Juliette Substation Expansion - Geotechnical Report.pdf

16531 Orangehaven Lane, Riverside, CA 92503 951-264-9023 noorzaygeo.com

May 10, 2024

AECOM Project No. 23074 2020 L Street, Suite 300 Sacramento, California 95811 Attn: Mr. Eyassu Rumicho

Dear Mr. Rumicho:

Attached herewith is the preliminary geotechnical investigation prepared for the proposed expansion to the existing Juliette Substation located at 3600 Juliette Lane, Santa Clara, California 95054

(Coordinates: 37.386612, -121.967538).

We appreciate this opportunity to provide geotechnical services for this project. If you have questions or comments concerning this report, please contact us at your convenience.

Respectfully submitted, Noorzay Geotechnical Services, Inc.

Maihan Noorzay, G.E.

Principal Engineer

Distribution: Mr. Eyassu Rumicho (PDF)

PRELIMINARY GEOTECHNICAL INVESTIGATION

PROPOSED EXPANSION TO THE EXISTING

JULIETTE SUBSTATION

3600 JULIETTE LANE

SANTA CLARA, CALIFORNIA 95054

(COORDINATES: 37.386612, -121.967538).

PREPARED FOR AECOM

NGS PROJECT NO. 2307

Page No. i Job No. 23074

NoorzayGeo

TABLE OF CONTENTS

INTRODUCTION

SCOPE OF SERVICES

PROJECT CONSIDERATIONS

SITE DESCRIPTION

FIELD INVESTIGATION

LABORATORY INVESTIGATION

REGIONAL GEOLOGIC SETTING

FAULTING AND SEISMICITY

SUBSURFACE SOIL CONDITIONS

2022 CALIFORNIA BUILDING CODE - SEISMIC PARAMETERS

GROUNDWATER

LIQUEFACTION POTENTIAL AND SEISMIC SETTLEMENT

Lateral Spread

HYDROCONSOLIDATION

STATIC SETTLEMENT

LANDSLIDES AND SLOPE STABILITY

FLOODING POTENTIAL

Dam Inundation

Seiching

Tsunamis

EXPANSION POTENTIAL

CONCLUSIONS

RECOMMENDATIONS

Page No. ii

General Site Grading

Initial Site Preparation

Minimum Mandatory Removal Of Existing Soils

Dewatering

Preparation Of Fill Areas

Preparation Of Shallow Footing Areas

Compacted Fills

Shallow Foundation Design

Mat Foundation:

Deep Foundation Recommendations

Capacities of CIDH Piles

Pile Spacing and Group Efficiency

Load Testing for Pile Integrity Evaluation

CIDH Pile Installation

Structural Slabs (Deep Foundations)

Lateral Loading And Retaining Wall Design

Slabs-On-Grade

Flatwork

Excavations and Shoring

Lateral Pressures

Design of Soldier Piles

Lagging

Anchor Design

Anchor Installation

Page No. iii

Anchor Testing

Deflection

Monitoring

Corrosion Protection

Trench Bedding and Backfills

Trench Bedding

Backfill

Potential Erosion and Drainage

Soil Corrosion

Preliminary Flexible Pavement Design

Preliminary Rigid Pavement Design

Adjacent Properties Statement

Foundation Plan Review

Grading Plan Review

Construction Observation

LIMITATIONS

CLOSURE

REFERENCES

APPENDIX A - MAPS

APPENDIX B - EXPLORATORY LOGS

APPENDIX C - LABORATORY TESTING

APPENDIX D - GEOTECHNICAL CALCULATIONS

APPENDIX E - CORROSION AND RESISTIVITY TEST REPORT

INTRODUCTION

During December 2023 and January 2024, a preliminary geotechnical investigation was prepared for the proposed expansion to the existing Juliette Substation located at 3600 Juliette Lane, Santa Clara, California 95054 (Coordinates: 37.386612, -121.967538). The purposes of this investigation were to explore and evaluate the geotechnical engineering conditions at the subject site and to provide appropriate geotechnical engineering recommendations for design and construction of the proposed development.

The location of the site is depicted on the Index Map (Enclosure A-1). A preliminary site plan supplied by the client, undated, which exhibited the subject property boundaries and proposed expansion areas, was used as a base map for our Site Plan (Enclosure A-2).

The results of our investigation, together with our conclusions and recommendations, are presented in this report.

SCOPE OF SERVICES

The scope of services provided during this preliminary geotechnical investigation included the following:

A field reconnaissance of the site and surrounding area

Logging and sampling of exploratory borings for testing and evaluation

Laboratory testing on selected samples

Evaluation of the geotechnical engineering/geologic data to develop site-specific recommendations for site grading and foundation design

Preparation of this report summarizing our findings, professional opinions, and recommendations for the geotechnical aspects of project design and construction

Page No. 2

PROJECT CONSIDERATIONS

As we understand it, the existing substation will be improved by developing additional square footage for the substation. A plan was provided showing the areas of the proposed improvements. The site currently has an existing substation surrounded by driveways and parking lots. Although details were not provided during preparation of this report, we anticipate that the proposed improvements will be supported by cast-in-drilled-hole (CIDH) piers and by conventional shallow and mat foundations. A soil corrosivity evaluation including Wenner 4-pin testing was performed by Project X Corrosion

Engineers and their report is provided as Appendix E of this report. No additional information was provided during preparation of this report.

The final grading and foundation plans were not available for review during preparation of this report.

The final project grading and foundation plans should be reviewed by the geotechnical engineer.

