Exhibit_5_-_Geotechnical_Report.pdf

Prepared for:

County of Orange – Public Works 601 North Ross Street

Santa Ana, CA 92701

DRAFT – GEOTECHNICAL ENGINEERING

REPORT

SANTA ANA DELHI CHANNEL

OCFCD FACILITY NO. F01

NEWPORT BEACH, CALIFORNIA

Prepared by:

3530 Hyland Avenue, Suite 100

Costa Mesa, CA 92626

Project Number: HG1846

November 2022

D R A F T - For Discussion Purposes Only

HL1389\GBC13-01.doc 11/23/2022

GEOTECHNICAL ENGINEERING REPORT

SANTA ANA DELHI CHANNEL

OCFCD FACILITY NO. F01

NEWPORT BEACH, CALIFORNIA

This report was prepared by the staff of Geosyntec Consultants under the supervision of the professionals whose signatures appear hereon. The findings or professional opinions were prepared in accordance with generally accepted professional engineering and geologic practice. No attempt to verify the accuracy of the data provided by others was made. No warranty is expressed or implied.

DRAFT DRAFT

Rehan Khan Bora Baturay, Ph.D., P.E., G.E..

Project Engineer Principal Engineer

Chris Conkle, P.E., G.E.

Principal Engineer

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TABLE OF CONTENTS

Page

1. INTRODUCTION

1.1 General

1.2 Project Description

1.2.1 Site Location and Existing Conditions

1.2.2 Project Objectives

1.2.3 Proposed Improvements

1.3 Previous Studies

1.4 Scope of Services

2. DATA GAPS IN PREVIOUS STUDIES

3. GEOTECHNICAL INVESTIGATION

3.1 Site Visit and Pre-Subsurface Exploration Planning

3.2 Subsurface Explorations

3.2.1 Cone Penetration Testing

3.2.2 Hollow-Stem Auger Drilling and Sampling

3.3 Geotechnical Laboratory Testing Program

4. SITE CONDITIONS

4.1 Regional Geologic Conditions

4.2 Subsurface Conditions

4.2.1 Fill

4.2.2 Upper Paralic Deposits

4.2.3 Lower Paralic Deposits

4.2.4 Estimated Shear Strength Parameters

4.3 Groundwater Conditions

5. GEOLOGIC AND SEISMIC HAZARDS

5.1 Fault Surface Rupture

5.2 Strong Ground Shaking

5.3 Expansive Soils

5.4 Liquefaction

5.5 Lateral Spreading

5.6 Earthquake-Induced Landslides

5.7 Other Geologic Hazards

6. SEISMIC HAZARD EVALUATION

6.1 Input Parameters

TABLE OF CONTENTS (Continued)

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6.2 Ground Motion Models

6.3 Design Seismic Ground Motions for Pedestrian Bridge per AASHTO-CA

Bridge Design Specification-8

6.3.1 Probabilistic Safety Evaluation Earthquake Design

Spectrum

6.3.2 Safety Evaluation Earthquake Peak Ground Acceleration

6.4 Design Seismic Ground Motions for Channel Improvements

6.4.1 Maximum Design Earthquake

6.4.2 Operating Basis Earthquake

7. LIQUEFACTION EVALUATION

7.1 Introduction

7.2 Evaluation Approach

7.3 Liquefaction Susceptibility and Triggering Analysis Results

8. CHANNEL GEOTECHNICAL DESIGN RECOMMENDATIONS

8.1 Global Stability Evaluation

8.1.1 Cross-Sections Evaluated

8.1.2 Generalized Soil Profile

8.1.3 Design Criteria

8.1.4 Earth Retaining Systems

8.1.5 Analysis Results

8.1.6 Seismically Induced Deformation Analysis

8.2 Lateral Earth Pressures

8.2.1 Liquefaction Case

8.2.2 No Liquefaction Case

9. PEDESTRIAN BRIDGE GEOTECHNICAL DESIGN

RECOMMENDATIONS

Abutment

9.1 Slope Stability Evaluation

9.2 Bridge Foundation Recommendations

9.2.1 Foundation Type and Generalized Soil Profile

9.2.2 Driven Piles – Axial Capacity

9.2.3 Driven Piles – Lateral Load Analysis

10. CORROSION EVALUATION

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11. LIMITATIONS

REFERENCES

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LIST OF TABLES

Table 1: Summary of Geotechnical Subsurface Explorations

Table 2: Summary of Geotechnical Laboratory Test Results

Table 3: Summary of Soil Chemical Test Results

Table 4: Shear Strength Parameters of Observed Soil Units (in text)

Table 5: Summary of Groundwater Depth Measurements in Soil Borings (in text)

Table 6: Nearby Faults and Fault Rupture Scenarios

Table 7: Development of Safety Evaluation Earthquake Spectrum

Table 8: Development of MDE and OBE Spectra (USACE)

Table 9: Location and Extent of Liquefiable Layers (in text)

Table 10: Generalized Soil Profile for Channel Design (in text)

Table 11: Design Requirements and Considerations for Left Bank (in text)

Table 12: Static and Seismic Factors of Safety for Channel Design (in text)

Table 13: Seismically Induced Deformations along Channel Banks (in text)

Table 14: Generalized Soil Profile for Global Stability Analysis (in text)

Table 15: Design Requirements and Consideration for Bridge Left Abutment (in text)

Table 16: Static and Seismic Factors of Safety for Bridge Left Abutment (in text)

Table 17: Seismically Induced Deformations at Bridge Abutments (in text)

Table 18: Generalized Soil Profile and Shear Strength Parameters for Bridge

Foundation Analysis (in text)

