ATTACH 3 GeoTech Report 02.02.21.pdf

REPORT C OVER PAGE

Geotechnical Engineering Report

Sterile Process Supply Trailer and Modular Building

Palo Alto, Santa Clara County, California

February 2, 2021

Terracon Project No. ND205107

Prepared for:

Spur Design LLC

Phoenix, Arizona

Prepared by:

Terracon Consultants, Inc.

Concord, California

Terracon Consultants, Inc. 5075 Commercial Circle, Suite E Concord, California 94520

P (925) 609 7224 F (925) 609 5324 terracon.com

REPORT C OVER LETTER TO SIGN

Spur Design LLC

4425 East Agave Road

Phoenix, Arizona 85044

Attn: Mr. Ryan Gibson – Principal/Senior Architect

P: (602) 584 5011

E: ryan.gibson@spur-design.com

Re: Geotechnical Engineering Report

Sterile Process Supply Trailer and Modular Building

3801 Miranda Avenue

Palo Alto, Santa Clara County, California

Terracon Project No. ND205107

Dear Mr. Gibson:

We have completed the Geotechnical Engineering services for the above referenced project. This study was performed in general accordance with Terracon Proposal No. PND195107 dated

November 18, 2020. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations and pavements for the proposed project.

We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report or if we may be of further service, please contact us.

Sincerely, Terracon Consultants, Inc.

Hoda Alinasabbaboli, E.I.T. Noah T. Smith, P.E, G.E.

Project Engineer Principal

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REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

SEISMIC CONSIDERATIONS

SHALLOW FOUNDATIONS

PAVEMENT

CORROSIVITY

GENERAL COMMENTS

FIGURES

Note: This report was originally delivered in a web-based format. Orange Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the

GeoReport logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

ATTACHMENTS

EXPLORATION AND TESTING PROCEDURES

SITE LOCATION AND EXPLORATION PLANS

EXPLORATION RESULTS

SUPPORTING INFORMATION

Note: Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/

Sterile Process Supply Trailer and Modular Building ■ Palo Alto, Santa Clara County, California

February 2, 2021 ■ Terracon Project No. ND205107

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REPORT SUMMARY

Topic Overview Statement

Project Description

The project will consist of the placement of a Mobile Sterile Process Supply Trailer and a Pre-Fabricated Modular Building up to 2,000 square feet (sf) in size at the site. A historical road will be reconstructed to help facility traffic flow.

Max. Support Loads: 10 to 20 kips (assumed) Max. Slab Loads: 800 pounds per square foot (psf) (assumed)

Geotechnical Characterization

Subgrade soil conditions encountered in our borings generally consisted of 0 to 2½ feet of well gravel FILL underlain by interbedded layers of medium to very stiff clay with variable amounts of sand and medium to very dense sand with variable amounts of clay and silt.

Groundwater was not encountered in the borings at the time they were drilled.

Earthwork

■ Existing undocumented fill should be removed where encountered. The existing undocumented fill may be reused as engineered fill per the recommendations provided in the Earthwork section of this report.

■ The near surface soils have moderate to high plasticity and are sensitive to moisture variation.

■ Cuts and fills on the order of 2 feet or less are anticipated.

■ Grading should be conducted in accordance with the Earthwork section of this report.

Shallow Foundations

The trailer and building may be supported by shallow foundations. Footings should extend at least 18 inches below lowest adjacent grade and should bear on minimum firm native soil or compacted structural fill.

Allowable bearing pressure = 2,000 psf Expected settlements: 1-inch total, < ½-inch differential Recommendations for the design of shallow foundations are provided in the Foundations section of this report.

Mat Slab Foundations

As an alternative to shallow foundations, the trailer and building may be supported by a mat slab foundation Allowable bearing pressure = 800 psf Expected settlements: 1-inch total, < ½-inch differential Recommendations for the design of mat slab foundations are provided in the

Foundations section of this report.

Pavements

Pavement sections are provided for both rigid and flexible pavements. Alternate pavement sections utilizing chemical treatment or geogrid reinforcement are provided.

General Comments

This section contains important information about the limitations of this geotechnical engineering report.

1. If the reader is reviewing this report as a pdf, the topics above can be used to access the appropriate section of the report by simply clicking on the topic itself.

2. This summary is for convenience only. It should be used in conjunction with the entire report for design purposes.

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INTRODUCTION

Geotechnical Engineering Report

Sterile Process Supply Trailer and Modular Building

3801 Miranda Avenue

Palo Alto, Santa Clara County, California Terracon Project No. ND205107

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed Sterile Process Supply Trailer and Modular Building to be located at 3801 Miranda Avenue in Palo Alto, Santa Clara County, California. The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions ■ Pavement design and construction

■ Groundwater conditions ■ Soil corrosivity

■ Site preparation and earthwork ■ Seismic site classification per 2019 CBC

■ Foundation design and construction

The geotechnical engineering Scope of Services for this project included the advancement of six test borings to depths ranging from approximately 5 to 26½ feet below existing site grades.

