962-003_Mare Island_Geotechnical Report_2025-05-12.pdf

R e p o r t Co v e r P ag e

Mare Island Naval Cemetery Improvements Geotechnical Engineering Report

Vallejo, Solano County, California

May 12, 2025 | Terracon Project No. R1245107

Prepared for:

Anderson Engineering of Minnesota, LLC 13605 1st Ave N Ste 100 Plymouth, 55441-5454

1220 Concord Avenue, Suite 450 Concord, CA 94520

P 925-609-7224 Terracon.com

Facilities | Environmental | Geotechnical | Materials

R e p o r t Co v e r L et t e r t o S ig n

May 12, 2025

Anderson Engineering of Minnesota, LLC 13605 1st Ave N Ste 100 Plymouth, 55441-5454

Attn: Jeffrey W. Deitner P: (763) 412-4016 E: jdeitner@ae-mm.com

Re: Geotechnical Engineering Report Mare Island Naval Cemetery Improvements Mare Island Naval Cemetery Vallejo, Solano County, California Terracon Project No. R1245107

Dear Mr. Deitner:

We have completed the scope of Geotechnical Engineering services for the referenced project in general accordance with Terracon Proposal No. PR1245107 dated October 22, 2024. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations 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

Ramsey S. Zeidan, P.E. Anthony Argyriou, P.E., G.E.

Senior Engineer Senior Engineer

Geotechnical Engineering Report Mare Island Naval Cemetery Improvements | Vallejo, Solano County, California May 12, 2025 | Terracon Project No. R1245107

Facilities | Environmental | Geotechnical | Materials 1

Table of Contents

Report Summary Introduction Project Description Site Conditions Geotechnical Characterization

Groundwater Conditions Geologic Hazards

Faulting and Estimated Ground Motions Liquefaction Landslides and Debris Flow Flooding

Seismic Considerations Corrosivity Geotechnical Overview

Soft/Unstable Subgrade Potential Expansive Soils Pre-Existing Fill

Earthwork Site Preparation Existing Fill Subgrade Preparation Excavation Soil Stabilization Fill Material Types Fill Placement and Compaction Requirements Utility Trench Backfill Grading and Drainage Earthwork Construction Considerations Construction Observation and Testing

Shallow Foundations Design Parameters – Compressive Loads Flagpole Foundations Foundation Construction Considerations

Lateral Earth Pressures Design Parameters Retaining Wall Drainage

Pavements General Pavement Comments Pavement Design Parameters Pavement Section Thicknesses Pavement Drainage Pavement Maintenance Exterior Hardscape

General Comments

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Figures GeoModels

Attachments

Exploration and Testing Procedures Photography Log Site Location and Exploration Plans Exploration and Laboratory Results Supporting Information

Note: This report was originally delivered in a web-based format. Blue 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 logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/

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Report Summary

Topic 1 Overview Statement 2

Project Description

The project consists of various upgrades to the existing naval cemetery.

Improvements are expected to consist of new paved drive aisles and walkways within the cemetery and a parking lot adjacent to the northwest corner of the cemetery.

The existing retaining walls at the southwest side of the cemetery are expected to be rebuilt with concrete. The project also includes improvements to the existing drainage system and replacing existing flatwork, flagpoles, and other minor structures throughout the cemetery.

Geotechnical Characterization

Borings B1 through B3, advanced in the northern paved area generally encountered about 3 to 5 feet of fill consisting of loose clayey sand to medium stiff sandy lean clay with variable amounts of sand and gravel.

The fill also contained asphalt and concrete debris. Native medium stiff to very stiff lean-to fat clay and highly weathered claystone bedrock was encountered below the fill to the maximum depth explored of about 16½ feet below ground surface (bgs).

Borings B4 through B11 were advanced in the cemetery and generally encountered native medium stiff to very stiff lean-to fat clay underlain by residual soil and highly weathered claystone bedrock to the maximum depth explored of 10¼ feet bgs.

Groundwater was not apparent in the borings during our exploration.

Earthwork

Cuts on the order of 6 feet high, and fills on the order of about 2 feet, are expected for retaining walls and to develop final grades.

Existing on-site clays are sensitive to moisture variation and are not suitable for structural fill.

