TOMF_Geotechnical_Report_02.28.2024.pdf

PRELIMINARY

GEOTECHNICAL ENGINEERING REPORT

Proposed Transit Operations and Maintenance Facility (TOMF)

APN: 5746-025-907 and -908 2180 East Foothill Boulevard and 2211 East Walnut Street

Pasadena, California File No.: LA-01684-02

Project No.: 306890-001

Prepared For

HDR

February 28, 2025

Prepared By

Earth Systems Pacific 2122 East Walnut Street, Suite 200

Pasadena, California 91107

(626) 356-0955

February 28, 2025 File No.: LA-01684-02

HDR

350 South Grand Avenue, Suite 2900 Los Angeles, California 90071

Attention: Patrick Kim

Subject: Preliminary Geotechnical Engineering Report Proposed Transit Operations & Maintenance Facility (TOMF) APN: 5746-025-907 and -908 2180 East Foothill Boulevard and 2211 East Walnut Street Pasadena, California

Presented herewith is the Preliminary Geotechnical Engineering Report prepared, as authorized, for the site of the proposed Transit Operations & Maintenance Facility in the City of Pasadena, California. The conclusions and recommendations contained in this report are based upon Earth Systems’ understanding of the proposed parking structure and maintenance facility and on analyses of the data obtained from the field and laboratory testing programs.

The recommendations provided in this report generally pertain to criteria for site grading and foundation design. Earth Systems strives to provide analyses and recommendations in accordance with the applicable standards of care for the geotechnical engineering profession at the time the study is conducted. The submittal of this report marks the completion of the scope of geotechnical engineering services described in Earth Systems’ proposal dated March 27, 2024, and authorized on October 24, 2024. Other services which may be required, such as grading observation and construction testing, are additional services that will be billed according to the Fee Schedule in effect at the time such services are provided. Budgets for these services, which are dependent upon design and construction schedules, can be provided when requested.

Earth Systems appreciates this opportunity to provide professional geotechnical engineering services for this project. If you need clarification of the information contained in this report, or if Earth Systems can be of additional service, please contact the undersigned.

Respectfully submitted, Earth Systems Pacific

Christopher F. Allen, E.G.

Project Engineering Geologist

Distribution:

Patrick Kim – Patrick.Kim@hdrinc.com

TABLE OF CONTENTS

PAGE

INTRODUCTION

SITE DESCRIPTION

PROJECT DESCRIPTION

PURPOSE AND SCOPE OF SERVICES

SITE HISTORY

FIELD EXPLORATION

LABORATORY TESTING

GEOLOGIC SETTING

SUBSURFACE CONDITIONS

GROUNDWATER

INFILTRATION TEST PROCEDURES

GEOLOGIC HAZARDS

FAULT RUPTURE

SEISMIC SHAKING

SECONDARY SEISMIC HAZARDS

OTHER POTENTIAL HAZARDS

DISCUSSION AND CONCLUSIONS

SEISMIC DESIGN PARAMETERS

SITE GRADING

TEMPORARY EXCAVATIONS

SOIL COMPACTION

FOUNDATION DESIGN AND SETTLEMENTS

STORMWATER INFILTRATION

RECOMMENDATIONS

A. SITE PREPARATION

B. EXCAVATIONS

C. TEMPORARY SHORING

D. CONVENTIONAL FOUNDATIONS (PARKING STRUCTURE)

E. CONVENTIONAL FOUNDATIONS (MAINTENANCE STRUCTURE)

F. PIER DESIGN

G. PIER INSTALLATION

H. SLAB-ON-GRADE CONSTRUCTION

I. RETAINING WALLS

J. EXPANSIVE SOIL

K. UTILITY TRENCHES

L. PRELIMINARY PAVEMENT SECTIONS

M. SOIL CHEMICAL TESTING

N. SUB-DRAINAGE AND WATERPROOFING

CLIENT OPTIONAL SERVICES

LIMITATIONS AND UNIFORMITY OF CONDITIONS

CLOSURE

REFERENCES

PLATES

PLATE I Site Location Map PLATE II Regional Geologic Map PLATE III Seismic Hazard Zones Map PLATE IV Site Exploration Map PLATE V Geologic Cross Sections PLATE VI Retaining Wall Backdrain Details PLATE VII Shoring Wall Backdrainage Schematic APPENDIX A Previously Completed Test Borings and Laboratory Test Results APPENDIX B Logs of Test Borings APPENDIX C Laboratory Test Results APPENDIX D Seismic Data APPENDIX E Supporting Calculations

PRELIMINARY GEOTECHNICAL ENGINEERING REPORT

PROPOSED TRANSIT OPERATIONS AND MAINTENANCE FACILITY (TOMF)

APN: 5746-025-907 AND -908

2180 EAST FOOTHILL BOULEVARD

AND 2211 EAST WALNUT STREET

PASADENA, CALIFORNIA

INTRODUCTION

This Preliminary Geotechnical Engineering Report has been prepared for the site of the proposed transit operations and maintenance facility (TOMF). The purpose of this study was to evaluate the geotechnical engineering characteristics of the on-site subsurface soils relative to the anticipated development.

