geotechnical feasibility investigation 3721 mt. diablo

Geotechnical Engineering Engineering Geology

Storm Water Management Construction Observation & Testing Services

1600 Willow Pass Court • Concord, CA 94520 • Tel 925.688.1001

Mailing Address: P.O. Box 815, Concord, CA 94522-0815 Serving Northern and Central California, Sacramento, and Central Valley Regions

June 27, 2019

GEOTECHNICAL FEASIBILITY INVESTIGATION 3721 MT. DIABLO BOULEVARD RESIDENTIAL DEVELOPMENT

LAFAYETTE, CALIFORNIA SFB PROJECT NO. 864-1

Prepared For:

3721 Land LLC 2415 San Ramon Valley Boulevard, #4236

San Ramon, CA 94583

Prepared By:

Stevens, Ferrone & Bailey Engineering Company, Inc.

` Jonathan Bailey, P.E., G.E. Kenneth C. Ferrone, P.E., G.E., C.E.G. Civil/Geotechnical Engineer Civil/Geotechnical Engineer Certified Engineering Geologist

Stevens, Ferrone & Bailey Engineering Co., Inc. ii 3721 Mt. Diablo Blvd., 864-1.rpt June 27, 2019

TABLE OF CONTENTS

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

2.0 SCOPE OF WORK............................................................................................................2

3.0 SITE INVESTIGATION ...................................................................................................3

3.1 Site History and Surface Description ...................................................................3 3.2 Subsurface ..............................................................................................................3 3.3 Groundwater ..........................................................................................................4 3.4 Hydrologic Soil Group ...........................................................................................4 3.5 Geology and Seismicity ..........................................................................................5 3.6 Liquefaction & Lateral Spreading .......................................................................5

4.0 PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS ............................7

4.1 Earthwork ...............................................................................................................8 4.2 Building Foundation, Retaining Walls, and Pavement ....................................10

5.0 CONDITIONS AND LIMITATIONS............................................................................11

FIGURES

1 Site Plan APPENDICES A Field Investigation A-1

Figure A-1, Key to Exploratory Boring Logs Exploratory Boring Logs (SFB-1 and SFB-2)

B Laboratory Investigation B-1 C ASFE Guidelines C-1

Stevens, Ferrone & Bailey Engineering Company, Inc. Page 1 of 12 3721 Mt. Diablo Blvd., 864-1.rpt June 27, 2019

1.0 INTRODUCTION

This report presents the results of our geotechnical feasibility investigation for the proposed residential development to be located at 3721 Mt. Diablo Boulevard in Lafayette, California as shown on the Site Plan, Figure 1. The purpose of our assessment was to evaluate the geological and geotechnical conditions at the site and provide preliminary recommendations regarding the geological and geotechnical engineering aspects of the project for planning and cost estimating. Based on the information indicated on the Site Plan, as well as information provided by Mr. Steve Stone, and preliminary architectural plans prepared by HDO Architects and Planners, the project will consist of demolishing the existing building and constructing a new three-story residential structure with a single level of below grade parking. Excavation on the order of 10 to 15 feet is expected for the proposed underground parking. The preliminary conclusions provided in this report are based upon the information presented above. Stevens, Ferrone & Bailey Engineering Company, Inc. (SFB) should be consulted if any changes to the project occur to assess if the changes affect the validity of this report.


2.0 SCOPE OF WORK

This investigation included the following scope of work:

• Reviewing published and unpublished geotechnical and geological literature relevant to the site;

• Performing reconnaissance of the site and surrounding area; • Performing two exploratory borings to a maximum depth of about 41½ feet; • Performing engineering analysis of the field and laboratory data; and • Preparing this report.

The data obtained and the analyses performed were for the purpose of providing preliminary geologic and geotechnical recommendations for planning and cost estimating purposes. Toxicity potential assessment of onsite materials or groundwater (including mold) and flooding evaluations were beyond our scope of work.


3.0 SITE INVESTIGATION

Reconnaissance of the site and surrounding area and subsurface exploration was performed on June 13, 2019. Subsurface exploration consisted of drilling two exploratory borings to a maximum depth of 41½ feet below the existing site grades. Boring SFB-1 near Mt. Diablo Boulevard was drilled with a truck-mounted B24 drill rig with 4-inch diameter solid flight augers. Boring SFB-2 located behind (south) of the existing building was drilled using a portable minute-man drill rig. The approximate locations of our borings are shown on the Site Plan, Figure 1. Logs of the borings and details regarding our field investigation are included in Appendix A. The results of our laboratory tests are discussed in Appendix B. It should be noted that changes in the surface and subsurface conditions can occur over time as a result of either natural processes or human activity and may affect the validity of the conclusions and recommendations in this report.

