Appendix_E_Geotechnical_Design_Report_Amend0003.pdf

Geotechnical Design Report

P-1018 CMV-22B AIRFIELD IMPROVEMENTS PROJECT

Volume 1: Apron, Taxiway & Helipad

P-1024 MV-22 MAINTENANCE HANGAR PROJECT

NAVFAC Contract: N62473-16-D-1850

Delivery Order N624731F4484 eProject Number: 1389898

Naval Air Station North Island (NASNI) Naval Base Coronado, CA

December 2017 Revised February 2019

Prepared by:

HDR, Inc.

412 E. Parkcenter Blvd, Suite 100

Boise, ID 83706-6659

(208) 387-7000

1 Signed and stamped December 11, 2017. Minor revisions made in 2019 made by co-authors.

December 11, 2017 Revised February 13, 2019

NAVFAC Southwest Coastal IPT Naval Air Station North Island 2730 McKean St. Bldg. 291 San Diego, CA 92136

Attn: Ken Miller, R.A., Design Manager

Dear Mr. Miller, We are pleased to present this geotechnical design report summarizing results of our geotechnical study for the proposed P-1018 Apron, Taxiway and Helipad, and P-1024 MV-22 Aircraft Maintenance Hangar Project located at Naval Air Station North Island in Coronado, California. This report summarizes the work performed, data acquired, and our findings, conclusions, and geotechnical recommendations for design and construction.

We appreciate the opportunity to provide geotechnical services on this project and trust the information in this report meets the current project needs. If you have any questions regarding this report or if we may be of further assistance, please contact the undersigned.

Respectfully submitted, HDR ENGINEERING, INC.

1Mariusz Sieradzki, PhD, PE, GE 2864 Senior Engineer - Geotechnical

Manuel Guzman, PE C83361 Senior Engineer - Geotechnical

Gary R. Goldman, PE, GE 2587 Senior Project Engineer - Geotechnical

Table of Contents

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar i

Table of Contents EXECUTIVE SUMMARY ............................................................................................... 1-1

INTRODUCTION ............................................................................................................ 2-1

2.2 Purpose and Scope ............................................................................................ 2-2

2.3 Previous Investigations ...................................................................................... 2-2

GEOTECHNICAL FIELD AND LABORATORY INVESTIGATION ............................... 3-1

3.1 Subsurface Exploration ...................................................................................... 3-1

3.2 Geotechnical Laboratory Testing........................................................................ 3-3

GEOLOGY, GEOLOGIC/SEISMIC HAZARDS, AND SEISMIC DESIGN

CONSIDERATIONS ....................................................................................................... 4-1

4.1 Regional Geology ............................................................................................... 4-1

4.2 Site Geology ....................................................................................................... 4-1

4.3 Assessment of Potential Geologic Hazards ....................................................... 4-1

4.3.1 Fault-Rupture Hazard ................................................................................................ 4-1

4.3.2 Faulting and Seismicity .............................................................................................. 4-2

4.3.3 Liquefaction Potential and Seismic Settlement ......................................................... 4-3

4.3.4 Landslides and Lateral Spreading ............................................................................. 4-4

4.3.5 Seiches and Tsunamis .............................................................................................. 4-4

4.3.6 Subsidence ................................................................................................................ 4-5

4.4 Seismic Design Criteria ...................................................................................... 4-5

EXISTING SITE CONDITIONS ...................................................................................... 5-1

5.1 General ............................................................................................................... 5-1

5.2 Existing Pavements ............................................................................................ 5-1

5.3 Subsurface Earth Materials ................................................................................ 5-3

5.3.1 General ...................................................................................................................... 5-3

5.3.2 Expansive Soils ......................................................................................................... 5-3

5.3.3 Collapsible Soils ........................................................................................................ 5-4

5.3.4 Corrosion Potential .................................................................................................... 5-4

5.3.5 Infiltration ................................................................................................................... 5-4

5.3.6 Soil Contamination .................................................................................................... 5-5

5.4 Groundwater ....................................................................................................... 5-5

GEOTECHNICAL AND FOUNDATION DESIGN RECOMMENDATIONS ................... 6-1

6.1 General ............................................................................................................... 6-1

6.2 Design CBR ........................................................................................................ 6-1

6.3 Foundation Type ................................................................................................ 6-3

6.3.1 General ...................................................................................................................... 6-3

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar ii

6.3.2 Shallow Foundation on Improved Ground ................................................................. 6-3

6.3.3 Driven Piles ............................................................................................................... 6-5

6.3.4 Shallow Foundation for Lightly Loaded Uninhabited Structures ............................... 6-8

6.4 Slab-on-Grade Construction ............................................................................... 6-9

6.5 Lateral Earth Pressures .................................................................................... 6-10

6.6.1 General .................................................................................................................... 6-10

6.6.2 Asphalt Concrete Pavement for Roads and Parking Lots ....................................... 6-11

6.6.3 Portland Cement Concrete Pavement ..................................................................... 6-11

6.7 Site Drainage .................................................................................................... 6-12

EARTHWORK ............................................................................................................... 7-1

7.1 General ............................................................................................................... 7-1

7.2 Site Preparation .................................................................................................. 7-1

7.3 Fill Materials ....................................................................................................... 7-2

7.4 Temporary Excavations ...................................................................................... 7-2

7.4.1 General ...................................................................................................................... 7-2

7.4.2 Excavation Characteristics ........................................................................................ 7-3

7.5 Trench Backfill .................................................................................................... 7-3

7.6 Additional Geotechnical Services ....................................................................... 7-4

LIMITATIONS ................................................................................................................ 8-1

