B08_Amd2_Att3a_ZION_240182_Geotechnical_Evaluation_FINAL_0002.pdf

Prepared for:

HDR, Inc.

1670 Broadway, Suite 3400

Denver, CO 80202

Geotechnical & Environmental Services, Inc.

Las Vegas | Reno | Mesquite

GEOTECHNICAL EVALUATION

SOUTH ENTRANCE AND VISITOR CENTER ROAD REHAB

ZION NATIONAL PARK

1 ZION PARK BOULEVARD

SPRINGDALE, UTAH 84767

PROJECT NO. 20226035E1

April 16, 2024

GEOTECHNICAL &

ENVIRONMENTAL

SERVICES, INC.

• Geotechnical Engineering

• Construction Materials Testing & Inspections

• Environmental Services

• AASHTO

Accredited Testing Laboratories

• IAS

Accredited

Las Vegas

7150 Placid Street

Las Vegas, NV 89119 ●

702.365.1001

Reno

5301 Longley Lane, Bldg. H, Suite 116

Reno, NV 89511 ● 775.622.3844

Mesquite

530 Commerce Circle

Mesquite, NV 89027 ●

702.346.4489 We make the ground work for you…®

www.gesnevada.com

April 16, 2024 Project No. 20226035E1

Mr. Mike Flick, P.E.

HDR, Inc.

1670 Broadway, Suite 3400 Denver, CO 80202

RE: Geotechnical Evaluation South Entrance and Visitor Center Road Rehab Zion National Park 1 Zion Park Boulevard Springdale, Utah 84767

Dear Mr. Flick:

Geotechnical & Environmental Services, Inc. (GES) is pleased to present the Geotechnical Evaluation report for the South Entrance and Visitor Center Road Rehab project located in Zion National Park, Utah.

The content of this report presents the findings of the geologic review, the results of the field exploration and laboratory testing programs, conclusions, and recommendations for the site development.

We appreciate this opportunity to provide our professional services. If you have any questions or comments regarding this information, please feel free to contact our office.

Sincerely, Geotechnical & Environmental Services, Inc.

J. Nolan Dalpe, P.E. Anthony Todechiney, P.E.

Project Engineer Senior Engineer

David J. Salter, P.E.

Geotechnical Practice Leader

JND:AT:DJS:yf Enc: Appendix A, Appendix B, Appendix C, Appendix D, Appendix E Dist: PDF e-mailed to addressee at mike.flick@hdrinc.com