3.1 Site History and Surface Description

At the time of our investigation and as shown on Figure 1, the site was occupied by a two-story building that appeared to be supported on a drilled pier foundation. The site was bounded by existing commercial development to east and west, Mt. Diablo Boulevard to the north, and a small creek and associated embankments to the south. The site is roughly rectangular shaped and slopes from approximate Elevation 337 feet (WGS-84 datum) along Mt. Diablo Blvd to approximate Elevation 325 feet (WGS-84 datum) at the rear of the property. A retaining wall along the creek embankment appeared to be about 3 and 5 feet high and appears to be constructed with sandbags. Based on our review of historical aerial images available at NETRonline1, Google Earth2, and historical property data3 it is our understanding that the site was vacant prior to construction of the existing commercial building in 1961.

3.2 Subsurface

Our borings generally encountered up to four and a half feet of undocumented fill consisting of firm to stiff, silty clay with sand and gravel. Below fill materials and pavement, where encountered, our borings generally encountered firm to very stiff, silty and sandy clay with thin

1https://www.historicaerials.com accessed 05/28/2019 2Google Earth Pro, V 7.3.2, Lafayette, CA; accessed 06/10/2019 3 https://www.loopnet.com/Listing/3721-Mt-Diablo-Blvd-Lafayette-CA/9543465/ accessed 06/25/2019

https://www.historicaerials.com/

https://www.loopnet.com/Listing/3721-Mt-Diablo-Blvd-Lafayette-CA/9543465/


interbedded lenses of loose to medium dense sand to the maximum depth explored of about 41 ½ feet. The results of laboratory testing indicate that clayey surficial soils have high plasticity and expansion potential. Detailed descriptions of the materials encountered in our exploratory borings are included in Appendix A. Our attached boring logs and related information depict location-specific subsurface conditions encountered during our field investigation. The approximate locations of our borings were determined using pacing or landmark references, and should be considered accurate only to the degree implied by the method used. Elevations noted on the boring logs are based on Google Earth information; datum for these elevations is unknown.

3.3 Groundwater

At the time of drilling, groundwater was encountered in Boring SFB-1 (front of property) at a depth of about 25 feet and in Boring SFB-2 (rear of property) at a depth of about 9-½ feet. It should be noted that groundwater in the back of the property may be significantly affected by surface water in the adjacent creek. Our borings might not have been left open for a sufficient period of time to establish equilibrium groundwater conditions. In addition, fluctuations in the groundwater level could occur due to change in seasons, variations in rainfall, and surface water in the adjacent drainage among other factors.

3.4 Hydrologic Soil Group

The site’s surficial soils have been mapped as Clear Lake Clay (0 to 15 percent slopes). These soils are assigned to Hydrologic Soil Group C by USDA Natural Resources Conservation Service (NRCS); the soils have been categorized as having moderately low to moderately high water transmission rates of approximately 0.06 to 0.2 inches per hour with a high capacity for runoff during winter rains. Group C soils are defined as having a slow infiltration rate when thoroughly wet and may consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. Based on laboratory test results of samples retrieved from our borings, we recommend that near surface soils be categorized as Soil Group D. These soils have very slow infiltration rate and high runoff potential when thoroughly wet and consist chiefly of clays that have high shrink-swell potential, soils have a high water table, soils that have a claypan or clay layer at or near the surface and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission.