Maps showing the site and boring locations are shown in the Site Location and Exploration

Plan sections, respectively. The results of the laboratory testing performed on soil samples obtained from the site during the field exploration are included on the boring logs and as separate graphs in the Exploration Results section.

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SITE CONDITIONS

The following description of site conditions was derived from our site visit in association with the field exploration and our review of publicly available geologic and topographic maps.

Item Description

Parcel Information

The project is located at 3801 Miranda Avenue, Palo Alto, Santa Clara

County, California.

Approximate Project Latitude/Longitude:

37.4022°N 122.1379°W, See Site Location

Existing Improvements

The site is located within the Palo Alto VA Health Care System Palo Alto

Campus which is made up of healthcare and office buildings, parking structures, and paved driveways and access roads. The project site itself is about 1/3 acre in size and is located on the south side of the campus positioned between buildings 50 and 51 south of parking lots 7 and 51.

The proposed trailer and modular building location is currently undeveloped. A construction container and some construction debris were present at the site. It appears the site was most recently used for construction material staging, was used primarily for parking from 2007 to 2015, and consisted of landscaping prior to 2007.

Current Ground Cover Bare ground, gravel asphalt, and weeds.

Existing Topography

(From Google Earth Pro)

The site is relatively flat with approximately 2 to 3 feet or less of relief across the site.

Geology

Our previous experience near vicinity of the site and geologic maps indicate subsurface conditions consist of Holocene age alluvial sand, fine grained, silt, gravel, and clay.1 The subgrade soils encountered in our borings were consistent with the mapped geology and previous borings near vicinity of the site performed on April 13th, 2020 through April 15th, 2020.

1 Dibblee, T.W., and Minch, J.A., 2007, Geologic map of the Palo Alto and Mountain View quadrangles, Alameda, San Mateo, and

Santa Clara Counties, California: Dibblee Geological Foundation, Dibblee Foundation Map DF-350, scale 1:24,000

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PROJECT DESCRIPTION

Our initial understanding of the project was provided in our proposal and was discussed during project planning. A period of collaboration has transpired since the project was initiated, and our final understanding of the project conditions is as follows:

Item Description

Information Provided A project Scope of Work document for VA Project Number 640-398 was provided to Terracon by Spur via email.

Project Description

The project will consist of the placement of a Sterile Process Supply Trailer and a Modular Building at the site. A historical road will be reconstructed to help facility traffic flow.

Building Construction

■ Mobile Sterile Process Supply Trailer

■ Pre-Fabricated Modular Building approximately 1,000 to 2,000 square feet in size

Finished Floor

Elevation Not known.

Maximum Loads

(assumed values)

■ Supports: 10 to 20 kips

■ Slabs: 800 pounds per square foot (psf)

Grading Cuts and fills on the order of 2 feet of less are anticipated to develop final grade.

Pavements

We have assumed both rigid (concrete) and flexible (asphalt) pavement sections will be constructed.

Anticipated traffic indices (TIs) are as follows:

■ Auto Parking Areas: TI = 5.0

■ Auto Road: TI = 5.5

■ Truck Parking Areas: TI = 6.0

■ Truck Ramps and Roads: TI = 8.0

Average Daily Truck Traffic for rigid pavements

■ Car Parking and Access Lanes: ADTT = 1 (Category A)

■ Truck Parking: ADTT = 25 (Category B)

■ Dumpster Pads: Per Category C

The pavement design period is 20 years.

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GEOTECHNICAL CHARACTERIZATION

We have developed a general characterization of the subsurface conditions based upon our review of the subsurface exploration, laboratory data, geologic setting and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical calculations and evaluation of site preparation and foundation options. Conditions encountered at each exploration point are indicated on the individual logs. The individual logs can be found in the

Exploration Results section and the GeoModel can be found in the Figures section of this report.

As part of our analyses, we identified the following model layers within the subsurface profile. For a more detailed view of the model layer depths at each boring location, refer to the GeoModel.

Model Layer Layer Name General Description

Surface 2 to 3 inches of asphalt over 3 to 3½ inches of aggregate base in borings B2 and B4.

2 Fill Medium dense well graded gravel with sand.

3 Fat Clay Medium to very stiff fat clay with variable amounts of sand.

4 Lean Clay Stiff to very stiff lean clay with variable amounts of sand and gravel.

5 Sand Medium dense to very dense sand with variable amounts of clay, silt, and gravel.

Groundwater Conditions

Groundwater was not encountered in our borings while drilling or for the short duration borings could remain open. Due to low permeability of the soils encountered in the borings, a relatively long period may be necessary for a groundwater level to develop and stabilize in a borehole. Long term observations in piezometers or observation wells sealed from the influence of surface water are often required to define groundwater levels in materials of this type.

