CIANGS MAFFS Geotechnical Report.pdf

G E O T E C H N I C A L R E P O R T

ALLIED SUPPORT FOR MAFFS PROJECT

AIR NATIONAL GUARD BASE FACILITY

CHANNEL ISLANDS, CALIFORNIA

Prepared for

California Air National Guard 146th Airlift Wing Channel Islands, CA

Project No. 60589749

January 16, 2019

January 16, 2019

Major Shane Patty Contracting Office Representative Channel Islands Air National Guard Base Facility Channel Islands, CA

Subject: Geotechnical Report

Allied Support for MAFFS Project Air Nation Guard Base Facility Channel Islands, California

Major Patty, AECOM Technical Services, Inc. (AECOM) is pleased to present the results of our preliminary geotechnical investigation performed for the Air National Guard Base MAFFS project located in Channel Islands, California.

The scope of work included performing site-specific subsurface exploration, geotechnical laboratory testing, engineering analyses, and preparation of this report. This report presents the findings from our subsurface exploration, our interpretation of the subsurface conditions encountered, and conclusions and recommendations pertaining to design and construction of the proposed MAFFS improvements. Based on the results from our geotechnical investigation, the project is feasible from a geotechnical standpoint, provided the recommendations in this report are followed. Please contact us if you have any questions.

Sincerely, AECOM

Praveen Yerra, P.E. Christopher Goetz, P.G., C.E.G.

Senior Project Engineer Senior Engineering Geologist CE 81209 Exp. 9/30/19 CEG Exp. 07/31/19

AECOM

999 Town and Country Road Orange, CA 92868 Tel: 714-567-2400 Fax: 714-567-2441

Table of Contents

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

1.1 OBJECTIVES OF INVESTIGATION ................................................................................................................ 1-1

1.2 PROJECT DESCRIPTION .............................................................................................................................. 1-1

1.3 SCOPE OF WORK ....................................................................................................................................... 1-1

2.0 GEOTECHNICAL INVESTIGATION AND LABORATORY TESTING .......................................... 2-1

2.1 REVIEW OF EXISTING DATA ...................................................................................................................... 2-1

2.2 FIELD INVESTIGATION .............................................................................................................................. 2-1

2.2.1 General ................................................................................................................................................ 2-1

2.2.2 Exploratory Borings ............................................................................................................................ 2-1

2.2.3 Soil Logging ......................................................................................................................................... 2-1

2.2.4 Sampling and Field Tests ..................................................................................................................... 2-2

2.3 LABORATORY TESTING ............................................................................................................................. 2-2

3.0 GEOLOGY AND SUBSURFACE CONDITIONS .................................................................................. 3-1

3.1 REGIONAL GEOLOGIC SETTING ................................................................................................................. 3-1

3.2 LOCAL GEOLOGIC SETTING ...................................................................................................................... 3-2

3.3 SUBSURFACE CONDITIONS ........................................................................................................................ 3-2

3.4 GROUNDWATER ........................................................................................................................................ 3-2

4.0 GEOTECHNICAL EVALUATION ......................................................................................................... 4-1

4.1 SEISMIC PARAMETERS .............................................................................................................................. 4-1

4.2 SLOPE STABILITY ...................................................................................................................................... 4-1

4.3 STATIC SETTLEMENT ................................................................................................................................ 4-2

4.4 LIQUEFACTION, POST-LIQUEFACTION SETTLEMENT AND LATERAL SPREADING ...................................... 4-2

4.5 EXPANSION POTENTIAL ............................................................................................................................ 4-3

4.6 COLLAPSE POTENTIAL .............................................................................................................................. 4-3

4.7 SCOUR ...................................................................................................................................................... 4-4

5.0 CONCLUSIONS AND RECOMMENDATIONS .................................................................................... 5-1

5.1 SUMMARY OF FINDINGS ............................................................................................................................ 5-1

5.2 FOUNDATION DESIGN ............................................................................................................................... 5-1

5.2.1 Deep Foundations ................................................................................................................................ 5-1

5.2.2 Shallow Foundations ........................................................................................................................... 5-1

5.2.3 Allowable Bearing Pressures ............................................................................................................... 5-2

5.2.4 Settlement ............................................................................................................................................. 5-2

5.2.5 Resistance to Lateral Loads ................................................................................................................. 5-3

5.3 SETTLEMENT MITIGATION ........................................................................................................................ 5-3

5.3.1 Geopier Impact Rammed Aggregate Pier System ................................................................................ 5-3

5.4 GENERAL EARTHWORK REQUIREMENTS ................................................................................................... 5-4

5.4.1 Site Clearing ........................................................................................................................................ 5-4

5.4.2 Temporary Excavations ....................................................................................................................... 5-4

5.4.3 Subgrade Preparation.......................................................................................................................... 5-5

5.4.4 Structural Fill ...................................................................................................................................... 5-5

5.4.5 Fill Placement and Compaction .......................................................................................................... 5-6

5.4.6 Utility Trenches ................................................................................................................................... 5-6

5.4.7 Dewatering .......................................................................................................................................... 5-7

6.0 UNCERTAINTIES AND LIMITATIONS ............................................................................................... 6-1

