Appendix F - LMTF RF 35 Geotechnical Report Final.pdf

25004473.001A/SLC25R182194 Page 1 of 1 May 19, 2025 © 2025 Kleinfelder www.kleinfelder.com

849 West Levoy Drive, Suite 200, Taylorsville, UT 84123-2544 p | 801.261.3336 f | 801.261.3306

May 19, 2025 Kleinfelder Project No.: 25004473.001A

Mr. Brian Barnes, PE Studio Leader/Principal Dekker 7601 Jefferson NE, Suite 100 Albuquerque, NM 87109

SUBJECT: Geotechnical Engineering Investigation Report Boeing Little Mountain Test Facility Weber County, Utah

Dear Mr. Barnes:

Kleinfelder is pleased to submit our geotechnical engineering investigation report for the proposed Boeing Little Mountain Test Facility (LMTF) located in Weber County, Utah. This work was performed in general accordance with our proposal to you dated October 25, 2024, and your subsequent authorization.

Based on our geotechnical evaluation, we have provided geotechnical recommendations for site preparation, grading and excavation, foundation design, gravel surfacing, and fill placement and compaction for the proposed testing facility site.

We appreciate the opportunity to provide geotechnical services to you on this project. Please contact the undersigned at 801.261.3336 if you have any questions regarding this report or if we can provide assistance with other aspects of the project.

Respectfully submitted, KLEINFELDER

Adam Bean, EIT Matt Moriarty, PE Staff Geotechnical Engineer Senior Geotechnical Engineer http://www.kleinfelder.com/

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GEOTECHNICAL ENGINEERING INVESTIGATION REPORT

BOEING LITTLE MOUNTAIN TEST FACILITY

WEBER COUNTY, UTAH

KLEINFELDER PROJECT NO: 25004473.001A

MAY 19, 2025

Copyright 2025 Kleinfelder All Rights Reserved

ONLY THE CLIENT OR ITS DESIGNATED REPRESENTATIVES MAY USE THIS DOCUMENT AND ONLY FOR THE SPECIFIC PROJECT FOR WHICH THIS

REPORT WAS PREPARED.

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A Report Prepared for:

Mr. Brian Barnes, PE Studio Leader/Principal

GEOTECHNICAL ENGINEERING INVESTICATION REPORT

BOEING LITTLE MOUNTAIN TEST FACILITY

WEBER COUNTY, UTAH

Prepared by:

Adam Bean, EIT Staff Geotechnical Engineer

Matt Moriarty, PE Senior Geotechnical Engineer

KLEINFELDER

849 West Levoy Drive, Suite 200 Salt Lake City, Utah 84123 Phone: 801.261.3336 Fax: 801.261.3306

May 19, 2025 Kleinfelder Project No.: 25004473.001A

No. 10439373

MATTHEW DAVID

MORIARTY

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TABLE OF CONTENTS

1 INTRODUCTION

1.1 GENERAL

1.2 PROJECT DESCRIPTION

1.3 PURPOSE AND SCOPE OF SERVICES

2 FIELD EXPLORATION AND LABORATORY TESTING

2.1 FIELD EXPLORATION

2.2 LABORATORY TESTING

2.2.1 Geotechnical Laboratory Testing

2.2.2 Analytical Laboratory Testing

3 SITE CONDITIONS

3.1 SURFACE

3.2 SUBSURFACE CONDITIONS

3.3 GROUNDWATER

3.4 GEOLOGIC SETTING

3.5 GEOLOGIC HAZARDS

3.5.1 Seismicity and Faulting

3.5.2 Liquefaction and Lateral Spreading

4 CONCLUSIONS AND RECOMMENDATIONS

4.1 GENERAL CONCLUSIONS

4.2 EARTHWORK

4.2.1 General Site Preparation and Grading

4.2.2 Wet Weather Construction

4.2.3 Excavatability

4.2.4 Structural Fill and Compaction

4.2.5 Temporary Excavation Stability

4.2.6 Utility Trenches

4.3 SHALLOW FOUNDATIONS

4.3.1 Foundation Bearing Soil Preparation

4.4 LATERAL EARTH PRESSURES

4.5 RETAINING WALLS

4.6 CONCRETE SLABS-ON-GRADE

4.7 PAVEMENT DESIGN AND CONSTRUCTION

4.7.1 Pavement Subgrade Preparation

4.8 MOISTURE PROTECTION AND SURFACE DRAINAGE

4.9 SOIL CORROSION AND REACTIVITY

5 LIMITATIONS

6 REFERENCES

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TABLES

2-1 Analytical Laboratory Test Results 3-1 Generalized Soil Engineering Properties 3-2 General Ground Motion Parameters Based on ASCE 7-22 4-1 Criteria for use of Structural Fill 4-2 Criteria for Untreated Base Course 4-3 Criteria for Free-Draining Granular Backfill 4-4 Structural Fill Placement and Compaction Criteria 4-5 Recommended Equivalent Fluid Pressures (EFP) 4-6 Soil Subgrade Modulus Values for a one-foot Square Plate 4-7 Pavement Section Recommendations

FIGURES

4-1 Allowable Bearing Capacity of Spread Footings 4-2 Allowable Bearing Capacity of Continuous Footings 4-3 Foundation Zone Influence

APPENDICES

A Exploration Location Plan and Site Vicinity Map B Exploration Logs C Laboratory Test Results D Important Information About This Geotechnical Engineering Report

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1 INTRODUCTION

1.1 GENERAL

This report presents the results of Kleinfelder’s geotechnical evaluation to aid in design and construction of the proposed Boeing testing facility. The facility will be located at the Little Mountain Testing Facility

(LMTF) owned by the United States Air Force in Weber County, Utah. The location of the project site is shown in Appendix A. Our services for this study were performed in accordance with the scope of work outlined in our proposal dated October 25, 2024.