Groundwater level fluctuations can occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the borings were performed. Therefore, groundwater levels during construction or at other times in the life of the structures may vary. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

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GEOTECHNICAL OVERVIEW

The subject site has geotechnical considerations that will affect the construction and performance of the proposed improvements that are discussed in this report. The primary geotechnical considerations that have been identified at the subject site that will affect development are the following:

■ Moderately to highly plastic soil considerations

■ Undocumented fill considerations

Moderately to Highly Plastic Clay Considerations

As indicated in the Geotechnical Characterization section of this report, the near surface soils encountered in our borings consisted of 30 inches of medium dense well graded gravel with sand

FILL in Borings B1 and B3 and stiff to very stiff clay with variable amounts of sand in the remainder borings. The near surface clay is moderately to highly plastic and could become unstable with typical earthwork and construction traffic, especially after precipitation events. Effective drainage should be completed early in the construction sequence and maintained after construction to avoid potential issues. If possible, the grading should be performed during the warmer and drier times of the year. If grading is performed during the winter months, an increased risk for possible undercutting and replacement of unstable subgrade will persist. Additional site preparation recommendations, including subgrade improvement and fill placement, are provided in the

Earthwork section.

The surficial clay encountered in our borings exhibits the potential for shrink-swell movements with changes in moisture content from seasonal or manmade conditions. Additional areas of localized moderately to highly plastic clays are likely present in areas where borings were not performed. In order to help mitigate the effects of moderate to high volume change clay the trailer and building may be supported by spread footings or mat slabs provided they extend at least 18 inches below lowest adjacent grade.

The recommendations in this report may not eliminate all future subgrade volume change and resultant foundation movements. However, the procedures outlined herein should help reduce the effects of subgrade volume change on the proposed trailer and building.

This report provides recommendations to help mitigate the effects of soil shrinkage and expansion. However, even if these procedures are followed, some movement of the trailer and building should be anticipated. The severity of damage (mainly cosmetic) will likely increase if any modification of the site results in excessive wetting or drying of the expansive soils. Eliminating the risk of movement and distress may not be feasible, but it may be possible to further reduce the risk of movement if significantly more extensive measures, such as supporting the

Responsive ■ Resourceful ■ Reliable 6 improvements on deep foundations, are used during construction. We would be pleased to discuss other construction alternatives with you upon request.

Undocumented Fill Considerations

Approximately 30 inches of fill was encountered in borings B1 and B3. The fill consists of medium dense well graded gravel with sand. No compaction records for the fill were available for review.

As a result, the fill is considered to be undocumented. Such undocumented fill can result in differential settlement and damage to proposed structures relying on the fill for structural support.

As a result, the fill is not suitable to support the proposed trailer, modular building, and pavements and shall be completely over excavated and cleaned of any debris prior to reuse. The proposed trailer and modular building may be supported by Shallow Foundations or Mat Slab

Foundations provided all undocumented fill encountered is over-excavated and replaced as structural fill placed and compacted per the Earthwork recommendations provided in this report.

All undocumented fill in Pavement areas should also be over-excavated and replaced as structural fill placed and compacted per the Earthwork recommendations provided in this report.

Even with the recommended earthwork procedures, there is an inherent risk for the owner that the limits of the fill will not be not be discovered until grading operations begin. Additional test pits may be performed to determine the extent of the fil.

The General Comments section provides an understanding of the report limitations.

EARTHWORK

We anticipate grading for this project may consist of cuts and fills on the order of 2 feet or less. If greater cuts and fills are required, Terracon should be contacted to provide supplemental recommendations as needed. Earthwork is anticipated to include clearing and grubbing, excavations, and fill placement. The following sections provide recommendations for use in the preparation of specifications for the work. Recommendations include critical quality criteria, as necessary, to render the site in the state considered in our geotechnical engineering evaluation for foundations and pavements.

Site Preparation

Prior to placing fill, all existing debris, construction materials, vegetation and root mat should be stripped and removed from the site. This should include removal of any concrete slabs, buried footings and pavements, and underground utilities that may exist within the area of the proposed construction.

Utilities or underground facilities could be encountered during construction. If unexpected utilities, or underground facilities are encountered, such features should be removed and the excavation

Responsive ■ Resourceful ■ Reliable 7 thoroughly cleaned prior to backfill placement and/or construction. The subgrade should be proof-rolled with an adequately loaded vehicle such as a fully loaded tandem axle dump truck. The proof-rolling should be performed under the direction of the Geotechnical Engineer. Areas excessively deflecting under the proof-roll should be delineated and subsequently addressed by the Geotechnical Engineer. Such areas should either be removed or modified by stabilizing as noted in the following section Soil Stabilization. Excessively wet or dry material should either be removed or moisture conditioned and recompacted. Exposed surfaces should be free of mounds and depressions which could prevent uniform compaction.

Subgrade Preparation

After clearing, any required cuts should be made including complete over excavation of the undocumented fill. The undocumented fill shall be entirely over-excavated down to native soil in areas requiring structural support. The over-excavated undocumented fill may be stockpiled for use as structural fill provided it is cleaned of vegetation, debris, and any other deleterious material and meets the criteria for engineered fill specified in the Fill Material Types section of this report.

Once any required cuts and required over-excavations have been made, and prior to placing any fill, the subgrade soil should be scarified, moisture conditioned, and compacted. The depth of scarification of subgrade soils and moisture conditioning of the subgrade is highly dependent on the time of year of construction and the site conditions that exist immediately prior to construction.