SITE DESCRIPTION

The project area is a substation and surrounding area located at 3600 Juliette Lane in the City of Santa

Clara, Santa Clara County, California 95054. The project area currently contains a substation and is partially surrounded by paved driveway and parking areas. Unpaved areas within the project area are currently landscaped. The subject property is bounded on all sides by commercial / industrial properties.

The highest elevation in the project area is approximately 29 feet above mean sea level (MSL) near the east side of the site, and the lowest elevation on the property is approximately 27 feet MSL near the western side of the site. Maximum relief is about two feet. Based on topographic maps, the original gradient was less than one percent toward the west-northwest.

Page No. 3

FIELD INVESTIGATION

Soil conditions underlying the subject site were explored by means of five exploratory borings drilled to a maximum depth of 46.5 feet with truck-mounted CME 75 drill rig equipped for soil sampling. The approximate locations of the exploratory borings are indicated on Enclosure A-2.

Continuous logs of the subsurface conditions, as encountered within the exploratory borings, were recorded at the time of drilling by an engineer from this firm. Both a standard penetration test (SPT) sampler (2-inch outer diameter and 1-3/8-inch inner diameter) and a ring sampler (3-inch outer diameter and 2-1/2-inch inner diameter) were utilized in our investigation. The penetration resistance was recorded on the boring logs as the number of hammer blows used to advance the sampler in 6-inch increments (or less if noted). The samplers were driven with an automatic hammer that drops a 140-pound weight 30 inches for each blow. After the required seating, samplers are advanced up to 18 inches, providing up to three sets of blowcounts at each sampling interval. The recorded blows are raw numbers without any corrections for hammer type (automatic vs. manual cathead) or sampler size (ring sampler vs. standard penetration test sampler). Both relatively undisturbed and bulk samples of typical soil types obtained were returned to the laboratory in sealed containers for testing and evaluation.

The exploratory boring logs, together with the uncorrected blowcount data and in-place density data, are presented in Appendix B. The stratification lines presented on the boring logs represent approximate boundaries between soil types, which may include gradual transitions.

The exploratory borings were backfilled with excavated soils using reasonable effort and capped with black dyed, rapid set concrete patch where necessary to restore the areas to their initial condition prior to leaving the site, but they were not compacted to a relative compaction of 90 percent or greater. In an area as small and deep as a boring, consolidation and subsidence of soil backfill may occur over time causing a depression. The client is advised to observe exploratory boring areas occasionally and, when needed, backfill noted depressions.

Page No. 4

LABORATORY INVESTIGATION

Included in the laboratory testing program were field dry density and moisture content tests on relatively undisturbed samples. An optimum moisture-maximum dry density relationship was established to evaluate the relative compaction of the subsurface soils. Direct shear testing was performed on relatively undisturbed and remolded samples to provide shear strength parameters for bearing capacity and earth pressure evaluations. Expansion index testing was performed to evaluate the expansion potential of the subsurface soils. Hydroconsolidation testing was performed to evaluate the hydrocollapse potential of the subsurface soils. No. 200 washes and Atterberg limits tests were performed for soil classification purposes. Selected samples of material were delivered to Project X

Corrosion Engineering and tested for preliminary corrosivity analysis.

Laboratory test results for the current investigation are provided in Appendix C. Corrosion testing performed by Project X Corrosion Engineering is provided in Appendix E. Soil classifications provided in our geotechnical investigation are in general accordance with the Unified Soil

Classification System (USCS).

REGIONAL GEOLOGIC SETTING

The City of Santa Clara lies within the Coast Ranges Physiographic Province, one of eleven such provinces recognized in the State of California. The Coast Ranges encompass central and northern coastal California from the Transverse Ranges in the south, more than 500 miles northward to the

Oregon border. The province is characterized by northwest-trending mountain ranges that vary in elevation from 2,000 to about 6,000 feet above sea level. The uplifted coastline is commonly terraced.

The rocks in this province are generally composed of a complex of thick sequences of Mesozoic and

Cenozoic sedimentary rocks. Tilted rock strata tend to dip beneath the Great Valley province to the east. In addition to the sedimentary rocks, a granitic core, the Salinian Block, is present from the southern end of the Coast Ranges northward to the Farallon Islands.

Page No. 5

The San Andreas fault, the dominant structural feature in this province, extends northwestward from the Gulf of California to Point Arena. The structure of the Coast Ranges is controlled by movement along a complex of parallel and subparallel faults that are part of the San Andreas transform system.

The San Andreas and San Gregorio faults lie southwest of the Santa Clara Valley; the Hayward and

Calaveras faults lie northeast of the valley. Differential motion along these major faults and many smaller ones, have resulted in the Santa Clara Valley, which is a fault-controlled, down dropped valley filled with late Tertiary and Quaternary alluvium hundreds of feet in depth. The general geology in the area surrounding the subject site is shown on the Regional Geologic Map and legend (Enclosures A-4 and A-4a).

FAULTING AND SEISMICITY

The site does not lie within an Alquist-Priolo (AP) Earthquake Fault zone (Enclosure A-5a). There are no known, active faults crossing onto or trending toward the subject property. The probability the subject site will be adversely affected by fault-controlled ground rupture is considered to be low.

As with most of coastal California, the subject site is situated in an area of active and potentially active faults. Active faults present several potential risks to structures, the most common of which are strong ground shaking, dynamic densification, liquefaction, mass wasting, and surface rupture at the fault plane. The following four factors are the principal determinants of seismic risk at a given location:

● Distance to seismogenically capable faults.

● The maximum or "characteristic" magnitude earthquake for a capable fault.

● Seismic recurrence interval, in turn related to tectonic slip rates.

● Nature of earth materials underlying the site.