3.5 Geology and Seismicity

According to Helley and Graymer (1997)4, the site is underlain by Pleistocene alluvial fan and fluvial deposits that are generally composed of brown dense gravelly and clayey sand or clayey gravel that fines upward to sandy clay. These deposits display various sorting and are located along most stream channels in Contra Costa County, and can be related to modern stream courses. The project site is located about 10 miles inland from the San Francisco Bay shoreline, at the base of the Briones Hills, and east of the Berkeley Hills along the Highway 24 corridor. The San Francisco Bay Area is considered one of the most seismically active regions in the United States. Significant earthquakes have occurred in the San Francisco Bay Area which are believed to be associated with crustal movements along a system of sub-parallel fault zones that generally trend in a northwesterly direction. According to the Briones Valley Quadrangle Seismic Hazard Zones Map, no active fault traces have been mapped crossing the site by the State of California5. Earthquake intensities will vary throughout the San Francisco Bay Area, depending upon numerous factors including the magnitude of earthquake, the distance of the site from the causative fault, and the type of materials underlying the site. The U.S. Geological Survey (2016)6 indicated that there is a 72 percent chance of at least one magnitude 6.7 or greater earthquake striking the San Francisco Bay region between 2014 and 2043. Therefore, the site will probably be subjected to at least one moderate to severe earthquake that will cause strong ground shaking. According to the U.S. Geological Survey’s Unified Hazard Tool and applying the Dynamic: Conterminous U.S. 2008 (v3.3.1) model (accessed 6/25/2019), the resulting deaggregation calculations indicate that the site has a 10% probability of exceeding a peak ground acceleration of about 0.54g in 50 years (design basis ground motion based on stiff to very stiff site soil conditions; mean return time of 475 years). The actual ground surface acceleration might vary depending upon the local seismic characteristics of the underlying bedrock and the overlying unconsolidated soils.

3.6 Liquefaction & Lateral Spreading

Soil liquefaction is a phenomenon primarily associated with saturated, cohesionless, soil layers located close to the ground surface. These soils lose strength during cyclic loading, such as imposed by earthquakes. During the loss of strength, the soil acquires mobility sufficient to permit

4Helley, and Graymer, 1997, Quaternary Geology of Contra Costa County, California, and Surrounding Areas; Derived from the Digital Database Open-File 97-98. USGS Open File Report 97-98. 5State of California, Seismic Hazard Zones, Briones Valley Quadrangle, Official Map, Released: February 14, 2003. 6Aagaard, Blair, Boatwright, Garcia, Harris, Michael, Schwartz, and DiLeo, Earthquake Outlook for the San Francisco Bay Region 2014–2043, USGS Fact Sheet 2016–3020, Revised August 2016 (ver. 1.1).


both horizontal and vertical movements. Soils that are most susceptible to liquefaction are clean, loose, uniformly graded, saturated, fine-grained sands that lie close to the ground surface. As of the date of this report, the liquefaction potential of the site has not been evaluated by the State of California7. The site and surrounding land are mapped as being within an area having moderate susceptibility to liquefaction hazard by ABAG and the U.S. Geological Survey8,9. Based on the presence of saturated loose to medium dense lenses of silty sand as encountered in Boring SFB-2, it is our opinion that there is a moderate to high potential for surface damage at the site resulting from liquefaction of these sandy lenses during a major seismic event. During a major seismic event, there is also the potential for lateral spreading to impact the site. Lateral spreading occurs when soils liquefy during an earthquake event and the liquefied soils and any overlying soils move laterally to unconfined spaces which can cause significant horizontal ground displacements. Based on the presence of liquefiable subsurface soils and the unlined drainage swale south of the property, it is our opinion that there is a moderate to high potential for ground surface damage at the development resulting from lateral spreading.

7State of California, Seismic Hazard Zones, Briones Valley Quadrangle, Official Map, Released: February 14, 2003. 8Witter, Knudsen, Sowers, Wentworth, Koehler, and Randolph, 2006, Maps of Quaternary Deposits and Liquefaction Susceptibility in the Central San Francisco Bay Region, California”, USGS Open File Report 2006-1037. 9Knudsen, Sowers, Witter, Wentworth, and Helly, 2000, “Preliminary Maps of Quaternary Deposits and Liquefaction Susceptibility, Nine-County San Francisco Bay Region, California”, USGS Open File Report 00-444.


