C1034 Exploratory Shaft Geotechnical Baseline Report · PDF file · 2013-06-19C1034 Exploratory Shaft Geotechnical Baseline Report ... Baseline statements are contained in this document

C1034 Exploratory Shaft Geotechnical Baseline Report

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777 South Figueroa Street, Suite 1100 Los Angeles, CA 90017 July 13, 2012

Geotechnical Baseline Report – Exploratory Shaft

Table of Contents

W E S T S I D E S U B W A Y E X T E N S I O N P R O J E C T Page i July 13, 2012

Table of Contents

1.0 INTRODUCTION .................................................................................................................... 1‐1

2.0 PROJECT DESCRIPTION .......................................................................................................... 2‐1

2.1 Exploratory Shaft Site ...................................................................................................... 2‐1

2.2 Purpose of Exploratory Shaft ........................................................................................... 2‐1

3.0 GEOTECHNICAL DATA ACQUISITION ..................................................................................... 3‐1

3.1 Geotechnical Investigations ............................................................................................. 3‐1 3.1.1 Characterization of Asphalt and Asphalt Impregnated Soils (Tar Sands) ........... 3‐2 3.1.2 Basis of Soil Descriptions .................................................................................... 3‐2

3.2 Geophysical Surveys ........................................................................................................ 3‐2

3.3 Environmental Investigations .......................................................................................... 3‐2

3.4 Additional Investigations ................................................................................................. 3‐3

4.0 GEOLOGIC SETTING AND SUBSURFACE CONDITIONS ............................................................. 4‐1

4.1 Geologic Setting of WSE Project ...................................................................................... 4‐1

4.2 Geologic Units at Exploratory Shaft Site .......................................................................... 4‐1 4.2.1 Fill ........................................................................................................................ 4‐1 4.2.2 Lakewood Formation .......................................................................................... 4‐2 4.2.3 San Pedro Formation .......................................................................................... 4‐2

4.3 Asphalt Impregnated Soils ............................................................................................... 4‐2

4.4 Local Faulting ................................................................................................................... 4‐3

4.5 Groundwater .................................................................................................................... 4‐3

4.6 Subsurface Gases ............................................................................................................. 4‐3

5.0 ENGINEERING PROPERTIES OF THE SUBSURFACE MATERIALS ............................................... 5‐1

5.1 Engineering Characterization ........................................................................................... 5‐1 5.1.1 Particle Size Distributions ................................................................................... 5‐1 5.1.2 Density, Void Ratio, Moisture Content and Soil Plasticity .................................. 5‐1 5.1.3 Shear Strength Parameters ................................................................................. 5‐2 5.1.4 Hydraulic Conductivity ........................................................................................ 5‐3 5.1.5 At‐Rest Earth Pressure ........................................................................................ 5‐3 5.1.6 Soil Modulus and Poisson’s Ratio ....................................................................... 5‐3

5.2 Engineering Properties of Asphalt Impregnated Sands ................................................... 5‐3 5.2.1 Particle Size Distribution ..................................................................................... 5‐3 5.2.2 Asphalt Content of Soils ...................................................................................... 5‐3 5.2.3 Hydraulic Conductivity ........................................................................................ 5‐4 5.2.4 Environmental Testing ........................................................................................ 5‐5

6.0 MAN‐MADE FEATURES OF ENGINEERING AND CONSTRUCTION SIGNIFICANCE ..................... 6‐1


Table of Contents

W E S T S I D E S U B W A Y E X T E N S I O N P R O J E C T Page ii July 13, 2012

6.1 Previous Construction at Shaft Site ................................................................................. 6‐1

6.2 Nearby Buildings .............................................................................................................. 6‐2

6.3 Utilities ............................................................................................................................. 6‐2

6.4 Oil Fields ........................................................................................................................... 6‐2

6.5 Fossil Identification and Preservation Projects ................................................................ 6‐2

7.0 EXPLORATORY SHAFT EXCAVATION ...................................................................................... 7‐1

7.1 Subsurface Conditions at Exploratory Shaft .................................................................... 7‐1 7.1.1 Geologic Profile ................................................................................................... 7‐1 7.1.2 Paleontological Monitoring Zone ....................................................................... 7‐2 7.1.3 Groundwater ....................................................................................................... 7‐2 7.1.4 Gases ................................................................................................................... 7‐2 7.1.5 Asphalt Seeps ...................................................................................................... 7‐3

7.2 Ground Support ............................................................................................................... 7‐3 7.2.1 Soldier Piles and Lagging Systems ...................................................................... 7‐3

7.3 Excavation Methods ........................................................................................................ 7‐3 7.3.1 Drilling for Soldier Piles ....................................................................................... 7‐3 7.3.2 Shaft Excavation .................................................................................................. 7‐4 7.3.3 Groundwater Control .......................................................................................... 7‐5 7.3.4 Spoil Disposal ...................................................................................................... 7‐5 7.3.5 Groundwater Disposal ........................................................................................ 7‐6 7.3.6 Tieback Installation ............................................................................................. 7‐6

7.4 Anticipated Ground Behavior at Excavations .................................................................. 7‐6

8.0 BUILDING AND UTILITY PROTECTION MEASURES .................................................................. 8‐1

8.1 Settlement Adjacent to Shaft Excavation ........................................................................ 8‐1

8.2 Protection of Structures and Utilities .............................................................................. 8‐1

8.3 Testing Program ............................................................................................................... 8‐1

9.0 REFERENCES ......................................................................................................................... 9‐1

9.1 Geotechnical Baseline Report References ....................................................................... 9‐1

List of Figures Figure 2‐1: Westside Subway Extension Proposed Tunnel Alignment ...................................................... 2‐3

Figure 2‐2: Hancock Park Area of Los Angeles Showing the Location for the Exploratory Shaft .............. 2‐4

Figure 5‐1: Asphalt Content versus Depth ................................................................................................. 5‐4

Figure 5‐2: Composite Particle Size Distribution – Asphalt Impregnated Lakewood Formation.............. 5‐7

Figure 5‐3: Composite Particle Size Distribution – Asphalt Impregnated San Pedro Formation .............. 5‐8


Table of Contents

W E S T S I D E S U B W A Y E X T E N S I O N P R O J E C T Page iii July 13, 2012

List of Tables Table 3‐1: Geotechnical Explorations for Exploratory Shaft ...................................................................... 3‐1

Table 4‐1: Asphalt Content Classification .................................................................................................. 4‐3

Table 5‐1: Direct Shear Rate of Shearing ................................................................................................... 5‐2

Table 5‐2: Packer Test Results ................................................................................................................... 5‐5

Table 5‐3: Geotechnical Design Parameters ‐ Exploratory Shaft ............................................................... 5‐6

List of Appendices

APPENDIX A ASPHALT CONTENT TEST RESULTS ............................................................................ A‐1

APPENDIX B CASE STUDIES ........................................................................................................... B‐1

APPENDIX C GEOLOGIC PROFILE OF THE EXPLORATORY SHAFT .................................................... C‐1


1.0 - Introduction

W E S T S I D E S U B W A Y E X T E N S I O N P R O J E C T Page 1-1 July 13, 2012

1.0 INTRODUCTION

This Geotechnical Baseline Report (GBR) presents the subsurface conditions anticipated during construction of an exploratory shaft for the Westside Subway Extension Project. The subway project is to be built in west Los Angeles by the Los Angeles County Metropolitan Transportation Authority. It will be an extension of the Heavy Rail Purple Line from the existing Wilshire/Western Station to a station at the Veterans Affairs Hospital in Westwood. The exploratory shaft is required to investigate subsurface conditions in the vicinity of the proposed Wilshire/Fairfax Station where tar‐impregnated soils, methane and hydrogen sulfide gases and fossilized bones (paleontological artifacts) are anticipated to be encountered during construction of the underground works.

The purpose of the exploratory shaft is to investigate underground conditions in the field such that the designer, the contractor for the Wilshire/Fairfax station excavation and tunnel contractors have improved information regarding the ground, groundwater and subsurface gas characteristics and the performance of ground support systems. Because the purpose of this exploratory shaft is to develop information about the subsurface conditions, it is acknowledged that some uncertainty exists, particularly regarding their impacts on construction methods. It is important to the success of the work that the Contractor and Metro work to resolve construction issues in ways that will contribute to our understanding of subsurface behavior.

The GBR provides an interpretation of the geotechnical data, subsurface conditions and ground behavior that influence shaft excavation activities. It includes discussions of geologic and manmade features of engineering and construction significance, and the protection requirements for existing structures and infrastructure in close proximity to the shaft. In the interpretation of the data, the Engineer has made assumptions (described in this report) about construction methods to be selected and employed by the Contractor. If significantly different methods are actually employed, it must be expected that ground behavior will be different from that described herein.

Baseline statements are contained in this document with respect to the site conditions that are anticipated during the performance of the work. They were developed based upon consideration of geotechnical information and data gathered from soil borings; predictions and evaluations concerning anticipated ground behavior during construction assuming likely means and methods to be used by the Contractor; and the judgmental interpretation of information and data. The objectives for establishing the baselines are to:

Describe the subsurface conditions

Reduce uncertainty and therefore the level of contingency in the Contractor’s bid

Assist in the interpretation of the differing site conditions clauses contained in the Contract Documents.