HG1846\GBC13-01.doc v 11/23/2022

LIST OF FIGURES

Figure 1: Site Location Map

Figure 2: Exploration Location Plan

Figure 3: Local Geologic Map

Figure 4: Regional Fault and Historical Earthquake Epicenter Map

Figure 5: Seismic Hazard Map

Figure 6: Shear Wave Velocity Profile

Figure 7: Safety Evaluation Earthquake Spectrum

Figure 8: MDE and OBE Spectra

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LIST OF APPENDICES

Appendix A: Cross-sections

Appendix A-1: Proposed Channel cross-sections

Appendix A-2: Proposed Bridge cross-sections

Appendix B: Previous Geotechnical Investigations

Appendix B-1: Ninyo & Moore (2012, 2013) Boring Logs

Appendix B-2: Ninyo & Moore (2012, 2013) Laboratory Test Results

Appendix B-3: GMU (2020) CPT Report

Appendix C: Geosyntec CPT Report

Appendix D: Geosyntec - Hollow Stem Auger Drilling

Appendix D-1: Boring Logs

Appendix D-2: Hammer Calibration Certificate

Appendix D-3: Soil Analytical Test Results

Appendix E: Geosyntec Laboratory Test Results

Appendix E-1: Geotechnical Laboratory Test Results

Appendix E-2: Soil Chemical Laboratory Test Results

Appendix F: Geologic Cross-sections

Appendix G: Liquefaction Evaluation

Appendix H: Slope Stability Evaluations

Appendix I: Earth Retaining System: Lateral Earth Pressures

Appendix J: Bridge Foundation Axial Capacity

Appendix K: Bridge Foundation – Lateral Load Analysis

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1. INTRODUCTION

1.1 General

This geotechnical engineering report was prepared in support of the design of the proposed improvements as part of the Santa Ana-Delhi Channel Improvements Project.

The services documented in this report were performed in accordance with Geosyntec’s proposal dated July 2, 2021 and under the terms and conditions of the Contract numbered MA-080-22010258, dated October 19, 2021.

1.2 Project Description

1.2.1 Site Location and Existing Conditions

The subject reach (the Reach) of the Santa Ana-Delhi Channel is approximately 4,000 feet (ft) long located in between the intersection of Irvine Avenue and Mesa Drive at its northern end and approximately 800 ft downstream of the channel’s intersection with

Bay view trail pedestrian bridge (the Pedestrian Bridge) at the southern end in Newport

Beach, California, as indicated on the site vicinity map shown in Figure 1.

The Reach generally runs in a north-south direction and is bounded by Anniversary

Lane and residential buildings on its western side and a golf course and vacant land on its eastern side. The channel bottom is composite with the first 400 feet below Mesa

Drive being concrete, the next 2,400 linear feet of channel being a composite of riprap and earthen, and the remaining 1,200 feet in the project reach being earthen.

The western side of the channel (“left bank” looking upstream) consists of concrete lined sideslope with an approximately 10-foot-wide concrete maintenance road from the

Reach’s northern end to the southern end of Anniversary Lane and earthen sideslope with intermittent riprap lining from the southern end of Anniversary Lane to the

Pedestrian Bridge. Downstream of the Pedestrian Bridge the left bank is earthen.

The eastern side (“right bank” looking upstream) of the channel generally consists of earthen sideslope with intermittent riprap lining and an earthen levee (along the golf course) that varies in top width (unpaved). The originally designed earthen 1:1 sideslope along the right bank (e.g., levee and non-leveed section of channel) has been eroded to a nearly vertical sideslope. This condition persists to the downstream extent of the project.

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1.2.2 Project Objectives

Geosyntec understands that the overall project objective is for the channel to be able to convey a 100-year storm event (i.e., ultimate design discharge), reduce scour and sediment transport from erosion to the back bay, and provide sustainable habitat establishment throughout the Reach for mitigation. We understand also that the

Pedestrian Bridge will be replaced with a new bridge to span the improved and widened channel.

1.2.3 Proposed Improvements

In order to achieve the above-mentioned objectives, four alternatives (abbreviated “Alt” for brevity), Alt A, Alt B, Alt C, Alt D, were initially proposed and evaluated. Plan view and cross sections of these alternatives are provided in (Appendix A-1). The alignment is defined at the channel centerline as STA 0+00 at the south end and STA

40+34 at the north end.

The alternatives include:

• Alt A (Without Project) – Project would not occur and existing channel improvements would remain within the existing channel alignment.

• Alt B (Unwidened Bridge) – Project is designed and built within existing

OCPW owned right of way.

• Alt C (Northern Alignment) – Project utilizes OCPW owned right of way along right bank (looking upstream) and left bank until approximately STA 10+50 where the channel is widened to the north into OC Parks owned land until STA

6+75 to improve hydraulic conveyance.

• Alt D (Southern Alignment) – Project utilizes OCPW owned right of way along left bank to STA 7+25 downstream of the pedestrian bridge. Then on the right bank the channel habitat (e.g., coastal marsh mitigation area) is extended parallel to the channel until STA 4+25 through California Department of Fish and

Wildlife (CDFW) owned land where the habitat merges with existing coastal salt marsh.

The alternatives Alt B, Alt C, and Alt D differ only in the vicinity of the bridge location

(STA 4+00 to STA 11+00). The proposed span lengths of the bridge for Alt B, Alt C, and Alt D are about 104, 166, and 197 feet, respectively. As discussed above, Alt D

Slope differs from Alt D only beyond STA 19+00 on the righty bank. Appendix A-2

3 11/23/2022 shows the bridge spans and proposed grading at the abutment locations for the alternatives Alt D and Alt D Slope.

Hydraulic analysis (Rick Engineering Company, 2022) of the above alternatives identified Alt D as the preferred channel alignment having met project objectives

(hydraulic performance and erosion/scour potential).

To improve Alt D, additional channel lining sub-alternatives were investigated to improve the habitat stability (required habitat mitigation area) by refining the hydraulic performance (reduce water surface elevation, velocities, and shear stress) along the golf course section of the channel. The first sub-alternative created was Alt D “slope” and the final iteration was Alt D slope version 2 (v2).