This report includes our recommendations relating to the geotechnical aspects of project design and construction of the proposed structures and infrastructure for the testing facility. The conclusions and recommendations stated in this report are based on the subsurface conditions encountered in our exploratory borings at the time they were performed. They also are subject to the limitations and provisions stated in Section 5 of this report. Please also refer to the document titled “Important

Information About This Geotechnical Engineering Report,” contained in Appendix D.

1.2 PROJECT DESCRIPTION

Our understanding of the configuration for the proposed testing facility is based on the Request for

Proposal (RFP) documents dated October 22, 2024 as well as phone and email correspondence with

Dekker. From our discussions and review of the available information, we understand that the facility will be located southwest of existing structures within the property. The structure consists of a single- story, 29,100 square foot testing facility and a 7,400 square foot office space. The facility will also include elements such as asphalt paving, site concrete flatwork, and site structures.

Retaining walls with retained heights of up to 30 feet are planned. Structural loading information provided in the RFP indicates that anticipated column and wall loads for the structure will range from

80 to 200 kips and from 8 to 36 kips per linear foot, respectively.

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We have assumed a finish floor elevation of +4,278 feet. We understand that, at the current level of design development, detailed grading plans, structure loading and layouts, and floor elevations are not available. Additionally, we understand that aspects of the design such as facility layout, design of individual structures, etc., may be subject to change as the design continues to progress. Kleinfelder should review the final design to confirm that the recommendations provided in this report remain valid for the final configuration.

1.3 PURPOSE AND SCOPE OF SERVICES

The purpose of our study was to evaluate subsurface conditions at the proposed testing facility site and develop geotechnical recommendations based on the conditions encountered at the site.

The conclusions and recommendations presented in this report are based on our analyses of the data from our field exploration and laboratory testing programs. Kleinfelder’s scope of services included:

• Performing subsurface exploration and soil sampling to characterize the subsurface soil profile at the site.

• Performing laboratory testing of selected soil samples to evaluate the engineering properties and corrosion potential of the soils at the site.

• Performing engineering analyses and developing geotechnical conclusions and recommendations for design and construction of shallow foundations, roadways, seismic hazard, earthwork and grading, and site preparation.

• Preparation of this report, which includes a description of the proposed project, a description of the surface and subsurface site conditions found during our exploration and laboratory testing programs, and a summary of our conclusions and recommendations.

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2 FIELD EXPLORATION AND LABORATORY TESTING

2.1 FIELD EXPLORATION

The field exploration program for this project was performed from March 26 to March 31, 2025.

Approximate locations of the explorations are contained in Appendix A. The field program consisted of advancing eight (8) borings within the proposed facility footprint to the planned depth or practical refusal. The borings consisted of the following:

• Building footprint– five (5) soil borings ranging in depth of approximately 25 to 47 feet beneath existing ground surface (bgs).

• Perimeter wall alignment – Three (3) soils borings ranging in depth of approximately 45 to 56 feet bgs.

Borings were drilled using a truck-mounted CME-75 drill rig using 8-inch outer diameter (O.D.)

hollow-stem augers. Field penetration testing was performed using thick-wall samplers. The samplers were driven into the bottom of the boring at regular intervals during drilling into the undisturbed native soil to measure the resistance (i.e., blow count) and obtain disturbed samples of soil for visual characterization and laboratory testing. The standard penetration test (SPT) sampler has a 1.4-inch inside diameter and a 2-inch outside diameter. The California (Cal.) sampler has a 2.375-inch inside diameter and a 3.0-inch outside diameter. The number of blows required to drive the sampler 18 inches into the soil were recorded for each 6-inch increment of penetration on the boring logs. Where blow counts exceeded 50 (SPT) or 75 (Cal.) blows per 6 inches or less (i.e., refusal), the depth of penetration was recorded upon reaching 50 or 75 blows (example: 50/4” or 75/4”). Relatively undisturbed samples of fine-grained soils were also collected using a thin-wall (Shelby) sampler. The thin-wall sampler has a

2.875-inch inside diameter and a 3-inch outside diameter. Upon completion of drilling, all borings were backfilled with the soil cuttings generated while drilling. The hollow stem auger drilling and sampling was performed by Davis Drilling Services and was supervised and logged by a Kleinfelder geoprofessional. Samples obtained during the field exploration were transported to our laboratory for further evaluation and testing.

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The logs of the conditions encountered by Kleinfelder are presented in Appendix B. A key to the exploration logs and a summary of the Unified Soil Classification System (USCS) soil descriptions are also contained in Appendix B. The lines defining boundaries between soil types on the logs are based on

Kleinfelder’s field observations and are therefore approximate. Transition between soil types may be abrupt or may be gradual. Samples will be retained for a period of 90 days from the date of this geotechnical report, after which time the samples will be discarded unless otherwise requested.

2.2 LABORATORY TESTING

2.2.1 Geotechnical Laboratory Testing

Geotechnical laboratory tests were performed on selected soil samples to estimate their relative engineering properties and soil type. Testing for the following properties was performed in general accordance with recognized ASTM standards:

• Unit Weight and Water Content,

• Sieve Analysis,

• Unit Weight,

• Atterberg

• Unconsolidated Undrained (UU) Triaxial, and

• Direct Shear

Results of all geotechnical laboratory tests are included in Appendix C of this report. Selected geotechnical test results are also shown on the exploration logs contained in Appendix B.