REFERENCES ............................................................................................................... 9-1

List of Tables Table 3-1. Boring/Core Information ...................................................................................... 3-1 Table 4-1. Nearby Faults ..................................................................................................... 4-3 Table 4-2. Seismic Design Parameters – 2016 UFC 3-301-01 ............................................ 4-6 Table 5-1. Existing Pavements Sections ............................................................................. 5-1 Table 5-2. Recommended Soil Parameters at P-1024 Aircraft Maintenance Hangar.......... 5-3 Table 5-3. Measured Infiltration Rates ................................................................................. 5-5 Table 6-1. Pavement Supporting Capacities ....................................................................... 6-2 Table 6-2. Soil Parameters for Lateral Pile Capacity Analysis ............................................. 6-6 Table 6-3. Summary of Lateral Pile Capacities 14-inch-square Driven Pile ........................ 6-6 Table 6-4. Summary of Lateral Pile Capacities16-inch-square Driven Pile ......................... 6-7 Table 6-5. Lateral Load Reduction Factors .......................................................................... 6-7 Table 6-6. Lateral Earth Pressures .................................................................................... 6-10 Table 6-7. Preliminary Asphalt Concrete Pavement Sections ........................................... 6-11

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar iii

List of Appendices Appendix A Figures

Appendix B Geotechnical Boring Logs

Appendix C Geotechnical Laboratory Test Results

Appendix D Engineering Calculations

1.0 Executive Summary

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 1-1

EXECUTIVE SUMMARY

This report presents the results of our geotechnical study for the proposed P-1018 Apron Expansion, Taxiway and Helipad, and P-1024 MV-22 Aircraft Maintenance Hangar Project located within the Naval Air Station North Island (NASNI) in Coronado, California. The purpose of our study was to explore and evaluate subsurface conditions at the site and provide geotechnical recommendations for the design and construction of the proposed project. A summary of our findings and conclusions is presented below.

• The subsurface soils generally consisted of approximately up to 20 feet of fill placed as a part of land reclamation over native soil to the maximum depth explored of approximately 71 feet. At the locations explored, these soils consisted of loose to very dense silty sand, sand with silt and sand.

• The on-site near-surface soils meet gradation and Atterberg limit requirements for selected material as specified in Chapter 7 of the Unified Facilities Criteria (UFC) 3-260- 02.

• Based on laboratory test results, near-surface soils exhibit very low potential for expansion, low corrosive potential towards concrete, and should be considered mildly to moderately corrosive to buried ferrous metals.

• Groundwater was encountered at approximate depths between 14 and 19.5 feet below ground surface (bgs) in the exploratory borings at the time of our field exploration.

However, seasonal fluctuations of groundwater levels should be anticipated during periods of heavy precipitation.

• No active or potentially active faults are known to cross the site and the site is not located within a currently delineated State of California Alquist-Priolo Earthquake Fault Zone. Accordingly, the risk of surface rupture due to faulting is considered low. However, the project site area may be subjected to strong ground shaking during its lifetime. The closest mapped fault is the Newport-Inglewood Rose Canyon Fault Zone (Silver Strand Section-Spanish Bight Fault) located approximately 0.9 mile east from the site.

• The City of San Diego Seismic Safety Study (2008) has identified the site just outside the zone for liquefaction potential. However, since the project site is underlain primarily by medium dense granular soils within 35 feet bgs, there is a potential for liquefaction and seismic-induced settlement that may impact the proposed development. Results of our investigation and study indicate liquefaction-induced settlement may range between approximately 1 and 4 inches across the site during a major seismic event. Liquefaction potential and its effects should be considered in the foundation design.

• The probability of other geologic hazards such as tsunami, seiches, deep seated landslides, or ground subsidence affecting the site is considered low.

• The proposed hangar structure may be founded on shallow, conventional spread and continuous footings provided that the proposed ground improvement measures are employed. As an alternate foundation option, the proposed hangar can be supported on precast, prestressed driven piles.

• Overexcavation and recompaction is recommended for support of the proposed structures, pavements, and site improvements. Please see Sections 7.2 and 7.3 of this report for details.

1.0 Executive Summary

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 1-2

It is our professional opinion that the proposed project is feasible from a geotechnical standpoint provided that the recommendations presented in this geotechnical report are incorporated into the project design and construction.

The executive summary presented herein briefly summarizes results of our geotechnical investigation for the subject project and should be used only in conjunction with the findings and conclusions presented in the attached report. The conclusions presented in this report are subject to the limitations presented in Section 8.0.

2.0 Introduction

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 2-1

INTRODUCTION

2.1 PROJECT DESCRIPTION

2.1.1 P-1018 Apron, Taxiway and Helipad Reconstruction

The existing site conditions consist of an active Naval Air Station including a concrete paved aircraft apron and Taxiway Lima. The proposed P-1018 Apron, Taxiway and Helipad will include the reconstruction of the existing concrete parking Apron 3, approximately 960,000 square feet

(sf) in size with grounding system, airplane anchoring system and associated lighting and equipment. In addition, the replacement of the existing Taxiway Lima and construction of approximately 214,000 sf new Taxiway Lima that will provide sufficient pavement strength to support MV-22 and P-8 aircraft is planned. Other improvements will include a new 100-foot by 100-foot helipad designed for rotary wing aircraft, new hangar access apron and asphalt shoulders.

Appurtenant construction will include demolition of several existing structures including maintenance hangars/shops and installation of utility lines. We anticipate the finished grade of the proposed improvements will generally match the existing grades.