4.0 PRELIMINARY CONCLUSIONS AND RECOMMENDATIONS

The following are the primary geologic and geotechnical considerations for use in the planning, cost estimating, and preliminary design of the development. EXISTING FILL MATERIALS: As described previously, our borings encountered up to about 4-1/2 feet of weak undocumented fill which will compress under the proposed building loads. In order to reduce the potential for damaging differential settlement of overlying improvements (such as new fills, building foundations, driveways, exterior flatwork, and pavements), we recommend that these weak fills be completely removed and re-compacted. The over-excavation should extend to depths where competent soil is encountered. It is likely that the excavation for the below-grade parking will removed existing fill materials within the footprint of the proposed building. GROUNDWATER AND DEWATERING: At the time of drilling, our borings encountered groundwater at a depth of about 25 feet near Mt. Diablo Boulevard and at a depth of about 9-1/2 feet at the back of the existing building. Temporary dewatering of excavations may be necessary where excavations extend below groundwater levels, such as during the parking garage excavations and underground utility installations. If the proposed garage walls will not be permanently drained, then the garage walls should be designed to resist hydrostatic pressures. Portions of the garage walls below groundwater levels should also be waterproofed. PARKING GARAGE EXCAVATION: If temporary construction slopes are to be used at the perimeter of the parking garage excavation, we recommend the slopes be no steeper than 1 horizontal to 1 vertical. The top of the slopes should be appropriately setback from existing improvements, such as adjacent streets and properties. All temporary construction slopes and existing improvements should be monitored during the construction process and appropriate remedial measures should be immediately installed if detrimental movements are observed or measured. Where construction slopes cannot be used due to space constraints, temporary shoring should be installed. We recommend current OSHA standards be followed during the design and construction of any temporary construction slopes and/or shoring. The base of the garage excavation may be wet and unstable. If necessary, the subgrade soils can be mixed with 4 to 5 percent quicklime by weight and compacted to at least 90 percent relative compaction to aid in base stabilization prior to foundation construction. LIQUEFACTION: As described previously in this report, saturated loose to medium dense lenses of silty sand were encountered in Boring SFB-2 at the rear of the property. It is our opinion that there is a moderate to high potential for surface damage at the site resulting from liquefaction of these sandy lenses during a major seismic event. During a major seismic event, there is also the


potential for lateral spreading to impact the site. Lateral spreading occurs when soils liquefy during an earthquake event and the liquefied soils and any overlying soils move laterally to unconfined spaces which can cause significant horizontal ground displacements. Based on the presence of liquefiable subsurface soils and the unlined drainage swale south of the property, it is our opinion that there is a moderate to high potential for ground surface damage at the development resulting from lateral spreading. We recommend the building by supported on a drilled pier foundation system that gains support below the potentially liquefiable sandy soil lenses, and that the pier foundation be designed to resist lateral loads that could occur during lateral spreading of the ground toward the existing creek channel. EXPANSION POTENTIAL: The expansive clayey soils will be subjected to volume changes during seasonal fluctuations in moisture content. To reduce the potential for post-construction distress to the proposed structure and associated improvements resulting from swelling and shrinkage of these materials, we recommend that the proposed building and its associated features be designed to reduce the impact of the expansive soils. CORROSION POTENTIAL: We recommend soil samples be tested for pH (ASTM D4972), chlorides (ASTM D4327), sulfates (ASTM D4327), sulfides (ASTM D4658M), resistivity at 100% saturation (ASTM G57), and Redox potential (ASTM D1498) for use in evaluating the potential for corrosion on concrete and buried metal such as utilities and reinforcing steel. Please be aware that we are not corrosion protection experts; we recommend corrosion protection measures be designed and constructed so that all concrete and metal is protected against corrosion. ADDITIONAL RECOMMENDATIONS: General drainage, earthwork, and foundation recommendations for use in planning, cost estimating, and preliminary design of the project are presented below. Future subsurface explorations using borings should be performed in order to better evaluate the extent and impact of the potentially liquefiable sandy soil lenses, and to determine appropriate geotechnical engineering parameters that can be used to design the recommended pier foundation system. Retrieved soil samples from the additional borings will require laboratory testing to confirm the recommendations provided in this report and to engineer additional recommendations for the project. Upon completion of the subsurface explorations, laboratory testing, and engineering analyses, SFB will need to prepare a report providing detailed, final design and construction criteria for the project. We also recommend SFB be retained to provide consulting services during the interim. We assume no responsibility for misinterpretation of the preliminary recommendations contained in this report.