List of Tables, Figures and Appendices

FIGURES

Figure 1 Site Location Map Figure 2 Geotechnical Exploration Plan Figure 3 Regional Geologic Map Figure 4 Historic Highest Groundwater Map

APPENDICES

Appendix A Field Exploration Appendix B Laboratory Testing Appendix C Analyses and Calculations Appendix D References

Geotechnical Report Air National Guard Base Facility

Allied Support for MAFFS Project

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1.0 INTRODUCTION

1.1 OBJECTIVES OF INVESTIGATION

This report presents the results of AECOM’s preliminary geotechnical investigation performed for the proposed Modular Air FireFighting System (MAFFS) improvements at the Channel Islands Air National Guard Base facility located at 100 Mulcahey Drive, Port Hueneme, California. The location of the project is shown on Figure 1. The proposed work includes constructing a new MAFFS support structure for proposed fire retardant storage tanks near the existing landing strip. This report provides findings from our subsurface explorations, geotechnical laboratory testing, the geologic, and pavement and soil conditions, and presents our geotechnical recommendations for the proposed structure.

Conclusions and recommendations presented in this report are based on subsurface conditions encountered at our exploration locations. As subsurface conditions may vary at different locations, these conclusions and recommendations should not be extrapolated to other areas, or used for other facilities, without our prior review.

1.2 PROJECT DESCRIPTION

The site is located at the 146th Airlift wing Channel Islands Air National Guard Station (CIANGS), adjacent to the Point Mugu Naval Air Station in Port Hueneme, California. The major cross streets in the vicinity of the project site are East Hueneme Road and Pacific Coast Highway, as shown on Figure 2.

The approximate site coordinates are 34.140692° N and 119.110047° W. The primary access to CIANGS is via Mulcahey Drive. In order to aid firefighting efforts using aircraft and to have quick access to fire retardant, it is proposed to store fire retardant material in up to three to four storage tanks mounted on a single concrete slab 4,300 square feet in area. The proposed system is called MAFFS.

1.3 SCOPE OF WORK

The following tasks were completed for this preliminary investigation:

• Prepared a project-specific Health and Safety Plan (HASP);

• Coordinated field work with representatives from the Air National Guard Base Facility;

• Notified Underground Service Alert (USA) in advance of field work;

• No permits were necessary as it is a private property;

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• Explored subsurface conditions by drilling one (1) hollow-stem auger (HSA) boring to a maximum depth of 51.5 feet (ft) below ground surface (bgs), logged the subsurface strata, and collected soil samples for laboratory analyses;

• Backfilled the HSA borehole with cement grout and capped with soil cuttings after completion of exploration;

• Soil samples collected during drilling were transported to AECOM’s laboratory for geotechnical testing and soil classification;

• Performed engineering analyses to evaluate subsurface conditions for proposed MAFFS foundation; and

• Prepared this report presenting our findings and recommendations.

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2.0 GEOTECHNICAL INVESTIGATION AND LABORATORY TESTING

The preliminary geotechnical investigation included a review of available geotechnical and geologic information, completion of subsurface explorations, and laboratory testing on selected soil samples to evaluate physical properties.

2.1 REVIEW OF EXISTING DATA

The site has been characterized by previous subsurface investigations performed during original construction of the base facility starting in the late 1980s. The preparation of this report relied on available geological and geotechnical documents as well as the geotechnical exploration conducted during the current phase of preliminary design.

2.2 FIELD INVESTIGATION

2.2.1 General

The field investigation, performed on December 20, 2018, consisted of drilling one geotechnical boring to a maximum depth of 51.5 ft below ground surface (bgs) to explore subsurface conditions and to collect samples for laboratory testing. The location of the boring is shown on Figure 2. The boring location was selected based on the proposed MAFFS improvement location. Details of the field investigation, including sampling procedures, are presented in Appendix A.

2.2.2 Exploratory Borings

One exploratory boring (designated B-18-001) was drilled at the location shown on Figure 2.

The HSA boring was drilled using a SIMCO 2800 drill rig, advancing hollow-stem augers with an 8-inch diameter bullet-tooth bit. Boring B-18-001 was drilled to a maximum depth of 51.5 ft bgs. The upper 5 ft of the subgrade was cleared for potential utilities at the borehole location using a hand auger prior to drilling. The soils encountered during drilling were visually classified in accordance with the Unified Soil Classification System (USCS).

The entire depth of the boring was backfilled using cement grout up to 1 foot bgs. The upper 1 foot of the borehole was backfilled with soil cuttings to the existing ground surface to match surrounding ground conditions.

2.2.3 Soil Logging

AECOM’s field representative visually classified the soil samples and cuttings and maintained a record of subsurface materials encountered in the exploratory borings. A description of the field program, different

2-2 soil types encountered during drilling, and other information are shown on the boring log presented in Appendix A.