Subsurface gases and ground and groundwater contamination can affect construction activities. The GBR discusses these conditions and provides a baseline for the environmental conditions to be encountered.

The Contractor should not rely upon the baselines in isolation for the planning or performance of any aspects of its work, without limitation as to the means, methods, techniques, sequences and procedures


1.0 - Introduction


of construction, and safety precautions to be employed by the Contractor. The Contractor must undertake its own independent review of the entire set of Contract Documents to arrive at decisions concerning the planning of the work and the means, methods, techniques, sequences and procedures of construction to be used.

The GBR is a Contract Document and is binding upon both Metro and the Contractor. In the event of apparent conflicts, discrepancies, or inconsistencies with any other geotechnical data made available to the Contractor, the GBR takes precedence in reconciliation of the conflict. Precedence of contract documents is given in the General Conditions of the Contract.

The description of the subsurface conditions is given in the GBR. While based on substantial investigations and analyses that are described in the geotechnical data reports, the conditions are not guaranteed or warranted. No amount of investigation or analysis can precisely predict the characteristics, quality or quantity of anticipated subsurface and site conditions and/or the behavior of such conditions during construction operations. Such behavior will also vary and will depend upon and be influenced by the specific construction means and methods selected and utilized by the Contractor.


2.0 - Project Description


2.0 PROJECT DESCRIPTION

The Westside Subway Extension (WSE) lies within the Cities of Los Angeles and Beverly Hills, and within portions of unincorporated Los Angeles County. It will follow an alignment westward from the existing Wilshire/Western Station to the West Los Angeles Healthcare Center campus of the Veterans Affairs (VA) Greater Los Angeles Healthcare System located in Westwood (see Figure 2‐1).

Within the alignment corridor for the WSE tunnels, there is an approximately 1.1‐mile long reach along Wilshire Boulevard between South Burnside Avenue and South La Jolla Avenue (Wilshire/Fairfax area) where subsurface conditions are markedly affected by naturally occurring hydrocarbon products seeping from depth (see Figure 2‐2). The phenomenon is demonstrated most notably by the La Brea Tar Pits located in Hancock Park. Hydrocarbon seeps (locally termed “tar seeps” although more properly called asphaltum or asphalt) occur throughout the park with the large pool in the park being the result of asphalt quarrying activities in the early twentieth century and the later search for fossilized mammal bones preserved in the asphalt. The asphalt, as well as being present in pools, has also impregnated the soils within the proposed subway reach from South Burnside Avenue to South La Jolla Avenue. In addition, gases such as methane and hydrogen sulfide associated with the deep hydrocarbon deposits are to be found.

During subway construction, it is anticipated that the twin tunnels, five cross passages and the Wilshire/Fairfax Station excavation will encounter these asphalt impregnated soils and must contend with high gas concentrations in the soils. Given the challenges associated with excavating through this reach, an exploratory shaft is to be constructed to provide information on the subsurface conditions and their impact on the underground construction of tunnels, cross passages and a station excavation near the intersection of Wilshire Boulevard and Fairfax Avenue.

2.1 Exploratory Shaft Site The exploratory shaft is located at a site on the south west corner of the intersection of South Ogden Drive with Wilshire Boulevard on the opposite side of Wilshire Boulevard to the Los Angeles County Museum of Art (LACMA). The site is bounded by an existing commercial building (6010 Wilshire Boulevard) on the west, a multi‐family residential structure (733 South Ogden Drive) to the south, South Ogden Drive to the east, and Wilshire Boulevard to the north.

The site is located on two property parcels that Metro will lease from LACMA. The north parcel fronting on Wilshire Boulevard is 6006 Wilshire Boulevard and the south parcel is 731 South Ogden Drive. These parcels have been used as a parking lot for the museum staff and are paved with asphalt. Previous uses for the site are discussed further in Section 6.1.

The shaft is to be approximately 18 feet by 36 feet in plan dimension and about 74 feet deep. The excavation is to be supported by means of soldier piles and shotcrete lagging with an internal system of walers and struts. The proposed layout for the support system is shown on the Contract Drawings.

2.2 Purpose of Exploratory Shaft The Exploratory Shaft will provide information for the designers and prospective bidders concerning the characteristics of the ground and how it behaves during construction. In addition, it is anticipated that the shaft will provide the opportunity to prospective bidders for the construction contracts for the tunnels and for the excavation for the Wilshire/Fairfax Station to observe the ground and its behavior prior to completing their bids.




Specific objectives of the exploratory shaft are the investigation of:

1. Engineering characteristics of tar sands and the influence of tar content on engineering behavior

2. Concentrations, quantities and pressures of methane and hydrogen sulfide ‐ naturally occurring gases associated with hydrocarbon deposits

3. Gas inflows that impact tunnel and station designs

4. Information on constructability considerations with regard to:

a. Excavation, support and dewatering of the tar sands

b. Handling and disposal of tar sands from tunneling and station excavations

c. Ventilation requirements for the underground construction in tunnels and in station boxes

5. The approaches and techniques for finding fossils and removing undisturbed soil samples – necessary for the preservation of fossils in excavations.

6. The performance of initial ground support systems.

7. The response of the ground to underground construction.




Figure 2-1: Westside Subway Extension Proposed Tunnel Alignment




Figure 2-2: Hancock Park Area of Los Angeles Showing the Location for the Exploratory Shaft

Note: The red markers indicate locations where fossils have been found previously in the vicinity of Hancock Park. This is not a comprehensive survey and may only reflect where finds have been reported. It is included to demonstrate that there is an expectation that fossil remains can be found at the Exploratory Shaft site.


3.0 - Geotechnical Data Acquisition


3.0 GEOTECHNICAL DATA ACQUISITION

The Geotechnical and Environmental Investigations for the Exploratory Shaft site including the locations of geotechnical borings and monitoring wells and general geologic logs are documented in Metro, 2012. The geologic logs aid in visualizing subsurface conditions and illustrate their variability.

Additional information is available for the entire WSE project alignment in Metro, 2011 including the locations of geotechnical borings and monitoring wells.

3.1 Geotechnical Investigations The three borings drilled at the exploratory shaft site are identified in Table 3‐1. Their locations are presented in the Contract Drawings.

Table 3-1: Geotechnical Explorations for Exploratory Shaft

Exploration Type Investigation

Rotary wash Borings G-350 & G-351

Sonic Continuous Core Boring S-350

CPTs BAT C-350

The following exploration methods were used for the exploratory shaft borings:

Mud rotary drilling – Two borings were advanced using mud rotary techniques to depths of about 100½ to 101 feet below ground surface.

Rotosonic Drilling –One boring using rotosonic drilling techniques was advanced to about 112 feet.

CPT probing – One cone penetration test (CPT) was performed to a depth of about 59 feet below ground surface. This CPT could not be extended further due to refusal.

The equipment and methods used for advancing these borings and the sampling techniques used are described in Metro, 2012.

The following field tests were performed in the borings:

Seven pressuremeter tests at depths ranging from 14 to 83 feet below ground surface. Six of the seven tests were performed in tar‐impregnated silty sand soils.

Vane shear tests attempted at five depths (30 to 70 feet below ground surface) at 10‐foot interval

Three packer tests to monitor hydraulic conductivity of the formation:

To monitor groundwater and sample gases from the formation, the following instrumentation was also installed: Vibrating wire piezometers at depths of about 22 and 52 feet below ground surface in Boring G‐350

and at depths of about 30 and 60 feet below the ground surface in Boring G‐351.

Two nested groundwater monitoring wells screened at depths of 55 to 65 and 84 to 94 feet below ground surface in Boring S‐350.




Three methane probes at three discrete depths in Boring S‐350.

The procedures for testing and monitoring are given in Metro, 2012.

3.1.1 Characterization of Asphalt and Asphalt Impregnated Soils (Tar Sands)

The specific gravity, API gravity and kinematic viscosity have been determined following protocols substantially conforming to procedures described in ASTMs D1298‐05, D175‐08, D445‐12 and D341‐09.

An ASTM standard for determining asphalt content of soil samples is not available. Therefore, a modified version of ASTM D 6307 (Asphalt Content of Hot‐Mix Asphalt by Ignition Method) was used. The procedure is described in Metro, 2012.

3.1.2 Basis of Soil Descriptions

The subsurface conditions depend on the characteristics of the geologic formations, the range of particle sizes being excavated, the asphalt content of the soils, the presence of asphalt filled fractures (termed veins and vents) in the sand, and the groundwater and gas conditions. Since the presence of asphalt within the soil matrix and asphalt filled fractures, veins and vents in the soils will significantly impact the behavior of the subsurface conditions, asphalt impregnated soils are identified within the geologic profile. However, the location and frequency of asphalt filled fractures, veins and vents has not been established by the exploration program and therefore, their locations and dimensions are not specifically identified.

The descriptions of the soils are based on visual logging of samples, review of sonic core log photographs, CPT data, and the laboratory index testing. Blow counts measured by Standard Penetration Tests (SPT) were used to estimate relative densities.

For the purposes of this report, mixed‐soil conditions are defined as variations in soil composition producing layers, lenses or pockets of materials with different soils classification (according to the Unified Soil Classification System). Such conditions will be found within each geologic unit and also at transition zones where two geologic units are exposed in the excavation simultaneously. Mixed‐soil conditions are to be expected both within each geologic unit and as a result of transitions between strata.