Based upon proximity to regionally significant, active faults, ground shaking is considered to be the primary hazard most likely to affect the site. Characteristics of the major active fault zones selected

Page No. 6 for inclusion in analysis of strong ground shaking are listed in the following table. Numerous significant fault zones are located at distances exceeding 40 kilometers from the site, but greater distances, lower slip rates, and/or lesser maximum magnitudes indicate much lower risk to the site from the latter fault zones than those listed below.

Fault Zone1 Distance from

Site (km)

Fault Length (km)1

Slip Rate (mm/yr)1

Reference Earthquake

M(Max)1

Fault Type1

Silver Creek

(rl, r)

3.6 62±6 unk unk unk

Stanford 5.9 45±5 unk unk unk

Hayward

(rl, ss)

9.7 53±5 9.0±2.0 6.7 A

Monte Vista-Shannon

(r, 45SW to 90) 11 45±5 0.4±0.3 6.7 B

Calaveras 15 59±6 15.0±3.0 6.2 B

San Andreas Santa Cruz Mountains segment

(rl, ss)

17 62±8 17.0±4.0 7.0 A

San Andreas Peninsula segment

(rl, ss) 17 85±13 17.0±4.0 7.1 A

Butane

(rl, ss) 26 8±1 unk unk unk

Sargent-Berrocal

(r, 22SE to 90) 27 29±3 3.0±2.0 unk B

Verona 27 11±1 unk unk unk

Las Positas

(ll, r) 28 15±2 unk unk unk

San Gregorio (rl, ss)

37 131±13 3.0±2.0 7.0 B

Greenville

(rl, ss) 39 27±3 2.0±1.0 6.6 B

Page No. 7

Fault Zone1 Distance from

Site (km)

Fault Length (km)1

Slip Rate (mm/yr)1

Reference Earthquake

M(Max)1

Fault Type1

1. California Department of Conservation, Geological Survey, 2007 (Appendix A), California Fault Parameters for the National Seismic Hazard Maps and Working Group on California Earthquake Probabilities, CGS Special Report 203A, USGS Open File Report 2007-1437A.

2. U.S. Department of the Interior, Geological Survey, 2008, website: 2008 National Seismic Hazards Maps – Source Parameters, https://earthquake.usgs.gov/cfusion/hazfaults_2008_search/query_results.cfm.

3. Southern California Earthquake Data Center, website: Significant Earthquakes and Faults, http://scedc.caltech.edu/significant/fault-index.html.

4. Fault Geometry: (ss) strike slip; (r) reverse; (n) normal; (rl) right lateral; (ll) left lateral; (O) oblique; (45 N) direction.

SUBSURFACE SOIL CONDITIONS

In the project area, near-surface soils consisted predominantly of artificial fill, which is underlain by young, alluvial deposits. Fill soil was encountered in all five borings with ranging from 9 to 10.5 feet in depth. More fill may be encountered beyond and between borings. The fill soil was composed of silty sand to clayey sand (SM/SC) and lean to fat clay (CL/CH) with some gravel, which was light gray to dark gray or black, brown to dark brown and gray brown, moist to wet, and very loose to medium dense or firm to very stiff. A small amount of various debris was noted within the fill. The underlying alluvium was composed of lean to fat clay (CL/CH) and lean clay (CL), clayey silt to silty lean clay

(ML/CL), poorly graded sand to silty sand (SP/SM), and silty fine- to coarse-grained sand (SM) with varying amounts of gravel, which was gray to bluish gray and dark gray and light brown to dark brown, tan to reddish brown, moist to saturated, and firm to very stiff or medium dense.

Groundwater was encountered in all five exploratory borings at depths ranging from 9.7 to 11 feet below ground surface. Slight to moderate caving was encountered in some exploratory excavations.

More detailed descriptions of the subsurface soil conditions encountered are included within our exploratory logs (Appendix B).

Page No. 8

2022 CALIFORNIA BUILDING CODE - SEISMIC PARAMETERS

Based on our review of the geologic setting, the site is underlain by alluvium. The borings were not excavated down to a depth of 100 feet. However, based on the mapped geology of the site coupled with the density of the subsurface materials encountered, the soils underlying the site may be classified as Site Class E – soft clay soil, according to the 2022 California Building Code (CBC).

Per ASCE 7-16, a ground motion hazard analysis was performed to determine the design response spectra. Both probabilistic and deterministic response spectra were developed. The UCERF3 fault models were used to develop the probabilistic spectrum while the faults determined by the deaggregation analysis were used to develop the deterministic spectrum. The probabilistic and deterministic response spectra are provided below.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 1 2 3 4 5 6 7 8 9 10

M ax

. D ire ct io n

RT

G M

(g

Period (Sec)

ASCE7-16 Probabilistic Response Sprectum

MCER_7-16

MCER_Shahi&Baker

Page No. 9

Based on the results of our analysis, the site-specific response spectra and seismic parameters according to the 2022 CBC are provided below.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

M ax

. D ire ct io n Sp ec tr al A cc el er at io n

(g

Period (Sec)

ASCE7-16 Deterministic Response Sprectum

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0M ax

. D ire ct io n Sp ec tr al A cc el er at io n

(g

Period (Sec)

Site-Specific Response Spectra

MCER

Design Sa

Page No. 10

2022 CBC – Site-Specific Seismic Parameters

Spectral Acceleration Parameters Ss = 1.500 and S1 = 0.6

Site Coefficients Fa = 1.0 and Fv = 4.0

Adjusted Maximum Considered Earthquake Spectral Response Parameters

SMS = 1.350 and SM1 = 2.245

Design Spectral Acceleration Parameters SDS = 0.900 and SD1 = 1.497

Peak Ground Acceleration (PGAM) 0.600g

Deaggregated Magnitude (mean, over all sources) 6.97

Seismic Design Category D

It should be noted that the above seismic parameters should be reviewed by the civil/ structural design engineer and approved by the appropriate governmental agency prior to using for this project. The civil/ structural design engineer should consult with the project geotechnical consultant if additional geotechnical information is needed for structural design.