If construction occurs during the winter or spring, when the subgrade soils are typically already in a moist condition, scarification and compaction may only be 12 inches. If construction occurs during the summer or fall when the subgrade soils have been allowed to dry out deeper, the depth of scarification and moisture conditioning may be as much as 18 inches. A representative from

Terracon should be present to observe the exposed subgrade and specify the depth of scarification and moisture conditioning required.

Following scarification and compaction of the subgrade, over-excavated areas may be backfilled with compacted structural fill and any additional fill may be placed and compacted. The moisture content and compaction of subgrade soils should be maintained until foundation/pavement construction. Care should be taken to prevent wetting or drying of the bearing materials during construction. Grading for the proposed structures should incorporate the limits of the structures plus a lateral distance of 5 feet beyond the outside edge of foundations.

Soil Stabilization

Methods of subgrade improvement, as described below, could include scarification, moisture conditioning and recompaction, and removal of unstable materials and replacement with granular fill (with or without geosynthetics) and/or chemical treatment with lime and/or cement. The appropriate method of improvement, if required, would be dependent on factors such as schedule, weather, the size of the area to be stabilized, and the nature of the instability. More detailed

Responsive ■ Resourceful ■ Reliable 8 recommendations can be provided during construction as the need for subgrade stabilization occurs. Performing site grading operations during warm seasons and dry periods would help to reduce the amount of subgrade stabilization required.

If the exposed subgrade is unstable during proof rolling operations, it could be stabilized using one of the methods outlined below.

◼ Scarification and Compaction – It may be feasible to scarify, dry, and compact the exposed soils. The success of this procedure would depend primarily upon favorable weather and sufficient time to dry the soils. Stable subgrades likely would not be achievable if the thickness of the unstable soil is greater than about 1 foot or if construction is performed during a period of wet or cool weather when drying is difficult.

◼ Aggregate Base – The use of Caltrans Class II aggregate base is the most common procedure to improve subgrade stability. Typical undercut depths would be expected to range from about 6 to 18 inches below finished subgrade elevation with this procedure. The use of high modulus geosynthetics (i.e., engineering fabric or geogrid) could also be considered after underground work such as utility construction is completed. Prior to placing the fabric or geogrid, we recommend that all below-grade construction, such as utility line installation, be completed to avoid damaging the fabric or geogrid. Equipment should not be operated above the fabric or geogrid until one full lift of aggregate base is placed above it. The maximum particle size of granular material placed over geotextile fabric or geogrid should meet the manufacturer’s specifications.

◼ Chemical Treatment – Chemical treatment involves treating the unstable or pavement subgrade soils with a certain percentage of high calcium quicklime or Portland cement.

Usually 4.0 to 5.5 percent based on the dry unit weight of the soil, for a depth of 12 to 18 inches. For estimating purposes, we recommend using 4.5 percent lime and a soil unit weight of 110 pounds per cubic foot. For 12-inch and 18-inch treatment depths, this results in an estimated minimum spread rate of 5 and 7.5 pounds per square foot lime/cement, respectively. The actual amount of lime/cement to be used should be determined by Terracon and by laboratory testing at least three weeks prior to the start of grading operations.

Chemical treatment is performed after rough grading is completed.

Further evaluation of the need and recommendations for subgrade stabilization can be provided during construction as the geotechnical conditions are exposed.

Fill Material Types

Fill required to achieve design grade should be classified as structural fill and general fill.

Structural fill is material used below, or within 5 feet of structures and pavements. General fill is

Responsive ■ Resourceful ■ Reliable 9 material used to achieve grade outside of these areas. Earthen materials used for structural and general fill should meet the following material property requirements:

Fill Type USCS Classification Acceptable Location for Placement

Lean Clay/Clayey

Sand

CL, SC

(LL<40)

All structural and general locations and elevations, except as LVC material unless material explicitly meets LVC requirements.

Moderate Plasticity

Material

CL

(50>LL≥40 or 30>PI≥25) All general fill locations and elevations.

Well-graded

Granular

GW, GM,

SM, SW

All structural and general fill locations and elevations.

Low Volume

Change (LVC)

CL, SC (LL<30 & PI<12)

or

Well-graded Granular

All structural and general fill locations and elevations.

On-site Soils

GW, CL, SC, SM As indicated above.

CH All general fill locations

1. Compacted structural fill should consist of approved materials that are free of organic matter and debris and should contain no material larger than 3 inches in greatest dimension. A sample of each material type should be submitted to Terracon for evaluation and approval at least 2 weeks prior to construction.

2. Delineation of moderate to highly plastic clays should be performed in the field by a qualified geotechnical engineer or their representative and could require additional laboratory testing.

3. Caltrans Class II aggregate base may be used for this material.

4. Low plasticity cohesive soil or granular soil having low plasticity fines. Material should be approved by the geotechnical engineer.