2.2.2 Analytical Laboratory Testing

The following analytical laboratory testing was performed on soil samples by an independent analytical laboratory:

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• pH,

• Resistivity,

• Water Soluble Sulfate, and

• Water Soluble Chloride.

The analytical laboratory test results are presented in Appendix C and are summarized below in

Table 2-1.

Table 2-1: Analytical Laboratory Test Results

Exploration No.

Depth

(feet bgs) pH

Resistivity (ohms-cm)

Water Soluble Sulfate

(mg/kg dry)

Water Soluble Chloride

(mg/kg dry)

KLF-24-06 20.0 9.8 310 206 104

Kleinfelder’s scope of services does not include corrosion engineering and, therefore, a detailed analysis of the corrosion test results is not included. A qualified corrosion engineer should be retained to review the test results for further evaluation and design protective systems, if considered necessary.

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3 SITE CONDITIONS

3.1 SURFACE

The project site is generally undeveloped. Existing buildings and paving lie to the northeast, and west of the facility. At the time of our investigation, the site consisted of sparsely vegetated undeveloped land, with the northeastern quarter being landscaped grass. The site slopes to the northwest at approximately a 10 percent grade.

3.2 SUBSURFACE CONDITIONS

Subsurface conditions encountered in our explorations generally consist of loose to very dense sand and gravel interbedded with stiff to hard clay and silt mixtures. Subsurface conditions are variable due to the lacustrine depositional environment but generally become denser and harder with depth. Based on the results of our laboratory testing, fine grained soils within the top 5 feet at the site generally exhibit high plasticity. Surficial soils with high plasticity are generally weaker, less pervious, and may be susceptible to volumetric changes with changes in moisture (shrinking as they dry and swelling as they become wet). These volumetric changes can damage lightly-loaded structures and pavement unless mitigated.

As shown in the generalized profile, Figure 3-1, the soil stratigraphy varies at the site. Table 3-1 below provides a summary of the soil type and engineering properties.

Table 3-1: Generalized Soil Engineering Properties

Soil Type γtot

(pcf) ϕ’

(deg) c’

(psf) Su

(psf)

1 - Clayey to Silty SAND 110 32 50 -

2 - Lean to Fat CLAY 110 22 600 2,000

3 - Loose to Med. Dense SAND 110 32 50 -

4 - Dense to Very Dense SAND 135 38 50 -

5 - Medium Stiff SILT 110 30 100 -

4 - Dense to Very Dense SAND 135 38 50 -

Notation and units: γtot = Total Unit Weight, ϕ’ = Effective Friction Angle, c’ = Effective Cohesion, Su = Undrained Shear Strength, pcf = pounds per cubic foot, psf = pounds per square foot.

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Note 1: Not to scale.

Note 2: Refer to individual logs for detailed information and the graphic legend keys for graphical symbol information.

Note 3: Borings shown on figure are generally from northwest to southeast. Refer to Appendix A for boring locations

Figure 3-1 – Generalized Soil Profile

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The exploration logs presented in Appendix B and the laboratory test results presented in Appendix C should be referred to for more detailed information regarding the subsurface soil conditions at the site.

3.3 GROUNDWATER

Groundwater was not encountered within the depths explored (55 feet) at the time of drilling

(March 2025). Groundwater levels are dependent on seasonal precipitation and groundwater fluctuations, irrigation practices, land use, and runoff conditions. However, we do not expect that groundwater will adversely impact the planned development.

3.4 GEOLOGIC SETTING

The site is located within Weber County, Utah, on the eastern margin of the Basin and Range

Physiographic Province. The site is located east of the Promontory Mountain Range, and just west of the

Little Mountain summit. The Basin and Range Province is characterized by approximately north-trending valleys and mountain ranges, which have been formed by extensional tectonics and displacement along normal faults (Hunt, 1967). The Great Salt Lake, located adjacent to the site, is a remnant of the prehistoric Pleistocene-aged Lake Bonneville. The Great Salt Lake is an endorheic saline lake, which receives inflow of water from a number of rivers in the region.

Published geologic maps of the Ogden Bay Quadrangle (Kleber 2024) mapped the shallow deposits at the site as consisting of Holocene to Late-Pleistocene lacustrine gravel and sand deposits with a matrix of sand, silt, and clay. Explorations conducted as a part of this report are generally consistent with the published geologic map.

3.5 GEOLOGIC HAZARDS

3.5.1 Seismicity and Faulting

The proposed project site is located within the Intermountain Seismic Belt – a seismically-active region that extends from Arizona to Montana (Smith and Arabasz, 1991). Active faults in the region are potential sources for seismic loading hazards for the site. Active earthquake faults are typically

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Fault Zone is mapped by the USGS approximately 10.8 miles to the southwest of the proposed facility and the Wasatch Fault Zone is mapped about 16.5 miles to the east of the proposed facility.

Seismic design parameters consistent with the 2024 International Building Code (IBC) are based on the

American Society of Civil Engineers (ASCE) 7-22 Minimum Design Loads and Associated Criteria for

Buildings and Other Structures. Based on our site investigation and subsequent analysis, the underlying soil at the site corresponds with a Site Class C per Table 20.2-1 of ASCE 7-22. The general seismic design parameters were obtained per 2024 IBC/ASCE 7-22 based on the site class, site coordinates, and the risk category of the structure using the ASCE Online Hazard Tool (https://ascehazardtool.org/). The design parameters for the site are summarized in Table 3-2. If a multi-period spectrum is required per Section

11.4.5 of ASCE 7-22, one can be provided upon request.