2.1.2 P-1024 MV-22 Aircraft Maintenance Hangar

Based on information provided, the proposed project includes the construction of the P-1024 MV-22 Aircraft Maintenance Hangar with a total footprint area of approximately 90,044 sf (which includes the square footage of the hangar door pockets and hangar door track area, but does not count against the UFC Gross square footage calculation). The proposed facility will be comprised of two distinct operational areas including:

• Two-bay aircraft Type II maintenance hangar; one bay capable of housing three (3) open aircraft and the other housing three (3) aircraft where one has rotors and wings in the folded storage position.

• A two-story squadron support facility including administration and shops, maintenance units, command office suites, training, special access program facilities areas, storage, restrooms and locker room facilities, and supporting utility rooms.

In addition, a freestanding prefabricated utilities control building will be installed to support the wash rack. We anticipate the new hangar will consist of concrete masonry units (CMU) walls and concrete floors with a structural steel building frame, steel roof trusses, structural metal deck and Thermoplastic Polyolefin (TPO) single ply roof membrane over rigid roof insulation.

Five-ton capacity, Class C Duty Service overhead bridge cranes will be installed at each aircraft maintenance bay. The hangar foundation loads are not known at this time; however, we assume column and wall loads up to 25 kips and 15 kips per linear foot, respectively. The proposed hangar will be supported either on a shallow foundation system with improved ground or on driven precast, prestressed concrete piles.

Appurtenant construction will include parking areas for approximately 160 vehicles, roadways, fire lanes, curbs, sidewalks, trash enclosures, irrigation and landscaping. We understand that the finished grade for the proposed new hangar and other site improvements will generally match the existing grades with cuts and fills on the order of ± 2 feet or less.

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 2-2

The site location is shown on Figure 1, Site Location Map, in Appendix A. Locations of the existing and proposed site improvements are shown on Figures 2, Boring and Coring Location Map, in Appendix A.

2.2 PURPOSE AND SCOPE

The purpose of this geotechnical study was to review existing geotechnical data and perform subsurface exploration, laboratory testing, and geotechnical analyses to provide geotechnical design recommendations for the proposed project.

Our scope of services for this project included the following tasks:

• Literature Review: We reviewed various documents pertinent to the project site. A list of references used in preparation of this report is presented in Section 9.0.

• Pre-Field Activities: We performed a site reconnaissance to visually evaluate the accessibility of the site for drilling equipment and to locate and mark the proposed boring locations. Underground Services Alert (USA) of Southern California was contacted to identify subsurface utilities and obtain clearance for drilling at the site. Prior to drilling, the Naval Base staff were notified and on-site utility clearance staff cleared each boring location. Additionally, an independent third-party geophysical subconsultant (Southwest Geophysics, Inc.) was used to clear each boring location prior to drilling.

• Field Exploration and Laboratory Testing: We performed a subsurface exploration that included drilling, logging, and sampling of thirty-three (33) 8-inch diameter, hollow-stem auger borings to a maximum depth of approximately 12.5 feet bgs and six (6) 8-inch diameter, hollow-stem auger/mud rotary borings to a maximum depth of approximately

71.5 feet bgs. To address infiltration ability of on-site soils, two percolation tests were performed at two boring locations drilled to a depth of approximately 5 feet bgs.

Additionally, twenty-five (25) pavement core samples were taken throughout the aprons, taxiway, and helipad. Each drilling/coring location was patched a rapid set concrete mix.

Laboratory testing was performed on selected soil samples collected from field exploration to evaluate the engineering properties of the subsurface soils. Boring logs and laboratory test results are included in Appendices B and C, respectively.

• Seismic Analysis: Based upon the subsurface conditions encountered and regional seismicity of the area, we developed seismic parameters for use in structural analysis and design in accordance with UFC 3-301-01 criteria.

• Geotechnical Design and Analysis: Geotechnical analysis was performed on the collected data to develop recommendations for design and construction of the proposed project in general accordance with UFC 3-220-01, UFC 3-260-02, TM 5-822-14, and TM 5-822-5 requirements.

• Report Preparation: Relevant geotechnical data were compiled in this report along with our findings, conclusions, and recommendations for the proposed project.

2.3 PREVIOUS INVESTIGATIONS

A geotechnical Investigation was performed by K2 Engineering, Inc. (K2) for a proposed Helicopter Maintenance Hangar (MILCON Project P-750) in 2011. The existing helicopter hangar is located approximately 900 feet northeast of the Project site. The report for the MILCON Project P-750 indicates that the site is underlain by fill soils up to approximately 20 feet

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 2-3 thick overlying Quaternary-aged marine (Bay) deposits that extend to a depth of approximately 40 feet, and by the Pleistocene-age Paralic deposits to the maximum explored depth of 70 feet bgs. The fill soils reported by K2 consisted of loose to medium dense silty fine to medium sand.

Bay deposits consisted of very loose to medium dense sand and silty sand. Old Paralic Deposits consisted of medium dense to dense fine grained sand and silty sand. Groundwater was encountered at depth of approximately 15 feet bgs.

3.0 Geotechnical Field and Laboratory Investigation

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 3-1

GEOTECHNICAL FIELD AND LABORATORY INVESTIGATION

3.1 SUBSURFACE EXPLORATION

Field exploration consisted of advancing thirty-three (33) 8-inch diameter, hollow-stem borings to a maximum depth of approximately 12.5 feet bgs, six (6) 8-inch diameter hollow-stem auger/mud rotary borings to a maximum depth of 71.5 feet bgs, and extracting twenty-five (25) pavement core samples. Borings were designated as B-1 through B-37. Two borings for percolation tests were designated as B-9A (I) and B-27A (I). Pavement coring locations were designated as C-1 through C-25. The boring and core locations were marked in the field by measuring from known locations of existing features and by using a global positioning system (GPS). The approximate location of the borings is shown on Figure 2, Boring and Coring Location Map in Appendix A. Boring coordinates, approximate surface elevations, depths explored, and general location are summarized in Table 3-1.