This report includes:

1. Descriptions of the field exploration and laboratory tests performed.

2. Conclusions and recommendations relating to construction of the proposed parking structure and maintenance facility based upon analyses of data obtained from the exploration and testing programs, and on knowledge of the general and site-specific characteristics of the subsurface soils.

SITE DESCRIPTION

The approximate one and one quarter-acre site is comprised of two contiguous properties; 2180 East Foothill Boulevard and 2211 East Walnut Street in the City of Pasadena, Los Angeles County, California. The westerly property fronts on East Foothill Boulevard and extends south to East Walnut Street on the south. The site is one lot east of Craig Avenue and is currently occupied by a single-story structure with an asphalt parking lot that was previously used as a restaurant; the southern portion of the property off of Walnut Street was previously a railroad right-of-way. An approximately two-foot-tall masonry wall separates the two portions of this property. This property has more recently been used as a temporary fire station and is now used for Pasadena Transit parking. The easterly property that fronts on East Craig Avenue was previously used as an automobile repair shop.

The northern wall of the repair shop structure is constructed up to the northern property line and two commercial buildings located on the contiguous property to the north are also constructed to that property line.

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Access to the property is available from both East Foothill Boulevard from the north and East Walnut Street from the south (see Site Exploration Map, Plate IV). Topographically, the property descends approximately six feet from East Foothill Boulevard to East Walnut Street.

PROJECT DESCRIPTION

Based on a review of the preliminary site plan provided by HDR, Earth Systems understands that the proposed project will consist of a transit parking structure and a maintenance facility. The facility will include a four-level parking structure on the westerly property and a two-story maintenance and operations building on the easterly property, the buildings will extend to the property lines. The parking structure will include one subterranean level that will be 14 to 23 feet deep. The maintenance and operations building will be at-grade construction (see Geologic Cross Sections, Plate V). Earth Systems has not received foundation plans for the proposed structure as of this writing. However, based upon the discussions with the project structural engineer (Miyamoto International, Inc.) structural loads for the parking structure will be up to 30 kips per linear foot (plf) for bearing walls and 1,800 kips for isolated columns. Structural loads for the maintenance facility will be up to 12 kips per linear foot (plf) for bearing walls and 600 kips for isolated columns

Temporary shoring and export grading will be required during construction and sewage disposal will be provided by the public sewer system. These assumptions were used as the basis for the exploration, testing, and analyses programs, and for the recommendations contained in this report.

If the anticipated foundation loads or other site conditions vary significantly from the values stated herein, the recommendations should be reconfirmed prior to completing project plans.

PURPOSE AND SCOPE OF SERVICES

The purpose of Earth Systems’ services was to evaluate the project site soil conditions, and to provide preliminary geotechnical engineering conclusions and recommendations relative to the project site and the proposed construction. Earth Systems’ scope of services included the following:

A. A general reconnaissance of the site and review of previous geotechnical reports for the site.

B. Shallow subsurface exploration of the project site by drilling five hollow-stem auger test borings (B10 through B14).

C. Percolation tests were completed in one boring to aid in the design of a stormwater mitigation system.

D. Geotechnical laboratory testing of selected soil samples obtained from the exploration program conducted for this project.

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E. Geotechnical engineering analyses of the data obtained from the exploration and testing programs.

F. A summary of findings and recommendations in this written report.

Contained in this report are:

A. Discussions on local and site-specific soil conditions.

B. Results of laboratory tests and field data.

C. Recommendations relating to the proposed parking structure and maintenance facility, including allowable foundation bearing capacity, recommendations for foundation design, estimated total and differential foundation settlements, site grading criteria, lateral earth pressures, soil expansion characteristics, soil corrosion characteristics, and preliminary pavement section design.

SITE HISTORY

The City of Pasadena Building and Safety Division archives were reviewed for available geotechnical or grading reports for the subject site and contiguous properties; however, no reports were available.

According to the Los Angeles County Assessor’s database, the northern property was developed in 1967. Based on aerial imagery of the area, two structures existed on the northern property by 1960.

The southern portions of the properties were part of a previous railroad bed.

In 2016, Earth Systems Southern California (ESSC) prepared a geotechnical report dated January 23, 2016, in support of a maintenance and parking facility with a basement level at 2180 East Foothill Boulevard. At that time, the project plans only included the western parcel. Exploration for that report included drilling nine borings (B1 through B9) to a maximum depth of 50 feet. Those borings are included in Appendix A and are plotted on the attached Site Exploration Map (Plate IV). The laboratory testing from that report are also included in Appendix A. Since the completion of that report, 2211 East Walnut Street was acquired by the City of Pasadena and the project plans have changed to include both properties.

FIELD EXPLORATION

The field exploration for this study was conducted on October 28, 2024. Field exploration included drilling and sampling five exploratory hollow-stem auger test borings (B10 through B14) to depths of approximately 30 to 50 feet below the existing ground surface. The approximate locations of the exploratory test borings, as indicated on the attached Site Exploration Map (Plate IV), were determined by sighting and tape measuring from existing surrounding improvements. The locations

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of the borings should be considered accurate only to the degree implied by the measurement method used. The logs of the test borings are included in Appendix B.

A bulk (disturbed) sample of the subsurface soils was obtained from tailings generated during excavation. This sample was secured for classification and testing purposes and represents a mixture of soils within the noted depths.