Minor excavation is anticipated other than retaining wall and foundation construction.

Shallow Foundations

Shallow foundations may be used to support the proposed improvements.

Allowable bearing pressure = 1,500 psf for foundations bearing on at least 2 feet of structural fill. 1,000 psf for foundations bearing on native clay soils.

Expected settlements: < 1-inch total, < 1/2-inch differential

Pavements Pavement sections are provided for both rigid and flexible pavements, with subgrade prepared as noted in Earthwork.

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 in the table 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

This report presents the results of our subsurface exploration and Geotechnical Engineering services performed for the proposed improvements planned at Mare Island Naval Cemetery in Vallejo, Solano County, California. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil (and rock) conditions

■ Groundwater conditions

■ Seismic site classification per the 2022 California Building Code (CBC)

■ Site preparation and earthwork

■ Demolition considerations

■ Foundation design and construction

■ Floor slab design and construction

■ Lateral earth pressures

■ Pavement design and construction

The geotechnical engineering Scope of Services for this project included the advancement of test borings, laboratory testing, engineering analysis, and preparation of this report.

Drawings showing the site and boring locations are shown on the Site Location and Exploration Plan, respectively. The results of the laboratory testing performed on soil samples obtained from the site during our field exploration are included on the boring logs and/or as separate graphs in the Exploration and Laboratory Results section.

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

An initial email request for proposal was provided by Jeffrey Deitner of Anderson Engineering on October 10, 2024. The request included a scope of work document outlining the proposed improvements.

Terracon also discussed the project with Anderson during a meeting on October 16, 2024.

An existing conditions survey, dated February 14, 2025, prepared by Anderson was also provided during project preparation.

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Item Description

Project Description

The project consists of various upgrades to the existing naval cemetery. Improvements are expected to consist of new paved drive aisles and walkways within the cemetery and a parking lot adjacent to the northwest corner of the cemetery. The existing retaining walls at the southwest side of the cemetery are expected to be rebuilt with concrete. The project also includes improvements to the existing drainage system and replacing existing flatwork, flagpoles, and other minor structures throughout the cemetery.

Proposed Structures

Structures associated with the project include reconstructed concrete or masonry block retaining walls, flagpoles, and other minor structures associated with the cemetery.

Grading/Slopes

A preliminary grading plan was not available for review at the time this proposal was prepared. We anticipate up to 6 feet of cut for reconstructed retaining walls and 2 feet of fill at other areas, excluding remedial grading requirements.

Free-Standing Retaining Walls

The retaining walls at the southwest side of the cemetery range from about 4 to 6 feet in height and will likely be rebuilt as concrete walls of similar height.

Existing retaining walls up to about 3½ feet high are also located along the northern/downslope side of the existing pavement area adjacent to the northwest corner of the cemetery. We understand that these walls may also be replaced as part of the project.

Pavements

We understand both rigid (concrete) and flexible (asphalt) pavement sections will be constructed at the site.

The anticipated ACI traffic categories and daily truck traffic are assumed to be:

■ Category A: Car parking areas and access lanes, 1 truck per day

■ Category B: Entrance and truck service lanes, 10 trucks per day

■ Category E: Garbage or fire truck lanes

The following assumed traffic indices (TIs) are used for Caltrans method pavement design:

■ Auto Parking Areas: TI = 5.0:

■ Auto Road: TI = 5.5

■ Truck Parking Areas: TI = 6.0

■ Truck Ramps and Roads: TI = 8.0

The pavement design period is 20 years.

Building Code 2022 California Building Code (CBC)

Terracon should be notified if any of this information is inconsistent with the planned construction, especially the grading limits, as modifications to our recommendations may be necessary.

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Site Conditions

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

Item Description

Parcel Information

The project is located at Mare Island Naval Cemetery in Vallejo, Solano County, California.

Geographic coordinates: 38.0795° N, 122.2531° W APNs 006-604-008-0, 006-604-002-0, roughly 2.5 acres

See Site Location

Existing Improvements

The site consists of an existing naval cemetery. Various improvements consisting of headstones, flatwork, flagpoles, and retaining walls are located on the property.