4.1 Earthwork

The site should be cleared of all obstructions including existing structures and their entire foundation systems, existing utilities and pipelines and their associated backfill, designated trees


and shrubs and their associated entire root systems, and debris. Wells, if they exist, should be abandoned in accordance with Contra Costa County standards. From a geotechnical standpoint, any existing trench backfill materials, clay or concrete pipes, pavements, and concrete that are removed can be used as new fill onsite provided debris is removed and it is broken up to meet the size requirements for fill material. After clearing, portions of the site containing heavy surface vegetation should be stripped to an appropriate depth to remove these materials. From a geotechnical and mechanical standpoint, onsite soils having an organic content of less than 3 percent by volume can be used as fill. Fill should not contain rocks or lumps larger than 6 inches in greatest dimension with not more than 15 percent larger than 2.5 inches. If required, imported fill should have a plasticity index of 25 or less and have a significant amount of cohesive fines. Within the upper 5 feet of the finished ground surface, we expect structural fill will need to be compacted at least 88 to 92 percent relative compaction, and structural fill below a depth of 5 feet be compacted to at least 90 percent relative compaction, as determined by ASTM D1557 (latest edition). Fill should be compacted with a moisture content approximately 3 to 5 percent above optimum. Onsite trench backfill should be compacted to at least 90 percent relative compaction. Imported trench sand backfill should be compacted to at least 95 percent relative compaction with sufficient added water during backfill operations to prevent the soil from "bulking" during compaction. The upper 3 feet of trench backfill in foundation, slab, and pavement areas should be entirely compacted to at least 95 percent relative compaction. To reduce piping and settlement of overlying improvements, we recommend rock bedding and rock backfill (if used) be completely surrounded by a filter fabric such as Mirafi 140N (or equivalent); alternatively, filter fabric would not be necessary if Caltrans Class 2 permeable material is used in lieu of rock bedding and rock backfill. Surface water ponding must not be allowed on pavements, adjacent to foundations, and at the top or adjacent to retaining walls. Ponding of water should also not be allowed on the ground surface adjacent to or near exterior slabs, including driveways, walkways, and patios. Surface water should not be allowed to flow over retaining walls. We recommend positive surface gradients of at least 2 percent be provided adjacent to foundations to direct surface water away from the foundations and toward suitable discharge facilities. Roof downspouts and landscaping drainage inlets should be connected to solid pipes that discharge the collected water into appropriate water collection facilities. We recommend the surface drainage be designed in accordance with the latest edition of the California Building Code.


4.2 Building Foundation, Retaining Walls, and Pavement

The proposed building should be supported on a drilled pier and grade beam foundation system where the piers gain their vertical support below the potentially liquefiable sand soils. The piers should also be designed to resist potential lateral earth pressures that occur during a lateral spreading event. We recommend the garage slab bear entirely on the pier and grade beam foundation system. Alternatively, the garage slab can bear upon the underlying subgrade provided it is understood that the subgrade may settle during or immediately after a liquefaction event. In order to reduce the potential for vapor transmission through the garage slab, we recommend a vapor retarder be placed between the subgrade soils and the bottom of the garage slabs. We recommend the vapor retarder consist of a single layer of Stego Wrap Vapor Barrier 15 mil Class A or equivalent. Concrete slabs retain moisture and often take many months to dry; construction water added during the concrete pour further increases the curing time. If the slabs are not allowed to completely cure prior to constructing the super-structure, the concrete slabs will expel water vapor and the vapor will be trapped under impermeable flooring. The concrete mix design for the slabs should have a maximum water/cement ratio of 0.45; the actual water/cement ratio may need to be reduced if the concentration of soluble sulfates or chlorides in the supporting subgrade is detrimental to the concrete. Where walls retain soil, they must be designed to resist both lateral earth pressures and any additional lateral loads caused by surcharging such as building and roadway loads. We anticipate that the restrained walls will need to resist an active pressure of at least 50 pounds per cubic foot (pcf) plus a uniform pressure of about 10H pounds per square foot, where H is the height of the wall in feet.. For retaining walls that need to resist earthquake induced lateral loads from nearby foundations, walls that are to be designed to resist earthquake loads, and any retaining walls that are higher than 6 feet (as required by the 2016 CBC), we recommend the walls also be designed to resist seismic pressures developed from a design basis earthquake; we expect the seismic pressure will be on the order of 30 pcf. Some movement of the walls may occur during moderate to strong earthquake shaking and may result in distress as is typical for all structures subjected to earthquake shaking. Walls should be fully-back drained to prevent the build-up of hydrostatic pressures and should be protected against vapor transmission. Concrete pavements will likely consist of about 6 inches of Portland cement concrete overlying 6 inches of compacted Caltrans Class 2 baserock.