GROUNDWATER

The site is situated in the northwest quarter of projected Section 27, Township 6 South, Range 1 West, Mount Diablo Principal Meridian, at Latitude: 37.38662847° North, Longitude: 121.967545° West. It is located about 280 feet east of San Tomas Aquinas Creek. Geotracker indicates the subject site lies within the Santa Clara Valley – Santa Clara, groundwater basin. Groundwater was encountered within all five borings, with the highest groundwater measured at 9.7 feet below ground surface during our investigation.

The closest water well data available from the California Department of Water Resources was well number 373804N1219385W001, which was located about 1.6 miles east-southeast of the subject site next to the Guadalupe River. The highest recorded groundwater in this well was at elevation 23 feet

Page No. 11

MSL, which was 13 feet below ground surface at the well. The second closest well, number

374036N1219442W001, was located about 1.7 miles northeast of the project site, near the Guadalupe

River, and more than a mile closer to the Bay. The highest groundwater within this well was about two feet below ground surface. Groundwater was encountered 9.7 feet below ground surface, and it should be expected to occasionally rise higher during and following seasons with above average precipitation.

LIQUEFACTION POTENTIAL AND SEISMIC SETTLEMENT

Liquefaction is a process in which strong ground shaking causes saturated soils to lose their strength and behave as a fluid (Matti and Carson, 1991). Ground failure associated with liquefaction can result in severe damage to structures. Soil types susceptible to liquefaction include sand, silty sand, sandy silt, and silt, as well as soils having a plasticity index (PI) less than 7 (Boulanger and Idriss, 2004) and loose soils with a PI less than 12 and a moisture content greater than 85 percent of the liquid limit (Bray and Sancio, 2006). The geologic conditions for increased susceptibility to liquefaction are: 1) shallow groundwater (generally less than 50 feet in depth); 2) the presence of unconsolidated sandy alluvium, typically Holocene in age; and 3) strong ground shaking. All three of these conditions must be present for liquefaction to occur.

The State of California, Seismic Hazards map for the Milpitas Quadrangle places the subject site within a zone of potential, seismically induced liquefaction (Enclosure A-5a).

Severe seismic shaking may cause dry and non-saturated sands to densify, resulting in settlement expressed at the ground surface. Seismic settlement in dry soils generally occurs in loose sands and silty sands, with cohesive soils being less prone to significant settlement.

A quantitative method using an index called the liquefaction potential index (LPI) was developed and presented by Iwasaki et al. (1978, 1982). The LPI is defined as:

Page No. 12

𝐿𝑃𝐼 = න 𝐹ଵ

ଶ

𝑊(𝑧)𝑑𝑧 where W(z) = 10 – 0.5z, F1 = 1 - FS for FS < 1.0, F1 = 0 for FS > 1.0 and z is the depth below the ground surface in meters. The LPI presents the risk of liquefaction damage as a single value with the following indicators of liquefaction-induced damage:

LPI Range and Damage

LPI Range Damage

LPI = 0 Liquefaction risk is very low.

0 < LPI ≤ 5 Liquefaction risk is low.

5 < LPI ≤ 15 Liquefaction risk is high.

LPI > 15 Liquefaction risk is very high.

The original liquefaction potential index (LPI) was improved by Maurer et al (2015) by assessing liquefaction hazard utilizing the Ishihara (1985) boundary curves for liquefaction surface effects. The new index is named Ishihara-inspired index, LPIISH.

where and

Page No. 13

The LPI range and damage is modified as below:

LPIISH Range and Damage

LPIISH Range Damage

LPIISH = 0 Liquefaction risk is very low.

0 < LPIISH ≤ 5 Liquefaction risk is low.

5 < LPIISH ≤ 10 Liquefaction risk is medium.

10< LPIISH ≤ 15 Liquefaction risk is high.

LPIISH > 15 Liquefaction risk is very high.

The most recent development for quantitative descriptions of liquefaction-induced surface damage, called "liquefaction vulnerability", was made by Tonlin & Taylor (2013) after the Christchurch earthquakes occurred between 2010 and 2011 and was based on field observations and analyses of approximately 7,500 CPT investigations. A new index, the liquefaction severity number (LSN), was proposed and defined as:

𝐿𝑆𝑁 = න

𝜀௩ 𝑧 𝑑𝑧 where εv is the calculated volumetric densification strain in the subject layer from Zhang et al. (2002) and z is the depth to the layer of interest in meters below the ground surface. The typical behaviors of sites with a given LSN are summarized in following table.

Page No. 14

LSN Ranges and Observed Land Effects

LSN Range Predominant Performance

0-10 Little to no expression of liquefaction, minor effects

10-20 Minor expression of liquefaction, some sand boils

20-30 Moderate expression of liquefaction, with sand boils and some structural damage

30-40 Moderate to severe expression of liquefaction, settlement can cause structural damage

40-50 Major expression of liquefaction, undulations, and damage to ground surface, severe total and differential settlement of structures

>50 Severe damage, extensive evidence of liquefaction at surface, severe total and differential settlements affecting structures, damage to services

Both LPIISH and LSN indices were calculated for a representative soil profile with the results presented in Appendix D. The results indicate that the liquefaction risk of the site is "very low" per the LPIISH index. The site exhibits little to no expression of liquefaction per the LSN index. Little to no expression of liquefaction means that minor effects of liquefaction will be observed per Tonlin & Taylor (2013).