Current Ground Cover

The cemetery is lightly vegetated with maintained grass. Some large trees are located near the front/northeast side. Some flatwork areas are located at the southwest side and a paved parking area/sport court is located to the northwest.

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Item Description

Existing Retaining walls

Existing retaining walls are located along the northwest/downslope side of the site and parking area and at the southwest and south side of the cemetery.

The retaining wall along the downslope side of the northwestern parking area consisted of an approximately 3½-foot high, buttressed concrete wall. The wall was generally in very poor condition and appeared to be damaged/failing at several locations along the alignment. The base of the wall was supported on a moderate slope that sloped down to Imhoff Road.

The retaining walls at the southwest/upslope side of the cemetery consisted of a stacked block retaining wall up to about 6 feet high at the flagpole/rostrum area and a concrete wall up to about 4 feet high at the Key Family burials near the south side of the cemetery. These walls generally appeared to be performing well with no indications of significant distress.

Existing Topography

The cemetery is located on gently sloping terrain generally sloping down from the southwest toward the northeast. The cemetery is located at elevations that range from approximately 40 feet to 110 feet. (NAVD88).1 Boring depths have been estimated in part with this information and improved topographic information should be provided if available.

We also collected photographs at the time of our field exploration program.

Representative photos are provided in our Photography Log.

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 the site. Conditions observed at each exploration point are indicated on the individual logs. The individual logs can be found in Exploration and Laboratory Results and the GeoModel can be found in the Figures attachment of this report.

1 United States Geological Survey (USGS) National Map 3D Elevation Program (3DEP) , “3DEP Demonstration Elevation Viewer” May 16, 2023 https://apps.nationalmap.gov/3depdem/ .

https://apps.nationalmap.gov/3depdem/

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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

1 Fill Loose clayey sand to medium stiff sandy lean clay with variable amounts of sand and gravel, and asphalt and concrete debris

2 Clay Medium stiff to very stiff lean-to fat clay with variable amounts of sand

3 Clayey Sand Dense clayey sand

4 Bedrock Claystone bedrock, generally highly weathered

Additional borings, auger probes, test pits, or geophysical testing could be performed to obtain more specific subgrade information.

Groundwater Conditions

Neither groundwater nor seepage were encountered within the maximum depths of the borings at the time of our field exploration, or for the short duration the borings could remain open.

Since the borings were backfilled relatively soon after completion, and due to the low permeability of 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. Long-term groundwater monitoring was outside the scope of services for this project. Terracon is experienced in installing groundwater monitoring wells/piezometers to provide more groundwater data prior to construction if required.

Groundwater conditions may change because of seasonal variations in rainfall, runoff, tide, and other conditions not apparent at the time the borings were performed.

Therefore, groundwater levels during construction or at other times in the life of the project may be higher or lower than the levels indicated on the boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

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Geologic Hazards

Geologic maps indicate subsurface conditions at the site consist of clay shale or claystone with sandstone of the Panoche formation1. Surficial alluvial soils are located above the mapped bedrock unit. The subgrade soils encountered in our borings were generally consistent with mapped geology.

Faulting and Estimated Ground Motions

The site is located in the North 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 Hayward Fault, which is located approximately 12½ kilometers from the site, are considered to have the most significant effect at the site from a design standpoint.

Fault Name Approximate Contribution

Approximate Distance to

Site (kilometers)

Maximum Credible

Earthquake (MCE) Magnitude

Hayward (north) (6) 35.91 12.57 7.23

Franklin (5) 13.00 1.38 7.13

Based on the ASCE 7-16 Standard, the peak ground acceleration (PGAM) at the subject site is approximately 0.572g. Based on the USGS 2023 interactive disaggregations, 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 0.833g. The site is not located within an Alquist- Priolo Earthquake Fault Zone based on our review of the State Fault Hazard Maps.2

1 Dibblee, T.W., and Minch, J.A., 2005, Geologic map of the Mare Island quadrangle, Contra Costa, Solano, Marin, & Sonoma Counties, California, Dibblee Geological Foundation, Dibblee Foundation Map DF-145, scale 1:24,000

2 California Geological Survey (CGS), “California Earthquakes Hazards Zone Application (EQ Zapp)”, September 23, 2021, https://maps.conservation.ca.gov/cgs/EQZApp/app/.

https://ngmdb.usgs.gov/Prodesc/proddesc_71813.htm

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Liquefaction

Liquefaction is a mode of ground failure that results from the generation of high pore water pressures during earthquake ground shaking, causing loss of shear strength.