3.2 Geophysical Surveys Geophysical surveys were performed at the proposed exploratory shaft site to locate abandoned piles. The results of the surveys are reported in Appendix A of Metro, 2012 and shown on the Contract Drawings.

3.3 Environmental Investigations An Environmental Site Assessment for the proposed Wilshire/Fairfax Station, located immediately north of the exploratory shaft site has been performed during preliminary design investigations for the WSE. The results of this investigation are documented in Metro, 2011.

An investigation of land use for the site showed a gasoline and oil service station and auto service station being there from the late 1930’s until the early 1950’s. Considering the historic land use, an environmental sampling and testing program was performed on soil and groundwater samples obtained




from the sonic core Boring S‐350. Details of the environmental investigation are provided in Section 7.0 of Metro, 2012.

3.4 Additional Investigations Additional information available to bidders is provided in Metro, 2011. A link to this report is given by http://www.metro.net/projects/westside/final‐eis‐eir/ (under Preliminary Geotechnical and Environmental Report, Volumes I‐III). This report contains geologic and geotechnical data along the complete WSE alignment. Metro, 2011 is not a contract document for the exploratory shaft.

Geotechnical Baseline Report – Exploratory Shaft 4.0 - Geologic Setting and Subsurface Conditions


4.0 GEOLOGIC SETTING AND SUBSURFACE CONDITIONS

4.1 Geologic Setting of WSE Project The WSE Project is located within the La Brea and Santa Monica plains of the Los Angeles Basin. The basin is a broad elongated northwest‐trending structural depression that has been filled with sediments up to 13,000 feet thick since the middle Miocene. This sedimentary basin occupies the northernmost portion of the Peninsular Ranges geomorphic province that is characterized by elongated northwest‐southeast trending geologic structures such as the nearby Newport‐Inglewood fault zone. It typically contains a sequence of Holocene through early Cenozoic marine and non‐marine sediments. The Holocene deposits consist of unconsolidated to weakly consolidated alluvium, marine terrace and sand dune deposits. These sediments are underlain by Pleistocene Deposits including the marine San Pedro Formation and the non‐marine to shallow marine Lakewood Formation.

The La Brea and Santa Monica plains comprise primary geomorphic surfaces. These gently sloping alluvial surfaces extend from the Santa Monica Mountains to the alignment and were formed by accumulation of sediments shed out from the mountain front over the course of the late Pleistocene epoch. This process was accelerated by tectonic uplift along the eastern portion of the Santa Monica Mountain range. The net result of this periodic uplift was the formation of alluvial surfaces at varying elevations and ages adjacent to the mountain front. Older alluvial surfaces are generally located at higher elevations and are dissected by stream channels.

The deep sedimentary Los Angeles basin is a known major source of hydrocarbons. The rocks and soils overlying the hydrocarbon deposits contain naturally occurring products that include methane, hydrogen sulfide and asphalt. These products have migrated upward from the deeper formations through discontinuities (fractures, faults, etc.) in the bedrock and through the soils. They are found in the groundwater, and also near‐surface in the soils both below and above the groundwater table. These impacted soils are predominantly found in the Mid‐Wilshire area between South Burnside Avenue and La Jolla Avenue. Seeps (generally referred to as tar seeps) and the La Brea Tar Pit in Hancock Park illustrate the continued upward seepage of asphaltum from the deep hydrocarbon deposits that is part of the process that has preserved the fossilized remains of animals.

4.2 Geologic Units at Exploratory Shaft Site The geologic units and other subsurface materials encountered at the Exploratory Shaft Site are as follows:

4.2.1 Fill

Artificial Fill (symbol on geologic profiles: af) consists primarily of variable silts and clays with occasional sand layers. The fill contains scattered man‐made debris such as concrete, asphalt, and glass.

At the exploratory shaft excavation site, the site is used as a parking lot with an engineered asphalt surface. Within the shaft excavation, abandoned piles from a demolished building remain in place. A group of these piles is located within the proposed shaft excavation (see the Contract drawings for location of abandoned piles).



4.2.2 Lakewood Formation

Lakewood Formation, (symbol on geologic profiles: Qlw) underlies the fill material. These sediments typically consist predominantly of light colored silty sands and poorly graded sands, with infrequent sandy silts and gravelly beds. Layers containing bivalve shell fragments sometimes indicate the base of the Lakewood Formation and have lateral continuity.

At the shaft site, the Lakewood Formation is impregnated with naturally occurring asphalt that significantly impacts its behavior (see Section 4.4 for description of asphalt‐impregnated soils).

4.2.3 San Pedro Formation

The San Pedro Formation (symbol on geologic profiles: Qsp) underlie the Lakewood Formation. Typically, the San Pedro Formation consists of dense interbedded gray to dark gray to greenish‐gray, poorly graded sand, silty sand, and sandy silt and variable clay/silt mixtures with occasional gravelly beds. A number of fossiliferous beds containing bivalve shell fragments are encountered within the San Pedro Formation, as well as local concretionary beds with calcium carbonate cement. Sands are generally fine‐grained and micaceous.

At the shaft site, the San Pedro Formation is impregnated with naturally occurring asphalt that significantly impacts its behavior (see Section 4.4 for description of asphalt impregnated soils).

4.3 Asphalt Impregnated Soils The exploratory shaft is located within an approximately 1.1 mile reach along Wilshire Boulevard between South Burnside Avenue and South La Jolla Avenue (Wilshire/Fairfax area) where asphalt‐impregnated soils are to be found.

The soils are formed from seeps of heavy oil fractions referred to as “asphaltum” emanating from deep hydrocarbon deposits. These heavy oil fractions are a complex continuous mixture of diverse organic compounds, spanning a wide molecular weight/carbon number range (Boduszynski et al, 1998). An assessment of the composition of the asphaltum from samples taken from Borings G‐310, G‐311 and G‐312 (refer to Metro, 2011 for boring locations and geologic logs) is provided in Appendix A.

The oil seeps up through vents (fissures and fractures) along the 6th Street Fault from the Salt Lake Oil Field, which underlies much of the Fairfax district north of Hancock Park. Near the surface, the oil becomes asphalt as the lighter fractions of the petroleum products biodegrade.

Mostly, the asphalt has impregnated the pore spaces of the Alluvium, Lakewood and San Pedro Formations. However, in some places, the asphalt appears in vents, fractures and fissures in the ground. It hardens as it oozes up and in some cases can spread laterally forming asphaltic rich pockets and mounds. It also can seep from the ground and active seeps can be viewed in Hancock Park.

Locally, these asphalt impregnated soils are collectively referred to as “tar sands” and where this term is used in this Geotechnical Baseline Report, it refers to the impacted soils regardless of grain size distribution. However, the term does not fully represent the particle size distribution of the asphalt impregnated soils. The Lakewood and San Pedro Formations are heterogeneous geologic units comprised of interbedded layers and lenses of fine‐ and coarse grained materials and as a result, the asphalt‐impregnated soils contain both fine and coarse grained material. The asphalt impregnated fine grained soils, typically sandy silts, sandy clays, and silty clays are sometimes referred to as Petroliferous Silt/Clay.



The saturation of the geologic units with asphalt varies with location and depth. Typically, the asphalt content is higher in the coarser grained material (SP‐SM, SM) as the void sizes being larger are more easily penetrated by the viscous asphalt. As a result, the finer grained materials have lower asphalt contents.

For purposes of classifying the soil samples based on the percentage of asphalt content, a classification system was developed as presented in Table 4‐1. This system was developed for the project to describe the asphalt content of samples.

Table 4-1: Asphalt Content Classification

Asphalt Content Classification

< 5% Slightly Infused with Asphalt

5% - 15% Moderately Infused with Asphalt

>15% Saturated with Asphalt

4.4 Local Faulting Southern California is a seismically active region, well known for its active faults and historic seismicity. Active faults in the area include: the Hollywood Fault, approximately two and one half miles north; the Newport‐Inglewood Fault Zone (and associated West Beverly Hills Lineament) approximately three miles to the west‐south‐west; and, the Santa Monica Fault approximately three and one half miles to the west.

There are no known active or inactive faults at the shaft site (see Metro, 2011 for definition of fault activity). The Sixth Street Fault is found to the north of Wilshire Boulevard in the vicinity of Hancock Park. It is inactive but is considered to be considered to be associated with the asphalt seeps and the formation of the La Brea Tar Pits.

4.5 Groundwater The shaft site is located within the Central Basin hydrogeologic region in Los Angeles County. Groundwater in the Central Basin typically occurs within aquifers in the Lakewood and San Pedro Formations. The water bearing zones within these formations consist generally of permeable sands and gravels that are separated by semi‐permeable to impermeable sandy clay and clay layers. A groundwater‐level contour map of the Hollywood Quadrangle shows the historically highest groundwater levels to be approximately 10 feet below ground surface at the shaft location (Metro, 2011).

Near the ground surface, groundwater occurs as semi‐perched or perched water. Levels fluctuate with seasonal rainfall, infiltration and with groundwater extraction activities. Groundwater levels and piezometric measurements taken in borings at the shaft site since April 2012 are provided in Metro, 2012.

The groundwater contains dissolved methane and hydrogen sulfide.