• Alt D Slope – This is the same as Alt D except the right bank wall upstream of

STA 19+00 is replaced with a 2:1 slope (unsupported) beginning at the toe of the Alt D right bank wall. The top of slope then has a short gravity wall/levee to contain the 25-year discharge then transitioning to a 12 ft wide maintenance road and a short retaining wall. The maintenance road on the levee along the right bank is pushed further away from the channel and occupies a portion of the

20-ft flood easement OCPW would seek from the golf course to construct the project.

• Alt D Slope v2 – This project included several additional modifications from

Alt D Slope following input received from OCPW during and following the

Alternatives Workshop (16 May 2022). The main changes included incorporating a minimum 14 ft wide maintenance roads with 20 ft clear (for equipment operations and access) on both banks consistent with OCPW standards. On the left bank this resulted in pushing the wall alignment on average 2.5 ft into the channel for the project length. On the right bank upstream of Station 19+00, the 25-year storm wall was removed, the levee height lowered to only contain the 10-year storm (consistent with current channel performance), and the maintenance road (20 ft total width) on top of the levee was moved east fully within the 20-ft flood easement.

After evaluating the hydraulic performance and erosion/scour potential, Alt D Slope v2 was presented at the Design Seminar (30 June 2022) compared to all alternatives.

Given the improved hydraulic performance, decreased scour, and improved habitat stability of Alt D Slope v2 over all other alternatives, OCPW selected Alt D Slope v2 as the preferred alternative to advance to 35% Plans Specifications and Estimate (PS&E).

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The proposed improvements to the existing channel as part of Alt D Slope v2 generally consist of the following:

• STA 4+00 to STA 7+40: The left bank remains undisturbed while the right bank (earthen sideslope) is widened east about 85 to 110 feet to establish coastal salt marsh habitat as part of the required mitigation.

• STA 7+40 (bridge at STA 8+00) to STA 18+40: Widening of the channel further east (i.e., right bank) with earthen side slopes by about 85 to 110 feet, and vertical face along the left bank supported by an earth retaining system

(ERS) with exposed height varying from 9 to 12 feet.

• STA 18+40 to STA 26+00: Widening of the channel further east (i.e., right bank) with earthen side slopes by about 15 to 30 feet; vertical face along the left bank supported by an ERS.

• STA 26+00 to STA 35+00: Widening of the channel further east (i.e., right bank) with earthen side slopes by no more than 15 feet; vertical sides along the left bank supported by an ERS.

• Scour protection will be incorporated in the design to protect the proposed ERS, embankments, and foundations. The pattern of this scour protection will be established to match approximately the existing morphology of the low flow channel (width and thalweg elevation) as it presently exists (i.e., existing condition).

These improvements are illustrated in Appendix A-1.

1.3 Previous Studies

Geosyntec utilized previous geotechnical studies performed at this site in developing recommendations presented in this report. These studies include the following:

• Ninyo & Moore (2012), “Geotechnical Evaluation, Bay View Bridge – Task 2, 2301 University Drive, Newport Beach, California”, prepared for GHD, dated

February 9, 2012

• Ninyo & Moore (2013), “Geotechnical Evaluation of Santa Ana-Delhi Channel

(F01), Mitigation, Rehabilitation and Coastal Access Improvement Project from

Upper Newport Bay to Mesa Drive”, prepared by Ninyo & Moore, dated July

2013.

5 11/23/2022

• GMU (2021a), “Geotechnical Assessment, Santa Ana Delhi Channel (F01)

Permanent Sheet Pile System, from Upper Newport Bay to Mesa Drive, Newport Beach, California”, prepared by GMU, dated January 2021.

• GMU (2021b), “Bridge Type Selection Report – Bay View Pedestrian Bridge, Santa Ana Delhi Channel (F01), Newport Beach, California”, prepared by

GMU, dated January 2021.

Review of previous geotechnical reports preceded the subsurface exploration program conducted as part of this study. The soil boring logs and laboratory testing results from previous investigations conducted by Ninyo & Moore (2012, 2013) are included in

Appendices B-1 and B-2 and the Cone Penetration Test (CPT) report from GMU (2021) investigation is included in Appendix B-3. The locations of both previous investigations are included in Figure 2.

1.4 Scope of Services

Geosyntec performed the following tasks in preparation of this report:

• Review reports of previous geotechnical studies and identify data gaps for the proposed channel alternatives;

• Developed a geotechnical investigation (subsurface exploration and laboratory testing) program to cover the data gaps identified;

• Site visits to assess the feasibility of explorations at the locations identified and mark those locations;

• Obtain well and encroachment permits;

• Subsurface utility clearance: USA DigAlert and Geophysical survey;

• Geotechnical subsurface exploration, in-situ testing, and sampling via geotechnical borings and CPTs;

• Geotechnical and analytical laboratory testing on representative samples;

• Site-specific seismic ground motion study;

• Geotechnical analyses including liquefaction triggering, slope stability, and pile capacity; and

• Preparation of this report outlining investigation and testing performed, relevant findings, assessment of site conditions and geotechnical parameters, and findings of the analyses.

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2. DATA GAPS IN PREVIOUS STUDIES

Based on a review of the reports mentioned in Section 1.3, we concluded that the following data gaps existed.

• Limited data from deeper soils in the CPTs performed along the left bank.

Shallow refusal (4 to 34 feet) was encountered in majority of CPTs performed along the left bank of the channel, probably because a light-weight rig was utilized.

• Limited strength test data along the right bank of the channel from STA 8+00 to STA 22+00;

• Investigation locations were situated close to the channel. The majority of these locations showed the presence of liquefiable soils. Investigations were needed further away from the channel to be able to delineate the lateral extent of the liquefiable layer.

• Limited geotechnical laboratory testing to support liquefaction susceptibility evaluation; and

• Lack of geotechnical laboratory test on compressibility characteristics of site soils.