Liquefaction is typically a hazard where loose sandy soils or low plasticity fine grained soils exist below groundwater. The California Geological Survey (CGS) has designated certain areas within California as potential liquefaction hazard zones. These are areas considered at a risk of liquefaction-related ground failure during a seismic event, based upon mapped surficial deposits and the presence of a relatively shallow water table. The project site has not yet been mapped by the CGS for liquefaction hazards.

Due to the proposed improvements consisting of voluntary upgrades to existing, non-habitable structures, a liquefaction analysis for the site was not warranted. In addition, due to the depth of bedrock beneath the site, the potential for liquefaction at the site is considered very low.

Landslides and Debris Flow

The improvements will be constructed on or near both natural slopes and graded areas.

Cut slopes, fill slopes, and retaining walls will be constructed to help develop final grades across the site. Slope movement occurs on sloping sites when surficial soils are saturated, increasing the weight and decreasing the shear strength of the soils.

Generally, movement of the slope due to such conditions occurs within the upper near surface clayey soils. Soil movement also occurs when the upper portion of the slope is excessively loaded (such as by fills) and/or the bottom portion of the slope is undercut and not retained, causing the driving force to exceed the resisting force, and this type of slope instability can occur in deeper soils/rock. Slope movement can also be triggered by strong ground shaking from a seismic event due to the lack of lateral confinement. In addition, the clayey surficial soils at the site are susceptible to seasonal slope creep.

Slope creep is the downward movement of plastic soils due to seasonal contraction and expansion as a result of variations in moisture content.

The California Geological Survey (CGS) has designated certain areas within California as potential seismically-induced landslide hazard zones. These are areas considered at risk of slope failure during a seismic event, based upon mapped surficial deposits. The project site is not located within a mapped CGS seismically-induced landslide hazard zone.

The following hazard maps were reviewed:

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■ Summary Distribution of Slides and Earth Flows in the San Francisco Bay Region, California1

■ Map of Debris-Flow Source Areas in the San Francisco Bay Region, California2

Our review of the foregoing literature indicated that the site is not located within a mapped landslide deposit and historical landslides were not mapped in the vicinity or upslope of the site. While we did not observe any slope failures in or near the location of the improvements at the time of our visit, we believe the potential for slope movement above and adjacent to the area of the improvements is moderate based on the site conditions (i.e. relatively steep slopes, and claystone bedrock).

Static and seismic slope stability analyses of the site and adjacent slopes were not requested or intended and were beyond the scope of this report. If the current global stability of the site is a concern, Terracon is qualified to perform a more detailed geologic hazard investigation and perform the subsequent slope stability analyses for the site.

Flooding

Based on a review of the Federal Emergency Management Agency (FEMA) National Flood Layer (NFHL), the project site is not located within a mapped flood zone. The project site is mapped in an area with a FEMA Flood Zone X designation of minimal flood hazard.

Seismic Considerations

The 2022 CBC Seismic Design Parameters have been generated using the ASCE Hazard Tool. This web-based software application calculates seismic design parameters in accordance with ASCE 7-16, and 2022 CBC. The 2022 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, an exception to this requirement is included in Supplement 3 to ASCE 7 that states: “A ground motion hazard analysis is not required where the value of the parameter SM1 determined by Eq. (11.4-2) is increased by 50% for all applications of SM1

1 U.S. Geological Survey, 1997, Summary Distribution of Slides and Earth Flows in the San Francisco Bay Region, California, Open File Report 97-745C

2 U.S. Geological Survey, 1997, Map of Debris-Flow Source Areas - San Francisco Bay Region Folio Part E, Open File Report 97-745E

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Based on this exception, the spectral response accelerations presented in the following table 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 2022 CBC.