4.6 Subsurface Gases The exploratory shaft is located within an area designated as a "Methane Zone" on the Methane and Buffer Zone map published in 2004 by the City of Los Angeles, Department of Public Works (Metro,



2011). Methane and hydrogen sulfide gas associated with deep hydrocarbon deposits and that have been transported to the surface through the fissures are found at the shaft site. They are present within the Lakewood and San Pedro, both within pore spaces and dissolved within the ground‐water whether it is perched groundwater or found below the ground‐water table.

Methane: ‐ Methane is a naturally occurring gas associated with the decomposition of organic materials. Methane is common in oil and gas fields and often occurs associated with hydrogen sulfide gas. Methane gas, while explosive, is not highly toxic. Rather, it asphyxiates as it displaces oxygen. Methane (density ~0.72 g/l) is lighter than air and therefore tends to rise through the ground and dissipate. It is moderately soluble in water. Approximately 40 to 50 cubic centimeters of methane can be dissolved in a liter of water at atmospheric pressure.

Hydrogen Sulfide: ‐ Hydrogen sulfide, produced by the anaerobic decomposition of organic and inorganic matter that contains sulfur is highly toxic when inhaled. Hydrogen sulfide (density ~1.54 g/l) is heavier than air and therefore, within the ground tends to accumulate above the groundwater table and within depressions.

Hydrogen sulfide is highly soluble in water. Approximately 2,800 cubic centimeters of hydrogen sulfide can be dissolved in a liter of water at atmospheric pressure. The off‐gassing of hydrogen sulfide from a liter of water that is saturated with the gas can produce a one part per million within a 3 cubic meter air space. See Section 7 of Metro, 2012 for detailed discussion of test results determining soils to be non‐hazardous.


5.0 - Engineering Properties of the Subsurface Materials


5.0 ENGINEERING PROPERTIES OF THE SUBSURFACE MATERIALS

The engineering properties of the subsurface materials to be encountered within the exploratory shaft excavation will be significantly influenced by the impregnated asphalt. The engineering properties that typically characterize these formations when they are not impregnated with asphalt are not applicable. For the purposes of this characterization of baseline conditions, the subsurface materials are characterized as:

Fill

Lakewood Formation ‐ not impregnated with asphalt

Asphalt impregnated Lakewood and San Pedro Formation Soils.

The subsurface materials have been characterized at the exploratory shaft site based on in situ tests, laboratory tests, empirical correlation, local experience, and engineering judgment. The data from the laboratory and field‐testing programs, used to estimate the engineering characteristics of the geologic materials are documented in Metro, 2012.

5.1 Engineering Characterization Corrected blow counts for SPTs (NSPT) obtained during mud rotary borings and the results from the laboratory testing program were used to estimate engineering properties. Some properties (i.e., void ratio) have been estimated from other soil parameters and by using local experience and engineering judgment.

From the laboratory determined grain‐size distributions, soils were identified in accordance with the classification system presented in ASTM D2487, Standard Test Method for Classification of Soils for Engineering Purposes.

5.1.1 Particle Size Distributions

Soil gradations were conducted on samples obtained from the mud rotary and rotosonic borings. Grain size distributions for materials sized less than 3 inches) and fines content (percentage by weight passing No. 200 sieve) are presented for samples from the exploratory shaft exploration. The distribution curves also present mean, mean plus one standard deviation, and mean minus one standard deviation to provide a basis for estimating the variability within ranges.

The results of individual gradation tests reflect the particle size distributions of soil samples actually obtained and not necessarily the in situ material. Coarse‐grained materials larger than the sampler size were not sampled, (split spoon and Crandall sampler with inside diameters of 1.375 and 2.625 inches, respectively).

Cobbles are defined as particles between 3 and 12 inches and boulders as particles that will not pass through a 12‐inch square opening. For the mud rotary borings along the full alignment, cobbles have been reported in the boring logs. However, cobbles and boulders were not encountered in the borings within the shaft.

5.1.2 Density, Void Ratio, Moisture Content and Soil Plasticity

Based on AASHTO, 1988, the relative density of the soil profile has been determined based on blow counts from the Standard Penetration Tests (SPT).




For the fine grained materials, the soils are identified as follows:

Soft to medium stiff fine‐grained soils ‐ SPT blow counts per foot ranging from 2 to 8

Medium to stiff fine‐grained soils – SPT blow counts per foot ranging from 8 to 16

Very stiff to hard fine‐grained alluvium ‐ SPT blow counts ranging from 16 to 60.

For the coarse‐grained materials, the soils are identified as follows:

Very loose to loose granular soils ‐ SPT blow counts per foot ranging from 0 to 10

Medium dense granular soils ‐ SPT blow counts per foot ranging from 11 to 30

Dense granular soils ‐ SPT blow counts per foot range from 31 to 50)

Very dense granular soils ‐ SPT blow counts per foot greater than 50.

In combination with the soil classifications and index testing (specific gravity, moisture content and dry density), the SPTs have been used to provide the basis for establishing baseline parameters for soil relative density and void ratio.

The soils in the shaft excavation contain fines (particle size smaller than No. 200 sieve size). For the fines fraction of selected soil samples, Atterberg Limit Tests were carried out and the results plotted on plasticity chart to assist in characterizing the fines content.

5.1.3 Shear Strength Parameters

Shear strength data from direct shear and tri‐axial compression tests are provided in Metro, 2012. Direct shear tests were performed on selected undisturbed samples obtained from rotary‐wash borings to determine the strength of the soils in accordance with ASTM D 3080. The test procedures are provided in Metro, 2012.

Table 5-1: Direct Shear Rate of Shearing

Test Material Rate of Shearing

(inch/minute) Test Duration

(minutes)

Asphalt Sand 0.005 100

Petroliferous Silt/Clay 0.002 180

The rate of shearing varied depending on the type of soil tested. The rate of shearing was estimated using time‐consolidation rate results from one‐dimensional laboratory consolidation tests performed in accordance with ASTM D 2435. The rate of shearing for different materials is listed in Table 5‐1.

Vane shear tests were performed in Boring G‐350‐A (drilled approximately 5 feet away from Boring G‐350) to determine the undrained shear strength of the soils. Four tests were attempted. The test at 30 foot depth was successful but three other tests at deeper depths were not with the equipment either bending or the rated capacity of the vane shear being exceeded before the peak shear resistance was reached.




5.1.4 Hydraulic Conductivity

Hydraulic Conductivity was based on a review of the boring logs, packer tests, and engineering judgment.

Within the asphalt‐impacted soils, the in situ material is less permeable than soils that are not asphalt impregnated. This is a result of the void space within the soils being penetrated by the asphalt making the void spaces smaller and less interconnected.

5.1.5 At-Rest Earth Pressure

Pressuremeter tests have been carried out as part of geotechnical investigations for the exploratory shaft. The results, interpreted from loading/unloading behavior are presented in Appendix E of Metro, 2012.

5.1.6 Soil Modulus and Poisson’s Ratio

The soil modulus and Poisson’s ratio were estimated on the basis of the seismic velocity surveys (for dynamic modulus) and the results of the pressuremeter tests (for static modulus, Em).

5.2 Engineering Properties of Asphalt Impregnated Sands

5.2.1 Particle Size Distribution

For the asphalt impregnated sands, properties are provided for samples obtained from coarse‐grained and from fine‐grained samples. Because of the methods of sampling used (split spoon and Crandall sampler with inside diameters of 1.375 and 2.625 inches, respectively), the results of gradation tests reflect the particle size of the soil samples actually obtained and not necessarily the in situ material. Coarse‐grained materials larger than the sampler opening were not sampled.

Results of grain size distribution (of materials sized less than 3 inches) and fines content (percentage by weight passing No. 200 sieve) tests on tar sands are presented in Figure 5‐2 and Figure 5‐3 for samples from the exploration program for the shaft excavation and also for asphalt impregnated samples taken within the reach from South Burnside Avenue to La Jolla Avenue along Wilshire Boulevard. The mean and standard deviations given in Figure 5‐2 and Figure 5‐3, respectively, provide a basis for estimating the variability within the range. It is to be anticipated that 95 percent of the particle size distributions of the material excavated will be between the mean ± two times the standard deviation.

5.2.2 Asphalt Content of Soils

Within the reach along Wilshire Boulevard where asphalt impregnated soils are found, samples were tested to determine their asphalt content. The results indicate the asphalt content for samples varies up to 25%, with an average value of about 15%. Applying the classification system identified in Table 4‐1, the results indicate that about 10% of the samples were slightly infused with asphalt; about 45% were moderately infused; and the remaining 45% were saturated with asphalt.

Asphalt content results are plotted in Figure 5‐1 for the full suite of tests performed along the alignment and for the tests on samples from the Exploratory Shaft. For the samples from the Exploratory Shaft site, the asphalt content varies from 5.6 percent to 18 percent. The average asphalt content is 15.4 percent (Standard Deviation of 2.5 percent). Below a depth of 20 feet, the asphalt content within the shaft excavation is within a range of 11 to 19 percent. The results from the exploratory shaft indicate that 40 percent of the asphalt impregnated soils to be excavated will be moderately infused with asphalt




with the remaining 60 percent saturated with asphalt (in accordance with the classification system from Table 4‐1).

Figure 5-1: Asphalt Content versus Depth

The samples selected for testing were the coarser grained materials that visually had higher asphalt contents. The asphalt impregnated soils also contain layers and lenses within the borings where finer grained materials with lower asphalt contents are visually observed. It is estimated that the finer grained layers represent 10 percent of the borings within the asphalt impacted zone, primarily located in the upper level.