Additional soil samples (“ring samples”) were secured from within the test borings using a three-inch outside diameter ring sampler (ASTM D 3550). A 140-pound hammer falling approximately 30 inches (ASTM D 1586) drove the sampler. The hammer was operated by an automatic trip mechanism. The hammer operated at a rate of approximately 30 to 40 blows per minute. The number of blows required to drive the sampler 18 inches was recorded in 6-inch increments and recorded on the boring logs. Recovered ring samples were sealed in plastic containers and transported to the Earth Systems laboratory for further classification and testing.

Further sampling and collection of disturbed soil samples was accomplished using the Standard Penetration Test (SPT) sampler in accordance with ASTM D 1586. The SPT sampler is a split barrel sampler with a 1-3/8 inch inside diameter. This sampler is also driven by a 140-pound hammer falling approximately 30 inches. The number of blows required to drive the sampler 18 inches was recorded in six-inch increments and recorded on the boring logs. Soil samples recovered by this method were sealed in plastic bags. Recovered soil samples were transported to the Earth Systems laboratory for further classification and testing.

The logs of test borings for this report, included in Appendix B, represent Earth Systems’ interpretation of the field logs prepared for each test boring by Earth Systems’ staff, along with their interpretation of soil conditions between samples and results of laboratory tests. While the noted stratification lines represent approximate boundaries between soil types, the actual transitions may be gradual.

LABORATORY TESTING

After visual and tactile classification in the field, the soil samples were brought to Earth Systems’ laboratory. Soil samples were classified visually in accordance with the Unified Soil Classification System and the following tests were conducted:

A. Moisture content and dry unit weight for soil ring samples were evaluated (ASTM D 2937 and

ASTM D 2216).

B. Soil grain size was evaluated using Particle Size Analysis: Mechanical Method and Hydrometer

Method (ASTM D 422).

C. The relative strength characteristics of selected ring samples and a compacted bulk sample of the near-surface soils were estimated from the results of direct shear tests (ASTM D 3080).

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One of the compacted samples were remolded to approximately 92% of the maximum dry density (ASTM D 1557). The specimens were placed in contact with water for at least 24 hours before testing and then sheared under normal loads ranging from approximately 1 to 4 kips per square foot (ksf). Samples were sheared to sufficient strains so that both peak and ultimate values were evaluated.

D. Consolidation tests (ASTM D 2435) were conducted on selected soil ring samples. The maximum stress during testing was 12.8 ksf. The samples were saturated at 0.8 ksf to check the hydroconsolidation potential and unloaded to 0.8 ksf to check the rebound characteristics.

E. Expansion potential was evaluated using the Expansion Index (EI) test (ASTM D 4829).

F. Compaction characteristics were evaluated using the “modified Proctor” (Maximum Density-

Optimum Moisture) test (ASTM D 1557).

G. Soil chemistry tests consisted of pH, resistivity, conductivity, and a variety of cations and anions including soluble sulfate. Soil chemistry tests were performed by HDR-Schiff on a soil sample provided by Earth Systems.

Refer to Appendix C for the laboratory test results. Presentation of the test results provides only that information considered pertinent. References to ASTM and other test standards refer to the standard currently in effect.

GEOLOGIC SETTING

The project site is within the northwestern limits of the San Gabriel Valley which is located in the Transverse Ranges geomorphic province. The Transverse Ranges is one of the most active tectonic/seismic areas of the United States and is composed of parallel, east-west trending mountain ranges and sediment-filled valleys, one such valley is the San Gabriel Valley. The distinctive geologic structure of the Transverse Ranges is dominated by the effects of north-south compressive deformation that result in thrust faulting, strike-slip faulting and bedrock folding. These active geologic features are attributable to convergence between the “Big Bend” of the San Andreas fault and northwestern motion of the Pacific Plate and have caused thrust fault related earthquakes such as the 1994 Northridge, the 1971 San Fernando, and the 1987 Whittier Narrows earthquakes.

The active Raymond fault zone is one of the most significant geologic features of the area and is located approximately one and a half miles south of the site. Other active or potentially active faults in the immediate vicinity of the site include the Verdugo fault located approximately two and a half miles west of the site and the Sierra Madre fault located approximately three miles north of the site.

The site does not fall within a currently designated Earthquake Fault Rupture Hazard (“Alquist- Priolo”) Zone, liquefaction hazard zone nor slope hazard zone as currently identified by CGS on the

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Seismic Hazard and Earthquake Fault Zones Map for the Mount Wilson Quadrangle dated 1999 and 2017, respectively.

SUBSURFACE CONDITIONS

Artificial fill (af) soils were observed to vary across the site. The observed depth of fill ranged from negligible at borings B1 through B6 and B9, approximately four feet at the location of B8, approximately 7.5 feet around the locations of B10 through B12 and B14, and up to nine feet at B7.

These fill soils were found to consist of loose to medium dense sand and silty sand and medium stiff to hard sandy silt (SP, SM and ML soil types based upon the Unified Soil Classification System).

Native soils comprised of alluvium (Qa) were found to consist predominantly of loose to very dense sands and silty sand (SP, SW and SM soil types). The logs of the test borings in Appendix B contain more detailed descriptions of the soils encountered.