Description Value

2022 California Building Code (CBC) Site Classification1 D2

Risk Category I

Site Latitude3 37.0795º

Site Longitude3 -122.2531º

SS, Spectral Acceleration for a Short Period4 1.500

S1, Spectral Acceleration for a 1-Second Period4 0.600

Fa, Site Coefficient 1.0

Fv, Site Coefficient (1-Second Period) 1.7

SDS, Spectral Acceleration for a Short Period 1.000

SD1, Spectral Acceleration for a 1-Second Period 1.0205

1. Seismic site soil classification in general accordance with the 2022 California Building Code, which refers to ASCE 7-16. Site Classification is required to determine the Seismic Design Category for a structure.

2. The Site Classification is based on the upper 100 feet of the site profile defined by a weighted average value of either shear wave velocity, standard penetration resistance, or undrained shear strength in accordance with Section 20.4 of ASCE 7-16 and the 2022 CBC.

Subsurface explorations at this site were extended to a maximum depth of approximately 16½ feet bgs. The site properties below the maximum exploration depth to 100 feet bgs were estimated based on our experience and knowledge of geologic conditions of the general area. Additional deeper exploration or geophysical testing may be performed to confirm the conditions below the current maximum depth of exploration.

3. Provided coordinates represent a point located at the general center of the site.

4. These values were obtained using online seismic design maps and tools provided by the

ASCE Hazard Tool (https://ascehazardtool.org/).

5. The value of SD1 is increased by 50 percent in accordance with Item 1 Exception in ASCE 7-

16 Supplement 3, Section 11.4.8.

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

https://ascehazardtool.org/

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Corrosivity

The following table lists the results of laboratory soluble sulfate, soluble chloride, electrical resistivity, and pH testing. The values may be used to estimate potential corrosive characteristics of the on-site soils with respect to contact with the various underground materials which will be used for project construction.

Corrosivity Test Results Summary

Boring Sample Depth (feet)

Soil Description

Soluble Sulfate

Soluble Chloride

Electrical Resistivity

(Ω-cm) pH

B2 2.5-4.0 Lean Clay with Sand

0.012 0.011 1,000 9.01

Results of soluble sulfate testing can be classified in accordance with ACI 318 – Building Code Requirements for Structural Concrete. Numerous sources are available to characterize corrosion potential to buried metals using the parameters presented in the previous table. ANSI/AWWA is commonly used for ductile iron, while threshold values for evaluating the effect on steel can be specific to the buried feature (e.g., piling, culverts, welded wire reinforcement, etc.) or agency for which the work is performed. Imported fill materials may have significantly different properties than the site materials noted in the table and should be evaluated if expected to be in contact with metals used for construction. Consultation with a NACE certified corrosion professional is recommended for buried metals on the site.

Mapping by the NRCS includes qualitative severity of corrosion to concrete and steel.

This source rates the near-surface materials as “Low” for corrosion to concrete and “High” for corrosion of steel.

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:

■ Soft/Unstable subgrade potential

■ Expansive soils

■ Pre-Existing fill

■ Existing Retaining Wall Conditions

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Soft/Unstable Subgrade Potential

Relatively soft clayey soils were noted near the surface in our soil borings. These soils may become unstable when disturbed. During periods of dry weather, these soils may be stable upon initial exposure, however, these soils could become relatively soft and unstable under construction traffic. Furthermore, depending upon site conditions during construction, over-excavation, or stabilization of the subgrade and/or base of over-excavations may be needed to achieve a suitable working surface. Accordingly, we recommend that the owner budget for the possibility that over-excavation and/or stabilization may be required, and contractors be prepared to handle potentially unstable and/or soft conditions. Stabilization may consist of aerating/drying the soil, a composite section of aggregate base and geogrid, or chemical stabilization using high calcium quick lime or Portland cement.

Expansive Soils

Expansive soils are present on this site. This report provides recommendations to help mitigate the effects of soil shrinkage and expansion. However, even if these procedures are followed, some movement and (at least minor) cracking in the structures should be anticipated. The severity of cracking and other damage such as uneven slabs will probably increase if 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 expensive measures are used during construction. Some of these options are discussed in this report such as complete replacement of expansive soils.

The near surface, medium stiff to very stiff moderate to high plastic clays could become unstable with typical earthwork and construction traffic, especially after precipitation events. The 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 soils which form the bearing stratum for shallow foundations are plastic and exhibit potential for shrink-swell movements with changes in moisture. Additional areas of localized highly plastic soils are likely present where borings were not performed.