Table 3-2: General Ground Motion Parameters Based on ASCE 7-22

Parameter Value ASCE 7-22 Reference

Latitude (degrees) 41.248941 N/A

Longitude (degrees) -112.250482 N/A

Assumed Building Risk Category II N/A v̅s (ft/s) 1551.7 Equation 20.4-1

Velocity Profile Method MAM1 N/A

SS (g) 0.86 USGS Seismic Design Geodatabase

S1 (g) 0.28 USGS Seismic Design Geodatabase

TL (s) 6 USGS Seismic Design Geodatabase

/ Figure 22-14

Site Classes Considered for Derivation of Ground Motion Parameters

C Table 20.2-1 / Section 20.3

SMS (g) 0.92 USGS Seismic Design Geodatabase

/ Figure 22-1

SM1 (g) 0.4 USGS Seismic Design Geodatabase

/ Figure 22-2

SDS (g) 0.62 USGS Seismic Design Geodatabase

SD1 (g) 0.26 USGS Seismic Design Geodatabase

PGAM (g) 0.38 USGS Seismic Design Geodatabase

/ Figure 22-9

Note 1: Microtremor Array Measurements (MAM)

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3.5.2 Liquefaction and Lateral Spreading

Liquefaction is a phenomenon whereby loose, saturated, granular soil deposits lose a significant portion of their shear strength due to excess pore water pressure buildup resulting from dynamic loading, such as that caused by an earthquake. Among other effects, liquefaction can result in densification of such deposits causing settlements of overlying layers after an earthquake as excess pore water pressures are dissipated. Horizontally continuous liquefied layers may also have a potential to spread laterally where sufficient slope or free-face conditions exist. The primary factors affecting liquefaction potential of a soil deposit are: (1) magnitude and duration of seismic ground motions; (2) soil type and consistency;

(3) degree of soil saturation; (4) geologic age and origin; and (5) depth below ground surface.

Based on the soil conditions encountered during our field investigation at the site, including the relatively high density of the granular soils as indicated by blow counts, it is our opinion that the potential for liquefaction at this site is low and does not warrant further consideration.

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4 CONCLUSIONS AND RECOMMENDATIONS

4.1 GENERAL CONCLUSIONS

Based on the results of our field exploration and laboratory testing, it is our opinion that the site is suitable for the construction of the proposed improvements provided that the recommendations contained in this report are followed. These opinions, conclusions, and recommendations are based on our field exploration, engineering analysis, the properties of the materials encountered in our borings, the results of the laboratory testing program, and our understanding of the proposed development of the site.

This report is intended to support the design of the project elements at the current level of project development. The recommendations presented herein are based on information provided by Dekker at the time this report was prepared. As development plans are finalized, it is possible that design information, including structure location, loading, and design grade may change. Where changes occur, Kleinfelder should be notified to re-evaluate our recommendations considering the refined design information and modify our recommendations, as warranted.

The following sections of this report present our recommendations for general site preparation and grading, structural fill material requirements and compaction, site pavements, design of foundations and slabs-on-grade.

4.2 EARTHWORK

4.2.1 General Site Preparation and Grading

We understand that site grading will primarily consist of cutting existing soils to final grade. Cuts of up to

30 feet are planned for the site with the thickest parts of the cuts being planned for the southeast end of the site and very minor cuts on the northwest end of the site. Upon completion of the cuts, planned building, pavement, and parking areas should be stripped of any remaining vegetation, topsoil, loose/soft surficial soils, and other debris/deleterious materials to expose competent native soils.

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Following mass grading and stripping, exposed native soils should be proof-rolled with a fully loaded tandem-axle dump truck or fully loaded water truck and observed by the geotechnical engineer or his representative to identify soft, loose, or unstable areas.

Where encountered during proof-rolling, unstable soils should be stabilized under the observation of the geotechnical engineer. Unstable subgrade could be over-excavated 12 to 24 inches below existing grade and replaced with approved structural fill underlain by geotextile fabric and/or geogrid, depending on the severity of the instability. The geotextile fabric should consist of a woven geotextile, such as Mirafi 600X or equivalent. The final depth of removal will depend upon conditions observed in the field once overexcavation begins and should be assessed by the geotechnical engineer. The overexcavated areas should be backfilled with structural fill in accordance with Section 4.2.4. Geotextile fabric and/or geogrid should be placed in accordance with the manufacturer’s recommendations. Specific recommendations regarding the depth of overexcavation, type and thickness of granular material to use and the type and placement of geotextile to stabilize the subgrade should be provided by the geotechnical engineer based on observation of the site-specific conditions exposed.

The contractor should be aware that high plasticity fine-grained soils were observed within anticipated excavation depths. These high plasticity clay soils will be easily disturbed and will likely become unstable, especially during wet weather. Based on our understanding of the site grading, most of the high plasticity clay soils will be removed; however, where they remain in place, these soils should not be allowed to dry out as the near-surface high plasticity clays and silts will experience surficial cracking that will result in unstable conditions. Allowing high plasticity clays to dry will also increase the risk that the soils will swell upon introduction of water.

4.2.2 Wet Weather Construction

If exposed to excess moisture and repeated construction traffic, native near surface soils will become unstable, especially during wet weather. The use of track-mounted equipment with low ground pressure tracks and/or the use of dump and spread techniques to place material should be considered, particularly if construction occurs during the wet seasons of the year. Subgrade soils that become unstable or disturbed due to exposure to excess moisture will require replacement or remedial measures as outlined in Section 4.2.1.