Based upon results of the Expansion Index (EI) tests (ASTM D 4829) conducted for this investigation, the upper on-site soils are considered to have a very low expansion potential. Refer to the Expansive Soil section in the Recommendations for explanations and recommendations for dealing with expansive soils.

Per ASCE 7-16 Table 20.3-1, the site should be classified as a stiff soil profile (Site Class D).

GROUNDWATER

Free groundwater was not encountered to the maximum depth drilled of 50 feet. The nearest well monitored by the Los Angeles County Department of Public Works (LACDPW) is well #4085A (located approximately half a mile northwest of the subject site at a ground elevation of 791.20 feet above mean sea level). Groundwater was most recently measured in this well at a depth of 259 feet (October 17, 2022). The highest groundwater level was measured in this well at a depth of 197.7 feet (October 27, 2005). Based on the Seismic Hazards report for the Mount Wilson Quadrangle (CDMG, 1998), the historic shallowest groundwater near the project site is approximately 100 feet.

Fluctuations in groundwater levels may occur due to variations in rainfall, regional climate, and other factors.

INFILTRATION TEST PROCEDURES

On October 29, 2024, the percolation rate of near-surface soil was evaluated in an 8-inch diameter borehole (B10). The infiltration testing was conducted in general conformance with the Boring Percolation Test Procedure (L.A.Co. GMED, 6/30/2021).

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Upon completion of the excavation a perforated PVC pipe was installed in the test hole. The percolation test hole was then filled with clean water to pre-soak the hole prior to testing. The hole was later refilled to the specified depth with clean water. During the test, successive readings of the percolation flow were completed over 10-minute intervals. The water level in the test hole was first recorded and then the water level was raised back up to the initial depth. Readings continued until a stabilized flow was recorded. The infiltration rate has been determined by dividing the percolation rate by a reduction factor in accordance with GMED guidelines; the results are summarized in the following table.

Summary of Infiltration Test Results

Test Pit/Boring

Test Depth (feet)

Estimated Infiltration Rates

(inches per hour) (gal/sf/day)

B10 20 to 50 0.3 3.8

GEOLOGIC HAZARDS

Geologic hazards that may affect the proposed development include seismic shaking and other earthquake-related hazards, flooding, and erosion.

Fault Rupture

The site is not located within a currently delineated Earthquake Fault Hazard (“Alquist-Priolo”) Zone (Hart and Bryant, 1999). In addition, no known active faults have been identified on the site.

Therefore, the potential for active fault rupture is very low. While fault rupture would most likely occur along previously established fault traces, future fault rupture could occur at other locations.

Seismic Shaking

Based on the current understanding of the geologic framework of the site area, the seismic hazard with the highest probability of affecting the site is ground shaking resulting from an earthquake occurring along any of several major active and potentially active faults in the site vicinity. The site is located in Southern California, which is a seismically active area where large numbers of earthquakes are recorded each year. The closest known fault to the site is the Raymond fault as discussed above. The Raymond fault most recent produced a magnitude 4.4 earthquake in August of 2024.

Secondary Seismic Hazards

Secondary seismic hazards related to ground shaking include liquefaction, ground deformation, areal subsidence, tsunamis, and seiches.

Liquefaction: Liquefaction is defined as a loss of strength of saturated cohesionless soil caused by seismic shaking. Soil types most susceptible to liquefaction are loose, saturated silty to clean fine

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sands. The project site is not located within a defined liquefaction hazard zone as shown on the Mount Wilson Quadrangle (CDMG, 1998). Based on the soil borings and the regional groundwater data provided by the LACDPW, groundwater beneath this site is in excess of 50 feet below the existing ground surface. It is generally accepted that liquefaction of soils in excess of 50 feet below grade has a minimal impact on structures at the surface. Therefore, because of the lack of near-surface groundwater beneath the site, the potential for liquefaction-induced damage to structures at this site is considered negligible.

Seismic-Induced Subsidence: The degree of earthquake-induced ground subsidence was estimated using commonly accepted procedures (Tokimatsu and Seed 1987, Pradel 1998). In the event of a nearby earthquake as discussed above, liquefaction-induced ground subsidence of approximately

0.4 inches may be anticipated. The resulting differential settlement may be assumed to be approximately one-half of the maximum total ground subsidence value for design purposes (SCEC, 1999). Thus earthquake-related differential settlement is estimated to be approximately 0.2 inches.

Refer to Appendix E for results of the analyses.

Ground Damage and Lateral Spreading: The potential for ground damage (i.e. sand boils and ruptures) and lateral spreading are considered negligible due to the depth of groundwater and relatively flat topography surrounding the vicinity of the site.

Earthquake-Induced Slope Instability: The site is not located within a mapped earthquake slope hazard zone (CDMG, 1998). The slopes surrounding the site have been graded to a two horizontal to one vertical gradient, include drainage structures, and are vegetated; therefore, the potential hazards from earthquake-induced slope instability and landslides are considered negligible.

Other Potential Hazards

Flooding: According to FEMA map number 06037C1400F dated 9/26/2008), the site lies within a “Zone X”: an “area of minimal flood hazard.” Earthquake-induced flooding is caused by failure of dams or other water-retaining structures triggered by earthquakes. Based the Summary of Hazards Map (II) in the Safety Element of the General Plan City of Pasadena, California (Earth Consultants International, 2002), the site does not fall within the approximate inundation limits of this dam.