Table 3-1. Boring/Core Information

Boring/Core Number Latitude Longitude

Approximate Ground Surface

Elevation (feet)

Depth of Boring/Core

(feet) Location

B-1 32.71050 -117.20896 16 11 Proposed Helipad

B-2 32.70637 -117.20328 24 10.75 Taxiway Lima

B-3 32.70751 -117.21021 17 12 Taxiway Lima

B-4 32.70730 -117.20884 18 12 Taxiway Lima

B-5 32.70690 -117.20747 21 12.5 Taxiway Lima

B-6 32.70651 -117.20609 22 12.5 Taxiway Lima

B-7 32.70631 -117.20471 24 12 Taxiway Lima

B-8 32.70744 -117.20412 20 11.5 Apron 3

B-9 32.70833 -117.20718 21 71.5 Proposed Hangar

B-9A (I) 32.70856 -117.20747 19 5 Apron 5

B-10 32.70818 -117.20670 21 11 Proposed Apron Extension

B-11 32.70774 -117.20755 18 11 Apron 5

B-12 32.70849 -117.20584 21 11 Proposed Apron Extension

B-13 32.70918 -117.20561 20 51.5 Proposed Hangar

B-14 32.70891 -117.20483 20 11 Proposed Apron Extension

B-15 32.70745 -117.20724 19 11 Apron 5

B-16 32.70784 -117.20656 20 9.5 Proposed Apron Extension

B-17 32.70750 -117.20635 20 9.5 Proposed Apron Extension

B-18 32.70816 -117.20591 21 11 Proposed Apron Extension

B-19 32.70799 -117.20546 20 12 Proposed Apron Extension

B-20 32.70880 -117.20515 20 11 Proposed Apron Extension

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 3-2

Boring/Core Number Latitude Longitude

Approximate Ground Surface

Elevation (feet)

Depth of Boring/Core

(feet) Location

B-21 32.70815 -117.20515 21 11 Proposed Apron Extension

B-22 32.70683 -117.20414 20 11.25 Apron 3

B-23 32.70895 -117.20587 21 51.5 Proposed Hangar

B-24 32.70713 -117.20617 20 11.75 Apron 3

B-25 32.70723 -117.20573 19 12 Apron 3

B-26 32.70726 -117.20511 20 12 Apron 3

B-27 32.70821 -117.20478 19 12 Proposed Apron Extension

B-27A (I) 32.70822 -117.20432 19 5 Apron 3

B-28 32.70900 -117.20638 21 51.5 Proposed Hangar

B-29 32.70654 -117.20520 22 11.5 Taxiway Lima

B-30 32.70777 -117.20462 20 11.5 Apron 3

B-31 32.70686 -117.20337 22 11.25 Apron 3

B-32 32.70737 -117.20338 20 11.5 Apron 3

B-33 32.70787 -117.20390 20 11.5 Apron 3

B-34 32.70929 -117.20594 22 61.5 Proposed Hangar

B-35 32.70806 -117.20330 20 11.5 Apron 3

B-36 32.70857 -117.20650 21 51.5 Proposed Hangar

B-37 32.70660 -117.20715 20 10.75 Taxiway Lima

C-1 32.71040 -117.20869 17 0.88 Proposed Helipad

C-2 32.71065 -117.20887 16 0.65 Proposed Helipad

C-3 32.71054 -117.20922 16 0.65 Proposed Helipad

C-4 32.71024 -117.20909 18 0.65 Proposed Helipad

C-5 32.70811 -117.20762 18 0.69 Apron 5

C-6 32.70723 -117.20744 19 0.75 Apron 5

C-7 32.70762 -117.20948 16 0.67 Taxiway Lima

C-8 32.70764 -117.21064 18 1.5 Taxiway Lima

C-9 32.70715 -117.20957 18 0.38 Taxiway Lima

C-10 32.70641 -117.20634 22 0.25 Taxiway Lima

C-11 32.70609 -117.20499 22 0.23 Taxiway Lima

C-12 32.70607 -117.20426 24 1.08 Taxiway Lima

C-13 32.70790 -117.20282 22 0.75 Apron 3

C-14 32.70615 -117.20369 24 0.25 Taxiway Lima

C-15 32.70597 -117.20293 24 0.21 Taxiway Lima

C-16 32.70669 -117.20309 23 0.63 Apron 3

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 3-3

Boring/Core Number Latitude Longitude

Approximate Ground Surface

Elevation (feet)

Depth of Boring/Core

(feet) Location

C-17 32.70730 -117.20287 23 0.75 Apron 3

C-18 32.70828 -117.20307 20 1.13 Apron 3

C-19 32.70951 -117.20585 20 0.63 Proposed Hangar

C-20 32.70943 -117.20703 21 0.58 Proposed Hangar

C-21 32.70891 -117.20770 19 0.67 Apron 5

C-22 32.70885 -117.20453 21 0.5 Proposed Apron Extension

C-23 32.70931 -117.20517 20 0.54 Proposed Hangar

C-24 32.70852 -117.20770 19 0.67 Apron 5

C-25 32.70857 -117.20415 23 0.42 Proposed Apron Extension

Standard Penetration Tests (SPT) were performed within the borings using a 140-pound automatic hammer free falling for 30 inches. The samplers were driven for a total penetration of 18 inches and the blow counts per 6 inches of penetration were recorded in the boring logs, unless refusal was encountered. Driving refusal was defined as fifty hammer blows without six inches of penetration. Relatively undisturbed samples were collected from the borings using a Modified California ring sampler. The field sampling procedures were conducted in general accordance with ASTM International Standard Specifications D 1586 and D 3550 for SPT and split-barrel sampling of soil, respectively. In addition to driven samples, bulk soil samples were also collected from the borings. The sampling intervals were performed in general accordance with the Scope of Architect-Engineer (A-E) Services (SAES) for this task, dated 17 November 2016.