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4.2.3 Excavatability

We anticipate that excavation of the on-site materials can generally be performed using conventional earth-moving equipment. The contractor should conduct their own evaluation of site conditions, the potential difficulties involved, and the type of equipment needed.

4.2.4 Structural Fill and Compaction

Structural fill placed below proposed structures should be comprised of imported or native material that meets the specifications outlined in Table 4-1. Criteria for fill used in parking areas are outlined in

Table 4-2. Criteria for fill used as free draining granular backfill area are outlined in Table 4-3.

The near surface soils encountered within practical excavation depths on the site contain significant amounts of fine-grained material. These soils generally do not meet the requirements set forth in Table

4-1 and are not suitable for use as structural fill. They may be used in non-structural areas; however, these soils will be very sensitive to moisture and will be more difficult to place and compact. Soils encountered in deeper cuts could meet the requirements shown in Table 4-1 and may have potential for reuse as structural fill. Soils intended for reuse as structural fill should be stockpiled separately from soils other site soils.

Table 4-1: Criteria for use of Structural Fill

Gradation Requirements

Standard Sieve Size Percent Passing

4 inch 100

¾ inch 100-70

No. 40 10-60

No. 200 0-151

Plasticity Requirements of Fines (Atterberg Limits)

Plasticity Index 6 or less

Note 1: Fill with more than 15 percent fines may be acceptable as approved by Kleinfelder.

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Table 4-2: Criteria for Untreated Base Course

Gradation Requirements

Standard Sieve Size Percent Passing

1-1/2 inch 100

1 inch 90-100

¾ inch 70-851

½ inch 65-80

3/8 inch 55-75

No. 4 40-65

No. 16 25-40

No. 200 7-11

Plasticity Requirements of Fines (Atterberg Limits)

Plasticity Index 6 or less2

Note 1: For improved performance and maintenance of aggregate-surfaced pavements, this value may be increased to 100.

Note 2: For improved performance and maintenance of aggregate-surfaced pavements, this value may be increased to 12 or less.

Table 4-3: Criteria for Free-Draining Granular Backfill

Gradation Requirements

Standard Sieve Size Percent Passing

1½ inch 90-100

1 inch 20-55

¾ inch 0-15

3/8 inch 0-5

Imported fill materials should be approved by the testing agency prior to importing. Also, prior to placing structural fill, the excavation should be observed by the testing agency to note that unsuitable material has been removed, and the exposed soil is in a firm and unyielding condition.

Structural fill should be placed in maximum 8-inch-thick loose lifts and compacted to at least 95 percent of the maximum dry density as determined by ASTM D1557 (Modified Proctor). The contractor will need to moisture condition the soils to be within the range outlined in Table 4-4 at the time of compaction.

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Table 4-4: Structural Fill Placement and Compaction Criteria

Fill Location Material Type Percent Compaction*

(ASTM D1557)

Moisture Content

Minimum Compaction Testing Frequency Per Lift

Top 12 inches below interior and exterior concrete slabs

Imported Gravel or Aggregate Base

95 minimum -2% to +2% of optimum

5,000 Square Feet

Below foundation bearing level Granular Structural Fill 95 minimum -2% to +2% of optimum

5,000 Square Feet

Site grading fills placed below building areas (extending 1H:1V beyond outside perimeter footings) Granular Structural Fill 95 minimum

-2% to +2% of optimum

5,000 Square Feet

Foundation wall backfill Granular Structural Fill 95 minimum -2% to +2% of optimum

500 Square Feet

Utility trench backfill Granular Structural Fill or Approved Trench Backfill

Material 95 minimum

-2% to +2% of optimum

100 Linear Feet

Landscape/Undeveloped Areas On-site soil / Granular

Structural Fill 85 minimum

-2% to +3% of optimum

15,000 Square Feet

4.2.5 Temporary Excavation Stability

Stability of construction excavations is the contractor’s responsibility. If stability of an excavation becomes questionable, the excavation should be evaluated promptly by Kleinfelder. The soils classification and strength properties presented in this report may be used for the planning of excavations and trench slopes in accordance with OSHA requirements or for the design of excavation slopes, shoring, and/or the use of trench boxes. Construction personnel should be aware that soil conditions may change rapidly if soil moisture conditions change or if soils that have been disturbed by previous excavations are encountered. Measures should be taken to protect construction personnel from raveling of trench sidewalls. If sloughing or free water is encountered, it may be necessary to reduce trench slopes beyond OSHA requirements or provide shoring. All excavations should comply with current OSHA safety requirements. If unstable conditions, or conditions other than those described in the geotechnical explorations are encountered during construction, excavation slopes should immediately be evaluated by the contractor’s Competent Person.

4.2.6 Utility Trenches

The Contractor is responsible for the safety of all personnel working in utility trenches. All utility trenches should be excavated in accordance with Section 4.2.5 of this report and applicable OSHA

25004473.001A/SLC25R182194 Page 16 of 30 May 19, 2025 standards. Prior to placement of pipe bedding material, the trench bed should be inspected to identify soft or unstable soils. If soft or unstable soils are identified, subgrade stabilization or over-excavation and replacement should be performed in accordance with the recommendations of Sections 4.2.1 and

4.2.4. Pipe bedding material should conform to the pipe manufacturer’s recommendations. Bedding or fill material should be properly placed and compacted to provide adequate support for the pipe. Trench backfill should be placed and compacted according to the requirements of Section 4.2.4.