Tsunamis and Seiches: Tsunamis are large ocean waves generated by large-scale, short-duration submarine earthquakes. Tsunami waves are capable of traveling great distances (over 1,000 miles) at high speeds and damaging low-lying coastal regions. As the project site is several miles from the sea shore, the risk of tsunami inundation is considered remote at the site. Seiches are waves formed from oscillations in enclosed or restricted bodies of water (i.e., harbors, lakes). Seiches can also cause water to overtop reservoirs and lakes. The risk of flooding from a seismically-induced seiche is considered improbable because of the site’s location with respect to restricted bodies of water.

Hydroconsolidation: Hydroconsolidation or hydrocollapse typically occurs in relatively dry, slightly cemented, loose sandy soils and poorly compacted fills that shrink or “collapse” when saturated.

The earth materials at the site consist of fill overlying alluvial sands. Hydroconsolidation of 0.6 to

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1.4% was indicated by the consolidation testing conducted on the site soil directly below the proposed structure. Therefore, hydrocollapse is not considered a significant potential hazard for the subject site.

Slope Stability: The site is relatively level; therefore, the potential hazards from earthquake-induced slope instability and landslides are considered negligible.

DISCUSSION AND CONCLUSIONS

Seismic Design Parameters

The 2022 California Building Code (CBC) will be applicable to the proposed project. The building code includes several seismic design parameters that are influenced by the geographic site location with respect to active and potentially active faults, and with respect to subsurface soil or rock conditions.

The seismic design parameters presented herein were calculated by determining the jobsite coordinates and entering them into the Structural Engineers Association of California (SEAOC), Seismic Design Maps Calculator. The current ground motion calculator determines ground motions in accordance with procedures outlined in the 2022 CBC and ASCE 7-16. These parameters are appropriate for a 2 percent probability of exceedance in 50 years, are included in Appendix D and summarized in the table below.

Summary of Seismic Parameters

Site Class (ASCE 7-16 – Table 20.3-1) D

Risk Category (CBC 2022 – Table 1604.5) II

Maximum Considered Earthquake (MCE) Ground Motion

Site Modified Peak Ground Acceleration - PGAM 1.005g

Spectral Response Acceleration, Short Period – Ss 2.096g

Spectral Response Acceleration at 1 sec. – S1 0.768g

Site Coefficient – Fa 1.0

Site Coefficient – Fv 1.7

Site-Modified Spectral Response Acceleration, Short Period – SMS 2.096g

Site-Modified Spectral Response Acceleration at 1 sec. – SM1 1.306g

Design Earthquake Ground Motion

Short Period Spectral Response – SDS 1.397g

One Second Spectral Response – SD1 0.870g

Reference: SEA, 2024, Latitude: 34.149 degrees, Longitude: -118.105 degrees

The seismic factor S1 is greater than 0.2g and the Site Class is D. Therefore, a site-specific ground motion hazard analysis may be required. Per ASCE 7-16, Table 11.4-2, 1.7 has been used for Fv in the summary above since S1 is greater than 0.6. The project structural engineer shall determine if an

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exemption can be applied in accordance with ASCE 7-16 Section 11.4.8. If it is determined that a site-specific ground motion hazard analysis is necessary, Earth Systems can provide that analysis under a separate cover.

Site Grading

As mentioned in the Soil Conditions Section, artificial fill soils are present within the project site to depths of up to approximately nine feet below existing grade. To provide more firm uniform bearing for the proposed at-grade structure foundations and slab-on-grade construction, it is recommended that at a minimum the upper eight feet of near surface soils with a minimum of three feet below proposed foundations be removed and recompacted. The subterranean parking structure may be supported on firm native soil; however, the finished grade for the parking structure should be scarified, moisture conditioned and properly compacted. At least one foot of soil should be removed and recompacted beneath all exterior pavements and slabs. The bottom of all remedial excavation bottoms should expose firm, native soil. Refer to Section A of the Recommendations of this report for more detailed discussions and recommendations regarding site preparation.

Temporary Excavations

Excavations up to at least 23 feet in depth are anticipated for the parking structure basement walls and approximately eight feet in depth for the remedial grading in support of at-grade construction.

Those excavations will undermine adjacent properties and foundations. Refer to Sections B and C of the Recommendations section of this report for more detailed discussions and recommendations regarding site excavations.

Soil Compaction

Consideration should be given to the type of equipment to be used for compaction at the site.

Different types of equipment are more effective with some soil types than with others. Failure to provide the most appropriate equipment could result in an inability to achieve the required degree of relative compaction, disturbance or displacement of subsequent and adjacent layers of fill, and/or the potential cost of removal of inadequately compacted fill that has been placed and subsequent delay in the grading progress.

Conventional compaction equipment (bulldozers, self-propelled or static or dynamic sheepsfoot compaction rollers, heavy rubber-tired construction equipment, etc.) has a limited ability to consolidate layers of fill to the required density. Typically, loose layer thickness should not exceed 6- 8 inches for heavy construction equipment and 2-4 inches for light manual equipment. Thicker layers of fill may be consolidated by utilizing specialized deep dynamic compaction; however, this requires detailed geotechnical evaluation prior to being used.