PDF saved to Project File http://www.gesnevada.com/

TABLE OF CONTENTS

1. INTRODUCTION

1.1. PURPOSE AND RESOURCES

1.2. PROJECT DESCRIPTION

1.3. SITE DESCRIPTION

2. GEOTECHNICAL SITE CHARACTERIZATION

2.1. GEOLOGY

2.2. SEISMICITY

2.3. LIQUEFACTION

2.4. MAPPED SOIL CONDITIONS

2.5. GROUNDWATER

2.6. FIELD EXPLORATION

2.7. LABORATORY TESTING

2.8. VISUAL PAVEMENT OBSERVATION

2.8.1. EXISTING PAVEMENT SECTIONS

2.9. SUBSURFACE MATERIALS AND CONDITIONS

2.9.1. FILL SOIL

2.9.2. NATIVE SOIL

2.9.3. GENERALIZED SUBSURFACE PROFILE

3. FINDINGS

4. RECOMMENDATIONS

4.1. EARTHWORK

4.1.1. DEMOLITION

4.1.2. SITE PREPARATION

4.1.3. STRUCTURAL FILL AND BACKFILL SUITABILITY

4.1.4. FILL PLACEMENT

4.1.5. OBSERVATION AND TESTING

4.2. EXCAVATION CONSIDERATIONS

4.2.1. TEMPORARY EXCAVATIONS

4.3. EXCAVATIONS NEAR EXISTING STRUCTURES

4.4. UNDERGROUND UTILITIES

4.5. FOUNDATIONS

4.5.1. SHALLOW FOUNDATIONS

4.5.2. DRIVEN PILE FOUNDATIONS

4.5.2.1. STEEL STRUCTURAL SPECIFICATIONS

4.5.2.2. GEOTECHNICAL RESISTANCE FACTORS

4.5.2.3. PILE DRIVEABILITY AND FIELD VERIFICATION

4.5.2.4. DRIVEN PILE CONSTRUCTION CONSIDERATIONS

4.5.2.5. GEOTECHNICAL BEARING RESISTANCE

4.5.2.6. UPLIFT RESISTANCE

4.5.2.7. LATERAL PILE RESISTANCE

4.5.2.8. DOWNDRAG (NEGATIVE SKIN FRICTION)

4.5.2.9. RESISTANCE OF PILE GROUPS IN COMPRESSION

4.5.3. DRILLED SHAFT FOUNDATIONS

4.5.3.1. AXIAL LOADING

4.5.3.2. LATERAL LOADING

4.5.3.3. DRILLED SHAFT CONSTRUCTION CONSIDERATIONS

4.5.4. LATERAL EARTH PRESSURES

4.5.4.1. RETAINING WALL DRAINAGE RECOMMENDATIONS

4.6. EXTERIOR CONCRETE FLATWORK CONSTRUCTION

4.7. SEISMIC SITE CLASS

4.8. PAVEMENT SECTIONS

4.8.1. RECOMMENDED MINIMUM FLEXIBLE PAVEMENT SECTIONS

4.8.2. RECOMMENDED MINIMUM RIGID PAVEMENT SECTIONS

4.9. SOIL CORROSIVITY

4.10. DRAINAGE AND MOISTURE PROTECTION

4.11. PRE-CONSTRUCTION MEETING

4.12. CONTINUITY

5. LIMITATIONS

6. REFERENCES

TABLES

Table 2.6 Field Exploration Summary Table 2.8.1 Approximate Asphalt and Aggregate Base Thickness Table 2.9.3-1 Generalized Subsurface Profile for Shallow Foundations Table 2.9.3-2 Generalized Subsurface Profile and Input Parameters - North Abutment Table 2.9.3-3 Generalized Subsurface Profile and Input Parameters - South Abutment Table 4.1.2 Recommended Minimum Overexcavation Depths Table 4.1.3 Imported and/or On-site Structural Fill Recommendations* Table 4.5.2.1-1 Pile Properties, Factored Axial and Flexural Resistance with 1/16” Section Loss. Fy = 50 ksi – Severe Driving Condition Applies Table 4.5.2.1-2 Pile Properties, Factored Axial and Flexural Resistance with 1/16” Section Loss. Fy = 50 ksi – Severe Driving Condition Applies Table 4.5.2.2 Geotechnical Resistance Factors (φ) Table 4.5.2.3 Driveability Design Data Table Table 4.5.2.6 Geotechnical Resistance Design Data Table Table 4.5.3.-1 Abutment 1 Loads (per shaft) Table 4.5.3.-2 Abutment 2 Loads (per shaft) Table 4.5.3.-3 Performance Measures Table 4.5.3.1. Group Effects Table 4.5.4-1 Lateral Earth Pressure Design Parameters – Yielding Structures Table 4.5.4-2 Lateral Earth Pressure Design Parameters – Non-Yielding Structures Table 4.7 Seismic Design Ground Motion Parameters Table 4.8 60-Foot Bus Weight Distribution and Design ESAL Table 4.8.1 Minimum Asphalt Concrete Pavement Sections Table 4.8.2 PCC Pavement Sections Table 4.9-1 Concrete Recommendations for S2 Exposure Table 4.9-2 Compiled Results of Chemical Testing

FIGURES

Figure 2.1 Geologic Map Figure 2.6 On-Site Drilling Figure 4.5.2.4 Pile Tips Figure 4.5.3.2 P-Multiplier for Single Row Drilled Shafts

APPENDICES

APPENDIX A – SUBSURFACE STUDY

APPENDIX B – LABORATORY TEST RESULTS

APPENDIX C – DESIGN FIGURES

APPENDIX D – PAVEMENT EVALUATION DOCUMENTS

APPENDIX E – L-PILE INPUT PARAMETERS

Geotechnical & Environmental Services, Inc. Project No. 20226035E1

EXECUTIVE SUMMARY

SOUTH ENTRANCE AND VISITOR CENTER ROAD REHAB

ZION NATIONAL PARK

SPRINGDALE, UTAH 84767

This Executive Summary is for reference only and is not fully comprehensive of the findings and recommendations specified in this Geotechnical Evaluation. Select the topics and underlined subjects to go to the appropriate section of the report. GES will not be held responsible for interpretations made by others based solely on the information presented in the Executive

Summary. We encourage a full reading and a clear understanding of the conclusions and recommendations presented in the full report.

Topic Overview

Project

Description

Rehabilitation of existing improvements, as well as the design and construction of new improvements, including a new roundabout, new roadway, new pedestrian and vehicular bridge, pedestrian underpass below the new bridge, culvert, and solar shade structures located within Zion National Park, Utah.

Geotechnical

Site

Characterization

Native soils are generally coarse-grained within the upper 60 to 80 feet.

Increasing fine-grained soils beyond this depth.

Groundwater was encountered in our borings at depths ranging from 33.75-feet to 39.5-feet.

A portion of the project site lies in an area previously mapped with a very high liquefaction potential, however, based on our analysis of soil properties discussed in this report it’s our opinion the potential for liquefaction is low.

Seismic site class: D

Earthwork

Excavate deleterious material including uncontrolled fill, soft, loose or disturbed native soils from improvement areas. Overexcavation is recommended due to the potential for loose soils.

Shallow and

Deep

Foundations

Shallow footings are acceptable for associated improvements.

Allowable bearing pressure = 2,000 psf with depth and width increases up to a maximum of 4,000 psf.

Deep foundations consisting of driven piles or drilled shafts are acceptable for bridge abutments.

Concrete

Flatwork

4-inch minimum concrete thickness with 4-inch minimum aggregate base thickness.

Concrete should contain Type V cement and have a design compressive strength of at least 4,500 psi and maximum water-cement ratio of 0.45 by weight.

Pavements Drive lanes and parking areas designed for a Traffic Index of 8.5: 6-inches AC / 7.5-inches aggregate base

GEOTECHNICAL EVALUATION REPORT

SOUTH ENTRANCE AND VISITOR CENTER ROAD REHAB

ZION NATIONAL PARK

SPRINGDALE, UTAH

1. INTRODUCTION

This report presents the results of a geotechnical evaluation performed by Geotechnical &

Environmental Services, Inc. (GES) for the South Entrance and Visitor Center Road Rehab project located in Zion National Park, Springdale, Utah. Figure A-1 presents a vicinity map showing the approximate location of the site. Figure A-2 presents the exploration location map within the project site. The following sections present the purpose and scope of our geotechnical exploration, project and site descriptions, field exploration, laboratory testing, summary of findings, and recommendations for site development.

1.1. PURPOSE AND RESOURCES

The purposes of our geotechnical study were to evaluate subsurface soils within the proposed project site and provide a design level geotechnical evaluation to aid in the design and construction of the proposed project improvements. The scope of this study included a review of referenced geologic literature and maps to gather relevant information related to site geology, and geologic hazards, subsurface exploration, soil sampling, laboratory testing of selected soil samples, engineering evaluations, and preparation of this report. The scope of work contained herein is provided in general accordance with our proposal, dated April 13, 2022, and modification to our proposal, dated July 31, 2023.

1.2. PROJECT DESCRIPTION

Our understanding of the project is based on correspondence with HDR, Inc., a review of aerial photographs and documents, and our experience with similar projects. Our design recommendations are based on the 2018 International Building Code (IBC) and the FHWA Project

Design and Development Manual (PDDM).