The Idriss and Boulanger (2010-16) and Pradel (1998) methods were used to evaluate liquefaction-induced and dry sand settlements. As input into our calculations a deaggregated modal moment magnitude of 6.97 and an acceleration of 0.6g were utilized for the representative soil profile provided in Boring B-3. A historic groundwater table of 5 feet below the existing ground surface was used.

The results indicate that a maximum seismic settlement to be negligible at the project site. The result of our analysis is provided in Appendix D.

Page No. 15

Lateral Spread

Lateral spread is the most pervasive type of liquefaction-induced ground failure. Lateral spreads can occur on gently sloping ground or where nearby drainage or stream channels can lead to static shear stress biases on essentially horizontal ground. During lateral spread, blocks of mostly intact, surficial earth material displace downslope or towards a free face along a shear zone that has formed within the liquefied sediment. The resulting ground deformation typically has extensional fissures or a graben at the head of the failure, shear deformations along the side margins, and compression or buckling of the earth material at the toe. The amount of lateral displacement typically ranges from a few centimeters to several meters and can cause considerable damage to engineered structures and lifelines.

Past earthquakes indicated that significant damage to structures occurred even with less than one foot of lateral spread. Consequently, the determination of lateral spread potential, an assessment of its likely magnitude, and the development of appropriate mitigation, need to be addressed as part of the hazard assessment process.

The lateral spread potential of the subject site was evaluated in general accordance with procedures proposed by Idriss and Boulanger (2008). A slope of 2 percent was used for the existing gentle sloping conditions.

The results of our lateral spread evaluation indicate that the estimated lateral ground displacement for the subject site is less than one inch (see Appendix D).

HYDROCONSOLIDATION

To evaluate the potential deformation that may be caused by the addition of water, hydroconsolidation testing was performed on a selected, representative relatively undisturbed sample, obtained at a depth of approximately 5 feet bgs. The results are shown in Appendix C. The test result indicates negligible hydroconsolidation settlement.

Page No. 16

STATIC SETTLEMENT

Potential static settlement was evaluated utilizing field and laboratory data and foundation load assumptions. The calculations indicate total static settlement of less than one inch beneath shallow foundations and less than 1/2-inch beneath deep foundations. Most of the potential static settlement should occur during construction. Based on the uniformity of the materials encountered, differential settlement is anticipated to be on the order of 1/2 the total settlement over 40 feet.

LANDSLIDES AND SLOPE STABILITY

The State of California Seismic Hazards map for the Milpitas Quadrangle indicates the subject site does not lie within a zone of potential, seismically induced landslides. The subject site and surrounding area in all directions are very low relief with shallow gradients. There are no mapped landslides on or near the subject site. Landslides are not considered to be a geologic constraint at this site.

FLOODING POTENTIAL

Flood Insurance Rate Maps (FIRM) were compiled by the Federal Emergency Management Agency

(FEMA) for the Flood Insurance Program and are available for most areas within the United States at the FEMA web site (http://msc.fema.gov/). The attached FEMA Flood Map (Enclosure A-6) was created from FIRMs specific to the area of the subject site. The FEMA Flood Map shows the site is located within ‘Zone X’. In this case, Zone X is defined as an area with a 0.2 percent annual flood chance, and areas protected by levees from one percent annual flood risk.

Dam Inundation

Based on the State of California Dam Breach Inundation Map website, the subject site lies outside of any dam breach inundation areas.

Page No. 17

Seiching

Seiching is the oscillation of an enclosed body water, usually due to strong groundshaking following a seismic event. Seiching can affect lakes, water towers, swimming pools. There are no known enclosed bodies of water near enough to adversely affect the subject property.

Tsunamis

According to the State of California, California Tsunami Maps website, the subject site does not lie within a tsunami hazard zone (Enclosure A-5b).

EXPANSION POTENTIAL

Materials tested during this investigation indicated a "very low" potential for expansion. Specialized construction procedures to specifically resist expansive soil forces are not anticipated at this time.

Requirements for reinforcing steel to satisfy structural criteria are not affected by this recommendation.

Additional evaluation of soils for expansion potential should be conducted by the geotechnical engineer during the grading operation as warranted.

CONCLUSIONS

On the basis of our field and laboratory investigations, it is the opinion of this firm that the proposed development is feasible from geotechnical engineering and engineering geologic standpoints, provided the recommendations contained in this report are implemented during design and construction.

Moderate to severe seismic shaking can be expected at the site. There are no known active faults on or trending toward the subject site; the site does not lie within an Alquist-Priolo Special Studies zone.

Slight to moderate caving was observed in our exploratory excavations. The contractor should be prepared to deal with caving soils as applicable.

Page No. 18

Groundwater was encountered within our exploratory borings at a depth of 9.7 feet. Water may be expected to rise somewhat during and following heavy precipitation seasons.

Based on results of our analysis, total seismic settlement could be considered negligible.

Total static settlement of less than one inch beneath shallow foundations and less than 1/2-inch beneath deep foundations should be anticipated. Differential static settlement is anticipated to be on the order of 1/2 the total settlement over 40 feet.

Landslides are not considered to be a geologic constraint on the subject site. Temporary excavations are anticipated to conform to local and State codes with regard to the geologic materials present at the site.

Materials tested during this investigation indicated a "very low" potential for expansion. Specialized construction procedures to specifically resist expansive soil forces are not anticipated at this time.