The asphaltic material is highly viscous with a kinematic viscosity estimated to be approximately 100,000 centiStoke at 65 degree Fahrenheit .

5.2.3 Hydraulic Conductivity

Hydraulic conductivity of the asphalt‐impregnated soils was determined based on three Packer tests performed in Boring S‐350. The intervals tested and the estimated hydraulic conductivity values from the tests are given in Table 5‐2.

‐120

‐100

‐80

‐60

‐40

‐20

0

0.00% 5.00% 10.00% 15.00% 20.00% 25.00%

Dep

th of Samples (in feet)

Percent of Asphalt (%)

Data from Shaft Site Data from alignment




Table 5-2: Packer Test Results

Boring No. Test Zone

(ft.) USCS Soil Classification Hydraulic Conductivity (cm/sec)

S‐350

24 – 30 Clayey to Silty Sand

(saturated with asphalt) 2.8 x 10‐5

46 – 51 Sandy Silt to Silty Sand (saturated with asphalt)

1.1 x 10‐5

67 – 72 Sandy Silt to Silty Sand (saturated with asphalt)

6.9 x 10‐6

The test results indicate that the hydraulic conductivity of the asphalt impregnated soils is similar to that of fine‐grained silty clay to clay soils. The mean of these results is 1.5 x 10‐5 cm per second.

5.2.4 Environmental Testing

Analytical tests were performed on two samples of asphalt‐impacted soils for VOCs/SVOCs/TPH and Title 22 metals by American Scientific Labs. The results are included in Appendix F of Metro, 2012. In addition, soil samples from drill cuttings stored in the drums were analyzed. Based on the test results, the asphalt‐impacted soils were determined to be non‐hazardous waste per the Resource Conservation and Recovery Act (RCRA). Because of the asphalt content, they require handling and disposal as a contaminated material.




Table 5-3: Geotechnical Design Parameters - Exploratory Shaft

Geologic Unit Artificial Fill Non Asphalt Impregnated - Lakewood Formation (Qlw) Asphalt Impregnated Lakewood & San Pedro Formation (Qsp)

CL, SM, SC, SP Fine-Grained Coarse-Grained Fine-Grained Coarse-Grained

Soil Classification CH, CL, CL-ML, ML SM, SC, SP ML, CL-ML SM, SP, SP-SM, SW-SM

SPT Blow counts Range: 18-20

Best Estimate 19 Range: 22-35

Best Estimate 33 Range: 21-50+

Best Estimate 50+ Range: 43-50+

Best Estimate 49

Total Unit Weight of Soil (pcf)1 125 125 125

Water Content (%)

Mean 5% St Dev 3%

Asphalt Content 0% Mean 15% St Dev 2.5%

Cohesion (psf) 200 550 300

Angle of Friction (degrees) 25 24 27

Young’s Modulus (ksf) 1,240 1,240 2,700

Poisson’s Ratio 0.35 0.35 0.35

Soil Pressure Coefficient, At-Rest Ko4 0.50 0.73 0.65

Hydraulic Conductivity (cm/sec) 1.5 x 10-5 1.5 x 10-5

Friction Value for Tieback Testing (psf)

1,500

1 Laboratory test data from ACE and PE phase investigations 2 For Formations based on pressuremeter test results; for artificial fill assumed as 0.5




Figure 5-2: Composite Particle Size Distribution – Asphalt Impregnated Lakewood Formation




Figure 5-3: Composite Particle Size Distribution – Asphalt Impregnated San Pedro Formation


6.0 - Man-Made Features of Engineering and Construction Significance


6.0 MAN-MADE FEATURES OF ENGINEERING AND CONSTRUCTION SIGNIFICANCE

This section identifies the man‐made features that will affect the construction of the exploratory shaft.

6.1 Previous Construction at Shaft Site The exploratory shaft is located on a parcel at 6006 Wilshire Boulevard at the southwest intersection of South Ogden Avenue with Wilshire Boulevard.

The 6006 Wilshire Boulevard property was occupied by a gasoline and service station from the late 1930’s until the early 1950’s. This was removed and replaced by a midrise office building that was built in the 1950’s. This seven story structure was supported on piles. The building was demolished in 2009 but its foundations consisting of groups and lines of Raymond piles were abandoned in‐place. Their locations are indicated on the contract Drawings

Following the building demolition, the site together with the adjacent property at 731 S. Ogden Drive was converted into a staff parking lot for LACMA.

Based on observations documented during grading, demolition and construction at the site (GPI, 2010), the following work was performed to convert the parcels into a parking lot:

At 6006 Wilshire Boulevard:

Building demolished and removed from site

Piles supporting the building were removed to a depth of at least 3 feet below finished grade. The deeper portion of the piles were abandoned in –place. Information on the location of piles based on as‐built information and a site investigation program is provided in the Contract Drawings.

Four to Six feet of fill was placed below finish subgrade. Fills were compacted using a vibratory roller and by rolling with a rubber tired loader.

A group of nine piles is shown to be located within the footprint of the exploratory shaft. Based on available information, these are Raymond piles driven to a depth of 30 feet. They are embedded in asphalt‐impregnated soils

Within the 731 South Ogden Drive part of the site, construction activities have also preceded the parking lot. Although not within the area where the shaft is to be excavated, a shored excavation up to 22 feet deep supported with soldier piles and lagging, by rakers on three sides and by sixteen tiebacks on the east wall was constructed. To make way for the parking lot, the following site work was performed:

Rakers were removed. This was accomplished after 12 feet of excavation fill was placed to support shoring.

Fifteen of the sixteen tiebacks were removed. The tiebacks were approximately 27feet long (according to records). The tieback connections to the wall were located about 12 feet from the top of the shored excavation. One tieback, designated as A‐56 could not be removed and was left entirely in‐place.

The upper three feet of the soldier piles and lagging were removed.


6.0 - Man-Made Features of Engineering and Construction Significance


Fills up to 22 feet were placed. Fills were compacted using a vibratory roller and by rolling with a rubber tired loader. Hand‐held vibratory equipment was used around the perimeter.

6.2 Nearby Buildings The proposed shaft excavation is adjacent to 6010 Wilshire Boulevard. This is a five story commercial building built in the 1950’s. The building footprint is approximately 4,500 square feet and is bounded on its east by a covered drive that abuts the construction site for the Exploratory Shaft. Foundations consist of continuous footings along the walls at 4‐ft below grade and a series of spread footings within the building beneath the building columns.

The residential building at 733 South Ogden Drive is a four story structure. Because of its proximity to the shaft site, the impact of noise, malodorous smells, dust and construction traffic must be controlled in accordance with the specifications to assure that the residences are not severely affected by construction activities.

6.3 Utilities Locations, types and configurations of the utilities on site and within South Ogden Drive are presented in the Contract Drawings. Utilities include water, telephone, gas, electrical and telecommunication lines, oil pipelines, storm drains, and sewers are located within the street rights‐of‐way along the proposed underground segment alignment. A County storm drain is identified in South Ogden Drive.

6.4 Oil Fields Although the shaft excavation is impacted by the hydrocarbon products in the form of the tar sands and by associated methane and hydrogen sulfide, the site does not contain known facilities associated with past oil production such as oil wells, sumps, drilling ponds, areas of past spills, storage tanks, and exploration and production wells.

6.5 Fossil Identification and Preservation Projects Although the asphalt from the deep hydrocarbon deposits is a natural phenomenon, it was quarried commercially in late nineteenth century and early twentieth century in the Rancho La Brea area of Los Angeles. With the discovery of fossil accumulations in the asphalt materials, the quarry pits were deepened and additional pits dug to recover the fossils. Eventually, the area became known as the La Brea Tar Pits and developed into the Hancock Park and museum buildings that now occupy the area. Currently, only Pit 91 remains open within the park as a recovery site although this is on hold.

With the development of the LACMA underground parking structure, more fossils were found. To allow their identification, removal and preservation to proceed on a site geared towards construction, careful fossil recovery techniques were developed by the Page Museum. These techniques and procedures are to be adopted at the Exploratory Shaft site to identify, preserve and remove fossils. They are provided in Specification Section 01170, Archaeological and Paleontological Coordination.

It should be noted that tar seeps are not confined to the Hancock Park and asphalt can be found seeping up into streets and into building basements. Buildings in the area use drainage systems to collect, contain, and remove asphalt that has intruded through walls and into basements.


7.0 - Exploratory Shaft Excavation


7.0 EXPLORATORY SHAFT EXCAVATION

The purpose of the exploratory shaft is to provide field information that benefits the design and construction of the open cut box to be constructed for the Wilshire/Fairfax Station proposed for the WSE. Typically, the initial ground support for open cut boxes for Los Angeles Metro Stations has used soldier pile and lagging systems. Since it is important that the initial ground support system for the exploratory shaft be consistent with that to be used for the station box, soldier pile and shotcrete lagging is specified as the support for the exploratory shaft.

The contractor is responsible for the design and installation of the ground support system including any necessary groundwater control measures needed to stabilize the ground.

Excavation is subject to the requirements of applicable federal, state and local codes and regulations and must take into account measures to control/mitigate gas inflows to the excavation. It will also be restricted when excavating through materials potentially containing fossils by the requirements of the Paleontological Mitigation Plan that is contained in Technical Specification Section 01075, Archeological and Paleontological Coordination.