2.2.4 Sampling and Field Tests

Where subsurface conditions permitted, relatively undisturbed drive sampling and standard penetration tests (SPT) were performed in an alternating order at 5-foot vertical intervals in boring B-18-001. Drive samples were obtained using a California soil sampler (2.42-inch inside diameter, 3.0-inch outside diameter) with three 6-inch long liners. The SPTs were performed with an SPT sampler (1.4-inch inside diameter), without liners, in accordance with ASTM D1586 guidelines. Both SPT and California samplers were driven 18 inches into the subsurface soils using a 140-pound automatic hammer with successive 30-inch drops. The number of blows (the “N” value) required to drive the last 12 inches of the sampler are recorded on the boring logs. A bulk sample was collected from the boring (upper 5 ft) for evaluating the characteristics of the soil necessary for slab design.

2.3 LABORATORY TESTING

Soil samples obtained from the borings were carefully sealed and packaged in the field to reduce moisture loss and disturbance. The samples were then delivered to AECOM’s geotechnical laboratory, located in Santa Ana, California, where they were further examined and classified. Laboratory testing was performed on selected samples to confirm the field visual classification of the soils and to evaluate their physical properties. Tests performed by AECOM included:

• Soil classification (ASTM D2487);

• Water content and dry unit weight test (ASTM D2216 and D7263);

• Atterberg limits for fine-grained materials (ASTM D4318);

• Grain size analysis (ASTM D6913);

• Direct shear test (ASTM D3080);

• Unconfined Compression (ASTM D2166);

• One-Dimensional Consolidation (ASTM D2435)

• Expansion Index (ASTM D4829); and,

• Corrosivity Analyses (California Test Method [CTM] 532, & 643 and United States Environmental Protection Agency [USEPA] 8051 & 8225)

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A description of the laboratory testing and the test results are presented in Appendix B. For reference, results from moisture content and dry density tests, plasticity index tests, and percent fines analyses of soils are also shown on the boring log, presented in Appendix A.

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3.0 GEOLOGY AND SUBSURFACE CONDITIONS

The site geology and subsurface conditions have been characterized based on review of the published geologic literature, previous site investigations and the field and laboratory programs undertaken for the current investigation.

3.1 REGIONAL GEOLOGIC SETTING

The project site is situated within the Santa Clara River floodplain, about 6 miles south of the river channel, within the Transverse Ranges geomorphic province. The Transverse Ranges are characterized by a complex series of mountain ranges, intervening valleys, and active faults with dominant east-west trends. The nearest hills are the Santa Monica Mountains, rising above the floodplain about 2 miles southeast of the project site, where the underlying rocks are predominantly early to mid-Miocene age interbedded siltstone, sandstone and shale of the Topanga Formation, overlain and intruded by Conejo Volcanics (principally basalt, andesite and dacite).

The project site is located in a seismically active area dominated by numerous active faults that have formed along a tectonic plate boundary known as the San Andreas transform zone. The San Andreas transform zone, which separates the North American plate to the east from the Pacific plate to the west, is dominated by northwest-trending, right-lateral, strike-slip faults of the San Andreas fault system. In the Transverse Ranges the right-lateral strike-slip environment of the San Andreas fault system is affected by a north-south component of compression that is caused by a convergent left bend of the San Andreas fault. This north-south directed compression is expressed by thrust, reverse or oblique slip faults and folds that trend approximately east-west.

Major east-west trending reverse or thrust faults in the vicinity of the project site include the Santa Monica-Hollywood-Raymond fault system, which is located about 4.4 miles (7 km) to the southeast of the site, and the Simi-Santa Rosa fault, which is located about 5.2 miles (8.9 kilometers) to the north of the site. The nearest faults mapped with latest Pleistocene to Holocene activity (less than 15,000 yrs) are the Simi-Santa Rosa fault and an unnamed fault located about 5.8 miles (9.4 km) southeast of the site associated with the Santa Monica-Hollywood-Raymond system (USGS, 2019). The nearest fault mapped with latest Pleistocene movement (less than 130,000 yrs) is the Bailey fault about 2.4 miles (4.4 km) southeast of the site.

Several historic earthquakes have produced relatively strong ground shaking within the vicinity of the project site. Notable examples include the magnitude 6.4, 1933 Long Beach earthquake; the magnitude 6.5, 1971 San Fernando earthquake; the magnitude 5.2, 1972 Point Mugu earthquake; the magnitude 6.0, 1987 Whittier Narrows earthquake; and the magnitude 6.7, 1994 Northridge earthquake.

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3.2 LOCAL GEOLOGIC SETTING

The project site is within the flat topography of the Santa Clara River floodplain, at elevations of about 9 ft above mean sea level (National Geodetic Vertical Datum of 1929). Rovolon Slough, the nearest watercourse, passing about 1.5 miles east of the site, flows into Callegaus Creek, which drains to the Pacific Ocean about 3 miles to the south of the site. The nearest hills are the Santa Monica Mountains, about 2 miles to the southeast of the site.

According to the published geology map for the area (Dibble, 1990) the site is underlain by Holocene-age alluvium consisting of “gravel, sand and clay of flatlands,” as shown on Figure 3.

The site is mapped as being an area susceptible to earthquake liquefaction by the California Geologic Survey (CGS), formerly known as the California Division of Mines and Geology (CDMG) (CGS, 2002a).

