, 2 to 5 percent slopes – Linoyer soils are on fan remnants, alluvial fans, alluvial flats, basin floors, fan skirts, inset fans, axial stream terraces, lake terraces, and lake plains at elevations of 1,370 to 1,830 meters in Utah and up to 2,130 meters in Nevada. Slopes are 0 to 10 percent.

They formed in alluvium and lacustrine deposits derived from sandstone and limestone. The climate is semiarid and the average annual precipitation ranges from 200 to 305 mm. Mean annual air temperature ranges from 7 to 11 degrees C. Frost-free period is 100 to 140 days. (USDA-NRCS, web soil survey)

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

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

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 low 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 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. 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 native soil or engineered fill, we recommend a net allowable bearing pressure of 2,000 psf. 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.

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.

Geotechnical Report 4-2 North Wind Resource Consulting, LLC

4.3 Lateral Earth Pressure and Sliding Analyses

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

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 for the general soil type identified on the Subject Property, CL. These values are based on the correlated soil

Geotechnical Report 4-3 North Wind Resource Consulting, LLC 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 CL

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

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 β (Effective

Stress Envelope Degrees)

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 40-80 300-500

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, 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.

Geotechnical Report 4-4 North Wind Resource Consulting, LLC

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 to be low 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 4-3. Flexible Pavement Section Design.

Traffic Min Subgrade

CBR

Asphalt Concrete

Aggregate Base

Aggregate Sub-Base (Pit-Run)

Access Road/Maneuvering Areas 8 4 in. 6 in. 12 in.

Geotechnical Report 4-5 North Wind Resource Consulting, LLC

Parking 8 3 in. 4 in. 8 in.

Table 4-4. 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.

Geotechnical Report 4-6 North Wind Resource Consulting, LLC

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 top soils 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 site soils (CL) can be excavated using conventional excavation equipment. These soils should be excavated as needed but should extend a minimum of 3 ft beyond the footprint, for over excavations and large cuts. Bedrock or coarse cobbles were 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.

Geotechnical Report 4-7 North Wind Resource Consulting, LLC

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 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 onsite 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 clay loam (type 5 in Table 1.2 of the Utah onsite wastewater code). This classification group can be used to determine application rates for use of a subsurface sewage disposal system. It is recommended to utilize the most recent version of “Utah Administrative Code R317-4. Onsite Wastewater Systems” for site specific evaluations and design characteristics.

Geotechnical Report 4-8 North Wind Resource Consulting, LLC

4.7 Structural Fill and Aggregate Recommendations

Granular structural fill will be required beneath any over excavated shallow foundations including improved concrete and asphalt sections and areas adjacent to retaining wall structures. The onsite soils encountered during the field exploration are not suitable to be used as structural. If granular materials are found on the site, laboratory testing for these soils should be performed to confirm that they are within the granular structural fill specifications established in this Section. Onsite native soils classified as lean 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 4-5.Table 4-5. Structural Fill Specifications.

Structural Fill Product Allowable Use Material Specifications Sieve

Size

Passing

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

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

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

4 in. 100 3 in. 90-100 No. 4 30-60

No.

200 <10

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

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

No.

200 0-15

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

Soil may not contain particles larger than 1 in.

in median diameter and must meet the required gradation

1 in. 100 ¾ in. 90-100 No. 4 40-65 No. 8 30-50 No.

200 3-9

General Structural Fill Lightly loaded floor slab and pavement

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

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

3 in. 100

No.

200 <50

General Fill General site grading

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

3 in. 100

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

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

Geotechnical Report 4-9 North Wind Resource Consulting, LLC

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

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.

ASCE, ASCE 7 Hazards Report, https://asce7hazardtool.online/, American Society of Civil Engineers

ASTM C150 / C150M-12, “Standard Specification for Portland Cement,” ASTM International, West Conshohocken, PA, 2012.

ASTM D698-12, “Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbf/ft3 (600 kN-m/m3)),” ASTM International, West Conshohocken, PA, 2012.

ASTM D2488-09a, “Standard Practice for Description and Identification of Soils (Visual-Manual Procedure),” ASTM International, West Conshohocken, PA, 2009.

IBC-2018, “International Building Code, 2018 Edition,” International Code Council, Washington, D.C.

2018.

Utah Office of Administrative Rules, “R317-4. Onsite Wastewater Systems.,” https://rules.utah.gov/publicat/code/r317/r317-004.htm, Utah Office of Administrative Rules.

NAVFAC DM-7.2, “DM-7.02 Foundations and Earth Structures,” Naval Facilities Engineering Command, Alexandria, VA, September 1986.

UGS, “Geologic Map,” https://geology.utah.gov/apps/intgeomap/, Soil Unit Map with descriptions, Utah Geological Survey.

USGS,…