4.3 SHALLOW FOUNDATIONS

The proposed structure may be supported by conventional continuous and spread footings supported by native granular soils or structural fill. Our recommendations were developed using expected footing sizes and loads provided by Dekker. In developing our recommendations for foundation design, we have assumed that proposed finished floor elevation will be at approximately elevation 4,278 feet. If the final finished floor elevation varies by more than one foot from our assumed elevation, Kleinfelder should be notified to evaluate and confirm the applicability of the recommendations provided herein.

Conventional continuous and spread footings placed on competent, undisturbed native soil or properly compacted structural fill may be proportioned using the allowable soil bearing pressures presented in

Figures 4-1 and 4-2, presented on the following page. Footings should be established a minimum of

30 inches below the lowest adjacent final grade for frost protection and confinement. The foundations should be constrained to the minimum and maximum sizes presented in Figures 4-1 and 4-2. A one-third increase to the allowable bearing capacity may be applied for transient wind or seismic load cases.

4.3.1 Foundation Bearing Soil Preparation

All shallow foundations should bear on native sand and gravel soils or properly compacted structural fill.

Native clay and silt soils are not suitable bearing soils for the planned structure. Where clay or silt soils are encountered in footing excavations, they should be overexcavated and replaced with structural fill. Based on our explorations and assumed finished floor elevations, clay and silt soils will likely be encountered intermittently in footing excavations at the northwest end of the site.

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Figure 4-1: Allowable Bearing Capacity of Spread Footings

2 3 4 5 6 7 8 9 10 11 12

A llo w a b le

B e a ri n g

P re s s u re k s f)

Spread Footing Width (ft)

Allowable Bearing Capacity - FS = 3

Service Limit Bearing Capacity - Settlement = 1 inch

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Figure 4-2: Allowable Bearing Capacity of Continuous Footings

2 3 4 5 6 7 8 9 10 11 12

A llo w a b le

B e a ri n g P re s s u re k s f)

Strip Footing Width (ft)

Allowable Bearing Capacity - FS = 3

Service Limit Bearing Capacity - Settlement = 1 inch

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Prior to construction of the foundations, the excavations should be observed by the geotechnical engineer or his representative to evaluate whether suitable bearing soils (consisting of native granular soils or structural fill) have been provided and whether the excavation bottoms are free of undocumented structural fill, loose, unstable or disturbed soils, rock, mud, water or frost. Concrete should never be placed on frozen subgrades.

Where overexcavation is required, structural fill should be placed within the zone of influence of the foundation defined by a 1Horizontal:1Vertical (1H:1V) plane extending downward from the edge of the foundations, schematically shown in Figure 4-3. This will facilitate proper distribution of the applied foundation pressures within the structural fill and meet the requirements for bearing capacity and settlement.

Figure 4-3: Foundation Zone Influence

4.4 LATERAL EARTH PRESSURES

Horizontal loads acting on foundations formed in open excavations will be resisted by friction acting at the base of foundations and by passive earth pressures acting on the embedded face of the foundation.

If design makes use of passive earth pressures, it is important that any backfill below or around footings is properly placed and compacted structural fill as described in Section 4.2.4. In this case, we would

25004473.001A/SLC25R182194 Page 20 of 30 May 19, 2025 recommend the geotechnical engineer, or his representative, be present during any footing backfill placement.

Lateral earth pressures may be proportioned according to Table 4-5. The friction acting along the base of footings, founded on native granular soils or structural fill, may be computed by using a nominal/ultimate coefficient of friction of 0.45 with the normal dead load. The structural designer should refer to Section 1807.2.3 of IBC 2024 for appropriate factors of safety for use in the foundation sliding analysis.

Table 4-5: Recommended Equivalent Fluid Pressures (EFP)

Unit

Active1,2,4

(EFPA)

At-rest1

(EFPo) Seismic1,3,4

(EFPAE)

Passive1,4,5

(EFPp)

Pounds per cubic foot (pcf)

Structural Fill φ’=34°, γ’=135 pcf

Ka=0.28, Kae=0.40, Kp=3.5

31.1 48.5 54.4 472.5

1 - Native Clayey to Silty Sand φ’=32°, γ’=110 pcf Ka=0.31, Kae=0.43

33.8 51.7 47.6 NA

2 - Native Lean to Fat Clay φ’=22°, γ’=110 pcf Ka=0.46, Kae=0.62

50.0 68.8 67.7 NA

3- Native Loose to Medium Dense Sand and Gravel φ’=32°, γ’=110 pcf Ka=0.31, Kae=0.43

33.8 51.7 47.6 NA

4 - Native Dense to Very Dense Sand and Gravel φ’=38°, γ’=135 pcf Ka=0.24, Kae=0.35

32.1 51.9 46.9 NA

5 - Native Medium Stiff Silt φ’=30°, γ’=110 pcf Ka=0.33, Kae=0.47

36.7 55.0 51.2 NA

Note 1: Assumes fully drained granular structural fill soil, level conditions at toe and crest of wall, and a vertical wall back face.

Note 2: Assumes deflection at crest of wall is 0.001H for active condition, where H is the wall height.

Note 3: Seismic combines the active and dynamic increment earth pressures and is distributed analogous to the active earth pressure.

Note 4: Neglects soil-wall interface friction.