Additional evaluation of soils for expansion potential should be conducted by the geotechnical engineer during the grading operation as warranted.

Based upon our field investigation and test data, it is our opinion that the upper existing soils will not, in their present condition, provide uniform or adequate support for the proposed structures.

Undocumented fill and/or variable in situ conditions may be present in the upper soils. These conditions may cause unacceptable differential and/or overall settlement upon application of the anticipated foundation loads.

Because of site conditions, it is our recommendation that all structures should be supported on deep foundations consisting of cast-in-drilled-hole (CIDH) piers or at least the upper 11 feet of existing artificial soils should be removed and replaced with compacted fill to support shallow and mat foundations. Dewatering and stabilization of the compacted fill mat using geogrid may be required.

Page No. 19

The final project grading and foundation plans should be reviewed by the geotechnical engineer to confirm that the recommendations provided in this report are implemented.

RECOMMENDATIONS

General Site Grading

It is imperative that no clearing and/or grading operations be performed without the presence of a representative of the geotechnical engineer. An on-site, pre-job meeting with the developer, the contractor and the geotechnical engineer should occur prior to all grading-related operations.

Operations undertaken at the site without the geotechnical engineer present may result in exclusions of affected areas from the final compaction report for the project.

Grading of the subject site should be performed, at a minimum, in accordance with these recommendations and with applicable portions of the CBC. The following recommendations are presented for your assistance in establishing proper grading criteria.

Initial Site Preparation

All areas to be graded should be stripped or cleaned of significant vegetation and other deleterious materials. These materials should be removed from the site for disposal. The cleaned soils may be reused as properly compacted fill. Rocks or similar irreducible material with a maximum dimension greater than 8 inches should not be used in compacted fills. If encountered, existing utility lines should be traced, removed, and rerouted from areas to be graded.

Minimum Mandatory Removal Of Existing Soils

For structures supported on shallow or mat foundations, all building areas (including at least 5 feet laterally beyond the footing lines, where possible) should have at least the upper 11 feet of existing soils or 36 inches below footings, whichever is greater, removed and the open excavation bottoms observed by our engineer/ geologist to verify and document in writing that all undocumented fills or

Page No. 20 loose native soils are removed prior to refilling with properly tested and documented compacted fill.

The removed and cleaned soils may be reused as properly compacted fill.

Further subexcavation may be necessary depending on the conditions of the underlying soils. The actual depth of removal should be determined at the time of grading by the project geotechnical engineer/geologist. The determination will be based on soil conditions exposed within the excavations.

At minimum, any undocumented fill, topsoil, or other unsuitable materials should be removed and replaced with properly compacted fill.

In-place density tests may be taken in the removal bottom areas where appropriate to provide data to help support and document the engineer/geologist's decision.

For this project, we anticipate that the bottom of the excavation will encounter groundwater. The excavation should be dewatered as recommended in the following section. We recommend that the compacted fill mat is stabilized by installing geogrid at the bottom of the overexcavation and in 18-inch vertical intervals for at least two additional layers as a minimum. The geogrid should be installed per the manufacturer's recommendation, which may require additional geogrid reinforcement.

Dewatering

Groundwater was encountered in all of our borings from 9.7 to 11.2 feet bgs. Dewatering may be required during construction. The contractor should design and install an appropriate dewatering system during construction to maintain the groundwater level a minimum of 3.0 feet below the proposed excavation. Most of the subsurface soils are classified as clayey soils and are considered to be low permeable. Open sump pumping may be adequate for dewatering if the groundwater level during construction is relatively low. However, if groundwater is relatively high, dewatering by well points may be needed in order to maintain the excavation. Design of such a system should be the sole responsibility of the contractor and should be developed based on the anticipated groundwater level at the time of construction and pumping tests carried out prior to construction.

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Preparation Of Fill Areas

Prior to placing fill, after the mandatory subexcavation operation, and prior to installing geogrid, the surfaces of all areas to receive fill should be scarified and moisture treated to a depth of 6 inches or more. The soils should be brought to near optimum moisture content and compacted to a minimum relative compaction of 90 percent in accordance with ASTM D1557.

Preparation Of Shallow Footing Areas

All footings should rest upon at least 36 inches of properly compacted fill material. The required overexcavation should extend at least 5 feet laterally beyond the footing lines, where reasonably possible. In instances where the lateral overexcavation may not be accomplished, this firm should be contacted to evaluate the effect. The bottom of this excavation should then be scarified and moisture treated to a depth of at least 6 inches, brought to near optimum moisture content and compacted to a minimum of 90 percent relative compaction in accordance with ASTM D1557 prior to refilling the excavation to the required grade as properly compacted fill.

Thickness of compacted fill underneath foundations should not be allowed to vary by more than

50 percent for a single structure or 2 feet, whichever is less. In areas where, by virtue of grading, the fill thickness will exceed this maximum allowable differential, the subexcavation depths should be increased as necessary to reduce the differential fill thickness. This deepening of the subexcavation may involve additional removals of native soils. A determination of specific structural areas that require additional subexcavation should be performed at the time of grading.

In no case should footings for a single structure span from cut to fill conditions.

All footing excavations should be observed by a representative of the project geotechnical engineer to verify that they have been excavated into compacted fill prior to placement of forms, reinforcement, or concrete. The excavations should be trimmed neat, level, and square. All loose, sloughed or moisture-softened soils should be removed from the excavations prior to placing of concrete.

Page No. 22

Compacted Fills

The on-site soils should provide adequate quality fill material provided they are free from organic matter and other deleterious materials. Rocks or similar irreducible material with a maximum dimension greater than 8 inches should not be used in compacted fills.