Geosyntec designed a geotechnical investigation program with additional subsurface exploration to fill the data gaps identified above. The details of the geotechnical investigation program conducted are described in Section 3.

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3. GEOTECHNICAL INVESTIGATION

Elements of the geotechnical investigation (subsurface exploration and geotechnical laboratory testing) are described in the following sections of this report.

The following subcontractors were engaged in the execution of the geotechnical investigation:

• Geophysical utility survey – Subsurface Surveys & Associates, Inc.;

• Cone Penetration Testing – Gregg Drilling, LLC and Kehoe Testing and

Engineering;

• Hollow-stem auger drilling – ABC Liovin;

• Geotechnical laboratory testing – AP Engineering and Testing, Inc. (AP ) and

Wood Environment & Infrastructure Solutions, Inc. (Wood) - now WSP USA

Environment & Infrastructure, Inc.;

• Analytical testing of drilling cuttings - Eurofins Calscience Environmental

Labs; and

• Investigation derived waste disposal – American Integrated Services.

3.1 Site Visit and Pre-Subsurface Exploration Planning

Prior to conducting subsurface explorations, Geosyntec conducted a site reconnaissance to visually assess the site conditions for site access and mark out the proposed exploration locations for utility clearance. Underground Service Alert (USA) was contacted a minimum of 48 hours prior to commencing the subsurface exploration program for member utility companies to mark their subsurface utilities at and near each proposed exploration location. Additionally, Geosyntec retained the services of

Subsurface Surveys & Associates, Inc., to perform limited geophysical utility survey at the proposed subsurface exploration locations to identify any potential underground obstruction or unmarked utilities. For the geotechnical explorations, encroachment permits were obtained from Orange County Flood Control District and well permits were obtained from Orange County Health Care Agency.

Geosyntec also prepared a Health and Safety Task Hazard Analysis (THA) outlining the appropriate personal protective equipment (PPE) and procedures to safely implement the scope of subsurface exploration work.

3.2 Subsurface Explorations

Geosyntec’s subsurface exploration program consisted of twenty-two (22) Cone

Penetration Tests (CPTs) and eight Hollow-stem auger (HSA) borings. The approximate locations of the CPTs and HSA borings are shown on Figure 2. Summary

8 11/23/2022 of the CPT and boring information including date, depths, locations, and approximate ground surface elevations are presented in Table 1.

3.2.1 Cone Penetration Testing

Prior to advancing the CPTs, the uppermost 5 feet below ground surface (ft bgs) of each

CPT location was hand-augered. The CPTs were advanced to depths ranging from 30 to

70 ft bgs.

The CPTs were advanced using a truck-mounted 30-ton CPT rig in accordance with

ASTM International Test Procedure (ASTM) D5578 and used a cone with a cone tip area of 15 cm2 (2.3 square inches). Instrumentation on the cone and within the rig measured cone bearing, sleeve friction, and dynamic pore water pressure at 2.5 cm

(~1-inch) intervals during penetration to provide a nearly continuous log. Measurements of CPT resistance were used to evaluate the variation of material types and engineering properties. Soil Behavior Type (SBT) and the stratigraphic interpretation are based on relationships between cone bearing, sleeve friction, and pore water pressure. The friction ratio is a calculated parameter (defined as the ratio of the sleeve friction to cone bearing) and is used to infer the SBT.

The CPT holes were backfilled with cement bentonite grout mix and patched with concrete on the surface, where applicable. The CPT logs are included in Appendix C.

3.2.2 Hollow-Stem Auger Drilling and Sampling

Prior to advancing the HSA drilling, the uppermost 5 ft bgs was hand-augered. Cuttings from hand-augering were collected as a bulk sample. The borings were drilled and sampled to approximate depths of 41.5 to 65.5 ft bgs using a truck-mounted CME-75 rig, with an 8-inch diameter hollow-stem auger.

Soil samples were collected at selected depths of interest using a 2-inch outside diameter split-spoon Standard Penetration Test (SPT) drive sampler or a 3-inch outside diameter California Modified sampler, using an automatic trip hammer (140-pound hammer falling approximately 30 inches).

Descriptions and visual classification of the subsurface materials were logged in the field by Geosyntec, and subsurface descriptions were based on the recovered soil samples and soil cuttings. The soil samples and boring logs were reviewed by a

California-licensed Geotechnical Engineer. The subsurface conditions were logged in general accordance with ASTM International (ASTM) Test Standard D2488, visual-manual procedure. The classifications were further revisited in general accordance with

ASTM D2487, Unified Soil Classification System, after laboratory tests were

9 11/23/2022 performed. A key to the boring logs and individual boring logs are included in

Appendix D-1. The hammer calibration certificate provided by the drilling subcontractor is included in Appendix D-2.

The boreholes were backfilled with cement bentonite grout mix and patched with concrete on the surface, where applicable. The soil cuttings were drummed in 55-gallon steel drums. Geosyntec collected composite soil samples from the drums, and Eurofins

Calscience performed analytical tests for waste disposal characterization. Based on the test results, the drums were disposed of at a non-hazardous waste disposal facility.

Results of the waste characterization analytical tests are included in Appendix D-3.

3.3 Geotechnical Laboratory Testing Program

Geosyntec sent representative soil samples collected during the subsurface exploration to AP and Wood laboratories for testing. The laboratory testing program consisted of:

• In-situ moisture content and density (ASTM D2216, D7263);

• Percent passing No. 200 sieve (ASTM D1140);

• Atterberg limits (ASTM D4318);

• Direct shear test (ASTM D3080);

• Unconsolidated Undrained (UU) Triaxial (ASTM D2850);

• One-dimensional consolidation (ASTM D2435).

Results of the laboratory testing program are summarized in Table 2 and test sheets are included in Appendix E-1. The results of the geotechnical laboratory testing program were used to corroborate field classifications and assist in selecting input parameters for geotechnical evaluations.