Fine grained soils (clays and silts) typically should not be subjected to vibration or heavy widely distributed loads (such as smooth rollers or wide rubber-tired construction equipment) during the compaction process, as this will cause an increase in the soil pore pressure resulting in ‘pumping’ or

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failure to consolidate the soil particles by expelling water and air. These soil types are best compacted by using a ‘kneading’ action (such as a ‘sheepsfoot’ compactor) or impact from a sharp blow on a small area (such as a dynamic or high-speed tamping foot).

Cohesionless, non-plastic soils (sands and sand/gravel combinations) typically are best compacted using a wide, smooth, heavy static device (roller, wheels, tires etc.) or with the addition of vibration to these types of equipment. Narrow profile wheels, tires, etc., and high point load equipment typically will not perform as efficiently and will cause displacement and loosening of the adjacent soil.

Foundation Design and Settlements

If the preliminary recommendations herein for site preparation and grading are followed, conventional shallow continuous and isolated foundations may be used to support the proposed structures. Footings will bear in firm native soils. Refer to the Recommendations section of this report for more detailed discussions and recommendations regarding foundation design.

If the preliminary recommendations for foundation design and construction are followed, seismic and static settlement of the proposed parking structure should not exceed approximately one inch (1”). Differential settlement of neighboring footings of varying loads, depths or sizes may be as high as fifty percent of the total settlement.

If the preliminary recommendations for foundation design and construction are followed, seismic and static settlement of the proposed maintenance structure should not exceed approximately three quarters of an inch (0.75”). Differential settlement of neighboring footings of varying loads, depths or sizes may be as high as fifty percent of the total settlement.

Differential settlement between the four-level parking structure and the two-story maintenance and operations building may be as much as one half of an inch (0.5”). Cosmetic repairs due to cracking of rigid wall coverings over time can be anticipated at the connection.

Stormwater Infiltration

Due to the relatively slow infiltration rate and the limited open area that will remain with the presently proposed development stormwater infiltration is not recommended for this project.

Instead, the design team should consider a capture and reuse or biofiltration type system.

RECOMMENDATIONS

Based upon field exploration, laboratory testing, interpretation of the data, and experience, the following recommendations should be incorporated into site preparation, design, and construction of the proposed parking structure and maintenance facility.

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A. Site Preparation

1. All vegetation, uncompacted fill, trash, pavements, abandoned underground utilities, and other debris should be removed from the proposed grading areas. Underground utilities (water, sewer, storm drain, electric, gas, cable, etc.) are anticipated within or adjacent to the proposed construction area. These utilities should be identified and relocated as required prior to performing excavations for any site grading or foundation excavations. All strippings and debris should be removed from the site to preclude their incorporation in site fill or remedial excavation backfill. Depressions resulting from such removals should have debris and loose soils removed and filled with suitable soils placed as recommended below.

2. Any seepage pits (i.e. cesspools), underground tanks, or other similar substructures should be removed in their entirety including any liquids or sediment remaining at the bottom of the pits or tanks. Any brick, concrete or steel lining should be completely removed. The void resulting from removal of the pits or tanks should be backfilled with suitable soils placed as recommended below. This may require ramping and/or laying back side slopes to an angle to allow safe entry of personnel and equipment. Alternatively, deep shaft seepage pit excavations may be backfilled with a low-cement concrete slurry mix to within 5 feet of proposed final grade or proposed footing elevations. The final 5 feet should consist of compacted engineered fill as described below.

3. To minimize potential settlement problems associated with structures supported on a non-uniform thickness of compacted fill, the geotechnical engineers should be consulted for site grading recommendations relative to backfilling large and/or deep depressions resulting from removals under Item 1.

4. To provide a more firm uniform bearing conditions for the proposed at-grade structure foundations and slab-on-grade construction, Earth Systems recommends the following:

a. Native soils and existing artificial fill beneath the proposed building areas, should be excavated a minimum of 3 feet below the bottom of proposed footings, 8 feet below existing grade, or through the existing fill, whichever is deeper. Remedial excavations should extend laterally, beyond the footings, to a minimum distance equal to the depth of fill below the bottom of footings, or a minimum of 5 feet, whichever is greater. The base of the remedial excavation across the building pad should be a level elevation.

Foundation plans and details should be checked carefully during grading to establish the actual bottom of footing elevations in the field.

b. All existing fill within the proposed building areas should be removed. The depth of fill ranged from approximately 4 feet (B8) to 9 feet (B7) where encountered. It should be realized that deeper depths of fill material may be encountered at the time of grading.

c. All exposed ground surfaces (subgrades) at the base of the remedial excavations should be firm, unyielding, and not excessively wet or excessively dry. If any of these conditions

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are not acceptable at the minimum recommended over-excavation depth, additional excavation will be required until suitable subgrade conditions are found. The density of the exposed ground may be tested and the "in-place dry density" ("IPD") of either 110.1 pounds per cubic foot (pcf) or 85% relative compaction may be used as criteria for acceptable subgrade.

d. The bottom of the remedial excavation should then be scarified (ripped) 6 inches and recompacted.

e. The excavated soils may be reused to backfill the remedial excavations provided they are processed to remove any deleterious materials, debris, particles greater than 6 inches maximum dimension, and are properly moisture conditioned and compacted. During replacement of the excavated soils in the remedial excavations, and recompaction of the scarified soils, the soils should be moisture conditioned to at or within 3% above optimum moisture content and be uniformly compacted to at least 90% of the maximum dry density as determined by ASTM D 1557 test procedures using mechanical compaction equipment. To aid in the compaction operation, fill should be placed in lifts not exceeding 6 inches compacted thickness. Compaction should be verified by testing.

f. The geotechnical consultant’s representative should review the site grading prior to scarification of the bottom of the remedial excavation. Local variations in soil conditions may warrant increasing the depth of remedial excavation. Any deeper areas of loose soils should be removed and be replaced as compacted, engineered fill.