3.3 SUBSURFACE CONDITIONS

Previously, shallow borings have been drilled within the Air National Guard property, which included five (5) HSA borings by Ninyo & Moore, which extended to maximum depths ranging from 6.5 ft to 8 ft bgs (N&M, 2010), and five (5) HSA borings by AECOM, which extended to maximum depths ranging from 5 ft to 25.5 ft bgs (AECOM, 2017). Based on the current investigation boring and the previous borings drilled at the site, very loose silty sand (SM) predominates from the surface to a depth of 5 ft bgs.

Below this, lean clay (CL) and fat clay (CH) predominate down to an approximate depth of 46 ft bgs, with minor silt (ML) and silty sand (SM) layers. Silty sand (SM) was observed from 46 ft bgs to the maximum depth explored of 51.5 ft bgs.

Soil samples were collected from the boring for laboratory testing as shown in Appendices A and B.

3.4 GROUNDWATER

Groundwater was encountered during drilling at a depth of 34.5 ft bgs. However, clayey soil can have a very low permeability and impede groundwater movement. Therefore, the measured groundwater depth may not reflect the actual groundwater depth. The CGS prepared a Seismic Hazard Report for the Camarillo Quadrangle (CGS, 2002b). Based on a review of this report, the historically highest groundwater levels for the project area are on the order of 5 ft bgs as shown on Figure 4. In the previous Ninyo & Moore site investigations, groundwater was not encountered to the maximum depths explored of 8 ft bgs; however, “wet zones” were observed in two borings at depths of 5 ft bgs and 7 ft bgs, respectively (N&M, 2010). In the previous AECOM site investigations, groundwater was encountered at a depth of 10 ft bgs in B-15-004 and 24 ft bgs in boring B-17-005 (AECOM, 2017). High water content was also present in a soil sample collected at 5 ft bgs in B-15-004, which is consistent with historical data.

Groundwater levels are likely to vary based on tidal, seasonal and anthropogenic factors.

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3.5 CORROSION EVALUATION

Corrosivity tests were performed as part of this investigation to assess the corrosion potential of the soils.

The corrosion tests were conducted in accordance with California test methods and United States Environmental Protection Agency (USEPA) test methods. The results are summarized in Table 1.

Caltrans (Caltrans, 2015) considers a site to be corrosive to foundation elements if one or more of the following conditions exist for the soil samples taken from the site:

• Chloride concentration is greater than or equal to 500 parts per million (ppm),

• Sulfate concentration is greater than or equal to 2,000 ppm, and

• PH is 5.5 or less

The minimum resistivity can be an indicator for the relative quantity of soluble salts present in the soil or water. In general, a minimum resistivity value less than 1,000 ohm-cm indicates high soluble salts and higher propensity for corrosion.

Table 1 - Summary of Corrosivity Test Results

Boring

Depth bgs (ft.)

pH Threshold ≤

5.5

Minimum Resistivity (ohm-cm)

Threshold ≤ 1,000

Sulfate Content (ppm)

Threshold ≥ 2,000

Chloride Content (ppm)

Threshold ≥

B-18-001 15 9 356 2,222 170 Notes:

1. ppm = parts per million.

2. ohm-cm = ohm-centimeter.

3. Resistivity is not a corrosion criterion, but an indicator of soluble salts per Caltrans Corrosion Guidelines

Based on the results of the corrosivity testing, the site is interpreted to be corrosive in accordance with the Caltrans corrosion guidelines (Caltrans, 2015). The results indicate that the sulfate content of site soils exceeds the threshold limit. Sulfates typically react to lime in concrete and causes it to soften and crack.

Water can seep into cracked concrete and accelerate the corrosion process, leading to structural failure.

Appropriate mitigation measures—such as using sulfate-resistant concrete mix designs; increasing the clear concrete cover over reinforcing steel, and using epoxy-coated reinforcing steel—may reduce the corrosion process and increase the service life.

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4.0 GEOTECHNICAL EVALUATION

4.1 SEISMIC PARAMETERS

Seismic ground motion parameters were developed using the U.S. Seismic Design Maps Web Services, Seismic Design Maps Tool by the Structural Engineers Association of California (SEAOC, 2018). The site coordinates used in the analysis were 34.140692° north, and 119.110047° west. The subsurface soil at the site corresponds to the International Building Code (IBC, 2015) Site Class Type E, based on the average SPT blow counts, average undrained shear strength (Su), and the presence of soft clays with plasticity index over 20, and water content over 40%.

Table 2 - Seismic Design Parameters Parameter Factor Value

Mapped Spectral Response Acceleration (0.2 sec Period) SS 1.72g

Mapped Spectral Response Acceleration (1.0 sec Period) S1 0.602g

Site Class Site Class E

Site Coefficient Fa 0.9

Site Coefficient Fv 2.4

Maximum Considered Earthquake Spectral Response Acceleration (0.2 sec Period)

SMS 1.548g

Maximum Considered Earthquake Spectral Response Acceleration (1.0 sec Period)

SM1 1.446g

Design Spectral Response Acceleration (0.2 sec Period) SDS 1.032g

Design Spectral Response Acceleration (1.0 sec Period) SD1 0.964g

The design parameters are based on the 2015 IBC as required by the United States Department of Defense Unified Facilities Criteria, UFC 3-301-01 with Change 4, dated November 1st 2018. It should be recognized that much of southern California is subject to some level of damaging ground shaking as a result of movement along the major active (and potentially active) fault zones that characterize this region. Design utilizing the 2015 IBC is not meant to completely protect against damage or loss of function. Therefore, the preceding parameters should be considered as minimum design values.