5. This material should be removed and recompacted if used as an engineered or structural fill as described in section Fill Compaction Requirements. Existing soils to be re-used as structural or general fill should be processed to remove any vegetation or debris present in the material prior to re-use.

For all import material, the contractor shall submit current verified reports from a recognized analytical laboratory indicating that the import has a “not applicable” (Class S0) potential for sulfate attack based upon current ACI criteria and is “mildly 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 project.

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Fill Compaction Requirements

Structural and general fill should meet the following compaction requirements.

Item Structural Fill General Fill

Maximum Lift

Thickness

8 inches or less in loose thickness when heavy, self-propelled compaction equipment is used.

4 to 6 inches in loose thickness when hand-guided equipment (i.e. jumping jack or plate compactor) is used

Same as Structural fill

Minimum Compaction

Requirements 1, 3

95% of max: Upper 12 inches of subgrade in pavement areas, for aggregate base and chemically treated soil, and below foundations.

90% of max: All other locations

90% of max.

Water Content

Range

Low plasticity cohesive: +1% to +3% above optimum

High plasticity cohesive: +2% to +4% above optimum

Granular: -2% to +2% of optimum

As required to achieve min.

compaction requirements

1. Maximum density and optimum water content as determined by the Modified Proctor test (ASTM D 1557).

2. Reduced lift thicknesses are recommended in confined areas (e.g., utility trenches, foundation excavations, and foundation backfill) and when hand-operated compaction equipment is used.

3. We recommend that engineered fill be tested for moisture content and compaction during placement.

Should the results of the in-place density tests indicate the specified moisture or compaction limits have not been met, the area represented by the test should be reworked and retested as required until the specified moisture and compaction requirements are achieved. This procedure is intended for soils with 30 percent or less material larger than ¾ inch. Accordingly, we recommend full time proof roll observation be performed instead of moisture density testing for materials containing more than 30 percent aggregate retained on the ¾-inch sieve.

4. Specifically, moisture levels should be maintained low enough to allow for satisfactory compaction to be achieved without the cohesionless fill material pumping when proof rolled.

Utility Trench Backfill

It is anticipated that the on-site soils will provide suitable support for underground utilities and piping that may be installed. Any soft and/or unsuitable material encountered at the bottom of excavations should be removed and be replaced with an adequate bedding material. A non-expansive granular material with a sand equivalent greater than 30 should be used for bedding and shading of utilities, unless allowed or specified otherwise by the utility manufacturer.

All trench excavations should be made with sufficient working space to permit construction including backfill placement and compaction. If utility trenches are backfilled with relatively clean granular material, they should be capped with at least 18 inches of cementitious flowable fill or cohesive fill in non-pavement areas to reduce the infiltration and conveyance of surface water through the trench backfill. Attempts should also be made to limit the amount of fines migration into the clean granular material. Fines migration into clean granular fill may result in unanticipated

Responsive ■ Resourceful ■ Reliable 11 localized settlements over a period of time. To help limit the amount of fines migration, Terracon recommends the use of a geotextile fabric that is designed to prevent fines migration in areas of contact between clean granular material and fine-grained soils. Terracon also recommends that clean granular fill be tracked or tamped in place where possible in order to limit the amount of future densification which may cause localized settlements over time.

Utility trenches are a common source of water infiltration and migration. Utility trenches penetrating beneath the building should be effectively sealed to restrict water intrusion and flow through the trenches, which could migrate below buildings. The trench should provide an effective trench plug that extends at least 5 feet from the face of the building exterior. The plug material should consist of cementitious flowable fill or low permeability clay. The trench plug material should be placed to surround the utility line. If used, the clay trench plug material should be placed and compacted to comply with the water content and compaction recommendations for structural fill stated previously in this report.

If chemical (lime/cement) treatment of subgrade soils occurs before utility construction, Controlled

Low Strength Material (CLSM) or sand/cement slurry should be used as backfill material to cap utility trenches in all areas where trenches have cut through the treated subgrade. The thickness of the CLSM or slurry should be at least the thickness or depth of chemically treated subgrade.

Such areas trenched through chemically treated soil should not be backfilled with aggregate base, native soil, or chemically treated soil.

Post construction trenching through geogrid may be accomplished with conventional trenching equipment. Repairs to the trenched section shall be accomplished using a full structural replacement of the displaced materials or with a repaired section that is identical to the original section. If the trench section is repaired to match the original, the trench backfill must be compacted to the same or higher density and the geogrid must be over-lapped a minimum 3-inches at the proper geogrid elevation.

Grading and Drainage

All grades must provide effective drainage away from the buildings during and after construction and should be maintained throughout the life of the structures. Water retained next to the buildings can result in soil movements greater than those discussed in this report. Greater movements can result in unacceptable differential foundation movements, cracked walls, and roof leaks. The roof should have gutters/drains with downspouts that discharge onto splash blocks at a distance of at least 10 feet from the buildings.