5. To provide a more firm uniform bearing conditions for the proposed subterranean structure foundations and slab-on-grade construction, the bottom of the excavation shall be scarified (ripped) 6 inches, moisture conditioned to at or within 3% above optimum moisture content and be uniformly compacted to at least 90% of the maximum dry density as determined by ASTM D 1557 test procedures using mechanical compaction equipment.

6. Soils beneath any proposed exterior pavement and concrete flatwork, including a minimum lateral distance of at least 2 feet beyond pavement edges (where space is available), should be excavated a minimum of one foot below the finished subgrade. The bottom of the remedial excavation should then be scarified (ripped) 6 inches. The scarified and excavated soils should be moisture conditioned to near optimum moisture content and be uniformly compacted to at least 90% of the maximum dry density using mechanical compaction equipment. Compaction should be verified by testing.

7. Import soils should be equal to, or better than, the on-site soils in strength, expansion, compressibility, and soil chemistry characteristics. In general, import material should be free of organic matter and deleterious substances, have 100% passing a 2-inch sieve and an Expansion Index less than 20. Import soils can be evaluated prior to their use but will not be prequalified by the geotechnical consultant. Approval of import soils will be given only after

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the material is on the project, either in-place, or stockpiled in adequate quantity to complete the project.

8. Suitable imported fill soils should be moisture conditioned to at or within 3% above optimum moisture content and be uniformly compacted to at least 90% of the maximum dry density as determined by ASTM D 1557 test procedures using mechanical compaction equipment. To aid in the compaction operation, fill should be placed in lifts not exceeding six inches compacted thickness.

9. Backfill around or adjacent to confined areas (i.e. interior utility trench excavations, etc.) may be performed with a lean sand/cement slurry (aka "flowable fill" or “controlled low strength material -CLSM”). The fluidity and lift placement thickness of any such material should be controlled to prevent "floating" of any "submerged" structure.

10. Shrinkage because of excavation and compaction of the upper site soils is expected to be approximately 5 percent of any excavated or scarified site soils. This estimate is based upon compactive effort needed to produce an average degree of relative compaction of approximately 90 percent and may vary depending on contractor methods. Losses from site clearing and grubbing operations may affect quantity calculations and should also be considered. The grading contractor should verify shrinkage and earthwork yardage estimates.

11. Roof drainage systems for the proposed structures should be designed so that runoff water is diverted away from any structure.

12. Final site grades should be designed and constructed so that all water is diverted away from all structures and not allowed to pond on or near pavement. Drainage devices should be constructed to divert drainage from the project site.

13. It is recommended that Earth Systems be retained to provide geotechnical engineering services during the grading, excavation, and foundation phases of the project. This continuity of services will allow for the geotechnical review of the design concepts and specifications relative to the recommendations of this report and will more readily allow for design changes if subsurface conditions differ from those currently anticipated.

B. Excavations

1. Standard construction techniques should be sufficient for temporary site excavations. All excavations should be made in accordance with applicable regulations (including CAL/OSHA).

Project safety is the responsibility of the contractor and the owner. Earth Systems will not be responsible for project safety.

2. Unshored, unsurcharged, temporary excavations may be cut vertically to a maximum height of no more than 4 feet. Excavations extending higher than 4 vertical feet should be sloped

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back above the 4-foot vertical cut to at least a 1.5 horizontal to 1 vertical (1.5H:1V) slope or flatter. If excavations dry out, sloughing will occur. No excavation should be made within a 1H:1V (45-degree) line projected outward from the toe of any existing footing or structure.

3. During the time excavations are open, no heavy grading equipment or other surcharge loads

(i.e. excavation spoils) should be allowed within a horizontal distance from the top of any slope equal to the depth of the excavation (both distances measured from the top of the excavation slope).

4. Adequate measures should be taken to protect any structural foundations, pavements, or utilities adjacent to any excavations.

5. The excavation for the remedial grading for the at-grade maintenance facility is anticipated to be as much as 8 feet in depth from existing grade to bottom of recommended remedial grading. Where the structure is proposed to be located adjacent to property lines, it may be necessary to complete the remedial grading by means of a series of slot cuts. Slot cuts should be completed in an “A-B-C” sequence. The width of any slot cut should not exceed 8 feet (see Slot Cut Calculations, Appendix E). The complete construction and backfill of the 'A' slot must be performed prior to excavation of the 'B' slot, and likewise the 'C' slot. After the cut for each slot is made, bracing and possibly shoring of the near vertical cut slope may be required for continued temporary stability of slot excavation and safety of personnel.