7.1 Subsurface Conditions at Exploratory Shaft

7.1.1 Geologic Profile

The geologic profile of the exploratory shaft excavation is given in Appendix C. It consists of:

Artificial Fill (af) – Ground Surface to an average depth of 10 feet (varying across the excavation from 9 to 10‐1/2 feet deep) – Fill material is heterogeneous and consists of medium stiff sandy clay and medium dense clayey sand with some concrete debris.

Lakewood Formation (Qlw) – from the bottom of the Artificial fill to an average depth of 20 feet below ground surface (varying across the excavation from 19‐1/2 to 20‐1/2 feet deep) – Lakewood Formation consists of inter‐layered grayish blue green stiff clayey silt and silty clay, with relatively thin lenses and layers of medium dense dark olive gray clayey sand and fine to coarse sand. It is anticipated that the Lakewood will be impregnated with asphalt (slight asphalt infusion to trace asphalt content) from a depth of 11 feet (El. 157).

San Pedro Formation – from 20 feet below ground surface to 112 feet below ground surface. Composition of the San Pedro Formation consists of variable layers and lenses of sands and silty sands with occasional layers of clay and silty clay. The formation contains asphalt over the full depth of the excavation. Within the San Pedro Formation, the excavation will encounter:

– Zones of well and poorly graded, dense to very dense, fine‐ to coarse‐grained sands, clayey fine‐grained sand and sandy silt – impregnated with asphalt

– Zones of sands and silty, fine‐ to medium‐ grained sands with occasional gravel (up to ½ inch in size) – impregnated with asphalt,

– Occasional zones of clayey silt and silty clay – impregnated with asphalt

– Silty fine‐grained sand with some fine‐ to medium grained sand is predominant between 25 and 85 feet depths below ground surface – impregnated with asphalt

– Trace shell fragments found between approximately 70 and 75 feet below ground surface




Nine Raymond piles (step tapered piles consisting of a steel shell driven into place and filled with concrete) that were part of the foundations for the demolished building and were abandoned in‐place within the excavation. They were cut‐off 3 feet below ground surface and were 30 feet long (the contractor must assume that 27 feet of each pile remains in the ground). The pile spacing is assumed to be 3 to 4 feet.

7.1.2 Paleontological Monitoring Zone

The excavation includes a Paleontological Monitoring Zone. This is a zone potentially rich in fossil remains, similar to those found at the La Brea Tar Pits. Because of their scientific significance, this zone is to be investigated to identify and, if found, recover fossils.

The Paleontological Monitoring Zone is from the base of the Artificial Fill (at 10 foot depth) to the top of the marine sediments (baselined at El. 125.5). Within this zone, the paleontological monitor will observe the construction and determine whether fossils are present. Should fossils be identified, Metro will direct the Contractor as to how to proceed. Metro will also determine whether the extent of the zone to be searched should be modified and will direct the Contractor accordingly.

7.1.3 Groundwater

The groundwater table is shown on the geologic profile (refer to Appendix C). Groundwater inflows from the tar sands into the shaft are estimated to be a maximum of 5 gallons per minute. The water is contaminated with asphalt and derived products and will also be a source for methane and hydrogen sulfide gases. Other constituents found in the groundwater that affect its disposal are reported in Metro, 2012.

Based on the information concerning the LACMA Underground parking structure, there is the potential for an inflow (up to 200 gallons within a one hour period) of water and hydrocarbon product entering the excavation through a fracture or vent in the Lakewood or San Pedro Formations. The Contractor must develop procedures to deal with such an event

7.1.4 Gases

Methane and Hydrogen sulfide gases are present in the ground and in the groundwater and can be anticipated to enter the shaft excavation. As a result of the gas conditions found at the site, Cal OSHA has classified the excavation as “gassy” and the regulations applicable to underground construction in “gassy” ground conditions apply.

Methane and hydrogen sulfide concentrations of approximately 81% (810,000 ppm) and 2 ppm, respectively have been measured at the S‐350 boring location. Based on the assumption that the dissolved gas concentrations in the groundwater are in equilibrium with the soil gas concentrations measured in the vadose zone and the increase in solubility of methane and hydrogen sulfide in water with pressure, it is estimated that:

At groundwater table level

Dissolved Methane Concentration in the groundwater is 20 mg/L

Dissolved Hydrogen Sulfide Concentration in the groundwater is 0.01 mg/L

These concentrations will increase linearly with depth until at El. 92 (shaft bottom):




Dissolved Methane Concentration in the groundwater is 60 mg/L

Dissolved Hydrogen Sulfide Concentration in the groundwater is 0.03 mg/L

With the reduction in water pressure caused by the excavation at this depth, off gassing volumes from the groundwater are estimated to be:

Methane: 56 cm3 per liter of groundwater (5.24E‐04 ft3/gallon)

Hydrogen Sulfide: 0.02 cm3 per liter of groundwater (7.00E‐07 ft3/gallon)

It should be noted that hydrogen sulfide concentrations as high as 6,500ppm have been measured within approximately one‐half mile of the site. Accordingly, hydrogen sulfide can be present in the excavation at levels in excess of the maximum value of 2ppm measured in Boring S‐350. Hydrogen sulfide has a strong, rotten‐egg like odor that is detectable, and is objectionable to people at concentrations as low as approximately 0.5ppm. The ventilation system for the shaft should be designed to achieve a maximum air effluent value of approximately 0.1ppm

7.1.5 Asphalt Seeps

Asphalt seeps are anticipated to progress upwards through vertical/sub vertical fractures in the soil formations into the excavation. Total asphalt inflows into the completed shaft are estimated to be a maximum of 4 gallons per day.

7.2 Ground Support Experience with construction support systems for similar subsurface conditions on other Los Angeles Metro Rail projects indicates that options for the initial excavation support include soldier piles and timber or shotcrete lagging, tangent pile walls, or slurry walls. For the exploratory shaft, a system of soldier piles and shotcrete lagging is proposed as ground support.

7.2.1 Soldier Piles and Lagging Systems

Design criteria and lateral earth pressure diagrams for the ground support system for the exploratory shaft excavation are given on the Contract Drawings.

Because of the depth of the exploratory shaft excavation, a structural system comprising soldier piles, walers, and struts is required for lateral support and is shown on the Contract Drawings. The Engineer has sized the basic support system. It is the Contractor’s responsibility to confirm the design of the support system is adequate and to design the connection details. The Contractor is responsible for the satisfactory performance of the support system.

Embedment requirements for the soldier piles to resist the anticipated lateral loads are provided in the Contract Drawings. Provisions must be implemented to prevent the piping of fines from the alluvial soils. With shotcrete lagging that will be relatively impermeable, effective drainage provisions must be provided to prevent build‐up of groundwater behind the lagging.

7.3 Excavation Methods

7.3.1 Drilling for Soldier Piles

Holes for the soldier piles must be drilled. Drilling can be accomplished with conventional drilling rigs with sufficient capacity/torque to penetrate dense to very‐dense alluvium containing sand and silt with




occasional gravel and cobbles. To mitigate disturbance to the public, driving of soldier piles is not permitted.

Instability of drilled holes for the soldier piles is to be anticipated when granular alluvial soils containing sand, gravel, and/or cobbles are encountered both above and below the water table. Casing or slurry can be used to prevent instability. Where caving occurs, it will result in large backfill and/or tieback anchorage quantities. The Contractor must take into account difficult drilling conditions, including potential hole deviations caused by encountering cobble nests, and should utilize appropriate drilling techniques, control the drilling rate to mitigate hole caving, and have casing available at the job site for rapid use.

7.3.2 Shaft Excavation

The Contractor’s means and methods must anticipate soil characteristics over the full range of values identified for each geologic unit. They must conform to:

The requirements and constraints contained in Technical Specification 02200A, Shaft Excavation

The requirements of the Paleontological Mitigation Plan in Technical Specification Section 01070 Archaeological Plan to excavate carefully and identify, protect and then remove fossils when they are found.

It is to be anticipated that 90 percent of the material encountered within the Lakewood and San Pedro Formations will lie within the curves represented by the mean ± two times the standard deviation as shown in the Particle Size Distribution Plots ‐ Figures 5‐2 and 5‐3 ‐ with the exception of any fossilized remains found.

Removal of Abandoned Piles Nine Raymond piles driven are embedded in asphalt‐impregnated soils. These piles must be removed, either by pulling out or cut off in sections as the excavation is advanced.

Shaft Excavation in the Artificial Fill The fill will contain concrete, asphalt rubble, and wood fragments as well as compacted soil backfill. The contractor will be required to locate abandoned and functioning utilities in the fill prior to the start of excavation.

It is anticipated that through the fill, the excavation for the exploratory shaft can be achieved using conventional excavation methods. Suitable excavation equipment such as a track mounted hydraulically operated backhoe will be required to excavate the material. The machine must be suitably sized to operate within the size of the shaft. The equipment used must be able to remove rubble up to 3 feet in dimension. Equipment must also be available to remove the piles in sections as the excavation proceeds.

During excavation, the temporary height of ground exposed in the excavation should not exceed five feet without the placement of lagging to ensure that the ground does not ravel. Once an excavation is supported, water build‐up behind the lagging must be prevented by appropriate measures such as placement of filter materials behind the lagging in areas where water seepage (due to residual inflows, perched groundwater inflow or broken utilities) persists. If the localized inflows through the shaft bottom are large enough, the water should be collected and pumped out of the excavation using ditches and sumps.