Maintaining above optimum moisture conditions in the bearing soils and a minimum dead load pressure on footings should reduce the anticipated swell movements to tolerable levels. The Shallow Foundations section addresses support of the building directly bearing on native stiff to hard lean/fat clay or structural fill.

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Pre-Existing Fill

Approximately 3 to 5 feet of pre-existing fill consisting of loose clayey sand to medium stiff sandy lean clay was encountered in our borings B1, B2, B3. Fill is also expected to be present behind the southwest stacked block retaining wall and below and around the flagpole landing area. Specific excavation, backfill, and site grading details for the fill are not known. The thickness of fill across the site may vary, and the thicknesses of fill encountered in our borings should not be construed as a minimum or maximum.

Additional fill may be present in areas where borings were not performed.

No compaction records were located or made available for review for the fill. The density of the fill encountered was generally loose to medium stiff indicating the fill may not have been placed with much compaction effort, if any. As a result, we have considered the fill to be undocumented and uncontrolled. Such uncontrolled fill can result in excessive erratic and differential settlements causing damage to proposed structures supported on shallow foundations, hardscapes, and pavements relying on the fill for structural support. Consequently, the pre-existing surficial uncontrolled fills across the site are not suitable for the support of shallow spread footing foundations which would be subject to unacceptable amounts of settlement.

While the uncontrolled fill is not suitable to support the proposed building, the fill should be adequate to support proposed pavements and hardscapes provided Earthwork is conducted per the recommendations provided herein. The pre-existing uncontrolled fill may be selectively reused, provided the material is cleaned of any debris and meets the criteria for general or structural fill in Fill Material Types.

Support of pavements on or above existing fill materials is discussed in this report.

However, even with the recommended construction procedures, an inherent risk remains for the owner that compressible fill or unsuitable material, within or buried by the fill, will not be discovered. This risk of unforeseen conditions cannot be eliminated without completely removing the existing fill but can be reduced by following the recommendations contained in this report. To take advantage of the cost benefit of not removing the entire amount of undocumented fill, the owner must be willing to accept the risk of increased differential performance which can result in increased cracking and abrupt differential settlement.

The recommendations contained in this report are based upon the results of field and laboratory testing (presented in the Exploration and Laboratory Results), engineering analyses, and our current understanding of the proposed project. The General Comments section provides an understanding of the report limitations.

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Earthwork

We do not anticipate significant earthwork to occur within the cemetery as part of the project. Grading may consist of cuts up to 6 feet for retaining wall reconstruction and fills on the order of 2 feet or less. Specific site grading information was unavailable at the time this report was prepared. If elevation and site grading differ from our stated assumptions, Terracon should be contacted to determine if additional earthwork recommendations are warranted, particularly with regard to potential ground settlement.

Earthwork is anticipated to include minor demolition, clearing and grubbing, excavations, and engineered 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, existing vegetation, topsoil, and root mats should be removed.

Complete stripping of the topsoil should be performed in the proposed building and parking/driveway areas. Stripping should extend laterally a minimum of 5 feet beyond the limits of proposed improvements, where practical.

Mature trees are located within or near the footprint of some of the proposed improvements. Tree root systems can remove substantial moisture from surrounding soils. Where trees are removed, the full root ball and all associated dry and desiccated soils should be removed. The soil materials which contain less than 3 percent organics can be reused as engineered fill provided the material is moisture conditioned and properly compacted.

Existing Fill

If the owner elects to construct pavements and exterior slabs on the existing fill, the following protocol should be followed. The fill below pavements and exterior slab areas should be over-excavated to a depth of 2 feet and the resulting subgrade should be scarified to a minimum depth of 12 inches, moisture conditioned, and compacted per the recommendations in Fill Placement and Compaction Requirements. Following compaction of the subgrade, the over-excavated areas may be backfilled with compacted structural fill. The existing fill may be reused, provided the material is cleaned of any debris and meets the criteria for general or structural fill in Fill Material Types. A representative from Terracon should be present to observe the over-excavation of fill.

Once the planned subgrade elevation has been reached, the entire pavement area should be proofrolled. Areas of soft or otherwise unsuitable material should be undercut and replaced with either new structural fill or suitable, existing on-site materials.