Exposed ground should be sloped and maintained at a minimum 5 percent away from the buildings for at least 10 feet beyond the perimeter of the building foundations. If a minimum 5 percent slope cannot be achieved due to site grades, a minimum 2½ percent slope could be used provided pavement or hardscape surrounds and extends to the improvements or a subdrain could

Responsive ■ Resourceful ■ Reliable 12 be installed around the perimeter of the foundations that carries water away from the improvements. Locally, flatter grades may be necessary to transition ADA access requirements for flatwork. After building construction and landscaping have been completed, final grades should be verified to document effective drainage has been achieved. Grades around the structures should also be periodically inspected and adjusted, as necessary, as part of the structure’s maintenance program. Where paving or flatwork abuts the structures, a maintenance program should be established to effectively seal and maintain joints and prevent surface water infiltration.

Planters and bio-swales located within 10 feet of the buildings should be self-contained or lined with an impermeable membrane to prevent water from accessing building subgrade soils.

Sprinkler mains and spray heads should be located a minimum of 5 feet away from the buildings’ lines.

Trees or other vegetation whose root systems have the ability to remove excessive moisture from the subgrade and foundation soils should not be planted next to the buildings. Trees and shrubbery should be kept away from the exterior of the buildings a distance at least equal to their expected mature height.

Implementation of adequate drainage for this project can affect the surrounding developments.

Consequently, in addition to designing and constructing drainage for this project, the effects of site drainage should be taken into consideration for the undeveloped portions of this property, and surrounding sites. Extra care should be taken to ensure irrigation and drainage from adjacent areas do not drain onto the project site or saturate the construction area.

Earthwork Construction Considerations

Excavations for the proposed buildings are anticipated to be accomplished with conventional construction equipment. Upon completion of filling and grading, care should be taken to maintain the subgrade moisture content prior to construction of foundations and pavements. Construction traffic over the completed subgrade should be avoided to the extent practical. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. If the subgrade should become desiccated, saturated, or disturbed, the affected material should be removed, or these materials should be scarified, moisture conditioned, and recompacted prior to pavement construction.

We recommend that the earthwork portion of this project be completed during extended periods of dry weather if possible. If earthwork is completed during the wet season (typically November through April) it may be necessary to take extra precautionary measures to protect subgrade soils.

Wet season earthwork operations may require additional mitigation measures beyond that which would be expected during the drier summer and fall months. This could include ground stabilization utilizing chemical treatment of the subgrade, diversion of surface runoff around

Responsive ■ Resourceful ■ Reliable 13 exposed soils, and draining of ponded water on the site. Once subgrades are established, it may be necessary to protect the exposed subgrade soils from construction traffic.

As a minimum, excavations should be performed in accordance with OSHA 29 CFR, Part 1926, Subpart P, “Excavations” and its appendices, and in accordance with any applicable local, and/or state regulations.

Construction site safety is the sole responsibility of the contractor who controls the means, methods, and sequencing of construction operations. Under no circumstances shall the information provided herein be interpreted to mean Terracon is assuming responsibility for construction site safety, or the contractor's activities; such responsibility shall neither be implied nor inferred.

Construction Observation and Testing

The earthwork efforts should be monitored under the direction of the Geotechnical Engineer.

Monitoring should include documentation of adequate removal of vegetation, existing fill, and topsoil, proofrolling, and mitigation of areas delineated by the proofroll to require mitigation.

Each lift of compacted fill should be tested, evaluated, and reworked, as necessary, until approved by the Geotechnical Engineer prior to placement of additional lifts. Each lift of fill should be tested for density and water content at a frequency of at least one test for every 2,000 square feet of compacted fill in the building areas and 2,500 square feet in pavement areas. One density and water content test should be performed per lift for every 50 linear feet of compacted utility trench backfill.

In areas of foundation excavations, the bearing subgrade should be evaluated under the direction of the Geotechnical Engineer. If unanticipated conditions are encountered, the Geotechnical

Engineer should prescribe mitigation options.

In addition to the documentation of the essential parameters necessary for construction, the continuation of the Geotechnical Engineer into the construction phase of the project provides the continuity to maintain the Geotechnical Engineer’s evaluation of subsurface conditions, including assessing variations and associated design changes.

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SEISMIC CONSIDERATIONS

The 2019 California Building Code (CBC) Seismic Design Parameters have been generated using the SEAOC/OSHPD Seismic Design Maps Tool. This web-based software application calculates seismic design parameters in accordance with ASCE 7-16 and 2019 CBC. The 2019 CBC requires that a site-specific ground motion study be performed in accordance with Section 11.4.8 of ASCE 7-16 for Site Class D sites with a mapped S1 value greater than or equal 0.2.

However, Section 11.4.8 of ASCE 7-16 includes an exception from such analysis for specific structures on Site Class D sites. The commentary for Section 11 of ASCE 7-16 (Page 534 of

Section C11 of ASCE 7-16) states that “In general, this exception effectively limits the requirements for site-specific hazard analysis to very tall and or flexible structures at Site Class

D sites.” Based on our understanding of the proposed structures, it is our assumption that the exception in Section 11.4.8 applies to the proposed structure. However, the structural engineer should verify the applicability of this exception.