Excavation within the Paleontological Monitoring Zone Within the Paleontological Monitoring zone (see Section 7.1.1) – the zone “Potentially Containing Fossils” ‐, the excavation must proceed in not more than 6‐inch lifts and the excavation must be observed by Metro’s Paleontological Monitor. Excavation must stop when directed by Metro to identify and if necessary remove fossils. To avoid destruction of fossils, the bucket should not have teeth. The bucket edge should be used to scrape the surface and allow fossil identification to be made, should they be made.

A description of the methods that will be used to remove fossils should they be identified is described in the Paleontological Mitigation Plan for the Westside Exploratory Shaft Project, Los Angeles, California. This document is a reference document to Technical Specification Section 01170, Archaeological and Paleontological Coordination.

Excavation within Asphalt Impregnated Soils not designated as Paleontological Monitoring Zone

Excavation within the asphalt impregnated soils that are not subject to the restrictions applying to excavation in the Paleontological Monitoring Zone can be carried out with conventional excavation equipment. Excavation should proceed in lifts not exceeding 5 feet without the installation of lagging to support the shaft walls between soldier piles.

Once the excavation is complete, a gravel layer will be placed in the bottom of the excavation with a concrete base slab placed above it. Penetrations through the concrete base slab will be used to monitor groundwater and gas inflows through the shaft bottom and to relieve water pressure build‐up beneath the slab.

7.3.3 Groundwater Control

A dewatering system consisting of deep wells is specified.

Groundwater inflows from the asphalt‐impacted soils into the shaft are estimated to be a maximum of 5 gallons per minute. The water will be contaminated with asphalt and derived products and will also be a source for methane and hydrogen sulfide gases.

7.3.4 Spoil Disposal

The Contractor is responsible for the disposal of spoil. The soldier pile drilling will contain 450 cubic yards of material (not including for bulking) and the shaft excavation will contain 1,800 cubic yards of material (not including for bulking)The asphalt impregnated soils contains naturally occurring non‐volatile hydrocarbons (crude oil). The asphalt concentrations exceed the disposal limits for diesel and oil range organics. As such, the asphalt‐impacted soils are classified as contaminated but considered as RCRA non‐hazardous. The excavated soils must be disposed of at a Class II landfill (refer to Metro list of approved landfills in Technical Specification 01175) or could be used at a recycling facility producing asphalt for commercial use.

The Contract contains provisions for excavating, transporting and disposing of this material. The Contract also contains provisions for monitoring for other hazardous and contaminated materials to identify their presence. From the evaluation of the environmental conditions, no contamination has been identified as hazardous (requiring special handling and disposal at a Class I landfill).




7.3.5 Groundwater Disposal

The contractor is responsible for disposal of groundwater and water collected on site. The water will be disposed of off‐site at a permitted water treatment recycling facility. This will require submittal of analytical results to a permitted water treatment facility and their acceptance that it meets the acceptance criteria. Groundwater pumped from the shaft can be stored on‐site in a tank and periodically removed using a vacuum truck and transported to the water recycling facility. For disposal of groundwater, its constituents must be identified and it disposed of in accordance with applicable regulations.

Alternative disposal options require treatment. Groundwater disposal into a storm drain at the shaft location would discharge into Ballona Creek. This is not acceptable without treatment due to arsenic, cadmium and nickel exceeding screening levels for discharge (refer to Table 8.1 of Metro, 2012. Discharge to the sanitary sewer is acceptable provided that the appropriate permits are obtained. This will require treatment of the water prior to discharge due to VOC concentrations.

A summary of the analytical laboratory test results for groundwater samples collected from Boring S‐350 at a depth of 95 feet is provided in Section 8.1 of Metro, 2012.

7.3.6 Tieback Installation

A tieback testing program will be performed in the shaft excavation to evaluate the performance of tiebacks in the asphalt –impregnated soils including their long term creep behavior and ultimate capacity. A total of four tiebacks will be tested using the procedures indicated in Technical Specification Section02162 with the tests for each tieback identified in the Contract Drawings. The tieback anchors have not been considered as part of the shaft shoring system and are not intended to support the earth load. Installing tieback anchors may likely require permission/easements from local agencies and owners of adjacent buildings and avoidance of underground obstruction such as basements, foundations, and utility lines. The tieback anchors will be under the site construction property and the street right‐of‐way. At completion of the testing, they will require to be removed to depths of at least 20 feet below ground surface. When drilling the holes for the tiebacks, caving of the holes should be anticipated and provisions should be made to minimize such caving. The anchors should be filled with concrete placed by pumping from the tip out, and the concrete should extend from the tip of the anchor to the anchor head. For preliminary design purposes, a post‐grouted anchor should be assumed to develop an average friction value of 1,500 pounds per square foot. To avoid reduction in the capacity due to group action, the anchors should be spaced at least 6 feet on centers.

7.4 Anticipated Ground Behavior at Excavations Ground behavior during excavation of the exploratory shaft depends on the asphalt content of the soils, the density and fines content of the granular soils, the stiffness of the fine‐grained soils, the groundwater conditions, and the means and methods of construction.

The excavated materials include both fine‐ and coarse‐grained alluvial and sedimentary materials, with particle sizes ranging from less than No. 200 sieve to granular material containing sands, gravels and




cobbles. In the field, particle size distributions for layers of sand and gravel can be expected to be coarser and include occasional cobbles. Exposed soil conditions within the shaft excavation will vary. Changes will be gradational or abrupt, and will occur across the exposed surface as the excavation is deepened and are described as mixed‐soil conditions.

Non-Asphalt Impregnated Soils

Non‐asphalt impregnated soils are found above a depth of 11 feet in the Artificial Fill and the Lakewood Formation. In gravelly sand and poorly‐graded sand above the groundwater table, unsupported sidewalls will ravel rapidly (within a few minutes) and running1 conditions must be anticipated. Unsaturated sand, silt, silty sand, and clayey sand which are moist or have some apparent cohesion can be expected to ravel (within an hour) from unsupported sidewalls.

Flowing2 conditions must be anticipated in gravelly sand, poorly‐graded sand, and well‐graded sand below the water table or where perched groundwater is encountered. Large areas of unsupported fine‐grained soils will tend to ravel, squeeze into the excavations, particularly where seepages from perched water occur.

Asphalt Impregnated Soils

Asphalt impregnated soils are found below 11 feet deep. This is within the Lakewood Formation and San Pedro Formation. Soils comprising, silt, silty sand, and clayey sand impregnated with asphalt will exhibit apparent cohesion and can be expected to stand for up to 24 hours before starting to ravel from unsupported walls. The asphaltic soils should stand long enough to permit placement of lagging prior to sloughing of side walls.

1 Running ground is defined as cohesionless material above the water table that runs immediately from unsupported sections of the tunnel and accumulates below the location of the run.

2 Flowing ground is defined as ground combined with water that immediately flows (like a viscous fluid) out of unsupported sections of tunnel.


8.0 - Building and Utility Protection Measures


8.0 BUILDING AND UTILITY PROTECTION MEASURES

8.1 Settlement Adjacent to Shaft Excavation Ground surface settlements adjacent to the shaft excavation were estimated using empirical surface settlement envelopes. It was assumed that the soils fall under the category of “stiff clay, residual soil, and sand” as described in Clough and O’Rourke (1990). The maximum settlements at the wall boundary were assumed to be 0.1 percent of the wall height with a triangular distribution of settlement for a lateral distance of twice the wall height extending from the wall boundary. The methodology assumes that maximum ground surface settlements are equal to the volume of ground displaced across the wall boundary.

Only one building is within the potential zone of influence of the shaft excavation. It is anticipated that damage to the building at 6010 Wilshire Boulevard will be limited to cosmetic, nonstructural damage.

8.2 Protection of Structures and Utilities As part of the program to protect 6010 Wilshire Boulevard, the Contractor is responsible for installing instrumentation. The geotechnical monitoring will establish:

1. Baseline conditions prior to start of shaft excavation.

2. Ground movements and building settlement caused by shaft excavation as it proceeds downwards and until the shaft is completed.

3. Confirmation that settlement effects due to construction have ceased.

To establish a baseline for assessment of actual damage resulting from shaft construction, Metro will conduct a preconstruction survey of the structure. This will include a photographic or video record of cracks and other pre‐existing signs of distress or damage in the building.

Metro will use the baseline assessment, inspections and the geotechnical instrumentation data to assess damage to the building at 6010 Wilshire Boulevard from the construction activities and to monitor Contractor performance. Should observation of excavation‐induced movements indicate that settlement in excess of ¾ inch, the Contractor will be required to take appropriate action in accordance with Technical Specification Section 02158, Compaction Grouting, Protection and Restoration of Structures.

8.3 Testing Program As well as the Contractor’s requirements for instrumentation for building and utility protection, geotechnical instrumentation to monitor ground behavior and the performance of the soldier pile and lagging support system will be installed. For this program, the contractor is required to support instrument installation and monitoring activities of instruments installed and monitored by others. The proposed testing program is described in the Contract Documents.


9.0 - References


9.0 REFERENCES

9.1 Geotechnical Baseline Report References American Association of State Highway and Transportation Officials (AASHTO), 1988, Manual of Subsurface Investigations, Washington D.C.