4.2 SLOPE STABILITY

The topography at the site is relatively flat with very gentle slopes. Due to the relatively flat-lying topographic character of the site, the potential for slope failure is considered low.

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4.3 STATIC SETTLEMENT

The estimated settlement prior to any soil improvements is estimated to be up to 5 inches (immediate and long-term settlement combined). The long-term settlement is anticipated to constitute the majority of the estimated settlement (up to 4 to 5 inches) and is expected to take approximately 5 to 6 years to achieve 90% of the estimated consolidation settlement.

4.4 LIQUEFACTION, POST-LIQUEFACTION SETTLEMENT AND LATERAL SPREADING

Liquefaction is a phenomenon in which loose to medium dense, saturated, granular materials undergo matrix rearrangement, develop high pore water pressure, and lose shear strength because of cyclic ground vibrations induced by earthquakes. This rearrangement and strength loss is followed by a reduction in the bulk volume of the liquefied soils. The effects of liquefaction can include the loss of bearing capacity below foundations, settlement in level ground, large horizontal deformations of relatively level ground with an unconfined vertical face (referred to as lateral spreading) and instability in areas of sloping ground (also known as flow sliding). Liquefaction is generally considered to occur within soils in the upper 50 ft below ground surface, though there are indications that it can occur at deeper depths.

California Geologic Survey (CGS), formerly known as the California Division of Mines and Geology (CDMG) (CGS, 2002a) shows that the entire site is located within a liquefaction-hazard zone. Some of the site soils contain some layers of loose coarse-grained soils. Additionally, based on the groundwater data collected from the borings, and the historical high water level, the groundwater table is expected to be relatively shallow; therefore, the liquefaction potential is high.

The 2015 IBC requires that liquefaction be evaluated for the peak ground acceleration, earthquake magnitude and source characteristics consistent with the mapped Maximum Considered Earthquake Geometric Mean (MCEG) PGA with adjustment for site class effects in accordance to the American Society of Civil Engineers (ASCE) 7-10 Standard (Sections 21.5 or 11.8.3).

Liquefaction potential was evaluated in general accordance with the recommendations provided in Soil Liquefaction during Earthquakes (Idriss and Boulanger, 2008).

Per ASCE 7-10, the value of PGAM, the site-specific MCEG PGA, should be taken as the lesser of the probabilistic and deterministic PGAG and used for liquefaction or seismic slope stability evaluations. The PGA of 0.58g was used for liquefaction analysis at the proposed site. A groundwater depth of 5 ft bgs was used in the liquefaction analysis, which corresponds to the historic high groundwater level. A modal magnitude of 7.69 (USGS, 2018) was used for evaluation of liquefaction potential.

The basic input parameters for liquefaction analysis were:

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• Earthquake Magnitude, Mw: 7.69

• Peak Ground Acceleration (PGA): 0.58g

• Groundwater Depth: 5 ft.

Based on the liquefaction analysis results, the site is susceptible to liquefaction and liquefaction-induced settlement at the ground surface of up to approximately 4 inches. Analysis results for liquefaction and seismic settlement are included in Appendix C.

Since the site is relatively flat and does not have an unconfined vertical face in close proximity to the proposed improvements, the potential for lateral spreading is considered low.

4.5 EXPANSION POTENTIAL

Expansive soils are fine-grained soils (clay) that can undergo a significant increase in volume with an increase in water content and a significant decrease in volume with a decrease in water content. Changes in the water content of an expansive soil can result in severe distress to structures constructed upon the soil.

The expansion index laboratory test indicates that the fine-grained soil (silt) near the historic high water depth has an expansion index of 57, which corresponds to medium expansion potential in accordance with the classification scale in ASTM D4829. Some heave due to expansion should be expected as well.

However, since the fine-grained foundation soils are predominately under the groundwater table (fully saturated), and are expected to remain below since they are below the mean sea level, soil expansion is not anticipated to be a significant design concern.

4.6 COLLAPSE POTENTIAL

Collapsible soils are those that undergo settlement upon wetting, even without the application of additional load. The process of collapse with the addition of water is known as hydro-compaction and occurs when water weakens or destroys the bonds between soil particles and severely reduces the bearing capacity of the soil. Typical collapsible soils are lightly colored, are low in plasticity, have relatively low densities and have a low degree of saturation. Collapsible soils are typically associated with alluvial fans, windblown materials (loess), colluvium, and residual soils.

The soils at the site are predominately saturated; therefore, soil collapse is not anticipated to be a design concern.

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4.7 SCOUR

Scour is not considered a design issue at this site. The proposed foundation is not located in or adjacent to a river/creek or drainage channel.