Based on this exception, the spectral response accelerations presented below were calculated using the site coefficients (Fa and Fv) from Tables 1613.2.3(1) and 1613.2.3(2) presented in

Section 16.4.4 of the 2019 CBC.

Description Value

2019 California Building Code Site Classification (CBC) D

Site Latitude 37.4022°N

Site Longitude 122.1379°W

Ss, Spectral Acceleration for a Short Period 2.018

S1, Spectral Acceleration for a 1-Second Period 0.72

Fa, Site Coefficient 1.2

Fv, Site Coefficient (1-second period) 1.7

SDS, Spectral Acceleration for a Short Period 1.614

SD1, Spectral Acceleration for a 1-Second Period

0.816

1. Seismic site classification in general accordance with the 2019 California Building Code.

2. The 2019 California Building Code (CBC) requires a site soil profile determination extending a depth of 100 feet for seismic site classification. Four borings were extended to a maximum explored depth of 26½ feet bgs. The current scope requested does not include the required 100-foot soil profile determination and this seismic site class assignment considers that similar soil conditions continue below the maximum depth of the subsurface exploration. Additional exploration to greater depths could be considered to confirm the conditions below the current depth of exploration. Alternatively, a geophysical exploration could be utilized in order to attempt to justify a more favorable seismic site class.

3. These values were obtained using online seismic design maps and tools provided by the SEAOC/OSHPD

(https://seismicmaps.org/).

https://seismicmaps.org/

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Typically, a site-specific ground motion study will generate less conservative coefficients and acceleration values which may reduce construction costs. We recommend consulting with a structural engineer to evaluate the need for such study and its potential impact on construction costs. Terracon should be contacted if a site-specific ground motion study is desired.

Faulting and Estimated Ground Motions

The site is located in the San Francisco Bay Area of California, which is a relatively high seismicity region. The type and magnitude of seismic hazards affecting the site are dependent on the distance to causative faults, the intensity, and the magnitude of the seismic event. The following table indicates the distance of the fault zones and the associated maximum credible earthquake that can be produced by nearby seismic events, as calculated using the USGS Unified Hazard

Tool. Segments of the San Andreas Fault system, which is located approximately 8 kilometers from the site, are considered to have the most significant effect at the site from a design standpoint.

Characteristics and Estimated Earthquakes for Regional Faults

Fault Name

Approximate

Contribution

Approximate

Distance to Site

(kilometers)

Maximum Credible

Earthquake (MCE)

Magnitude

San Andreas (Peninsula) [4], UC33brAvg_FM32

28.14 7.88 7.85

San Andreas (Peninsula) [4[, UC33brAvg_FM31

27.88 7.88 7.85

Monte Vista – Shannon [2], UC33brAvg_FM31

7.12 3.66 6.85

Monte Vista – Shannon [2], UC33brAvg_FM32

6.54 3.66 6.85

Based on the ASCE 7-16 Standard, the peak ground acceleration (PGAM) at the subject site is approximately 0.999g. Based on the updated USGS 2014 interactive deaggregations, the PGA at the subject site for a 2% probability of exceedance in 50 years (return period of 2475 years) is expected to be about 0.925g. The site is not located within an Alquist-Priolo Earthquake Fault

Zone based on our review of the State Fault Hazard Maps.1

1 California Department of Conservation Division of Mines and Geology (CDMG), “Digital Images of Official Maps of Alquist-Priolo

Earthquake Fault Zones of California, Southern Region”, CDMG Compact Disc 2000-003, 2000.

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SHALLOW FOUNDATIONS

If the site has been prepared in accordance with the requirements noted in Earthwork, the following design parameters are applicable for shallow foundations.

Design Parameters – Compressive Loads

Item Description

Maximum Net Allowable Bearing pressure 1, 2

2,000 psf

Required Bearing Stratum Firm native soil or compacted structural fill.

Minimum Foundation Dimensions Pad: 24 inches

Strip: 12 inches

Maximum Foundation Dimensions Pad: 84 inches

Strip: 48 inches

Passive Resistance 4, 8

(equivalent fluid pressures) 250 pcf

Coefficient of Sliding Friction 5,8

0.30

Minimum Embedment below

Finished Grade

18 inches

Estimated Total Settlement from

Structural Loads

Less than about 1 inch

Estimated Differential Settlement 2, 7

About 1/2 of total settlement

1. The maximum net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation. An appropriate factor of safety has been applied. These bearing pressures can be increased by 1/3 for transient loads unless those loads have been factored to account for transient conditions. Values assume that exterior grades are no steeper than 20% within 10 feet of structure.

2. Values provided are for maximum loads noted in Project Description. The settlement estimates are for static conditions.

3. Unsuitable or soft soils should be over-excavated and replaced per the recommendations presented in the Earthwork.

4. Use of passive earth pressures require the sides of the excavation for the spread footing foundation to be nearly vertical and the concrete placed neat against these vertical faces or that the footing forms be removed and compacted structural fill be placed against the vertical footing face.

5. Can be used to compute sliding resistance where foundations are placed on firm native soil or compacted structural fill. Should be neglected for foundations subject to net uplift conditions.