Additionally, two suite of soil corrosivity testing was performed, including minimum resistivity, sulfate content, chloride content, and pH (California Testing Method, CTM

643, CTM 417, and CTM 422). The results of this testing are summarized in Table 3 and test sheets are included in Appendix E-2.

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4. SITE CONDITIONS

The geological and geotechnical characterization of the Site presented herein are based on a review of available information from the California Geological Survey (CGS), review of previous geotechnical studies at the site, and information obtained from

Geosyntec’s exploration activities described in Section 3. The review of the site conditions includes a description of geologic and geotechnical conditions and an evaluation of both the current and historical groundwater elevations.

4.1 Regional Geologic Conditions

The project site is located at the southern edge of the Orange County Coastal Plain groundwater basin, near the northwest margin of the San Joaquin Hills, where Santa

Ana Delhi Channel empties into the Upper Newport Bay (DWR, 2003). Geologic materials exposed at the surface consist of Quaternary basin-filling sediments including marine terrace deposits, terrestrial alluvium, and paralic deposits (interfingered marine and fluvial/terrestrial deposits) (Morton and Miller, 2006). Approximately 0.5 miles to the southeast, across the Upper Newport Bay, Quaternary terrace deposits onlap the

Tertiary Fernando Formation, the uppermost Tertiary bedrock formation of the San

Joaquin Hills, where it is exposed in the bluffs beneath the East Bluff neighborhood of

Newport Beach (Vedder, et al., 1957). Quaternary basin filling sediments thicken to the north and west, toward the central trough of the Los Angeles Basin (Vedder, 1975).

Approximately 0.5 miles to the southwest of the mouth of Delhi Channel, a splay of the

Newport-Inglewood-Rose Canyon Fault Zone (NIRCFZ) transects the Upper Newport

Bay trending northwest-southeast. The NIRCFZ is a complex of en-echelon right-lateral strike slip faults that stretches from the foot of the Santa Monica Mountains near

Beverly Hills, to the San Joaquin Hills where it connects with the Pelican Hill Fault

(USGS and CGS, 2022). Although portions of the NIRCFZ are classified as Holocene-active faults by the California Geological Survey, meaning that they have experienced movement in the last 11,700 years and are therefore subject to the requirements of the

1972 Alquist-Priolo Earthquake Fault Zoning Act (A-P Act), the splay located closest to the site is not considered to be Holocene-active. The closest Holocene-active fault to the project site is a splay of the NIRCFZ that terminates in the vicinity of Newland

Street in Huntington Beach, approximately 5.5 miles to the west (CGS, 2016). A local geologic map is shown in Figure 3.

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4.2 Subsurface Conditions

The subsurface soil strata at this site can be divided into three broad soil units – fill material, upper Paralic deposits, and lower Paralic deposits. Geologic cross-sections based on the past and current investigations are presented in Appendix F.

4.2.1 Fill

Fill was encountered in most of the borings drilled by Ninyo & Moore (2012,2013) and in three borings performed by Geosyntec (this study).

At the bridge left abutment, even though no fill was reported in N&M (2012) boring B-

1, we believe that up to 15 feet of fill was placed as part of existing left abutment construction. On the left side of the channel, about 11 to 12 feet of fill containing glass debris, shell fragments, and asphaltic concrete debris was observed in the borings

(HSA-3 and HSA-4) drilled on top of the channel’s bank. On the borings that were drilled farther away from the channel (on Anniversary Lane), fill was not observed.

Fill was not observed at the bridge right abutment location. About 4-foot thick fill layer was observed along the right bank in between the bridge location and the Golf course.

This fill layer generally consisted of silty sands and clayey sands. Within the Golf course area, the fill layer varied in thickness from about 3½ to 8 feet, generally consisting of sands and silts.

4.2.2 Upper Paralic Deposits

Upper paralic deposits were observed beneath the fill material and generally consisted of interbedded clayey and silty sands of variable density, and stiff to very stiff, low to high plasticity, silty and sandy clays, lean clays, and silts. At some locations, these deposits were observed to contain layers of organics soils.

At the bridge left and right abutments, the upper paralic deposit was present down to a depth of EL -16 and EL -10, respectively. Along the channel’s banks, the upper paralic deposit was relatively thinner, extending down to elevations that range from EL -3 to

EL -10.

Based on their relative strength, these soils were further divided into Upper Paralic-1

(thicker section with relatively lower strength) and Upper Paralic-2 (present below

Upper Paralic-1 with higher strength and only about 2 to 4 feet thick, except at the bridge location where it is about 5 to 10 feet thick).

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4.2.3 Lower Paralic Deposits

Lower paralic deposits were observed beneath the upper paralic deposits and were characterized by higher strengths compared to the upper paralic deposits.

At the bridge abutment locations, lower paralic deposits generally consisted of coarse-grained soils with field blow counts that are representative of medium dense to dense soils. These soils at the left abutment were observed below EL -17 and consist of Niguel formation silty claystone with thin layers of clayey sandstone and weakly cemented conglomerate. At the right abutment, we observed lower paralic soils below EL -11 and the soils consisted of interbedded sands and sandy clays.

Along the channel banks, lower paralic deposits were observed below elevations that ranged from EL -5 to EL -10. Along the left bank, these soils were generally observed to be sandy. Along the right bank, these soils consisted of interbedded layers of sands, clays, and silts.

Similar to the Upper Paralic layer, the Lower Paralic deposits were further classified as

Lower Paralic-1 (relatively lower undrained strength but still stronger than Upper

Paralic) and Lower Paralic-2 (relatively stronger layer).