5.0 CONDITIONS AND LIMITATIONS

Exploratory borings, laboratory testing, and geotechnical engineering analyses will need to be performed in order to provide detailed geotechnical design and construction criteria for the project and to confirm the preliminary recommendations provided above. The future report should include detailed drainage, earthwork, foundation, and pavement recommendations for use in the design and construction of the project. Once the future, detailed investigation is complete, we recommend SFB review the project’s design and specifications to verify that the recommendations presented in the future report have been properly interpreted and implemented in the design, plans, and specifications. We also recommend SFB be retained to provide consulting services and to perform construction observation and testing services during the construction phase of the project to observe and test the implementation of our recommendations, and to provide supplemental or revised recommendations in the event conditions different than those described in our reports are encountered. We assume no responsibility for misinterpretation of our recommendations if we do not review the plans and specifications and are not retained during construction. SFB is not responsible for the validity or accuracy of information, analyses, test results, or designs provided to SFB by others or prepared by others. The analysis, opinions, and preliminary recommendations submitted in this report are based in part upon the data obtained from our field work and upon information provided by others. Variations of subsurface conditions from those analyzed or characterized in this report are not uncommon and may become evident during construction. In addition, changes in the condition of the site can occur over time as a result of either natural processes (such as earthquakes, flooding, or changes in ground water levels) or human activity (such as construction adjacent to the site, dumping of fill, or excavating). If changes to the site’s surface or subsurface conditions occur since the performance of the field work described in this report, we should be contacted immediately to evaluate the differing conditions to assess if the opinions and preliminary recommendations provided in this report are still applicable or should be amended. It should be understood that advancements in the practice of geotechnical engineering and engineering geology, or discovery of differing surface or subsurface conditions, may affect the validity of this report and are not uncommon. SFB strives to perform its services in a proper and professional manner with reasonable care and competence but we are not infallible. Geological engineering and geotechnical engineering are disciplines that are far less exact than other engineering disciplines; therefore, we should be consulted if it is not completely understood what the limitations to using this report are. In the event that there are any changes in the nature or location of the project, as described in this report, or if any future additions are planned, the preliminary conclusions and recommendations


contained in this report shall not be considered valid unless we are contacted in writing, the project changes are reviewed by us, and the preliminary conclusions and recommendations presented in this report are modified or verified in writing. Appendix C provides additional information about this report.

FIGURES

M

T

.

D

I

A

B

L

O

B

L

V

D

.

SF

B-1

SFB-2

APPROXIMATE LOCATION OF SFB

EXPLORATORY BORING (6/13/19)

KEY

APPROXIMATE PROJECT LIMIT

SFB-1

ailey

tevenserrone &

1

1600 Willow Pass Court

Concord, CA 94520

Tel 925.688.1001

Fax 925.688.1005

www.SFandB.com

864-1

June 2019

PROJECT NO.

DATE

FIGURE

SITE PLAN

Lafayette, California

3721 MT. DIABLO BOULEVARD

60'30'0

APPROXIMATE SCALE: 1" = 30'

NOTE: Base map was created by overlaying an architectural site plan prepared

by HDO Architects and Planners on a Google Earth image dated 4/2/18.

APPENDIX A Field Investigation

Stevens, Ferrone & Bailey Engineering Co., Inc. A-1 3721 Mt. Diablo Blvd., 864-1.rpt June 27, 2019

APPENDIX A Field Investigation

Our field investigation for the proposed development at 3721 Mt. Diablo Boulevard in Lafayette, California, consisted of a surface reconnaissance and a subsurface exploration program. Subsurface exploration was performed using both portable and truck-mounted drill rigs equipped with continuous flight, solid stem augers. Two exploratory borings were drilled on May 13, 2019. Our representative continuously logged the soils encountered in the borings in the field. The soils are described in general accordance with the Unified Soil Classification System (ASTM D2487). Logs of the borings as well as a key for the classification of the soil (Figure A-1) are included as part of this appendix. Representative samples were obtained from our exploratory borings at selected depths appropriate to the investigation. Relatively undisturbed samples were obtained using a 3-inch O.D. split barrel sampler with liners, and disturbed samples were obtained using a 2-inch O.D. split spoon sampler. All samples were transmitted to our offices for evaluation and appropriate testing. Both sampler types are indicated in the “Sampler” column of the boring logs as designated in Figure A-1. Resistance blow counts were obtained in our borings with the samplers by dropping either a 70-pound or 140-pound safety hammer through a 30-inch free fall. The sampler was driven 18 inches and the number of blows were recorded for each 6 inches of penetration. The blows per foot recorded on the boring logs represent the accumulated number of converted blows that were required to drive the last 12 inches, or the number of inches indicated where hard resistance was encountered. Blow counts recorded on the boring logs have been converted to equivalent SPT field blow counts, but have not been corrected for overburden, silt content, or other factors. Representative samples were obtained from our exploratory borings at selected depths appropriate to the investigation. The attached boring logs and related information show our interpretation of the subsurface conditions at the dates and locations indicated, and it is not warranted that they are representative of subsurface conditions at other locations and times.