We understand the proposed project will include the rehabilitation of existing improvements, as well as the design and construction of new improvements, including a new roundabout, new roadway, new pedestrian and vehicular bridge, pedestrian underpass under the new bridge, culvert, and solar shade structures within Zion National Park. Aside from the culvert, below grade structures are not anticipated. We assume finished grade will be within 2 feet of existing grades. We understand column loads will be up to 100 kips and wall loads will be up to 3 kips per lineal foot for the solar shade structures and any other ancillary structures.

1.3. SITE DESCRIPTION

The project site is located generally northeast of the existing visitor center at the South Entrance to

Zion National Park. The limits of the project site are shown on Figure A-2 in Appendix A. The project site includes a portion of Visitor Center Road, a portion of Zion Park Boulevard, and improved/unimproved areas in the vicinity including existing paved roads, trails, parking areas, an existing bridge, and natural vegetation including mature trees and shrubs.

2. GEOTECHNICAL SITE CHARACTERIZATION

The following sections describe the geology, seismicity, liquefaction, mapped soil conditions, field exploration, laboratory testing, and subsurface materials and conditions for the project site.

2.1. GEOLOGY

The subject site (identified in red on Figure 2.1) is located on the referenced, Interim Geologic Map of Springdale East Quadrangle, Washington

County, Utah (Doelling, H.H., 2002) within an area mapped as young alluvial-fan deposits (Qafc), level 3 (“historic”) alluvial terraced deposits

(historical) (Qath), talus (Holocene to Upper

Pleistocene) (Qmt), high-level alluvial terrace deposits (middle Holocene to upper Pleistocene)

(Qat4), and Petrified Forest Member of Chinle

Formation (TRcp). Qafc consists of coarse- to fine-grained sand and pebble to cobble gravel with silt and scattered boulders.

Figure 2.1 – Geologic Map

Qath consists of fine-grained overbank silt, sand, and clay deposits that form terraces 8 to 15 feet above the active channel. Qmt consists of coarse, angular blocks on steep slopes with a fine-grained component in varying amounts. Qat4 consists of moderately to well sorted cobble gravel with sand, silt, and clay in lenses and matrix. TRcp consists of shale, siltstone, claystone, sandstone, and pebble to small cobble conglomerate.

2.2. SEISMICITY

The U.S. Geological Survey Earthquake Catalog lists 55 events of magnitude greater than or equal to 4 with epicenters within about 120 miles of Springdale, Utah from 1800 to present day.

Based on a review of referenced geologic maps and literature, the nearest Quaternary-age (last 1.6 million years) fault is the Hurricane fault zone, which is located approximately 15-1/4 miles west of the site (USGS). Other mapped Quaternary-age tectonic faults are the Kolob Terrace faults and the

Sevier/Toroweap fault zone located approximately 16 miles northeast and 18 miles east of the project site, respectively. The nearest mapped Holocene active fault (i.e., a fault that has moved within the last 10,000 years) is the Hurricane fault zone. Based on a review of the Utah Geologic Hazards

Portal (Utah Geological Survey (UGS), updated 2020), the nearest surface fault rupture special study zone is located approximately 4.5 miles southwest of the site.

Based on the results of our review of available literature, it is our opinion that the potential for fault-related surface rupture at the site is negligible.

2.3. LIQUEFACTION

Liquefaction is a phenomenon in which loose, saturated soils lose shear strength under short-term (dynamic) loading conditions. Ground shaking of sufficient duration results in the loss of grain-to-grain contact in potentially liquefiable soils due to a rapid increase in pore water pressure causing the soil to behave as a fluid for a short period of time.

To be potentially liquefiable, a soil is typically cohesionless with a grain-size distribution generally consisting of sand and silt. It is generally loose to medium dense and has a relatively high moisture content, which is typical near or below groundwater level. The potential for liquefaction decreases with increasing clay and gravel content but increases as the ground acceleration and duration of shaking increase. Potentially liquefiable soils need to be subjected to sufficient magnitude and duration of ground shaking for liquefaction to occur.

Effects of liquefaction include relatively large total and differential settlements, flotation of subsurface structures, slope failures, lateral ground displacements (lateral spreading), surface subsidence, ground cracking, and sand boils.

Based on a review of the Utah Geologic Hazards Portal (Utah Geological Survey (UGS), updated

2020) the project site is generally located within an area mapped with very high liquefaction susceptibility. However, based on the information obtained from the borings which include medium dense to very dense coarse-grained soils below groundwater (with N160 blow counts of greater than

30 at the location of the planned bridge abutments), its our opinion the potential for liquefaction is low.

2.4. MAPPED SOIL CONDITIONS

Based on review of the Utah Geologic Hazards Portal (Utah Geological Survey (UGS), updated

2020), the project site is located within an area labelled “Collapsible Soil 1” (Unconsolidated geologic units with reported collapse values greater than or equal to 3 percent).

Based on review of the Utah Geologic Hazards Portal (Utah Geological Survey (UGS), updated

2020), the project site is located in a located within an area with low to moderate swell potential

(0 to 3 percent).

2.5. GROUNDWATER

Groundwater was encountered in six of our borings at the project site at depths ranging from

33.75 feet to 39.5 feet at the time of drilling.

Groundwater levels should be anticipated to fluctuate due to seasonal precipitation, groundwater withdrawal and recharge, irrigation practices, and potential future dewatering efforts within and/or near the subject site. A detailed evaluation of possible groundwater fluctuations is beyond the scope of this study.

2.6. FIELD EXPLORATION

GES evaluated the subsurface conditions within the vicinity of the project site, by drilling 15 borings: B-1 through B-10 from September 26, 2022 to September

29, 2022 and B-11 through B-15 from August 14, 2023 to August 17, 2023. Borings B-1, B-2, B-11, and B-12 were drilled to a total depth of approximately 100-feet below existing surface, borings B-3 through B-5 were drilled to a total depth of approximately 40-feet below existing surface, borings B-13 through B-15 were drilled to a total depth of approximately 25-feet below existing surface, and borings B-6 through B-10 were drilled to a total depth of approximately 10-feet below existing surface. Figure A-2, in Appendix A of this report, shows the approximate drilling locations within the project area. The boring location coordinates (datum NAD 1983 HARN) were recorded by GES staff using a handheld GPS unit and approximate surface elevation estimated from Google Earth. Coordinates and elevations are provided on the exploration logs included in

Appendix A.