The test borings were logged in the field by a member of HDR technical staff. Each soil sample collected was reviewed and described in general accordance with the Unified Soil Classification System. All samples were sealed and packaged for transportation to a subconsultant’s laboratory. After completion of drilling, the borings were backfilled with bentonite-grout and the surface was patched with rapid set concrete. Geotechnical logs of the borings are included in Appendix B.

3.2 GEOTECHNICAL LABORATORY TESTING

Laboratory tests were performed on selected soil samples to determine the geotechnical engineering properties of subsurface materials. The following laboratory tests were performed:

• In-situ moisture content and density;

• Grain-size distribution;

• Percent passing No. 200 sieve;

• Direct shear;

• Maximum density and optimum moisture;

• California Bearing Ratio (CBR); and

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 3-4

• Corrosivity (soluble sulfate and chloride contents, pH, and resistivity).

All laboratory tests were performed in general accordance with ASTM International procedures, except corrosivity tests, which were performed in accordance with Caltrans procedures. Results of the laboratory tests are presented in Appendix C.

4.0 Geology, Geologic/Seismic Hazards, and Seismic Design

Considerations

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 4-1

GEOLOGY, GEOLOGIC/SEISMIC HAZARDS, AND SEISMIC

DESIGN CONSIDERATIONS

4.1 REGIONAL GEOLOGY

The project site is located in Coronado Island, south of the San Diego Bay within the southern portion of California’s Peninsular Ranges Geomorphic Province (CGS, 2002). This province is characterized as an assemblage of north to northwest-trending, high-relief ranges stretching south from the Santa Monica Mountains in Los Angeles, through the county, and well into Baja California, Mexico. Notable ranges of Southern California include the Santa Ana Mountains, the Laguna Mountains, and the Cuyamaca Mountains. The development of this mountainous terrain is closely tied to the transform tectonics of the San Andreas Fault System (SAFS).

San Diego County encompasses three geomorphic sub-zones set in a series of north to northwest trending belts, roughly parallel to the coastline. From west to east, these zones are comprised of a relatively narrow, low-relief coastal plain; a central high-relief mountainous zone;

and a low-lying desert zone. The coastal plain and mountainous zones are part of a more extensive geomorphic province of the Peninsular Ranges. The desert zone is part of a larger geomorphic province known as the Colorado Desert.

4.2 SITE GEOLOGY

Historically, the project site was at or below sea level and consisted of mud flats and sandy beach deposits, occasionally covered by water during high tides. Early maps and drawings show North Island to have been far smaller with an uneven shoreline from the south “island” (now Coronado) by a shallow slough called the Spanish Bight (Peck, 2006). A 1930 revision of the USGS topographic map of Coronado Island (South Bay Historical Society, 2015) is shown on Figure 3 in Appendix A. During World War 2, by 1944, the extensive fillings including Spanish Bight were completed and over five hundreds new acres, primarily on the north and west sides of North Island were added. The project site was reclaimed by placing fill soils either hydraulically or mechanically to an elevation of approximately +20 feet Mean Sea Level (MSL).

The native soil deposits below the fill layer consist predominantly of the Old Lacustrine, Playa, and Estuarine (Paralic) deposits (Qol) of the late to middle Pleistocene era (Roffers and Bedrossian, 2010). The Qol unit consists of slightly to moderately consolidated, moderately dissected fine-grained sand, silt, mud, and clay from lake, playa, and estuarine deposits of various types. A regional geologic map of the site vicinity is presented on Figure 4, Geologic Map, in Appendix A.

4.3 ASSESSMENT OF POTENTIAL GEOLOGIC HAZARDS

4.3.1 Fault-Rupture Hazard

Based on available literature and reports, no active faults are known to traverse the project site, and the site is not located within a currently designated Alquist-Priolo Earthquake Fault Zone (Bryant and Hart, 2007 and City of San Diego, 2008). Therefore, the potential for surface fault rupture at the site is considered to be low. Maps of nearby faults and nearby Alquist-Priolo Special Studies Zones are presented on Figures 5 and 6, respectively in Appendix A.

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 4-2

4.3.2 Faulting and Seismicity

General

Southern California straddles the boundary between two global tectonic plates known as the North American Plate (on the east) and the Pacific Plate (on the west). The main plate boundary is represented by the San Andreas Fault, which stretches northwest from the Gulf of California in Mexico, through the desert region of the Imperial Valley, through the San Bernardino region, and into Northern California where it eventually trends offshore north of San Francisco (Jennings and Bryant, 2010).

Within southern California, the plate boundary is actually a complex system of numerous faults known as the San Andreas Fault System (SAFS) that span a 150-mile-wide zone from the main San Andreas Fault in the Imperial Valley westward to offshore of San Diego (Powell et al., 1993;

and Wallace, 1990). The major faults east of San Diego (from east to west) include the San Andreas Fault, the San Jacinto Fault, and the Elsinore Fault. Major faults west of San Diego include the Palos Verdes-Coronado Bank Fault, the San Diego Trough Fault, and the San Clemente Fault. The most dominant zone of faulting within the San Diego region consists of several faults associated with the Newport-Inglewood Rose Canyon Fault Zone (RCFZ), recognized as a trend of related fault traces. Although activity on any of the faults within the SAFS affects the seismicity of the San Diego region, activity within the RCFZ dominates the seismic hazard in the San Diego region.