4.2.4 Estimated Shear Strength Parameters

Geosyntec developed a characteristic summary of the shear strength parameters of the observed soil units as described above and derived from the current (Geosyntec) and previous (Ninyo & Moore 2012,2013, GMU 2020) investigations for use in our engineering analyses. Geosyntec performed a CPT interpretation analysis for geotechnical parameters using the computer program CPeT-IT v.2.0.2.10

(Geologismiki, 2018). Based on our review of the CPT and boring data, the fill soils were be assumed to be granular materials with no apparent cohesive strength. The paralic deposits are expected to exhibit undrained shear strength under transient loading and both upper and lower paralic deposits exhibit increasing undrained shear strength with depth. The summary of the estimated shear strength parameters is presented in

Table 4 below:

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Table 4: Estimated Shear Strength Parameters of the Observed Soil Units

Soil Strata Unit Weight

(pcf)

Undrained Strength

Parameters

Drained Strength

Parameters Residual Strength1

Cohesion

(psf)

Friction

Angle

Cohesion

(psf)

Friction

Angle

Cohesion

(psf)

Friction

Angle

Fill 125 0 300 0 300

--- --- Upper Paralic -1 125 1,300 00 100 280

Upper Paralic -2 125 1,800 00 100 280

Liquefiable Soil 120 0 290 0 290 30 to 400 00

Lower Paralic -1 120 2,000 00 0 300

Lower Paralic -2 120 2,500 00 0 300

1. Post-liquefaction strength of material identified as susceptible to liquefaction during an earthquake event. The residual strength of this material was taken as a function of the overburden stress.

4.3 Groundwater Conditions

The table below summarizes the groundwater depth across all borings performed by

Geosyntec for this project.

Table 5: Summary of Groundwater Depth Measurements in Soil Borings

Boring ID Boring Depth

(ft)

Ground Surface

Elevation

(ft)

Groundwater

Depth bgs (ft)

Groundwater

Elevation (ft)

HSA-1 41.5 16.2 38 -21.8

HSA-2 1 41.5 13.8 --- ---

HSA-3 1 41.5 18.4 --- ---

HSA-4 1 41.5 23.1 --- ---

HSA-5 65.5 14 14 0

HSA-6 1 57 21 --- ---

HSA-7 1 37 10 --- ---

HSA-8 57 26 35 -9

1. Groundwater not observed during or upon completion of drilling.

14 11/23/2022

Groundwater was generally encountered in the Ninyo & Moore (2013) borings within the downstream half of the project area at elevations of approximately EL +2.5 to EL -

17.5 and seepage was observed in couple borings at EL +7.5.

Geosyntec reviewed the seismic hazard zone report for the Anaheim and Newport

Beach Quadrangles (CGS, 2006) for historic high depth to groundwater levels.

Geosyntec compared the contours of depth to historic high levels provided in CGS

(2006) with the ground surface elevations. Based on this comparison, the historic high groundwater level is at approximately EL +5 feet MSL.

Geosyntec looked at a report titled “Fourth Quarter 2021 Groundwater Monitoring

Report”, prepared by Environmental Management Services (EMS 582) which was accessed from the California State Water Resources Control Board (SWRCB)

GeoTracker database. This report was for a project located at Back Bay Center on the southwest quadrant of the intersection of Irvine Avenue and Mesa Drive, across the street from the northern end of our project. This report includes data from groundwater monitoring wells within the shopping center and two wells located on the east side of

Irvine Avenue adjacent to the channel. Some of these wells are screened in a deep zone and some in the shallow zone. Groundwater level in the deep zone is summarized to be ranging from EL+3 to +5 feet MSL on the east side of the Center and adjacent to the channel and from EL 0 to EL -16 feet MSL on the west side of the Center and away from the channel. The change is speculated by the authors to be due to the presence of an inferred fault in the middle of the Center. Groundwater level in the shallow zone is summarized to be at about El +22 feet MSL and referred to as the perched zone. The

Back Bay Center report states that the flow direction in the deep zone was previously interpreted to be towards the west (away from the channel). The report also states that based on concentration of constituents, the flow direction in the shallow zone may be towards the east, i.e., towards the channel.

Based on the groundwater levels encountered in explorations and the data reviewed as discussed above, Geosyntec recommends a historical high groundwater level of EL +5 feet MSL for use in engineering analysis for the project.

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5. GEOLOGIC AND SEISMIC HAZARDS

5.1 Fault Surface Rupture

Seismically induced fault surface rupture occurs as the result of differential movement across a fault. The potential for fault surface rupture is generally considered to be significant along “active” faults and to a lesser degree along “potentially active” faults

(CDMG, 1998). A review of published geologic maps did not identify the presence of active or potentially active faults crossing or projecting towards the limits of the project site. Furthermore, the site is not located within an Earthquake Fault Zone as defined in the Alquist-Priolo Earthquake Fault Zoning Act (Hart and Bryant, 2007).

5.2 Strong Ground Shaking

The project is situated within a seismically active region and will likely experience moderate to severe ground shaking in response to a large magnitude earthquake occurring on a local or more distant active fault during the expected lifespan of the proposed structures. As a result, seismically induced ground shaking in response to an earthquake occurring on a nearby active fault, such as the San Joaquin Hills fault is considered to be a major geologic hazard affecting the project. Other major nearby active faults include Newport-Inglewood fault, Anaheim fault, Compton fault, Oceanside fault, etc.. Regional fault and historical earthquake epicenter map is provided in Figure 4. Details regarding design ground motions for to the design and construction of the proposed improvements are provided in Section 6.

5.3 Expansive Soils

Intermittent layers of high plasticity clay soils (fat clays) were observed in our borings within the upper paralic deposits. Fat clays when subject to changes in moisture content undergo volumetric strains which has a potential to impose additional lateral loads onto a retaining wall. We anticipate the existing high plasticity clays within the upper paralic is already near saturation and may not exhibit any significant change in moisture content because of the proposed improvements. In addition, expansive soils are prone to long-term softening and creep and therefore, the retaining wall anchor may be prone to long term creep movements if the bond zone (the material in which the anchor is grouted) is within expansive soils.