Note 5: Assumes deflection is 0.02H for passive condition

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4.5 RETAINING WALLS

We understand a retaining wall supporting up to 30 feet of native soil will be constructed along the perimeter of the site. We understand that the final wall type has not yet been determined. Several wall types could be considered; however, a wall type constructed using top-down methods would likely be most economical for the site as the native soils are favorable and this would reduce the amount of temporary excavation, and potential import and compaction of structural backfill. Soil nail walls and soldier pile and lagging walls are common wall types constructed using top-down methods. Wall types such as cast-in-place concrete or mechanically stabilized earth (MSE) walls are generally more suitable and cost efficient for fill conditions. Use of these wall types for cut conditions may require a significant amount of overexcavation, import, and placement of structural fill for construction. Therefore, we recommend that the benefits and cost of using a soil nail wall be considered by the development team.

Soil nail walls are earth retaining structures that use fully-grouted threaded bars, “soil nails”, to create a reinforced a soil mass. The main components of a typical soil nail wall are shown in Diagram 1 adapted from the Federal Highway Administration (FHWA, 2015) Geotechnical Engineering Circular No. 7.

Recommendations for soil nail walls are beyond the scope of work for this report. However, Kleinfelder could provide a technical memorandum or report addendum with soil nail wall recommendations under a separate scope of work upon request should this wall type be determined by Dekker to be more efficient and economical. Soil nail wall design is typically performed by the specialty contractor tasked with constructing the soil nail walls to better account for the means and methods of the contractor.

Diagram 1: Typical Soil Nail Components (FHWA, 2015).

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Geotechnical recommendations provided by the geotechnical engineer generally consist of the following:

• Minimum soil nail lengths required to satisfy global (external) stability of the soil nail wall.

Preliminary globally stability analysis conducted by Kleinfelder indicate that global stability of the wall can be achieved with reasonable nail lengths.

• Estimated ground deformations.

• Bar type.

• Grout to ground bond stress and unit pullout resistance estimates

• Verification and proof testing recommendations.

During construction, the geotechnical engineer reviews the soil nail design and other submittals

(e.g., excavation plan, quality control plan, soil nail and shotcrete testing results, etc.)

Regardless of the final wall type used, drainage of the retained soil mass must be provided. The drainage system implemented depends on the wall type being constructed. Drainage must be sufficient to prevent the buildup of hydrostatic pressures acting on the wall. This is typically accomplished using a free-draining material such as gravel or a strip drain at the soil wall interface, in conjunction with drainage pipes and weep holes to allow water to drain from the retained mass.

4.6 CONCRETE SLABS-ON-GRADE

Concrete slabs on grade should be designed with a minimum of 4 inches of free-draining gravel overlying dense native granular soils or 8 inches of untreated base course below the slab. Prior to placement of the free-draining gravel and base course layers below the slab, the native soil should be prepared as recommended in Section 4.2.1 of this report.

All concrete slabs should be designed to minimize cracking as a result of shrinkage. Special precautions must be taken during the placement and curing of all concrete slabs. Excessive slump (high water-cement ratio) of the concrete and/or improper curing procedures used during either hot or cold

25004473.001A/SLC25R182194 Page 23 of 30 May 19, 2025 weather conditions could lead to excessive shrinkage, cracking, or curling in the slabs. We recommend that all concrete placement and curing operations be performed in accordance with the

American Concrete Institute Manual (ACI, 2017).

As a basis for designing concrete slab thickness, soil subgrade moduli (kv1) may be proportioned according to Table 4-6. These values correspond to a 1-foot square plate and should be adjusted for the designed slab geometry.

Table 4-6: Soil Subgrade Modulus Values for a one-foot Square Plate

Location Subgrade Soil Type Soil Subgrade

Modulus, kv1 (pci)

Testing Facility Native Soils 450

4.7 PAVEMENT DESIGN AND CONSTRUCTION

We understand that the site will contain minor parking and drive areas that may be constructed using

Portland Cement Concrete (PCC), asphaltic concrete (AC) or gravel-surfaced pavements. Kleinfelder’s pavement designs were performed in general accordance with the AASHTO Guide for Design of

Pavement Structures (1993) and Federal Highway Administration Earth and Aggregate Surfacing Design

Guide (2017). Several parameters are needed for pavement design including:

• The Equivalent Single Axle Loads (ESALs), which will have a significant impact on the pavement design.

• The subgrade soil strength (soils below the pavement section) is often quantified by the

California Bearing Ratio (CBR) test. We have assumed a CBR of 3% for the design of pavements to account for the lean to fat clay present near the planned ground elevation on the northwest end of the site and the medium stiff silt present at the planned ground elevation at other portions of the site.

• Softer soils may be present at the site. We recommend the subgrade be proof-rolled with a fully loaded 10-wheel dump truck or water truck before construction of the pavement section.

Where soft spots are observed, these soils should be overexcavated and replaced in accordance with the recommendations of Section 4.2.1.

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Concrete pavement design was performed using a modulus of rupture of 650 psi and 10-foot joint spacings. Kleinfelder should be notified if the actual traffic and material conditions differ from our assumptions. Table 4-7 presents our recommended PCC and gravel pavement sections

Table 4-7: Pavement Section Recommendations

Assumed Number of Class

8/9/10 Trucks (HS-20 Eq. Class) per Day

Estimated W18

Allowable ESALs1

Min. Pavement Section2 (in.)

PCC (Rigid) AC (Flexible) Gravel Surfaced3

1 20,000

6.0 / 6.0

4.0 / 8.0 9.0

3 60,000 4.0 / 12.0 14.0

5 100,000 4.5 / 12.0 16.0

10 285,000 5.0 / 16.0 Not Recommended

20 380,000 5.0 / 16.0 Not Recommended

Note 1: Assumes 20-yr design life and 0% growth rate.

Note 2: AC or PCC / Untreated Base Course Thickness or Untreated Base Course Thickness Note 3: Does not include considerations for section or aggregate loss.