The borings were drilled with a truck-mounted Diedrich D-120 drill rig, using 8-inch hollow stem augers. Soil samples and penetration blow counts were obtained with a 3-inch outside diameter ring-lined drive sampler in general accordance with ASTM D3550, and with a 2-inch outside diameter split-spoon sampler in general accordance with ASTM D1586. The sampler was driven with a 140-pound automatic trip hammer falling about 30 inches. The penetration resistance

(hammer blows) measured by driving the sampler was used to evaluate the consistency of the in-place soil. Adequate samples were taken for laboratory testing (e.g. classification tests, consolidation test, soil strength parameters required for design, and corrosion testing). Table 2.6 provides a summary of the field exploration.

The borings were backfilled with bentonite chips and soil cuttings upon completion of drilling. Drill rates were generally obtained where layers of difficult to penetrate soils were encountered within the borings. Drill rates were obtained by measuring the time required to drill through a known depth. The measured time elapsed and the distance drilled were converted to drill rates and were recorded on the boring logs in minutes per foot where obtained.

Figure 2.6 On-site Drilling

The drilling rates are a qualitative indication of the relative hardness of the soils and are greatly influenced by drilling method, bit size, bit wear, drilling pressure and other features. The drill rates, given in minutes per foot, are listed on the exploration logs in Appendix A at the depths where difficult to penetrate soils were encountered.

Table 2.6 Field Exploration Summary

Exploration

ID

Depth (ft)

Latitude Longitude Approximate

Ground Elevation (ft)

Equipment Exploration Size / Type

B-1 100.1 37.201987 -112.98552 3928 Diedrich D-120 8-inch Hollow Stem Auger

B-2 100.4 37.201707 -112.985303 3927 Diedrich D-120 8-inch Hollow Stem Auger

B-3 40.8 37.202377 -112.98622 3937 Diedrich D-120 8-inch Hollow Stem Auger

B-4 41.4 37.202236 -112.985648 3934 Diedrich D-120 8-inch Hollow Stem Auger

B-5 41.5 37.201351 -112.985242 3935 Diedrich D-120 8-inch Hollow Stem Auger

B-6 11.5 37.202706 -112.987628 3956 Diedrich D-120 8-inch Hollow Stem Auger

B-7 11.5 37.201997 -112.986545 3936 Diedrich D-120 8-inch Hollow Stem Auger

B-8 11.5 37.201188 -112.986242 3931 Diedrich D-120 8-inch Hollow Stem Auger

B-9 11.5 37.200401 -112.985852 3941 Diedrich D-120 8-inch Hollow Stem Auger

B-10 10.2 37.200074 -112.984762 3952 Diedrich D-120 8-inch Hollow Stem Auger

B-11 100.1 37.201838 -112.986366 3932 Diedrich D-120 8-inch Hollow Stem Auger

B-12 100.9 37.201419 -112.986261 3926 Diedrich D-120 8-inch Hollow Stem Auger

B-13 26.5 37.200272 -112.984049 3949 Diedrich D-120 8-inch Hollow Stem Auger

B-14 26.5 37.200049 -112.985085 3949 Diedrich D-120 8-inch Hollow Stem Auger

B-15 25.2 37.200237 -112.98460 3949 Diedrich D-120 8-inch Hollow Stem Auger

A GES representative directed and supervised the subsurface explorations, while maintaining detailed logs of the subsurface conditions, classifying the soils encountered, and obtaining soil samples. The soils encountered were classified in general accordance with the Unified Soil

Classification System (USCS). A Key to Symbols and Terms utilized on the exploration logs is presented on Figure No. A-3. The boring logs are presented in Appendix A.

2.7. LABORATORY TESTING

The laboratory testing program consisted of tests to classify the on-site soils and to evaluate engineering and physical properties. The test results are presented on the exploration log in

Appendix A and on test reports presented in Appendix B. Detailed descriptions of the laboratory tests performed are also presented in Appendix B.

2.8. VISUAL PAVEMENT OBSERVATION

On various dates from September 8, 2022 to October 6, 2022, a representative of GES performed a visual reconnaissance across the project area documenting the types and severity of asphalt surface distress. The nature and severity of distress was observed and recorded in general accordance with

FHWA Distress Identification Manual (Publication No. FHWA-RD-03-031). The results of our evaluation are presented graphically on Figures A-2.1 through A-2.5 in Appendix A, with summary sheets compiled in Appendix D. The project area was split into sections in order to complete the pavement observation: Bus Parking Lot, Between Bus and RV Parking Lots, RV Parking Lot, South

Staff Parking Lot, South of Crosswalk on South Side of Bridge, and North of Crosswalk on South

Side of Bridge. These sections are labelled at the top of the pages in Appendix D.

2.8.1. EXISTING PAVEMENT SECTIONS

Existing asphaltic concrete pavements were penetrated in eight of the fifteen exploration locations.

The approximate thicknesses of the asphalt and aggregate base layers were measured with a metal tape in the field. Borings B-5, B-6, B-8, B-9, B-10, B-13, B-14 and B-15 had an asphalt thickness ranging from 3.5 to 11 inches followed by 2 to 7 inches thick of aggregate base. The approximate asphaltic concrete and aggregate base thicknesses encountered in each of the explorations are summarized in Table 2.8.1.

Table 2.8.1 Approximate Asphalt and Aggregate Base Thickness

Exploration No.

Approximate Thickness of

Asphalt (inches)

Approximate Thickness of

Aggregate Base Fill

(inches)

B-5 4 ½ 6

B-6 11 5

B-8 5 ½ 6

B-9 7 ½ 2

B-10 3 ½ 7

B-13 3 ¾ 14 ¼ *

B-14 2 ¾ 3 ¼

B-15 2 ½ 0

* No indication of an aggregate base separate from fill soils.