C. Temporary Shoring

1. The proposed excavation for the proposed parking structure will be approximately 23 feet deep and will be adjacent to property lines and city right of ways. Temporary shoring will be necessary to support this excavation during construction. The shoring may consist of a soldier pile and lagging type system or similar temporary shoring system. The shoring may be cantilevered or anchored with tie-backs or internal bracing.

2. Cantilevered, shoring should be designed to resist active lateral earth pressures of 30Z pounds per square foot (psf) per foot of depth, where Z = Depth (in feet) measured below the top of the retained ground surface behind the shoring. This value is based on level ground behind the shoring.

3. The lateral earth pressure to be resisted by retaining should be increased to allow for surcharge loads. Surcharge pressures should be added to this earth pressure for surcharges within a distance from the top of the shoring less than or equal to the shoring height. A lateral earth pressure coefficient of 0.5 (50%) of uniform vertical surcharges should be added as a horizontal shoring pressure for braced shoring or shoring with ground anchors. The resultant lateral surcharge from individual foundations or other loads behind the shoring may be estimated using commonly accepted formulas and charts based on elastic theory (e.g. NAVFAC DM7.2 Figure 11). Footing load surcharges are distributed non-uniformly with

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the resultant acting at an elevation typically 0.5 to 0.6H’ where H’ is the retained soil height below base of footing.

4. Lateral (horizontal) loads may be resisted by passive resistance of the soil against the soldier piles. An equivalent fluid weight (EFW) of 360 psf per foot of penetration in firm native soil may be used for lateral load design. The maximum passive pressure used for design should not exceed 5,400 psf. The resisting pressure provided is an ultimate value. An appropriate factor of safety should be used for design calculations (minimum of 1.5 recommended).

5. Axial loads on the soldier piles may be resisted by skin friction on the piles below the depth of the excavation (assumed to be approximately 25 feet below existing grade). The skin friction on the proposed soldier piles may be taken as 315 psf and should be multiplied by the perimeter surface area of the grouted soldier pile.

6. To limit sloughing, exposed soil between soldier piles should be supported by lagging and backfilled. Backfill behind lagging should consist of concrete slurry (1 to 2 sacks of cement per CY) placed so that no voids remain between the lagging and the excavation face of soil.

For design, the lateral earth pressure on lagging may be taken as 60% of the overall lateral earth pressure on the shoring system (need not include seismic pressure). All timber lagging to be left in the ground should be pressure treated in accordance with Standard Specifications for Public Works Construction, Section 204-2.

7. It is recommended that Earth Systems review the plans and specifications for the proposed shoring system and that an Earth Systems representative observe and monitor the installation of the shoring.

8. Vertical and lateral deflections of the shoring elements and the neighboring buildings should be verified periodically during construction by a licensed surveyor so that, if excessive deflections occur, they can be detected early and appropriate remedial measures can be taken.

9. A “baseline” condition survey (both photographic and topographic) is highly recommended prior to commencing excavation. A “baseline” survey will help identify potential areas of concern and minimize the potential for future questions regarding damage or distress due to the construction process.

10. A shoring monitoring program should be specified by the shoring/structural engineer. At a minimum, initial survey control points should be established at the top of each soldier pile prior to the start of any excavation. Soldier piles should be survey monitored at least weekly and the monitoring program should continue for a period of time to be determined by the shoring/structural engineer but continuing at least throughout the duration of all anchor installation, and grouting and all soil excavation. Monitoring points in the ground area above grouted anchors is also recommended. Real-time monitoring should take place during anchor grouting.

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11. Survey and other monitoring data should be promptly submitted to the shoring/structural engineer and the geotechnical engineer for review. The shoring/structural engineer and the geotechnical engineer should be given the opportunity to evaluate any movement more than the specified deflections and so a remedial shoring plan can be prepared. Remedial actions may involve installation of additional soldier piles, braces, tieback anchors, or re-tensioning or post grouting of existing anchors to minimize movement prior to further construction.

12. A temporary tied-back (or internally braced) soldier pile shoring system retaining a level ground surface should be designed to resist the apparent earth pressure envelopes as shown in Figure 1 below. The apparent earth pressure should be distributed to the bracing, tiebacks or struts in accordance with the following figure which is based on the Federal Highway Administration Publication No. FHWA-IF-99-015. This figure is for a cut in sand and is assumed to most accurately reflect the soil conditions anticipated during excavation. The apparent earth pressures shown in this figure do not account for surcharge pressures.

Figure 1 Diagrams illustrating lateral pressure envelope for sands. Diagrams based on Federal Highway Administration's "Geotechnical Circular No. 4 Ground Anchors and Anchored Systems”.

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13. Performance tests should be conducted on each tie-back anchor to verify capacity.

Performance testing should be performed by the shoring contractor under the supervision of the geotechnical engineer and shoring/structural engineer. The ground anchor test results must be approved by the geotechnical and shoring/structural engineers prior to excavation of soil below the tieback elevation. Specifications for anchor performance testing should be prepared by the shoring engineer and reviewed by the geotechnical engineer.

14. For design of tied-back shoring, it is assumed that the potential wedge of failure is determined to be a plane 60 degrees from vertical and passing through a point set…