Alternatively, if the existing on-site pavements have provided satisfactory performance, similar sections could be considered for this project, but information regarding these were not provided at this time.

4.7.1 Pavement Subgrade Preparation

Prior to pavement construction, planned parking/roadway areas should be prepared as outlined in

Section 4.2.1 of this report. The final subgrade should be graded to provide positive drainage and prevent ponding and/or moisture infiltration. Granular borrow should be placed soon after subgrade grading to prevent desiccation of near-surface fine-grained soils and to provide a weather-resistant working pad. Where surficial soils with high plasticity are allowed to dry prior to subgrade placement, there is an increased chance that these soils may swell as they become wet. These volumetric changes can damage pavement and therefore, the moisture of these soils should be carefully controlled during construction.

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Once the subgrade has been proof-rolled and approved, untreated base course should be placed. The untreated base course should be compacted to a minimum of 95 percent of the maximum dry density as determined in accordance with ASTM D1557 (Modified Proctor). Moisture content at the time of compaction should be within 2 percent of optimum.

4.8 MOISTURE PROTECTION AND SURFACE DRAINAGE

Precautions should be taken during and after construction to eliminate, or at least reduce the potential for saturation/desiccation of native subgrade soils. Over-wetting of the native soils prior to or during construction may result in softening and pumping, causing equipment mobility problems and difficulty in achieving compaction. The fill, building pads, and adjacent areas should be graded to allow water to drain away from structures to prevent ponding near foundational elements, pavement, or site flatwork.

4.9 SOIL CORROSION AND REACTIVITY

Kleinfelder has completed laboratory testing to provide data regarding corrosivity of onsite soils. Our services do not include corrosion engineering and, therefore, a detailed analysis of corrosion test results is not included in this report. A qualified corrosion engineer should be retained to review the test results, perform additional testing as required, and design protective systems that may be required.

Kleinfelder may be able to provide those services.

Laboratory resistivity, water-soluble sulfate, water-soluble chloride, and pH tests were performed on soil samples from the testing facility site. Results of these tests are listed in Appendix C and summarized in section 2.2.2 of this report. If fill materials will be imported to the project site, similar corrosion potential laboratory testing should be completed on the imported material.

Metal and concrete elements in contact with soil are subject to degradation due to corrosion or chemical attack. Therefore, buried metal and concrete elements should be designed to resist corrosion and degradation based on accepted practices. Chemical test results indicate the native near surface soils are corrosive to buried ferrous piping. We recommend that a corrosion engineer be consulted to recommend appropriate protective measures, as needed.

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The degradation of concrete or cement grout can be caused by chemical agents in the soil or groundwater that react with concrete to either dissolve the cement paste or precipitate larger compounds within the concrete, causing cracking and flaking. The concentration of water-soluble sulfates in the soils is a good indicator of the potential for chemical attack of concrete or cement grout.

The American Concrete Institute (ACI) in their publication Guide to Durable Concrete (ACI 201.2R-08) provides guidelines for this assessment.

The concentrations of soluble sulfates indicate that the subsurface soils at the commercial facility site represent a Class S1 exposure to sulfate attack on concrete in contact with the soil based on

ACI 318-19 Table 19.3.1.1. Therefore, in accordance with ACI Building Code 318-19, special provisions for selection of cement type are not required.

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5 LIMITATIONS

This work was performed in a manner consistent with that level of care and skill ordinarily exercised by other members of Kleinfelder’s profession practicing in the same locality, under similar conditions and at the date the services are provided. Our conclusions, opinions and recommendations are based on a limited number of observations and data. It is possible that conditions could vary between or beyond the data evaluated. Kleinfelder makes no other representation, guarantee or warranty, express or implied, regarding the services, communication (oral or written), report, opinion, or instrument of service provided.

This report may be used only by the Client and the registered design professional in responsible charge and only for the purposes stated for this specific engagement within a reasonable time from its issuance, but in no event later than three years from the date of the report.

The work performed was based on project information provided by Client. Any changes in the project information listed herein that will have an impact on recommendations in this report must be approved by Kleinfelder’s engineer.

It should be recognized that definition and evaluation of subsurface conditions are difficult. Judgments leading to conclusions and recommendations are generally made with incomplete knowledge of the subsurface conditions present due to the limitations of data from field studies.

Kleinfelder offers various levels of investigative and engineering services to suit the varying needs of different clients. Although risk can never be eliminated, more detailed and extensive studies yield more information, which may help understand and manage the level of risk. Since detailed study and analysis involves greater expense, our clients participate in determining levels of service, which provide information for their purposes at acceptable levels of risk. The client and key members of the design team should discuss the issues covered in this report with Kleinfelder, so that the issues are understood and applied in a manner consistent with the owner’s budget, tolerance of risk and expectations for future performance and maintenance.

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Recommendations contained in this report are based on our field observations and subsurface explorations, limited laboratory tests, and our present knowledge of the proposed construction. If soil, rock, or groundwater conditions are encountered during construction that differ from those described herein, the client is responsible for ensuring that Kleinfelder is notified immediately so that we may reevaluate the recommendations of this report. If the scope of the proposed construction changes from that described in this report, the conclusions and recommendations contained in this report are not considered valid unless the changes are reviewed, and the conclusions of this report are modified or approved in writing, by Kleinfelder.

As the geotechnical engineering firm that performed the geotechnical evaluation for this project, we recommend that Kleinfelder be retained to verify the design assumptions and confirm the recommendations of this report are properly incorporated in the design of this project, and properly implemented during construction.