6. Embedment necessary to minimize the effects of seasonal water content variations. For sloping ground, maintain depth below the lowest adjacent exterior grade within 5 horizontal feet of the structure.

7. Differential settlements are as measured over a span of 40 feet.

8. Passive pressure and sliding friction may be combined to resist sliding provided the passive pressure is reduced by 50 percent.

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Foundation Construction Considerations

As noted in Earthwork, the footing excavations should be evaluated under the direction of the

Geotechnical Engineer. The base of all foundation excavations should be free of water and loose soil, prior to placing concrete. Concrete should be placed soon after excavating to reduce bearing soil disturbance. Care should be taken to prevent wetting or drying of the bearing materials during construction. Excessively wet or dry material or any loose/disturbed material in the bottom of the footing excavations should be removed/reconditioned before foundation concrete is placed.

To ensure foundations have adequate support, special care should be taken when footings are located adjacent to trenches. The bottom of such footings should be at least 1 foot below an imaginary plane with an inclination of 1.5 horizontal to 1.0 vertical extending upward from the nearest edge of adjacent trenches.

If unsuitable bearing soils are encountered at the base of the footing excavations, the excavations should be extended deeper to suitable soils and the footings could bear directly on these soils at the lower level or on lean concrete backfill placed in the excavations. This is illustrated on the following sketch.

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MAT SLAB FOUNDATIONS

As an alternative to shallow foundations, the trailer and building may be supported by a Mat Slab

Foundation system. The following design parameters are applicable for a mat slab foundation at this site.

Item Description

Maximum Net Allowable Bearing pressure 1, 2

800 psf

Maximum Slab Width 25 feet

Required Bearing Stratum Firm native soil or compacted structural fill

Passive Resistance 4,8

(equivalent fluid pressure) 250 pcf

Coefficient of Sliding Friction 5,8

0.30

Minimum Embedment below

Finished Grade

18 inches

Estimated Total Settlement from

Structural Loads

Less than about 1 inch

Estimated Differential Settlement 2, 7

About 1/2 of total settlement

Design Modulus of Subgrade Reaction, k k1 = 40 psi/in

𝐾(𝐵𝑥𝐵) = 𝐾1 ( 𝐵 + 1

2𝐵

𝐾(𝐵𝑥𝐿) =

𝐾𝐵𝑥𝐵 (1 + 0.5 ∗ (

𝐵 𝐿

1.5

Where:

k1 = coefficient of subgrade reaction of foundations measuring 1 ft. x 1ft.

K(BxB) = coefficient of subgrade modulus for a square foundation having dimensions BxB.

K(BxL) = coefficient of subgrade modulus for a rectangular foundation having dimensions BxL.

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Item Description

1. The maximum net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the foundation base elevation. An appropriate factor of safety has been applied.

This bearing pressure can be increased by 1/3 for transient loads unless those loads have been factored to account for transient conditions. Values assume that exterior grades are no steeper than 20% within 10 feet of structure. The bearing pressure provided assumes a rigid mat slab design that applies a uniform pressure across the footprint of the slab.

2. Values provided are for maximum loads noted in Project Description. The settlement estimates are for static conditions.

3. Unstable or soft soils should be over-excavated and replaced according to the recommendations present in Earthwork.

4. Use of passive earth pressures require the sides of the excavation for the foundation to be nearly vertical and the concrete placed neat against these vertical faces or that the foundation forms be removed and compacted structural fill be placed against the vertical foundation face.

5. Can be used to compute sliding resistance where foundations are placed on suitable soil/materials. Should be neglected for foundations subject to net uplift conditions.

6. Embedment necessary to minimize the effects of seasonal water content variations. For sloping ground, maintain depth below the lowest adjacent exterior grade within 5 horizontal feet of the structure.

7. Differential settlements are as measured over a span of 40 feet.

8. Passive pressure and sliding friction may be combined to resist sliding provided the passive pressure is reduced by 50 percent.

PAVEMENT

General Pavement Comments

Pavement designs are provided for the traffic conditions and pavement life conditions as noted in

Project Description and in the following sections of this report. A critical aspect of pavement performance is site preparation. Pavement designs noted in this section must be applied to the site which has been prepared as recommended in the Earthwork section.

On most project sites, the site grading is accomplished relatively early in the construction phase.

Fills are placed and compacted in a uniform manner. However, as construction proceeds, excavations are made into these areas, rainfall and surface water saturates some areas, heavy traffic from concrete trucks and other delivery vehicles disturbs the subgrade and many surface irregularities are filled in with loose soils to improve trafficability temporarily. As a result, the pavement subgrades, initially prepared early in the project, should be carefully evaluated as the time for pavement construction approaches.

We recommend the moisture content and density of the top 12 inches of the subgrade be evaluated and the pavement subgrades be proofrolled within two days prior to commencement of actual paving operations. Areas not in compliance with the required ranges of moisture or density should be moisture conditioned and recompacted. Particular attention should be paid to high traffic areas that were rutted and disturbed earlier and to areas where backfilled trenches are located.