5.4 Liquefaction

Seismically induced soil liquefaction can be described as a significant loss of strength and stiffness due to cyclic pore water pressure generation from seismic shaking. The

16 11/23/2022 material types considered most susceptible to liquefaction are saturated and loose to medium dense granular soils and low-plasticity, fine-grained soils. Manifestations of soil liquefaction can include the loss of bearing capacity below foundations, surface settlements and tilting in level ground, and instabilities in areas of sloping ground. Soil liquefaction can also result in increased lateral and uplift pressures on buried structures.

Lightweight or unrestrained buried structures may float upward to the ground surface during a liquefaction event.

Based on the review of the available geologic data and the Newport Beach Quadrangle of the State of California Seismic Hazard Zones map (CDMG, 1997) the proposed project is located in an area where the historical occurrence of liquefaction or local geological, geotechnical, and groundwater conditions indicate a potential for permanent ground displacement. An excerpt of the CDMG seismic hazard map is shown in Figure

5. Liquefaction susceptibility and triggering analyses were performed as described in

Section 7.

5.5 Lateral Spreading

When liquefaction occurs, sloping ground or level ground near a steep slope or vertical face can potentially move as a mass downslope or towards the steep slope/vertical face, applying lateral forces to structures and their foundations, and potentially imposing large deformations.

When lateral spreading occurs, spreading of greatest magnitude generally occurs nearest the steep slope or vertical face and gradually diminishes with distance from the free face. Typically, portions of a site that may be impacted within a zone that extends away from the free face, a distance approximately 50 times the height of the free face, are considered to have a potential for lateral spread.

The geological, geotechnical, groundwater conditions, and free face conditions at the project site may exhibit lateral spreading potential if liquefaction triggering occurs.

Post-liquefaction stability of the channel banks are discussed in Section 8.

5.6 Earthquake-Induced Landslides

Based on the review of the Seismic Hazard Zones map (CDMG, 1997) the proposed project is not located in an area where the historical occurrence of landslide movement liquefaction or local topographic, geological, geotechnical and subsurface water conditions indicate a potential for permanent ground displacement. However, the native slopes near the south end of the project site on the east side is located in an area identified as a landslide area in the Seismic Hazard Zone map. A global slope stability

17 11/23/2022 of the overall hillside in that area was not included in our scope of work as it is outside the area to be graded.

5.7 Other Geologic Hazards

The proposed improvements falls within the mapped Tsunami hazard area (CGS, 2021).

Volcanic activity is not considered to be a significant hazard, given the geologic and topographic setting of the Site, and is unlikely to pose an impact on the Project.

18 11/23/2022

6. SEISMIC HAZARD EVALUATION

The seismic evaluations of proposed channel improvements will generally be based on the methods described in U.S. Army Corps of Engineers EM 110-2-1806 (USACE, 2016) and the seismic evaluations will be primarily performance-based as discussed in

Section 8.1.3. The seismic evaluations for the proposed pedestrian bridge will be based on AASHTO LRFD Bridge Design Specifications, 8th Edition with California

Amendments (AASHTO-CA BDS-8) which defers to the California Department of

Transportation (Caltrans) Seismic Design Criteria (SDC) Version 2.0 (Caltrans, 2019).

Therefore, two seismic hazard evaluations were performed, each in accordance with the respective references. While the two seismic hazard evaluations for the aforementioned features follow different standards, the input parameters and ground motion models are the same and have been summarized briefly in the first two sections below. The subsequent sections present the AASHTO-CA BDS-8 and USACE (2016) seismic hazard evaluations for the pedestrian bridge and channel improvements, respectively.

6.1 Input Parameters

The site location was identified with the following coordinates:

• Latitude = 33.6554°

• Longitude = -117.8822°

Site subsurface conditions are defined through a time-averaged shear wave velocity over 30 meters (100 ft), termed Vs30. The shear wave velocity data collected as part of this investigation provides information down to a depth of approximately 100 ft. Figure

6 presents the shear wave velocity test data. Based on the results of the shear wave velocity testing, the Vs30 for the site is estimated to be 950 ft/sec (290 m/s).

The shear wave velocity measurements and estimated Vs30 for the site were also used to estimate the depth to shear wave velocities of 1.0 km/s (Z1.0) and 2.5 km/s (Z2.5) for use with the NGA-West2 ground motion prediction equations (GMPEs). The estimates of Z1.0 and Z2.5 for the site were obtained from relationships presented by Chiou and

Youngs (2013) and Campbell and Bozorgnia (2013), respectively. The selected values for Z1.0 and Z2.5 for the site are 467 meters and 1.83 kilometers, respectively.

Development of these parameters address the requirements for considering basin effects in accordance with Caltrans SDC (2019).

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6.2 Ground Motion Models

The ground motion attenuation was modeled using the following four ground motion prediction equations (GMPEs) for shallow crustal earthquakes in tectonically active regions (NGA-West2) developed by the Pacific Earthquake Engineering Research

(PEER) Center NGA-West2 Project:

• ASK14: Abrahamson et al. (2014);

• BSSA14: Boore et al. (2014);

• CB14: Campbell and Bozorgnia (2014); and

• CY14: Chiou and Youngs (2014).

The Idriss (2014) model was not used because that particular model is not applicable for sites with Vs30 less than 1476 ft/s (450 m/s).

6.3 Design Seismic Ground Motions for Pedestrian Bridge per AASHTO-CA

Bridge Design Specification-8

The California amendments to the AASHTO Bridge Design Specification Article 3.10, dictate that the seismic analysis for bridges be performed in accordance with the

Caltrans SDC (2019). The pedestrian bridge was categorized as Ordinary as it does not fall under Important or Recovery designation per Section 1.2. In accordance with

Caltrans SDC, ground shaking shall be characterized for design by the Design Spectrum

(DS). The DS presented herein reflects the Safety Evaluation Earthquake (SEE) taken as a spectrum based on a 5% probability of exceedance in 50 years (975-yr return period) in accordance with the seismic hazard evaluation level for Ordinary bridges per

Section 1.3 (Caltrans, 2019). The seismic hazard evaluation consisted of developing site-specific 5% damped elastic acceleration response spectra based on a probabilistic seismic hazard analysis (PSHA) as discussed in the following section.