The SAFS is a transform plate boundary dominated by right-lateral fault displacement (Wallace, 1990; Weldon and Sieh, 1985) with the Pacific Plate moving northwest relative to the North American Plate. The significance of this lateral faulting is that transform plate interactions typically generate much smaller maximum magnitude earthquakes than convergent or subduction plate boundaries. Thus, in southern California the expected maximum moment magnitudes for most faults are typically in the M6.5 to 7.5 range, with only a few faults (San Andreas Fault, possibly some thrust faults of the Transverse Ranges) capable of generating earthquakes in the M8 range, such as the 1906 San Francisco and 1857 Fort Tejon earthquakes, on the San Andreas Fault itself.

Most of the seismic energy and associated fault displacement within the SAFS occurs along the fault structures closest to the plate boundary (i.e., on the Elsinore, San Jacinto, and San Andreas Faults) (Powell et al. 1993). Approximately 1.9 inches/year (49 millimeters per year, (mm/yr) of overall lateral displacement have been measured geodetically and as fault slip across the plate boundary. Combined, the Elsinore, San Jacinto, and San Andreas Faults account for up to 1.6 inches/year (41 mm/yr) of the total plate displacement (84 percent) or 16 percent is accommodated across the faults to the west (Bennett et al., 1996). At the latitude of San Diego, most of this, about 0.2 to 0.3 inches/year (5-8 mm/yr), is accommodated by the coastal and offshore system of faults, including the Rose Canyon Fault (Rockwell et al., 1991).

Rose Canyon Fault Zone

The Newport-Inglewood Rose Canyon Fault Zone (RCFZ) is an active system of faults that occurs both in the offshore and onshore (terrestrial) areas of the San Diego region. It trends northerly from offshore of Imperial Beach through Coronado, Downtown San Diego, continues along the I-5 corridor, into southern Rose Canyon, across Mount Soledad, and finally passing offshore just north of the La Jolla Beach and Tennis Club (Kennedy, 1975; Treiman, 1993; and

CDMG, 1991).

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 4-3

The RCFZ is composed of a complex system of many sub parallel fault strands, both active and potentially active, that occupy a band of deformation between 0.5 mile and 3 miles in width (Treiman, 1993; Lindvall and Rockwell, 1995; Rockwell and Murbach, 1999; Rockwell, 2000;

and Rockwell, 2010). The fault zone is widest in the south, in San Diego Bay, and Coronado Island, where it is composed of the Silver Strand Fault, the Coronado Fault, the Spanish Bight Fault, and several unnamed faults in San Diego Bay. Please see Figure 5 for details. In downtown San Diego, several potentially active faults have been identified along with two areas of active faulting, one on the west side of downtown near the Federal Courthouse, named the San Diego Fault, and the other on the eastern side of downtown near the City College, named the Downtown Graben Fault.

Nearby Faults

The project site is located in the highly seismic Southern California region within the influence of several fault systems including the Newport-Inglewood RCFZ that are considered active or potentially active. These active and potentially active faults are capable of producing potentially damaging seismic shaking at the site. Based on our review of the Quaternary Fault and Fold Database (USGS and CGS, 2006), Alquist-Priolo Special Studies Zone Map (Bryant, and Hart, 2007 and City of San Diego, 2008), and the Caltrans (2016) ARS website, the closest active faults that could affect the site, approximate distances, and magnitudes, are presented in Table 4-1.

Table 4-1. Nearby Faults

Fault Name Approximate Distance from Site (mi)

Potential Magnitude

(Mw) Fault Type

RCFZ (Silver Strand Section-Spanish Bight Fault) 0.9 6.8 Strike-slip

Point Loma Fault Zone 1.5 6.3 Normal

RCFZ (Silver Strand Section-Coronado Fault) 2.1 6.8 Strike-slip

RCFZ (Silver Strand Section-Silver Strand Fault) 2.7 6.8 Strike-slip

RCFZ (San Diego Section) 2.6 6.8 Strike-slip

RCFZ (Silver Strand Section-Downtown Graben Fault) 3.2 6.8 Strike-slip

Coronado Bank Fault Zone (Coronado Bank Section) 9.6 7.4 Strike-slip

RCFZ (Del Mar Section) 10.5 6.8 Strike-slip

The locations of these faults with respect to the site are shown on the Fault Map, Figure 5.

4.3.3 Liquefaction Potential and Seismic Settlement

The term liquefaction describes a phenomenon in which saturated, cohesionless soils temporarily lose shear strength (liquefy) due to increased pore water pressures induced by strong, cyclic ground motions during an earthquake. Structures founded on or above potentially liquefiable soils may experience bearing capacity failures due to the temporary loss of foundation support, vertical settlements (both total and differential), and/or undergo lateral

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 4-4 spreading. The factors known to influence liquefaction potential include soil type, relative density, grain size, and confining pressure, depth to groundwater, and the intensity and duration of the seismic ground shaking. Liquefaction is most prevalent in loose to medium dense, silty, sandy, and gravelly soils below the groundwater table. The City of San Diego Seismic Safety Study (2008) has identified the site just outside the zone for liquefaction potential as shown on Figure 6, Seismic Hazard Map in Appendix A. However, based on subsurface information obtained from our field exploration and assuming historic high groundwater level at the approximate depth of 10 feet bgs, the subsurface soils through the site are considered to have a high potential for liquefaction due to the presence of medium dense granular soils within the upper approximately 40 to 45 feet bgs.