2.9. SUBSURFACE MATERIALS AND CONDITIONS

The following sections describe the fill and native soils encountered at the site. Detailed information regarding subsurface materials and conditions is presented on the boring logs, Figure

No. A-4 through A-18.

2.9.1. FILL SOIL

Fill soil was encountered in borings B-5, B-6, B-8, B-9, B-10, B-13, and B-14 to a depth of up to approximately 2-feet. The fill material generally consisted of layers of dry sand with gravel and varying amounts of fines. Documentation for the fills encountered was not provided during our study.

Fill placed without documentation to indicate that the fill soils were placed under the supervision of a

Geotechnical Engineer are considered uncontrolled. Uncontrolled fill soils are considered unsuitable for the support of the proposed improvements and should be removed completely down to native soils and either removed from the project site or may be processed for use as structural fill. Our scope did not include an evaluation of the existing fill soils or certification of the existing fill or improvements.

2.9.2. NATIVE SOIL

The native material generally consisted of alternating layers of coarse-grained soils and fine-grained soils. The soils within the upper roughly 60 to 80 feet below existing grade were primarily coarse-grained with a notable increase in fine-grained soils below that depth. Coarse-grained soils were observed to be dry to wet, loose to very dense sands and gravels with varying amounts of clay and silt. The loose soils were generally observed in the upper fifteen feet. The fine-grained soils were observed to be dry to wet, very stiff to hard, lean and fat clay with varying amounts of gravel, sand, and silt. Cemented soils were not encountered, however, native rock fragments were observed in our explorations. These fragments were primarily cobble-sized, and consisted of slightly friable to friable sandstone. Detailed observations and laboratory results can be seen in Appendix A and Appendix B.

A detailed excavatability or rippability evaluation was beyond the scope of this study. The contractor should perform the independent investigations necessary to determine the type of equipment required for grading and excavation operations. If the contractor(s) have any questions regarding site conditions, site preparation, or the recommendations provided, they should contact a representative of GES for any needed clarifications prior to submitting earthwork bids.

2.9.3. GENERALIZED SUBSURFACE PROFILE

Based on a summary of the geotechnical data collected and reviewed for this project we have interpreted the following subsurface soil profiles for the conditions anticipated for both shallow and deep foundations.

Table 2.9.3-1 Generalized Subsurface Profile for Shallow Foundations

*Depth to Top of Layer (feet)

Layer Thickness

(feet) Soil Type Consistency

0 15 Sand Loose to medium dense

15 10 Sand Medium dense to very dense Note * - Depth to top of layer is measured from bottom of shallow foundation.

Table 2.9.3-2 Generalized Subsurface Profile and Input Parameters - North Abutment

Boring Log

N. Abut.

Soil Type

(USCS)

N60 or

N60-Eq.

Layer Thickness

Effective Soil Unit Weight

ʹ, (lb/ft3)

Undrained

Shear Strength

SU, (psf)

Friction Angle φ֯ , (degrees)

Top

(ft.)

Bottom

(ft.)

SM 12 0 10 115 --- 32

SP >100 10 16.5 135 --- 37

SM 50 16.5 34.5 130 --- 34

GW-GC >100 34.5 40 78 --- 40

SW-SM >100 40 60 73 --- 34

GW-GC >100 60 81 78 --- 40

CL >100 81 100 73 4000 ---

Referenced Boring Logs: B-11: Zero depth refers to elevation 3932 feet.

Groundwater was encountered at a depth of 34.5 feet.

N60-Eq. refers to blow counts extrapolated linearly based on penetration of less than 12 in.

N60-Eq. refers to blow counts converted from Modified California Sampler.

Ɣ’ = Effective Soil Unit Weight (pcf).

Table 2.9.3-3 Generalized Subsurface Profile and Input Parameters - South Abutment

Boring Log

N. Abut.

Soil Type

(USCS)

N60 or

N60-Eq.

Layer Thickness

Effective Soil Unit Weight

ʹ, (lb/ft3)

Undrained

Shear Strength

SU, (psf)

Friction Angle φ֯ , (degrees)

Top

(ft.)

Bottom

(ft.)

SP-SM 9 0 13.5 115 --- 32

SP-SC 50 13.5 34 130 --- 34

SM >100 34 60 73 --- 37

SM >100 60 79 73 --- 37

GW-GM >100 79 84 78 --- 40

CL >100 84 100 73 4000 ---

Referenced Boring Logs: B-12: Zero depth refers to elevation 3926 feet.

Groundwater was encountered at an average depth of 34 feet.

N60-Eq. refers to blow counts extrapolated linearly based on penetration of less than 12 in.

N60-Eq. refers to blow counts converted from Modified California Sampler.

Ɣ’ = Effective Soil Unit Weight (pcf).

3. FINDINGS

Based on the results of our field exploration and laboratory testing programs, it is our opinion that there are no known geologic or geotechnical conditions that would prevent development of the project. It is also our opinion that there are some geotechnical considerations that may affect site development. A summary of geotechnical considerations is described below.

• Fill materials were encountered within our explorations, up to a depth of approximately 2-feet. Documentation indicating placement and compaction of the fill encountered was not available for review as part of our study. Fill materials should be considered undocumented fill unless documentation of their placement and compaction is provided.

Alternatively, additional studies may be performed to evaluate whether the fill is acceptable in its current condition for support of the proposed structures. The term “undocumented fill” refers to fill which was placed without engineering observation, testing, or documentation and is considered unsuitable in its present condition and needs to be excavated from structural areas.

• Cemented soil was not encountered during our field explorations, but native rock fragments were encountered in the form of cobbles in the borings. Hard to very hard and difficult-to-excavate soils could be encountered beyond or between the boring locations at varying depths. A detailed excavatability and rippability evaluation is beyond the scope of this study. The earthwork and underground contractors should perform the independent investigations necessary to determine the type of equipment required to perform the work before preparing bids for work associated with this project.

• The tested onsite soils have soluble soil chloride content of up to 27 mg/Kg, as evaluated by AWWA Standard Test Method SM4500-CI B. Soils with soil chloride of 100 mg/Kg or higher are generally considered to be corrosive to steel.