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Subgrade Preparation

After clearing, any required cuts and overexcavation should be made.

Subgrade soils beneath proposed exterior hardscape and pavements should be removed to a depth of 1 foot beneath proposed slab or pavement section, or existing grade, whichever is greater.

The pre-existing uncontrolled fill below pavements and exterior slabs should be over-excavated to a minimum depth of 3 feet. The presence of over-sized debris or a high volume of organic material may warrant additional over-excavation at the time of grading operations. If needed, a geotextile fabric may be utilized as a separator between the uncontrolled fill and structural fill.

Where fill is placed on existing slopes steeper than 5H:1V (Horizontal:Vertical), benches should be cut into the existing slopes prior to fill placement. The benches should have a minimum vertical face height of 1 foot and a maximum vertical face height of 3 feet and should be cut wide enough to accommodate the compaction equipment. This benching will help provide a positive bond between the fill and natural soils and reduce the possibility of failure along the fill/natural soil interface.

Excavated material may be stockpiled for use as fill provided it is cleaned of organic material, debris, and any other deleterious material and meets the criteria for general or structural fill specified in the Fill Material Types section of this report.

Once cuts and over-excavation operations are complete, the resulting subgrade should be proofrolled with an adequately loaded vehicle such as a fully-loaded tandem-axle dump truck. The proofrolling should be performed under the observation of the Geotechnical Engineer or their representative. Areas excessively deflecting under the proofroll should be delineated and subsequently addressed by the Geotechnical Engineer. Such areas should either be removed or modified by stabilizing as noted in the Soil Stabilization section of this report. Excessively wet or dry material should either be removed, or moisture conditioned and recompacted.

Once proof rolling has been performed, all exposed areas which will receive fill, once properly cleared and benched where necessary, should be scarified moisture conditioned as necessary, and compacted per the compaction requirements in this report. The depth of scarification of subgrade soils and moisture conditioning of the subgrade is highly dependent upon 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 8 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 or more. A representative from

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

The exposed subgrade in the paved areas will likely be at an elevated moisture content because it has been covered by pavement and may require some drying to achieve the required compaction. The depth of required scarification and moisture conditioning of the subgrade may therefore likely be only 6 or 10 inches. A representative from Terracon should be present to observe the exposed subgrade and specify the depth of scarification and moisture conditioning required subsequent to grading cuts and prior to placing fill.

Following scarification, moisture conditioning, and compaction of the subgrade soils, compacted structural fill soils should then be placed to the proposed design grade and the moisture content and compaction of subgrade soils should be maintained until foundation, floor slab, or pavement construction.

Based upon the subsurface conditions determined from the geotechnical exploration, subgrade soils exposed during construction are anticipated to be relatively workable;

however, the workability of the subgrade may be affected by precipitation, repetitive construction traffic or other factors. If unworkable conditions develop, workability may be improved by scarifying and drying.

Excavation

We anticipate that excavations for the proposed construction can be accomplished with conventional earthmoving equipment. The bottom of excavations should be thoroughly cleaned of loose soils and disturbed materials prior to backfill placement and/or construction.

The bottoms of excavations should be thoroughly cleaned of loose soils and disturbed materials prior to backfill placement and/or construction. Individual contractors are responsible for designing and constructing stable, temporary excavations. Excavations should be sloped or shored in the interest of safety following local and federal regulations, including current OSHA excavation and trench safety standards.

Soil Stabilization

If work takes place during periods of precipitation such as the winter months, stabilization may be needed. Methods of subgrade stabilization, as described in this section, could include scarification, moisture conditioning and recompaction, removal of unstable materials and replacement with granular fill (with or without geosynthetics), and chemical stabilization. The appropriate method of improvement, if required, would be dependent on factors such as schedule, weather, the size of area to be stabilized, and

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Facilities | Environmental | Geotechnical | Materials 19 the nature of the instability. More detailed 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 reduce the amount of subgrade stabilization required.