To assess the potential for liquefaction of subsurface soils, we used the simplified liquefaction analysis procedures outlined in Youd et al. (2001), Seed et al. (2003), and Idriss and Boulanger (2008). For estimating the resulting ground settlement, we used the methods proposed by Tokimatsu and Seed (1987) and Idriss and Boulanger (2008). Both these methods utilize corrected standard penetration test (SPT) blow counts to estimate the amount of volumetric compaction or settlement during an earthquake. Based on our analyses, estimated average liquefaction-induced settlements are in range from approximately 1 to 4 inches during the design-level seismic event. A peak ground acceleration of 0.54g with an earthquake magnitude of 6.6 was used as the design-level event in our liquefaction analysis, which is defined as an earthquake event with 2 percent probability of being exceeded in 50 years (return period of about 2,475 years). The liquefaction analysis outputs are provided in Appendix D.

Based on the total thicknesses of liquefiable and non-liquefiable soils and the estimated site acceleration, surface manifestation of liquefaction in the form of sand boils based on Ishihara’s 1985 cart (Ishihara, 1985) has a high potential of occurring.

Differential seismic settlement is estimated between 1 and 2 inches over typical 20 to 30 feet structure column spacing. The adverse impact of liquefaction, such as loss of strength, and downdrag forces on deep foundation units supporting the proposed hangar, were considered in the design of foundation systems.

4.3.4 Landslides and Lateral Spreading

Landslides and other forms of mass wasting, including mud flows, debris flows, and soil slips occur as soil moves downslope under the influence of gravity. Landslides are frequently triggered by intense rainfall or seismic shaking. Based on the site topography and distances to the nearby existing slopes, landslides or other forms of natural slope instability are not considered to represent a significant hazard to the project.

Liquefaction-induced lateral spreading is defined as the finite lateral displacement of ground as a result of pore pressure build-up or liquefaction in shallow underlying soils during an earthquake. Lateral spreading can occur on sloping ground or where nearby steep banks are present. Based on the site configuration the potential for lateral spreading susceptibility is considered to be low.

4.3.5 Seiches and Tsunamis

Tsunamis are waves generated in large bodies of water by fault displacement or major ground movement. They can also develop in response to other events, such as submarine landslides.

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 4-5

In 2009, the State of California (California Emergency Management Agency and California Geological Survey published tsunami inundation maps for the California coastline (California Emergency Management Agency, 2009). The project site is in close proximity to large bodies of water, however the Tsunami Inundation Map for Emergency Planning for the San Diego Bay (CalEMA, 2009) shows that the project site is outside the Tsunami Inundation Area. Therefore, the potential for inundation at the project site due to tsunamis is considered to be low.

A seiche is an oscillatory wave that develops in an enclosed or partially enclosed body of water, such as a bay or lake, in response to seismic shaking from an earthquake. The size of the generated wave depends on several variables, such as the intensity and frequency of shaking and the size and shape of the water body. San Diego Bay lies about 2,200 feet north of the site.

Based on the distance to and elevated topography between the bay and the site (approx. +16 feet, Mean Sea Level, MSL), the potential for seiche to affect the site is considered low.

4.3.6 Subsidence

Ground subsidence is the gradual settling of the ground surface, and is often associated with the extraction of oil, gas or groundwater from subsurface reservoir rock, traps and aquifers. The area of the subject site is not known for subsidence related issues. Accordingly, the potential for subsidence occurring at the site due to the withdrawal of oil, gas, or water is considered remote.

4.3.7 Flood Hazard and Earthquake-Induced Flooding

Flooding occurs as a result of several factors in developed areas. These factors are rainfall rates that exceed an area’s ability to absorb or control the runoff; impounded water retained behind a flood control structure (upstream-inundation); failure of a flood control structure (inundation); and tsunami.

The flood hazard potential at the site was evaluated based on flood hazard maps available through the Federal Emergency Management Agency (FEMA) Map Service Center website.

Based on FEMA Flood Insurance Rate Map (FIRM) 06073C1880G (FEMA, 2012), the project the site has been designated as a Zone D, which indicates areas where flood hazards are undetermined, but possible.

Earthquake-induced flooding is caused by dam failures or other water-retaining structure failures as a result of seismic shaking. Based on our review of the Floodplain Management Plan (County of San Diego, 2007), the site is not located within an area susceptible to dam inundation.

4.4 SEISMIC DESIGN CRITERIA

To reduce the effects of ground shaking produced by regional seismic events, seismic design should be performed in accordance with the applicable building codes including Seismic Design of Building, UFC 3-310-04 (2016). If ground improvement will be performed at the subject site (as discussed in Section 6.3.2 of this report), the project site may be classified as Site Class D, Stiff Soil. Please note that according to ACSE/SEI 7-10 (2010), which is incorporated into the UFC 3-310-04 by reference, sites subject to liquefaction (no ground improvement) as discussed in Section 4.3.3, should be classified as Site Class F, which requires a site specific response analysis. However, ACSE/SEI 7-10 states that for a short period (less than ½ second) structure on liquefiable soils, Site Class D or E may be used instead of Site Class F to estimate design seismic loading on the structure. The selection of Site Class D or E is based on the assessment

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 4-6 of the site soil profile assuming no liquefaction. We have assumed that the period of the structures will be less than ½ second. This assumption is reasonable for a single story steel framed building with bracing in both orthogonal directions (Hangar) and two story masonry load bearing structure using reinforced masonry shear walls (Squad Ops). The assumption that the structures have a period of less than ½ second will be verified by the project structural engineer.

Based on information obtained from our geotechnical investigation, published geologic literature and maps, it is our opinion that the project site may be classified as Site Class D, Stiff Soil.