• The tested onsite soils have a sulfate exposure class S1 as defined in Table 19.3.1.1 of American Concrete Institute (ACI) Publication 318-14. GES recommends that concrete be designed for a sulfate exposure class of S2.

• The tested onsite soils had a solubility content of up to 0.22 percent. In our opinion, soils having solubility laboratory test results less than 2 percent by dry weight soluble solids, as determined by American Water Works Association (AWWA) standard test method 2540 C, are considered to have low solubility potential.

• Based on the results of our review of available literature and the distance to mapped faults, it is our opinion that the potential for fault-related surface rupture at the site is negligible.

• A seismic site class D is recommended for the project site.

• The project site falls in an area previously mapped as very high risk for liquefaction, however, based on blow count data and depth to groundwater, it’s our opinion the potential for liquefaction is low.

• Groundwater was encountered in borings B-1, B-2, B-4, B-5, B-11, and B-12 at depths ranging from of 33.75 feet to 39.5 feet below ground surface.

• When available, the project geotechnical evaluation, grading and foundation plans prepared by the Engineers of Record may be reviewed, if desired, by the owner’s geotechnical consultant to evaluate whether the project grading and foundation plans are consistent with the geotechnical design criteria presented in this report.

4. RECOMMENDATIONS

The following sections present recommendations concerning the proposed improvements at the project site. These recommendations are based upon our understanding of the project, the engineering properties of the tested on-site soils, the geologic conditions that are presented in this report, and the assumption that an adequate number of tests and observations will be made during construction to evaluate compliance with these recommendations.

4.1. EARTHWORK

Based on the results of our field exploration and laboratory testing programs, and our stated understanding of the proposed project, it is our opinion that the following earthwork recommendations are applicable to the project.

4.1.1. DEMOLITION

Construction of the proposed improvements may include demolition of some of the existing asphalt concrete pavement, and may include demolition of existing concrete curbs, gutters, and sidewalks.

Demolished structures should be removed from the project site in accordance with section 203 of

FP-14 (FHWA, 2014). Remnants from demolished structures and improvements should be removed from the construction area. The contractor should take adequate precautions when grading and excavating to reduce the potential for damage to any known or undocumented utilities along the alignment. The project’s geotechnical consultant should observe demolition activities to evaluate whether demolished structural materials and utilities are adequately removed, and that the resulting excavations are adequately backfilled, as described in the following sections.

4.1.2. SITE PREPARATION

Where encountered, all existing uncontrolled fill, deleterious material, soft, loose, wet, or disturbed native soils should be removed from improvement areas, in accordance with Section 201 of FP-14

(FHWA, 2014), and either removed from the site or processed to comply with the recommendations outlined in this report for structural fill.

Based on the finding of our observations, loose soils may be present in the near surface soils.

We recommend that the native on-site soils be overexcavated and a zone of processed, moisture-conditioned and compacted structural fill should be provided beneath site improvements in accordance with Table 4.1.2.

Table 4.1.2 Recommended Minimum Overexcavation Depths

Description Recommended Minimum Depth of Overexcavation

Structure Foundations 36 inches below existing grade or bottom of footings, whichever extends lower in elevation

Asphalt Concrete Pavement, Concrete Flatwork and Slabs-on-Grade

18 inches below existing grade or below the bottom of supportive gravel, whichever extends lower in elevation

After the removal of unsuitable soils (including uncontrolled fill) and overexcavation has been performed, the exposed soils should be scarified to 8-inches or more, moisture conditioned to near optimum moisture content, and compacted to a firm and unyielding state. The exposed subgrade may be observed and acceptable if probing yields 1 inch or less penetration into the subgrade.

Density testing of the exposed subgrade is not necessary. Cobbles that become dislodged during scarification should be removed and replaced with structural fill as specified below.

The geotechnical consultant should observe materials after needed removals of unsuitable materials to evaluate whether additional removal down to competent materials is needed. The soil preparation area should extend laterally a minimum of 5 feet beyond the edges of buildings and exterior foundations, where practical. For exterior concrete flatwork, the soil preparation area should extend laterally at least 2 feet beyond the edges. The vertical and lateral extent of the recommended excavations should be evaluated under the direction of the geotechnical consultant.

Where foundation seals are required, drive piles before placing seal concrete unless otherwise specified. Remove loose and displaced material and reshape the bottom of the excavation to the foundation elevation. Grade and compact the bed to receive the footing.

4.1.3. STRUCTURAL FILL AND BACKFILL SUITABILITY

In our opinion, materials meeting the specifications of Table 4.1.3 would be adequate for use as structural fill and backfill, however we understand FHWA FP-14 may govern fill suitability. If required by the contract documents, structural fill should conform to the appropriate section of FP-14 as opposed to Table 4.1.3. We assume the relevant materials of FP-14 would include Section 704.01 -

Foundation Fill, Section 704.04 - Structural Backfill, and Section 704.07 - Select Borrow; however other sections may also apply. From review of the laboratory test results, the majority of the near surface on-site materials are not anticipated to meet these specifications due to fines content. The majority of the on-site materials are anticipated to meet the recommendations specified in Table

4.1.3. Samples of materials proposed for use as structural fill should be submitted to the geotechnical consultant for testing and evaluation prior to being transported to the site.

Table 4.1.3 Imported and/or On-site Structural Fill Recommendations*

Description** Recommendation

3-inch Sieve Gradation*** 100 Percent Passing

¾-inch Gradation 100-70 Percent Passing

No. 200 Sieve Gradation*** 0-30 Percent Passing

Liquid Limit <35

Plasticity Index <15

Remolded Swell Potential Low expansion potential as determined by ASTM D4829

Dry Weight Soluble Solids <2.0% as determined by American Water Works Association (AWWA) Standard Method (SM) 2540 C

Dry Weight Soluble Sulfate <1% by dry weight soluble sulfate as determined by AWWA

SM 4500 SO4 E

Soluble Soil Chloride Content <500 ppm as determined by AWWA SM 4500-CL B unless appropriate corrosion protection is utilized in the design of proposed structures

* Recommendations are not in accordance with FP-14. FP-14 should govern the specifications if required by the contract documents.