Boduszynski M.M., C.E. Rechsteiner, A.S.G.Shafizadeh and R.M.K. Carlson, Composition and Properties of Heavy Crudes, UNITAR Centre for Heavy Crude and Tar Sands, 1998.

Clough G.W. and T.D. O’Rourke, 1990, Construction Induced Movement of In‐Situ Walls, Proceedings, Design and Performance of Earth Retaining Structures, Cornell University, American Society of Civil Engineers, Geotechnical Special Publication No. 25, pp 439‐470.

GPI, 2010, Report of Observation and Testing during Grading, Demolition and Construction, Surface Parking Lot, 6006 Wilshire Boulevard and 731 South Ogden Drive.

Los Angeles County Metropolitan Transportation Authority (Metro), 2012, Westside Subway Extension Geotechnical Data Report – Exploratory Shaft.

Los Angeles County Metropolitan Transportation Authority (Metro), 2011,. Westside Subway Extension Final Geotechnical and Environmental Report.


Appendix A - Asphalt Content Test Results

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APPENDIX A ASPHALT CONTENT TEST RESULTS




APPENDIX A ASPHALT CONTENT TEST RESULTS Test Results

The results of index tests on 15 samples from the three borings drilled at the Exploratory Shaft are presented in Table B‐1.

Table B-1: Index Test Results

Boring No. Depth (feet) USCS

Soil Classification Asphalt Content Water Content Bulk density

(lb/cu ft)

G-350

25.5 SP-SM 12.3% 10.3% 126

35.5 SP-SM 17.5% 3.7% 119

46.5 SP-SM 17.7% 8.3% 120

60.5 SP 10.8% 2.8% 127

70.5 SM 12.2% 7.0% 129

G-351

24.5 SM 14.3% 4.5% 120

35.5 SM 16.2% 3.4% 119

45.5 SP-SM 18.7% 3.4% 121

55.5 SP 15.7% 4.0% -

75.5 SM 13.0% 12.2% 120

S-350

26.5 SM 13.7% 4.7% -

36.5 SM 17.8% 3.4% -

46.5 SP-SM 16.3% 1.6% -

57.5 SP-SM 16.2% 1.4% -

69.0 SM 18.5% 3.6% -

AVERAGE 15.4% 5.0% 122

STANDARD DEVIATION 2.5% 3.1% 4

The asphalt content represents the percentage of asphalt by weight of the total dry weight of soil.




Results from the n‐Paraffin Atmospheric Equivalent Boiling Point scale (Refer to Boduszynski et al, 1998)

Tests performed on soil samples from Borings G‐310, G‐311 and G‐312 (refer to Metro, 2011 for boring locations)

0

100

200

300

400

500

600

700

800

1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 81

Temperature (C˚)

Percent of Sample Evaporated

Distillation Product of Asphalt Impregnated Soil Samples

G‐312 @ 50' G‐312 @ 85' G‐312 @ 90' G‐311 @55' G‐310 @ 70'

Gasoline

Jet Fuel

Diesel

Motor Oil Bunker Fuel

Asphalt or Tar


Appendix B - Case Studies

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APPENDIX B CASE STUDIES




APPENDIX B CASE STUDIES Case Study 1 - Shaft for Alvarado Crandall Relief Sewer

During construction of the Alvarado Crandall Relief Sewer for the City of Los Angeles, a shaft was excavated through ground impregnated with asphalt. The shaft was located in the Westlake/Silver Lake area of the City. It had an inside diameter of 14 foot and was drilled to a depth of approximately 100 feet through Puente Formation. Following the drilling of the shaft, it was supported with corrugated metal sheeting.

The asphalt was encountered in isolated seams within the Puente Formation bedrock. With the shaft unlined, asphalt could be observed oozing out of isolated seams within the bedrock formation. With the lining in‐place, the shaft walls were relatively well sealed. The shaft remained open for a period of about 6 months during which time asphalt deposits leaked into the shaft bottom from the underlying formation filling it with a 1 to 2 feet thick layer of asphalt during a period of about 1 month if left unattended and making for messy working conditions in the shaft bottom. As well as sticking to surfaces it came into contact with, the asphalt caused discoloration of clothes and equipment. Steam cleaning was used to remove the asphalt contamination from equipment.

Figure B-1 - Asphalt filled Shaft invert – Shaft on Alvarado Crandall Project

Methane and hydrogen sulfide were also anticipated during shaft construction. Methane was measured in the shaft and was recorded at 100 per cent of its lower explosive limit (LEL). This resulted in changes to the classification of the shaft. It was deemed “gassy” by Cal OSHA. With changed working conditions including 24‐hour ventilation, the methane concentrations became negligible. Hydrogen sulfide was not identified at the site.

Case Study 2 – Methane Gas Build-up in Fairfax District

Seepage of methane upwards through the soils in the Fairfax area is a known occurrence. Such incidents in the 1980’s led the City of Los Angeles to identify zones within the City where methane build‐up can occur and must be addressed for new buildings to obtain planning permission.




In 1985, an explosion occurred as the result of methane build‐up in a room at the “Ross Dress for Less” Store on Third Street. The accepted explanation for the gas build‐up was that the gas originated from the Salt Lake Oil field and had migrated to the surface along a combination of the 3rd Street Fault and possibly along abandoned well borings. The reinjection processes used to enhance oil recovery may have contributed to the accumulation of gases at the surface.

In 1989, a similar methane gas build‐up occurred on 3rd Street and although not resulting in an explosion, did produce a fountain of mud, water and methane gas at the surface. This resulted in further upgrading of the City Building Code.

Methane bubbling to the surface is a regular phenomenon within the tar pools in Hancock Park.

Case Study 3 –LACMA Underground Parking Structure and Project 23

In 2006, the Los Angeles County Museum of Art (LACMA) began construction of a twin 4‐story high steel structure facing Wilshire Boulevard and a 2‐levels deep underground parking structure behind the buildings. The parking structure was constructed with reinforced concrete. The garage is a two level structure constructed with cast‐in‐place reinforced concrete. The garage is supported on a mat foundation. It was constructed in an excavation approximately 25 feet deep.

The subsurface conditions at the site consist of shallow fill and stiff clay underlain by asphaltic sands. Groundwater was within 5 ½ feet of the ground surface (ground surface was approximately El. 169). The asphalt sand void spaces are filled with a mixture of asphalt and water. The water and asphalt will drain independently. The water drains relatively quickly but the presence of the asphalt reduces the permeability. Because of its high viscosity, the asphalt drains relatively slowly.

The excavation for the underground parking structure varied from about 16 to 22 feet deep. Excavation into the tar sands was anticipated and did occur. The excavation for the parking structure was supported by a combination of braced soldier pile and tiebacks. Altogether, 224 soldier piles (W16 x 89) were installed. The holes (nominal diameter of 24 inches) for the soldier piles were drilled using flight auger drill rigs. With the steel beams placed in the holes, concrete (2,500 psi) was placed into the holes to excavation subgrade with the remainder of the holes backfilled with sand/cement slurry. Continuous timber lagging was installed between the soldier piles. The timber was treated to prevent decay. Soil or sand/cement slurry was placed as backfill behind the lagging.

For the soldier piles with tiebacks, a single level of tiebacks (at El. 160) at 8‐ft center was installed. The holes for the anchors were drilled with a 6‐inch diameter continuous flight auger mounted on an excavator. Strand or rod anchors were installed in the holes. The shafts were backfilled with neat cement for the anchorage with sand/cement slurry used to backfill the rest of each hole following testing of each tieback anchor. Each anchor was post‐grouted with the post‐grouting procedures adjusted to achieve design capacities.

Dewatering was performed for the excavation. The dewatering system consisted of nine deep wells around the excavation perimeter and a system of interior trenches. The deep wells were installed using a 24‐inch diameter bucket‐type drill rig. The wells were drilled to depths of 50 to 60 feet. Water eventually filled the wells but because of the low permeability of the soils, only minor seepage occurred in the excavations. Asphalt present within the groundwater made maintenance of the dewatering system difficult. As a result, the wells and pumps periodically became plugged with asphalt and were required to be replaced periodically.




Based on information presented in the WSE Exploratory Shaft Paleo Mitigation Plan, a boring drilled at the LACMA underground parking structure site encountered fluid petroleum under pressure. As a result, several hundred gallons of petroleum surfaced within a few minutes, which were later removed by vacuum truck.

During the course of construction of the underground parking structure, 16 fossil deposits were discovered, including the semi‐articulated, largely complete skeleton of an adult mammoth. To save and remove the fossils, large wooden boxes were built around each deposit (see the Paleo Mitigation Plan for further details). There were 23 boxes in all with some deposits required to be divided into several boxes. In the late 2000’s, the boxes were removed from the excavation and moved to their present location immediately north of the Pit 91 complex In Hancock Park. The boxes are on view to the public and excavators from the Page Museum are working to recover the fossils with the project being called "Project 23." In addition to the boxes, there were 327 buckets of fossil material recovered from the LACMA salvage site for paleontologists to clean and sort through (see www.tarpits.org/ for further information on Project 23 and Pit 91).


Appendix C - Geologic Profile of the Exploratory Shaft

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APPENDIX C GEOLOGIC PROFILE OF THE EXPLORATORY SHAFT