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5.0 CONCLUSIONS AND RECOMMENDATIONS

5.1 SUMMARY OF FINDINGS

The geology, geotechnical, and seismic conditions of the subject site have been evaluated in terms of their impact on the proposed project. Based on the findings of our investigation, it is AECOM’s opinion that the project site is generally suitable for the proposed development. Provided that the following conclusions and recommendations are incorporated into the design and project specifications, and implemented during construction, it is anticipated that geologic hazards and geotechnical concerns will not significantly impact the project.

5.2 FOUNDATION DESIGN

5.2.1 Deep Foundations

Cast-in-drilled-hole (CIDH) piles and 14-inch square prestressed, precast driven concrete piles (DC) piles are considered feasible deep foundation options for the subject site. Driven steel H-piles (HP) are not recommended due to the severe corrosive environment under submerged conditions as well as high cost.

Due to the potential corrosive soil (high sulfate content), both precast concrete and CIDH piles may need to utilize corrosion-resistant concrete or other structural mitigation measures such as increased clear cover for prestressing steel, epoxy coated rebar. The structural designer and a corrosion engineer may need to be consulted to evaluate and provide recommendations on appropriate corrosion-resistant solutions for foundations. Appendix C provides capacity plots for axial capacity for both DC and CIDH piles.

Consequences of soil liquefaction and consolidation settlement on piles resulting in downdrag loads are to be considered for deep foundation design. Note that the vibrations induced in the soil during driving of DC piles as well as soil displacement are expected to have a beneficial effect on soil density and will tend to reduce the amount of liquefaction-induced settlement, though the extent of this benefit is difficult to quantify and will be variable and dependent on the order of pile driving. Groundwater may be encountered above the tip elevation of the piles, which will require the use of the wet construction method using drilling mud to stabilize the sidewalls of borehole for CIDH pile construction.

5.2.2 Shallow Foundations

Shallow foundations—such as mat foundations—were considered to provide support for the proposed storage tanks. However, due to the relatively soft to stiff clayey soils, continuous footings would experience large settlements (long term). Furthermore, differential settlement will pose a greater concern.

Shallow foundations may be considered feasible only if appropriate settlement mitigation measures that include ground improvement, such as rigid inclusions or rammed aggregate piers, are implemented.

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A mat foundation is recommended for the proposed storage tanks pad provided that ground is improved as recommended in Section 5.3.1. The slab thickness and reinforcement should be designed by the structural engineer for the anticipated floor loads and other structural considerations. These floors should be supported on a pad of compacted Structural Fill. A value of ks (modulus of subgrade reaction) of 50 pounds per cubic inch (pci) may be used for design if the site is improved as recommended in this report, where the ks value was estimated on the basis of a common correlation between soil type and relative density.

The site subsurface subsoils include highly saturated soft fat and lean clays below the structural fill. It is noted that a ks value is typically derived from the results of a 1-foot by 1-foot square plate load test. Mat foundations designed for the bearing value recommended above should be embedded at least 24 inches below lowest adjacent finished grade.

The water content of subgrade soil should be maintained at a level slightly over its optimum water content until the slab is poured. At the time of concrete placement, the subgrade soil should be firm and relatively unyielding.

5.2.3 Allowable Bearing Pressures

Lightly loaded facilities or structures can be founded on shallow footings. For design purposes, an allowable bearing pressure of 2,000 psf may be used for mat foundations. Mat foundations should be founded entirely in properly conditioned and compacted Structural Fill. The Structural Fill pad should extend at least 2 ft below the bottom of the footings or 2 ft below existing grade, whichever yields the greater depth. Footings should be embedded at least 24 inches below lowest adjacent finished grade.

No structures should be located partially on cut materials and partially on fill materials. In the event that a cut-fill transition will be encountered across the proposed structures, the cut portion should be over-excavated to a depth of 5 ft below the bottom of the footings. The over-excavated portions should be replaced with compacted Structural Fill as recommended in this report.

5.2.4 Settlement

Based on the assumed storage tanks pad bearing pressure of 1,000 psf, total post-construction static settlement of mat foundations without ground improvement is estimated to be on the order of 5 to 6 inches. Differential settlement on similarly loaded footings is expected to be on the order of 2 to 3 inches.

Ground improvement can reduce the differential settlement to acceptable values. The intensity of the ground improvement will vary based on allowable settlements.

Deep pile foundations can be driven/drilled deep enough to provide the required resistance necessary to counter the static (including downdrag) as well as dynamic vertical loads. This system can mitigate both liquefaction and static settlement. Due to the structure type (minimal vertical load), potential corrosive soils, and predominately soft to stiff fine grained alluvium, deep foundations may be relatively expensive.

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Over-excavation and replacement with compacted Structural Fill can improve the site soils. However, due to the shallow groundwater and the depth of over-excavation that would be required to get to firmer soils, over-excavation and replacement with Structural Fill will make a be a cost-effective design solution.

Preloading the site soils can typically reduce the static settlement. Due to the predominately soft to stiff saturated alluvium, preloading the site to consolidate the soil up to 90% of its expected consolidation may take 5 to 6 years or more, which is likely not practical. Moreover, preloading does not significantly influence the liquefaction settlement.