If the exposed subgrade is unstable during proofrolling operations, it could be stabilized using one of the following methods:

■ Scarification and Recompaction - It may be feasible to scarify, dry, and recompact 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, if the unstable soil is at or near groundwater levels, 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 a common procedure to improve subgrade stability. Typical undercut depths would be expected to range from about 12 inches to 18 inches below finished subgrade elevation. 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 Stabilization - Improvement of subgrades with Portland cement or quicklime could be considered for improving unstable soils. Chemical stabilization should be performed by a pre-qualified contractor who has experience with successfully stabilizing subgrades in the project area on similar sized projects with similar soil conditions. The hazards of chemicals blowing across the site or onto adjacent property should also be considered. Additional testing would be needed to develop specific recommendations to improve subgrade stability by blending chemicals with the site soils. Additional testing could include, but not be limited to, determining the most suitable stabilizing agent, the optimum amounts required, and the presence of sulfates in the soil. If this method is chosen to stabilize subgrade soils the actual amount of high calcium quicklime/Portland cement to be used should be determined by Terracon and by laboratory testing at least three weeks prior to the start of grading operations.

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

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Fill Material Types

Fill required to achieve design grades should be classified as structural fill and general fill. Structural fill is material used below, or within 10 feet of structures, pavements or constructed slopes. General fill is material used to achieve grade outside of these areas.

Reuse of On-Site Soil: Excavated on-site soil may be selectively reused as fill below pavement and landscaping areas. Excavated on-site soil is not suitable for reuse as Structural Fill and should not be placed beneath settlement sensitive structures and within foundation bearing zones. Portions of the on-site soil have an elevated fines content and will be sensitive to moisture conditions (particularly during seasonally wet periods) and may not be suitable for reuse when above optimum moisture content.

Material property requirements for on-site soil for use as general fill and structural fill are noted in the following table:

Property General Fill Structural Fill

Composition Free of deleterious material Free of deleterious material

Maximum particle size 6 inches

(or 2/3 of the lift thickness)

3 inches

Fines content Not limited Less than 40% Passing No. 200 sieve

Plasticity Not limited Maximum liquid limit of 30

Maximum plasticity index of 10

GeoModel Layer Expected to be Suitable1

1, 2, 3, 4 3

1. Based on subsurface exploration. Actual material suitability should be determined in the field at time of construction.

Imported Fill Materials: Imported fill materials should meet the following material property requirements. Regardless of its source, compacted fill should consist of approved materials that are free of organic matter and debris. 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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Soil Type 1 USCS Classification

Acceptable Parameters (for Structural Fill)

Low Plasticity CL, SC Liquid Limit less than 30

Plasticity index less than 10 Less than 70% passing No. 200 sieve

Granular2

GW, GM, GC,

SW, SM

Less than 40% passing No. 200 sieve

1. Structural and general fill should consist of approved materials free of organic matter and debris and should contain no material larger than 3 inches and 6 inches in greatest dimension, respectively. A sample of each material type should be submitted to the Geotechnical Engineer for evaluation at least two weeks prior to use on this site.

Additional geotechnical consultation should be provided prior to use of uniformly graded gravel on the site.

2. Caltrans Class II aggregate base may be used for this material. Recycled aggregate base should not be used without prior approval by the Geotechnical Engineer.

Fill Placement and Compaction Requirements

Compacted native soil and 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 1,2

95% of max. for structural fill below foundations and slabs, within 1 foot of finished pavement subgrade, for aggregate base and chemically treated soil, and for fills thicker than 5 feet.

90% of max. for all other locations

90% of max.

Water Content

Range 1

Granular: -2% to +2% of optimum Low plasticity cohesive: +1% to +3% above optimum Medium plasticity cohesive native subgrade only: +2% to +4% above optimum High plasticity cohesive native subgrade only:

+3% to +5% above optimum

As required to achieve min.

compaction requirements

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Item Structural Fill General Fill

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

2. If the granular material is a coarse sand or gravel, or of a uniform size, or has a low fines content, compaction comparison to relative density may be more appropriate. In this case, granular materials should be compacted to at least 70% relative density (ASTM D 4253 and D 4254). Materials not amenable to density testing should be placed and compacted to a stable condition observed full time by the Geotechnical Engineer or representative.

Utility Trench Backfill

Any soft or unsuitable materials encountered at the bottom of utility trench excavations should be removed and replaced with structural fill or bedding material in accordance with public works specifications for the utility be supported.