The data in Table 4-2 should be considered for the seismic analysis of the proposed structural improvements at the project site based on the Unified Facilities Criteria (UFC, 2016).

Table 4-2. Seismic Design Parameters – 2016 UFC 3-301-01

Category Coefficient

Site Class D

Latitude 32.70893

Longitude -117.20641

Mapped (5% damped) spectral response acceleration parameter at short period (0.2 sec), SS 1.210

Mapped (5% damped) spectral response acceleration parameter at long period (1.0 sec), S1 0.460

Short period (0.2 sec) site coefficient, Fa 1.016

Long period (1.0 sec) site coefficient, Fv 1.54

Spectral response acceleration parameter at short period (0.2 sec), SMS 1.229

Spectral response acceleration parameter at long period (1.0 sec), SM1 0.708

Design (5% damped) spectral response acceleration parameter at short period (0.2 sec), SDS 0.819

Design (5% damped) spectral response acceleration parameter at long period (1.0 sec) SD1 0.472

Peak Ground Acceleration (PGA) (g) 0.540

Geometric Mean PGA (PGAM) (g) 0.540

Design Magnitude(1) Mw 6.6

Note:

(1) Design magnitude based on USGS Probabilistic Deaggregation with 2% chance of exceedance in 50 years (2,475 year return interval) (USGS, 2014).

5.0 Existing Site Conditions

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 5-1

EXISTING SITE CONDITIONS

5.1 GENERAL

The existing site conditions consist of an active Naval Air Station including buildings, pavement, and aircraft aprons. The project site included 18 buildings or structures proposed for demolition.

In addition to buildings and structures, the site area includes areas of airfield paving, asphalt and concrete roadway paving and associated sidewalks, and parking/storage areas. The site area drains to existing catch basins around the site.

Numerous existing utilities are present at the project site. Some of the existing utilities at the project site will require relocation or removal.

Traffic patterns at the project site follow Curtis and Vought Streets which run parallel to each other in an east-west direction.

5.2 EXISTING PAVEMENTS

Table 5-1 presents a summary of the pavement section thickness encountered during field exploration at the site.

Table 5-1. Existing Pavements Sections

Boring/Core Number Pavement Section Boring/Core Number Pavement Section

B-1 7.5” PCC B-10

2” AC

4” PCC

B-2 3” AC B-11 8” PCC

B-3

8” AC

8.5” PCC

B-12

2” AC

5” PCC

B-4

8” AC

8” PCC

B-13 7” AC

B-5

13” AC

8” PCC

B-14 6” AC

B-6

10” AC

14” PCC

B-15

2” AC

5” PCC

B-7

10.5” AC

7.5” PCC

B-16

2” AC

5.5” PCC

B-8

12” PCC

1.5” AC

B-17

2” AC

5” PCC

B-9 6” AC B-18

5” AC

1” PCC

B-9A (I) 8 PCC B-19

14” PCC

2” AC

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 5-2

Boring/Core Number Pavement Section Boring/Core Number Pavement Section

B-20

1” AC

4” PCC

C-4 7.75 PCC

B-21 5.5” PCC C-5 8.25 PCC

B-22 9” PCC C-6

8” PCC

1” AC

B-23 7” AC C-7 8” PCC

B-24 13” PCC C-8

13” PCC

5” CTB

B-25

11” PCC

1” AC

4” PCC

C-9 4.5” AC

B-26 13” PCC C-10 3” AC

B-27 12” PCC C-11 2.75” AC

B-27A (I) 12.25” PCC C-12

7” AC

6” ATB

B-28

6” AC

2” AB

C-13 9” PCC

B-29

4” AC

6.5” PCC

C-14 3” AC

B-30

12” PCC

1.5” AC

C-15 2.5” AC

B-31 7.5” PCC C-16 7.5” PCC

B-32 12” PCC C-17 9” PCC

B-33

12” PCC

1.5” AC

C-18 13.5” PCC

B-34 6” PCC C-19 7.5” PCC

B-35 13” PCC C-20 7.0” PCC

B-36 7” AC C-21 8” PCC

B-37 2” AC C-22

0.75”AC

5.25”PCC

C-1 10.5” PCC C-23 6.5” AC

C-2 7.75” PCC C-24 8” PCC

C-3 7.75 PCC C-25 5.0” PCC

Note AC: Asphalt Concrete; PCC: Portland Cement Concrete; CTB: Cement Treated Base; ATB: Asphalt Treated Base

Selected photographs of extracted pavement cores are shown on Figure 7, Core Photographs in Appendix A.

P-1018 Apron, Taxiway & Helipad/P-1024 MV-22 Maintenance Hangar 5-3

5.3 SUBSURFACE EARTH MATERIALS

5.3.1 General

The on-site soils generally consist of an upper layer of fill, up to approximately 20 feet thick, comprised of loose to medium dense silty sand. Deeper and/or lower quality fill may be encountered at other locations not drilled within the project site. Native soils (Bay and Old Paralic Deposits) generally consisting of medium dense to dense fine-grained silty sand and sand with silt were encountered below the fill soils. The Old Paralic Deposits extend to the maximum explored depth of approximately 71 feet bgs. A generalized stratigraphic profile of subsurface soil below the proposed P-1024 Hangar is shown on Figure 7 in Appendix A.

The measured dry density in the upper 5 feet of subgrade soils varied from approximately 80 to 114 pounds per cubic foot (pcf) with an average of 101 pcf. The water content of the on-site soils in the upper 5 feet varied between 2.1 and 17.6 percent with an average of 7.8 percent.

The in-situ moisture content of the…