5.2.5 Resistance to Lateral Loads

Resistance to lateral loads may be developed by a combination of friction acting along the base of footings and passive earth pressure developed against the sides of footings. Ultimate passive pressure may be taken as equivalent to the pressure exerted by a fluid weighing 300 pounds per cubic foot (psf/ft) with a maximum value of 1,500 psf. The pressure should be used as a triangular distribution to the allowable limit and then should remain at the maximum limit. The ultimate coefficient of friction between poured-in-place concrete footings and the underlying soils may be taken as 0.30. The passive pressure will be reduced by 1/3 when used in combination with friction resistance on the bottom of the footing.

5.3 SETTLEMENT MITIGATION

5.3.1 Geopier Impact Rammed Aggregate Pier System

The Geopier® Rammed Aggregate Pier (RAP) system uses compacted aggregate to create stiff pier elements. This type of system can reinforce soft and loose soils below the groundwater table. This is a displacement process that allows for installation without spoils. They system displaces a zone where aggregate is introduced. The aggregate is placed and rammed in lifts to densify it, forming an undulating shaft or RAP. Grout may be added to create a rigid inclusion. The ramming of the grouted aggregate allows for improved density in granular soils. This system is recommended based on soil conditions, shallow groundwater, pad size, and cost.

An array of RAPs should be designed below the entire footprint of the proposed pad and one row beyond for confinement. The RAPs should extend down at least 20 ft below the recommended 2-foot over-excavation. A minimum center-to-center spacing of 7 ft between RAPs is estimated to be required for the ground improvement of the pad. The distance between RAPs can be increased to larger center-to-center spacing if the criteria for acceptable settlement levels can be relaxed.

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5.4 GENERAL EARTHWORK REQUIREMENTS

5.4.1 Site Clearing

Prior to earthwork, the areas to be excavated, to receive fill, or to receive stockpile materials should be cleared and stripped of all topsoil, organic material, vegetation, rubbish, deleterious material, and debris resulting from site demolition. Cleared and grubbed material, as well as all rubble waste that may be encountered or created, should be disposed of offsite. All active or inactive utilities within the construction limits should be identified, marked and relocated, while abandoned utility lines should be removed or backfilled. The project geotechnical consultant should observe any removals and test all backfill.

The project geotechnical consultant should be notified at the appropriate times to provide observation and testing services during clearing operations to verify compliance with the above recommendations. In addition, should any buried structures or unusual or adverse soil conditions be encountered during grading that are not described or anticipated herein, these conditions should be brought to the immediate attention of the project geotechnical consultant for corrective recommendations.

5.4.2 Temporary Excavations

Due to the anticipated loose/soft soils at the anticipated bottom of footing elevation, it is recommended that soils within 2 ft from the bottom of the foundation be removed and replaced with structural backfill following recommendations provided in this report. The compacted fill should extend a minimum of 5 ft beyond the edges of the foundation. The proposed structure may be supported on a conventional mat foundation bearing on compacted fill in addition to the ground mitigation recommended to minimize seismic impact on the proposed structure.

Excavations during construction should be performed in accordance with applicable local, state, and federal regulations, including the current California Occupational Safety and Health Administration (Cal/OSHA) excavation and trench safety standards. Unsupported temporary slopes with conditions similar to those encountered near the surface during the exploration should be made at an inclination no steeper than 2:1 (horizontal to vertical), and flatter if field conditions so dictate. Surcharge loads from vehicle and equipment parking and traffic, excavated materials, stockpiled materials or other sources should be set back from the top of the temporary excavation a horizontal distance equal to or greater than

1.5 times the depth of the adjacent excavation. Surface drainage should be controlled along the top of temporary excavations to prevent wetting of the soils and erosion of the excavated faces. Even with the implementation of these recommendations, sloughing of the surface of temporary excavations may still occur, and workers should be adequately protected. We anticipate that temporary construction excavation slopes (if any) will be stable during the anticipated duration that the excavation and backfilling work would take if earthwork proceeds in an expeditious and uninterrupted manner, provided the above

5-5 recommendations are followed. However, modifications to these recommendations may be required based on observations of the actual conditions exposed in the field or the findings of the contractor’s competent person. Our temporary excavation recommendations are provided only as general guidelines, as soil conditions may vary, the contractor should employ an excavation competent person as defined by Cal/OSHA to determine all aspects of excavation safety. The design and construction of temporary excavation support systems (e.g., shoring) and temporary slopes, as well as the maintenance and monitoring of these works during construction, is the responsibility of the contractor.

Trench excavations should be made with nearly vertical sides, using sheeting and shoring whenever required. All excavation should be observed by a competent person as described by Cal OSHA so that any necessary modifications based on variations in soil and groundwater conditions encountered can be performed in an efficient manner. Soils encountered during our field investigation should be rippable with conventional earthwork equipment. All applicable safety requirements and regulations, including California/OSHA regulations, should be satisfied.