6.3.1 Probabilistic Safety Evaluation Earthquake Design Spectrum

The probabilistic DS was developed in accordance with Caltrans SDC Appendix B:

Design Spectrum Development. The geometric mean spectral response accelerations for the 5% probability of exceedance in 50-year (975-year return period) PSHA were calculated using an open-sourced, Java-based program called OpenSHA Hazard

Spectrum application (version 1.5.2). The application provides a single interface for accessing various USGS National Seismic Hazard Models (NSHMs). The Uniform

California Earthquake Rupture Forecast Version 3 (UCERF3, Field et al, 2013) fault

20 11/23/2022 rupture data is included in the NSHMs, and ground motion attenuation was modeled using the four GMPEs mentioned in previous sections.

In accordance with near-fault considerations presented in Caltrans SDC Appendix B, a disaggregation of the site seismic hazard at a spectral period of 1-second was performed to determine whether the probabilistic mean or modal rupture distance is less than 25

km. The disaggregation, performed using the 2018 National Seismic Hazard Model

(NSHM) disaggregation web-based tool provided by the USGS, confirmed that the site ground motions should account for near-fault effects as the modal rupture distance was less than 25 km with a value of about 10 km. The geometric mean ground motions for each spectral period from OpenSHA were then scaled using the period-dependent near-fault amplifications factors presented in Caltrans SDC Appendix B (2019). For spectral periods less than or equal to 0.5 seconds, the near-fault factor was taken as 1. At spectral periods greater than or equal to 1.0 seconds, the near-fault factor was taken as

1.2. For periods between 0.5 and 1, the near-fault factor was linearly interpolated between 1 and 1.2. The period-dependent near-fault amplification scale factors are provided in Table 7. The resulting scaled spectrum represents the probabilistic SEE design spectrum as shown in Figure 7. This SEE design spectrum is intended for seismic design of the pedestrian bridge.

6.3.2 Safety Evaluation Earthquake Peak Ground Acceleration

Based on the results of the probabilistic analysis presented herein, the resulting PGA for the SEE for the pedestrian bridge is 0.468g.

6.4 Design Seismic Ground Motions for Channel Improvements

Design ground motions for the channel improvements were developed based on guidance from USACE (2016), which provides two performance-based design levels, the Maximum Design Earthquake (MDE) defined as an event with a probability of exceedance of 10% in 100 years (i.e., 950-year return period) and the Operating Basis

Earthquake (OBE) defined as an event with a probability of exceedance of 50% in 100 years (i.e., 144-year return period). The development of design ground motions corresponding to the MDE and OBE are discussed in the following sections.

6.4.1 Maximum Design Earthquake

The intent of designing with the MDE ground motions is to reduce the risk of damage from a “once in service life” event and large loss of life and economic damages. The

MDE was developed by calculating the geometric mean spectral response accelerations for the 950-year return period using the OpenSHA Hazard Spectrum application

21 11/23/2022 discussed previously in Section 5.3.2 with the inputs and GMPE’s discussed in Section

5.1 and 5.2, respectively.

In accordance with USACE (2016), the MDE spectral response accelerations need not be greater than the estimated accelerations from the mean DSHA, thus a DSHA was performed to determine the lesser of the PSHA and DSHA. The deterministic spectral response acceleration at each period was calculated as the 50th-percentile 5% damped spectral response acceleration using the controlling fault scenario (San Joaquin) discussed in Section 5.3.1. The resulting deterministic spectral accelerations are greater than the probabilistic spectral accelerations for all evaluated periods, and thus the PSHA controls the MDE for the site. Resulting response spectrum for the MDE is presented in

Figure 8 and summarized in Table 8.

The US Geologic Survey (USGS) deaggregation feature available in the web-based

Unified Hazard Tool (UHT) was used to inform the characteristic magnitude (Mw) for the MDE (950-year return period). The magnitude and the peak horizontal ground acceleration (PGA) of the MDE ground motions are 6.6 and 0.47 g, respectively.

6.4.2 Operating Basis Earthquake

The intent of designing with the OBE ground motions is to minimize the nonlinear response behavior of the proposed structure. The structure is intended to remain in operation or to be operational within a short period of time with minor repairs after the

OBE event.

The OBE was developed by calculating the geometric mean spectral response accelerations for the 144-year return period using the OpenSHA Hazard Spectrum application discussed previously in Section 5.3.2 with the inputs and GMPE’s discussed in Section 5.1 and 5.2, respectively. Resulting response spectrum for the OBE ground motions is presented in Figure 8 and summarized in Table 8.

The US Geologic Survey (USGS) deaggregation feature available in the web-based

Unified Hazard Tool (UHT) was used to inform the characteristic magnitude (Mw) for the OBE (144-year return period). The magnitude and the peak horizontal ground acceleration (PGA) of the OBE ground motions are 6.5 and 0.22g, respectively.

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7. LIQUEFACTION EVALUATION

7.1 Introduction

As discussed in Section 5.4, our project site is located in an area that has the potential for liquefaction-induced permanent ground displacement. Due to the project’s location within the zone of recognized liquefaction hazard, a site-specific liquefaction evaluation was conducted.

7.2 Evaluation Approach

Geosyntec performed CPT-based site-specific liquefaction triggering analyses for this study utilizing the CPTs performed by Geosyntec and by GMU (2020). Borings were drilled adjacent to some of the selected CPTs where liquefaction triggering was observed, to collect samples of the potentially liquefiable soils to perform liquefaction susceptibility testing. A discussion of the samples collected in boring HSA-5 at bridge right abutment in the vicinity of CPT-7, CPT-8, and GMU’s CPT-2 is discussed Section

7.3. The CPT data provides a near continuous subsurface profile and repeatable…