** Imported fill materials and excavated on-site material should be free of debris, organic materials, and other deleterious materials..

***Materials used as retaining wall backfill, which should have 10 percent, or less, of material passing the No. 200 sieve and 100 percent passing the 4-inch sieve.

4.1.4. FILL PLACEMENT

Areas to receive structural fill should be prepared prior to fill placement as described in Section 4.1.2 of this report. Structural fill should be uniformly moisture conditioned to near optimum moisture content, placed in horizontal, loose lifts up to 6 inches thick, and compacted to at least 95 percent of the maximum dry density, as determined by AASHTO T99. The optimal lift thickness of fill will depend on the type of soil and compaction equipment used but should generally not exceed approximately

6 inches in loose thickness per FP-14 (FHWA, 2014).

If fill material is placed where the existing ground surface is steeper than 5:1 (horizontal to vertical), the surface on which fill is to be placed should be benched. We recommend that benches be 8 feet or wider or be of sufficient width to permit operation by compaction equipment. Benches should include approximately 2-foot high vertical or near-vertical intervening steps, cut to expose suitable soil as evaluated in the field by the geotechnical consultant during earthwork operations. Preparation of the benching surface in areas to receive fill should include scarification and moisture-conditioning to a depth of approximately 6-inches, and compaction to a relatively non yielding condition, prior to placement of fill.

4.1.5. OBSERVATION AND TESTING

A qualified geotechnical consultant should perform appropriate observation and testing services during grading and construction operations. These services should include observation of removal of soft, loose, or otherwise unsuitable soils, evaluation of subgrade conditions where soil removals are performed, and performance of observation and testing services during placement and compaction of structural fill and backfill soils. In-place density and moisture tests should be performed in accordance with AASHTO T310 or other approved procedures (such as ASTM D6938 and ASTM

D1556).

Observation and testing of soils should be performed as indicated in the applicable section of Division

200 – Earthwork of FHWA FP-14. For areas not specified by FP-14, the test frequency should be at least one test per 100 cubic yards of fill material placed or at least two tests per 12-inch lift of fill material placed, whichever is more. Additional field tests may also be performed in structural and non-structural areas at the discretion of the geotechnical consultant. Soils to be used as structural fill should be tested for moisture-density by AASHTO T99, Method C (minimum of 5 points per proctor) before use.

4.2. EXCAVATION CONSIDERATIONS

The following sections provide recommendations to aid in the successful performance of excavations at the project site and include recommendations regarding temporary excavations.

It is the responsibility of the contractor to perform the independent investigations necessary to determine the type of equipment required to perform the work. The contractor should perform a pre-construction survey to establish a baseline survey prior to excavating.

4.2.1. TEMPORARY EXCAVATIONS

Temporary slope surfaces should be kept moist to retard raveling and sloughing. Water should not be allowed to flow over the top of excavations in an uncontrolled manner. Stockpiled material and/or equipment should be kept back from the top of excavations a distance equivalent to the depth of the excavation or more. Workers should be protected from falling debris, sloughing, and raveling in accordance with Occupational Safety and Health Administration (OSHA) regulations. Temporary excavations should be observed by the project’s geotechnical consultant so that appropriate additional recommendations may be provided based on the actual field conditions. Temporary excavations are time sensitive, and failures are possible.

Excavations greater than 4 feet in depth into uncemented soils are not anticipated to stand vertically.

Excavations greater than 4 feet in depth should be sloped back in accordance with the maximum allowable slope ratios presented in Appendix B to Subpart P of OSHA for the Construction Industry

29 Code of Federal Regulations (CFR), Part 1926. The soil type definitions in Appendix A to Subpart

P of OSHA 29 CFR, Part 1926 should be applied to soils encountered in excavations to determine the maximum allowable slope ratio. As an alternative to sloped excavation sidewalls, excavations could be shored and braced. Shoring and bracing should be designed in accordance with

Appendices C and D to Subpart P of OSHA 29 CFR, Part 1926. Safety of construction personnel is the responsibility of the contractor.

4.3. EXCAVATIONS NEAR EXISTING STRUCTURES

Excavations should not undermine existing foundations and should not extend below a plane that extends downward and outward from the bottom outside edge of existing foundations on a 1:1

(horizontal:vertical) slope. In areas where new foundations are constructed parallel to existing foundations, and/or where the 1:1 excavation criteria cannot be met, the excavations should be performed in relatively small (than 10 feet in length), independent stages to reduce the potential for undermining of existing footings. Staged excavations should not remain open for extended periods of time and should be adequately backfilled with structural fill prior to subsequent excavations. The geotechnical consultant should observe the exposed soils during excavations along the base of existing footings to assess the suitability and stability of the exposed soil.

Alternatively, the soils beneath the foundations of existing structures should be appropriately shored during grading and excavation activities.

The project’s contractor should take precautions to avoid damage to existing structures during earthwork and construction operations. These precautions may include pre-construction documentation of existing distress for structures near construction areas; monitoring of ground motions generated during demolition and construction; monitoring of existing buildings and other site improvements for movement, cracking, or other indications of distress; underpinning of existing structures; and other methods, or combination of methods, to reduce the potential for damage to existing structures and associated claims. The contractor’s monitoring/damage prevention plan should be approved by the project structural engineer and should include appropriate contingencies in the event that excessive movements or unwanted distresses are observed.

4.4. UNDERGROUND UTILITIES

Soils placed as common trench backfill in on-site utility trench excavations should meet the criteria for structural fill described in the Earthwork section of this report and should be moisture conditioned to within 2 percent of optimum moisture content and compacted to at least 95 percent of the maximum dry density (AASHTO T99). Suitability and compaction of trench backfill should be evaluated during construction.

Due to the nature of the on-site soils and anticipated drainage conditions, ponding or jetting of utility trench backfill will not be acceptable. Trench backfill should be compacted by mechanical means only.