If utilized, import fill should be inorganic, non-expansive granular soils free from rocks or lumps greater than 6 inches in maximum dimension. The contractor shall notify the geotechnical engineer of import sources sufficiently ahead of their use so that the sources can be observed and approved as to the physical characteristic of the import material. For all import material, the contractor shall also submit current verified reports from a recognized analytical laboratory indicating that the import has a

"not applicable" potential for sulfate attack based upon current American Concrete Institute (ACI) criteria and is "mildly to moderately corrosive" to ferrous metal and copper. The reports shall be accompanied by a written statement from the contractor that the laboratory test results are representative of all import material that will be brought to the job.

Fill should be spread in near-horizontal layers, approximately 8 inches thick. Thicker lifts may be approved by the geotechnical engineer if testing indicates that the grading procedures are adequate to achieve the required compaction. Each lift should be spread evenly, thoroughly mixed during spreading to attain uniformity of the material and moisture in each layer, brought to near optimum moisture content and compacted to a minimum relative compaction of 90 percent in accordance with

ASTM D1557.

Based upon the relative compaction anticipated for compacted fill soils, we estimate compaction shrinkage of approximately 0 to 5 percent. Therefore, 1.00 cubic yards to 1.05 cubic yards of in-place soil material would be necessary to yield one cubic yard of properly compacted fill material. In addition, we would anticipate compaction subsidence of approximately 0.0 to 0.6 feet in the upper 11 feet. These values are exclusive of losses due to disposal of oversized material, stripping, tree removal or removal of other subsurface obstructions, if encountered, and may vary due to differing conditions within the project boundaries and the limitations of this investigation.

Page No. 23

Values presented for shrinkage and subsidence are estimates only. Final grades should be adjusted, and/or contingency plans to import or export material should be made to accommodate possible variations in actual quantities during site grading.

Shallow Foundation Design

If the site is prepared as recommended, the proposed structures may be safely founded on spread foundations, either individual spread footings and/or continuous wall footings, bearing on a minimum of 36 inches of compacted fill.

Footings should be a minimum of 18 inches wide and should be established at a minimum depth of 24 inches below the lowest adjacent final subgrade level. Exterior footing reinforcement should consist of at least four No. 5 reinforcing bars (two on top and two on bottom). Interior footings should consist of at least four No. 4 reinforcing bars (two on top and two on bottom). The structural engineer may require additional reinforcement.

For the minimum width of 18 inches and depth of 24 inches, footings may be designed for a maximum safe soil bearing pressure of 1,500 pounds per square foot (psf) for dead plus live loads. This allowable bearing pressure may be increased by 250 psf for each additional foot of width and 500 psf for each additional foot of depth to a maximum safe soil bearing pressure of 2,000 psf for dead plus live loads.

These bearing values may be increased by one-third for wind or seismic loading.

For footings thus designed and constructed, we would anticipate a maximum static settlement of less than one inch. Differential static settlement between similarly loaded adjacent footings is expected to be approximately half the total settlement over 40 feet. Static settlement is expected to occur during construction or shortly after.

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Mat Foundation:

For a 12-foot wide or bigger mat foundation, an average bearing pressure of 2,000 psf should be used for conventional working stress design and 6,000 psf for ultimate limit state design. We would anticipate a maximum static settlement of less than one inch. Differential static settlement is anticipated to be less than one-half the total settlement in 40 feet.

A modulus of vertical subgrade reaction of 85 pounds per cubic inch (pci) can be utilized in the design of mat foundations.

Deep Foundation Recommendations

A representative soil profile was developed for all pile capacity calculations. A groundwater table of

5 feet bgs was used in the capacity calculations. It is anticipated that 24- and 48- inch-diameter CIDH piles may be utilized for this project. As a minimum, the piles should be installed to at least 20 feet below the existing grade. Deep foundations should be further embedded as per the direction of the structural engineer.

The capacities provided are based on shear strength data obtained during this investigation and should be confirmed with testing during grading/ excavation when the actual conditions are exposed. The following table lists the input values used in our analysis and may be used for LPILE design. The values of the modulus of subgrade reaction (k), the strain at 50 percent deflection in the P-Y curve

(e50), and the relative density of the soil (Dr), are estimated by the program AllPile Version 7.21h based on blowcounts. The blowcounts (Nspt) used in our analysis were corrected for hammer efficiency.

Since deflection or a service limit criterion will most likely control lateral capacity design, no safety/resistance factor is included with the parameters.

Page No. 25

Soil Properties for Pile Design Recommendations

Depth to Top of Layer

(ft)

Unit Weight

(pcf)

Friction angle

(degrees)

Cohesion (ksf)

Modulus of subgrade, k (pci) e50/Dr

Nspt Type Soil

0 114.0 29.8 0.250 1097.9 0.50 25 3 Silt

(Phi + C) 5 64.6 28.8 0.158 1070.2 0.50 25 2 Stiff Clay

10.5 57.6 28.8 0.158 646.1 0.64 17 2 Stiff Clay

15 69.0 29.8 0.250 1009.5 0.52 24 3 Silt

(Phi + C)

20 69.0 29.8 0.250 2461.1 0.33 50 3 Silt

(Phi + C) 25 57.6 28.0 0.150 1015.0 0.52 24 2 Stiff Clay 30 57.6 28.0 0.150 900.2 0.55 22 2 Stiff Clay 35 57.6 28.0 0.150 290.1 0.90 10 1 Soft Clay 40 57.6 28.0 0.150 610.1 0.65 16 2 Stiff Clay 45 57.6 28.0 0.150 646.1 0.64 17 2 Stiff Clay

Capacities of CIDH Piles

Vertical Capacities

Pile capacities were calculated utilizing a computer program, AllPile Version 7.21h. The maximum allowable downward capacity utilized a factor of safety of 2.0 for skin friction and zero tip bearing.