5.4.3 Subgrade Preparation

After performing any necessary excavation and prior to placing any fill, the ground surface within the structure footprint should be observed by the geotechnical engineer to confirm that satisfactory subgrade soils have been encountered. If unsatisfactory soil is encountered at the bottom of excavation or natural ground surface, additional removals may be required. The bottom of the exposed excavation should be scarified to a depth of at least 6 inches, moisture conditioned (as necessary) to above the optimum water content (OWC), and then compacted in-place to at least 95% relative compaction as determined by ASTM D1557 at 0 to 3 percentage points over optimum water content prior to placing compacted fills.

Relative compaction is a measure of the degree of soil compaction and is defined as the ratio of the in situ dry density (or unit weight) divided by of the material's maximum dry density (or unit weight) measured by a reference test procedure (in this case ASTM D1557). Following the scarification process, the subgrade should be rolled, probed and tested as appropriate. Proof rolling should involve making several passes over a subgrade with heavy equipment, preferably a sheepsfoot roller.

5.4.4 Structural Fill

Structure excavations and structural backfill should conform to the latest edition of the Greenbook (Section 300-3), OSHA safety regulations and recommendations herein. Fine-grained onsite soils may be encountered during the excavations. Fine-grained soils are not suitable for structural backfill. Structural Fill should not contain rocks or hard lumps greater than 3 inches in maximum dimension and should have at least 80 percent passing the ¾-inch sieve, at least 25 percent passing No. 4 sieve and less than 10 percent passing the No. 200 sieve. Structural Fill should have a minimum sand equivalent of 30 and expansion index less than 20 when tested in the laboratory in accordance with ASTM D4829. It is

5-6 recommended that Structural Fill be used beneath all foundations and floor slabs. Structural Fill materials shall be free of organic material, debris, or other deleterious materials. Materials greater than 1 inch in size shall be placed so that they are completely surrounded by compacted finer soils. Backfill material such as pea gravel and crushed rock do not meet the requirements for structural fill due to their relatively high permeability and thereby provide the potential to collect water.

The soils encountered in the borings are not expected to meet the above criteria for Structural Fill.

However, it is possible to mix on-site soil with new material to meet the gradation for import fill.

5.4.5 Fill Placement and Compaction

The maximum dry unit weight of the fill materials should be measured in accordance with ASTM D1557.

The field unit weight of fill should be measured in accordance with the sand cone method (ASTM D1556) or the nuclear method (ASTM D6938). The fill materials should be placed in lifts not exceeding 8 inches in depth. The engineered fill should be compacted to 95% relative compaction as determined by ASTM D1557 at 0 to 3 percentage points over optimum water condition.

Structural Fill material should be placed in lifts no greater than 8 inches, loose measurement. The water content of the fill material at the time of compaction should be at or above its optimum water content.

Particles larger than 1 inch for Structural Fill should be placed so that they are completely surrounded by compacted finer soils.

5.4.6 Utility Trenches

The bottom surfaces of all trench excavations to receive bedding/fill should be scarified to a depth of at least 6 inches, moisture conditioned, if necessary, and compacted to at least 90 percent relative compaction (as per ASTM Standard D1557) at 0 to 3 percentage points over optimum water content prior to placing compacted bedding/fills. Following the scarification process, the subgrade should be observed, probed and tested as appropriate. All identified loose or soft zones should be compacted in-place or excavated and replaced with properly compacted backfill to the satisfaction of the Geotechnical Engineer of Record in order to establish a competent subgrade on which to place compacted bedding/fill

Bedding is defined as the supporting material placed below the utility lines and should have a minimum thickness of 6 inches. To provide uniform and firm support for the pipe, compacted granular materials, such as ¾-inch crushed aggregate may be used as pipe bedding material.

Clean sands should be placed to surround the pipe completely and minimize voids. Mechanical compaction equipment may be used where feasible. The maximum dry unit weight of the bedding material should be measured in accordance with ASTM D1557.

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5.4.7 Dewatering

Groundwater has been encountered at the site as shallow as 10 ft below the ground surface during previous field explorations. Dewatering is not anticipated to be required if the ground improvements recommended in this report are implemented. Appropriate dewatering techniques should be implemented if any excavations below the groundwater table are necessary during construction.

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6.0 UNCERTAINTIES AND LIMITATIONS

AECOM has observed only a small portion of the pertinent subsurface conditions at the proposed project site. Conclusions and recommendations presented in this report are based upon the understanding of the project by AECOM and the assumption that the subsurface conditions do not deviate appreciably from those disclosed by the site subsurface exploration. In the event that the locations, configurations, layout, loadings, or features of the proposed excavations are modified, the recommendations presented in this report may not be applicable. It is the responsibility of the Owner to bring any such changes to the proposed excavations as well as any differences between the subsurface conditions described in this report and the subsurface conditions encountered during construction to the attention of the Geotechnical Engineer. In this way, supplemental recommendations, if required, can be made without delay to the project.

Professional judgments presented in this report are based on an evaluation of the technical information gathered and the general experience of AECOM in the practice of geotechnical engineering. AECOM does not guarantee the performance of the project in any respect, only that the engineering work and judgments rendered meet the standard of care of the geotechnical profession at this time. Our recommendations for this project may not be used for other projects.

Any person using this report for bidding or construction purposes should perform such independent investigations as they deem…