4.5. FOUNDATIONS

The following sections present recommendations for shallow foundations, conventionally reinforced slabs-on-grade, and driven pile foundations. As geotechnical engineer of record, we recommend that

GES perform appropriate observation and testing services during preparation and construction of foundations.

4.5.1. SHALLOW FOUNDATIONS

Shallow foundations (e.g. spread, continuous, or shallow circular footings) supporting site structures such as solar panel structures, retaining walls, underground utility vaults, or other ancillary structures should be supported entirely on medium dense to very dense native soils or on properly compacted structural fill prepared as described in section 4.1.

Spread footings should be at least 12-inches wide and founded at least 18-inches below the lowest adjacent final compacted subgrade and should be reinforced in accordance with the project structural engineer’s recommendations. Spread footings should be founded below the maximum anticipated frost depth, depth of scour, erosion, or undermining depth.

Footings may be designed based on an allowable net dead plus sustained live load bearing pressure of 2,000 pounds per square foot (psf). The allowable bearing pressure for conventional spread footings may be increased by 500 psf for each additional foot of embedment and/or 250 psf for each additional foot of width up to a maximum allowable pressure of 4,000 psf. The allowable bearing pressures may be increased by one-third for temporary wind or seismic loads.

The allowable bearing pressure presented above includes a factor of safety against generalized bearing capacity failure of 3.0.

Resistance to lateral loads may be estimated using both passive lateral earth support and friction developing between footings and underlying soil. Passive resistance may be used if foundation backfill soils in front of the foundation are level and compacted to 95 percent, or more, of the maximum laboratory dry density (AASHTO T99) or if the foundation is cast against undisturbed dense to very dense native soils, and if the ground surface in front of the footing is level. The upper

12-inches below the ground surface should be neglected if passive resistance is used, unless confined by concrete slab-on-grade or pavement. The ultimate passive lateral earth support for subsurface walls and footings may be estimated based on an equivalent fluid density of 390 pcf up to a maximum passive lateral pressure of 2,600 psf. A coefficient of friction of 0.58 may be used for the interface between the cast-in-place footings and underlying properly compacted structural fill. The values for the equivalent fluid density and coefficient of friction presented above do not include a specific factor of safety. The values above are nominal. The values can be combined to resist sliding only once an appropriate resistance factor is applied.

Provided that the earthwork recommendations presented are followed and structural loads are less than 100 kips for column loads and wall loads on the order of 3 kips per lineal foot, total and differential settlements are not anticipated to exceed 1-inch and ½-inch, respectively. If structural loads exceed these values, GES should be provided the opportunity to re-evaluate our settlement estimates. Structural loads in excess of these estimates may result in increased settlement that could exceed the design tolerance of the structure.

4.5.2. DRIVEN PILE FOUNDATIONS

The following provides design methodologies used for calculating pile resistance Strength, Extreme Event, and Service Limit States in accordance with LRFD Bridge Design Specifications

(AASHTO, 2020). The design and construction of the pile foundation elements should comply with all applicable requirements and guidelines listed in the LRFD Bridge Design Specifications

(AASHTO, 2020).

Foundation recommendations presented in this report are limited to driven steel piles. Foundation recommendations for alternate pile types can be provided upon request. It is our understanding that driven steel H-Piles are preferred to support the proposed bridge structure. Based on the soil conditions encountered at the subject site, it is considered suitable provided that the driving steel piles would be driven to underlying hard clay or ‘practical refusal’. The pile capacities provided in this report are combined skin and end bearing values.

Driven steel piles should consist of HP sections. Appropriate resistance factors were used in accordance with Table 10.5.5.2.3-1 (AASHTO, 2020). In our opinion, Steel "H" piles such as HP

14 x 89 driven to practical refusal can be used to support the proposed structure. If driven to practical refusal, the stress of the pile cross section would control the pile capacity. Lengths of steel H piles produced are usually in five foot increments up to 60 feet. Designers should consider pile availability before choosing pile size.

4.5.2.1. STEEL STRUCTURAL SPECIFICATIONS

Table 4.5.2.1-1 Pile Properties, Factored Axial and Flexural Resistance with 1/16” Section Loss. Fy = 50 ksi – Severe Driving Condition Applies

Table 4.5.2.1-2 Pile Properties, Factored Axial and Flexural Resistance with 1/16” Section Loss. Fy = 50 ksi – Severe Driving Condition Applies

4.5.2.2. GEOTECHNICAL RESISTANCE FACTORS

Appropriate resistance factors were used in accordance with AASHTO Table 10.5.5.2.3-1, and provided below in Table 4.5.2.2:

Table 4.5.2.2 Geotechnical Resistance Factors (φ)

Condition/Resistance Determination Method Resistance Factor, φ

Static Analysis

Compression 0.45

Uplift 0.35

Dynamic Analysis Pile Driving Analyzer (PDA)

(Dynamic Testing*)

Compression 0.65

Uplift 0.5

Dynamic Analysis (Wave Equation Analysis without pile dynamic measurement)

Compression 0.50

Uplift 0.40

Dynamic Analysis (FHWA Modified Gate

Dynamic Formula)

Compression 0.40

Uplift 0.30

If pile driving analyzer (PDA + CAPWAP) is used to monitor the pile driving, a resistance factor of

0.65 may be used per AASHTO (2020) Table 10.5.5.2.3-1. Per AASHTO (2020) recommendations, a resistance factor of 0.5 can be used for wave equation analysis only without pile dynamic measurements such as PDA + CAPWAP monitoring. If pile driving acceptance is determined using the Dynamic Formula (AASHTO 10.7.3.8.5), the FHWA Modified Gate Formula

(eq. 10.7.3.8.5-1), a geotechnical resistance factor (φ) of 0.4 (AASHTO Table 10.5.5.2.3-1) should be used. The driving formula should only be used to determine end-of driving (EOD) blow count criteria (AASHTO C10.7.3.8.5).

The resistance factor (ϕ) used to define the relationship between the nominal…