The maximum allowable uplift capacity utilized a factor of safety of 3.0 for skin friction and 2.0 for pile weight. Downdrag was assumed for the upper 11 feet in the capacity calculations due to artificial fill. Utilizing these values, the combined dead plus live loads should be limited to the values presented in Appendix D. These capacities may be increased by one-third for wind or seismic loading. The capacities provided are based on shear strength parameters obtained during this investigation and should be confirmed with testing during grading/ excavation when the actual conditions are exposed.

Structural capacities of piles must be verified by the design engineer.

Ultimate downward capacities for piles are also provided should calculations utilizing other factors of safety be desired (Appendix D).

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For properly installed piles, it is anticipated that a total settlement of less than 1/2 inch will be required to mobilize allowable vertical capacity.

Lateral Capacities

The allowable lateral bearing pressure based on the encountered soil types may be considered to be developed at a rate of 230 psf per foot of depth below natural grade to a maximum of 2,300 psf. The upper 11 feet of soils should be neglected from the allowable lateral bearing pressure. The allowable lateral bearing pressure may be increased by one-third for wind or seismic loading.

Pile Spacing and Group Efficiency

Both axial and lateral capacities recommended in the above sections are for single piles. In the case of grouped piles, the total capacity will be subject to pile spacing. Per the 2022 CBC (1810.2.5), group effects should be considered for axial downward capacities where the center-to-center spacing is less than 3.0D and for lateral capacities where the center-to-center spacing is less than 8.0D, where D is the pile diameter or width. For pile groups subjected to uplift, the allowable working uplift load for the group should be the lesser of:

a. The proposed individual pile uplift working load times the number of piles in the group.

b. Two-thirds of the effective weight of the pile group and the soil contained within a block defined by the perimeter of the group and the length of the pile. A conservative unit weight of 100 pcf may be utilized in the calculation of soil weight.

We recommend the following group effects in accordance with the current AASHTO (2012) and

FHWA (2010) design guidelines.

Group Effects for Downward Capacity of Drilled Group Shafts

The individual downward capacity of each shaft in the pile group should be reduced by a group efficiency factor η taken as:

Page No. 27

• η =0.65 for a center-to-center spacing of 2.5 diameters

• η =1.0 for a center-to-center spacing of 3.0 diameters or more

For intermediate spacing, the value of η may be determined by linear interpolation.

Group Effects for Lateral Capacity of Drilled Group Shafts

For general design of foundations composed of groups of drilled shafts, the P-multiplier, PM, values provided in the table below are suggested.

The following publications can also be referenced for the necessary group efficiency to be considered in the design of group piles.

• AASHTO, 2012, LRFD Bridge Design Specifications, 6th Edition

• FHWA, 2010, Drilled Shafts: Construction Procedures and Design Methods, Publication

No. FHWA-NHI-10-016

Recommended P-multiplier, PM, Values for Design by Row Position

Design P-multiplier, PM

Pile Spacing (center-to-center) 2.5D 3D 4D 5D ≥6D

Lead Row 0.65 0.7 0.85 1.0 1.0

Second Row 0.45 0.5 0.65 0.85 1.0

Third Row and Higher 0.3 0.35 0.5 0.7 1.0

Load Testing for Pile Integrity Evaluation

Where required by the building official, the pile contractor may verify axial and lateral pile capacities in the field in accordance with 2022 CBC. At least one pile should be load tested for each pile type.

Additional elements may be load tested where necessary to establish the safe design capacity. The

Page No. 28 appropriate test method should be selected by the contractor and approved by the client. The resulting allowable loads shall not be more than one-half of the ultimate load capacity of the test pile as provided in previous sections.

CIDH Pile Installation

The installation of the CIDH piles should be observed by the geotechnical engineer to verify the soil condition and that the desired diameter and depth of pile are achieved. CIDH piles should be true and plumb.

Caving could occur during the drilling and the construction of piles within the on-site soils.

Appropriate precautions should therefore be taken during the construction of piles to reduce caving and raveling.

The drilling speed should be reduced as necessary to minimize vibration and caving. Based on the data developed during our investigation, drilling for the piles may proceed without the need for casing.

However, the contractor should be prepared to use casing or other approved means to prevent caving should the need arise.

Closely spaced piles (closer than 2-1/2 diameter) should be drilled and filled alternately, allowing the concrete to set at least eight hours before drilling the adjacent pile. All excavations should be filled with concrete as soon after drilling as possible. In no event should pile shafts be left open overnight.

The concrete should be placed with appropriate equipment, so that the concrete is not allowed to fall freely more than 5 feet and to prevent concrete from striking the walls of the shaft, thus causing caving.

All loose materials should be cleared from the bottom of the pile excavation. If casing is necessary and is utilized, then the casing should be withdrawn concurrently with the concrete placement.

Prior to concrete placement, any disturbed soils within the area of the sides of pile caps should be compacted to at least 95 percent relative compaction (ASTM D1557).

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The pile contractor may confirm the homogeneity of the concrete in the CIDH piles using the gamma-gamma test method or alternative methods.

Structural Slabs (Deep Foundations)

Slabs supported by a deep foundation should be designed as a structural slab and not derive any support from the underlying soils.

Lateral Loading And Retaining Wall Design

Resistance to lateral loads will be provided by passive earth pressure and base friction.