A-1June 2019864-1

3721 MT. DIABLO BOULEVARDLafayette, California

1600 Willow Pass CourtConcord, CA 94520Tel: (925) 688-1001

Pitcher BarrelM odified California sampler(3" OD Split Barrel)

HQ Core

Standard Penetration sampler(2" OD Split Barrel)

SYM BOLS & NOTES

KEY TO EXPLORATORY BORING LOGS

Clayey sands, and-clay mixtures

CLEAR SQUARE SIEVE OPENINGS

Siltsand

Clays

Sand

Fine M edium

M ajor Divisions

SandAnd

SandySoils

200

Grained

Poorly-graded gravels or gravelsand mixture, little or no fines

Silty gravels, gravel-sand-siltmixtures

Clayey gravels, gravel-sand-claymixtures

Well-graded sands or gravellysands, little or no fines

Gravelly

M edium Dense

3"

Inorganic clays of low to mediumplasticity, gravelly clays, sandyclays, silty clays, lean clays

Organic silts and organic silt-claysof low plasticity

Inorganic silts, micaceous ordiatomaceous fine or silty soils,elastic silts

Organic clays of medium to highplasticity

Blows/Foot*

M L

CL

Fine

Inorganic clays of high plasticity,fat clays

Soils

Soils

12"U.S. STANDARD SERIES SIEVE

Clays

SiltsAnd

16 - 32

Soils

ltr

Inorganic silts and very fine sands,rock flour, silty or clayey finesands or clayey silts with slightplasticity

Very SoftSoftFirmStiff

Very Stiff

2 - 44 - 8

SM

Over 50

GW

GP

GM

Description

OH

PT

M ajor Divisions

1 - 2

4 - 8

grfgrf

Gravel

Dense

Coarse

Poorly-graded sands or gravellysands, little or no fines

Silty sands, sand-silt mixtures

40 10 4

Peat and other highly organic soils

ClaysLL > 50

Description

Highly Organic

OL

M H

Over 32

Loose

Over 8

Silts and ClaysSands and Gravels Blows/Foot*

Ground Water level initially encountered

Ground Water level at end of drilling

PI = Plasticity IndexLL = Liquid LimitR = R-Value

GRAIN SIZES

Hard

And

UNIFIED SOIL CLASSIFICATION SYSTEM

0 - 2

CONSISTENCYRELATIVE DENSITY

Very Dense

0 - 4

LL < 50

1/2 - 1

ltr

Gravel

SC

Very Loose

Well-graded gravels or gravel sandmixtures, little or no fines

CoarseCobbles Boulders

8 - 16

tracesomewith-y

<5%5-15%

16-30%31-49%

Constituent Percentage

SaturatedWet

M oistDampDry

I ncreasing VisualM oisture Content

California Sampler(2.5" OD Split Barrel)

4 - 10

10 - 30

Coarse

3/4"

Soils

CH

SW Silts

GC

Shelby Tube

*Number of Blows for a 140-pound hammer falling 30 inches, driving a 2-inch O.D. (1-3/8" I .D.) split spoon sampler.* *Unconfined compressive strength.

SP

30 - 50

FIGURE NO.

0 - 1/2

Strength (Ksf)* *

2 - 4

PROJECT NO. DATE

KE

Y 8

64-1

.GP

J S

TE

VE

NS

FE

RR

ON

E B

AIL

EY

.GD

T

6/27

/19

Concrete about 3" thick.Aggregate Base Rock (AB) about 3" thick.FILL: CLAY (CL), brown with gray mottling,silty, some sand(fine- to medium-grained),damp.CLAY (CL), brown, silty, somesand(fine-grained), moist.

Some sand(fine- to medium-grained).

Change color to olive gray.

Change color to brown, trace sand(fine- tocoarse-grained), moist.

2.5

3.7

24

18

22

22

26

96

110

104

7

15

13

13

14

7

13

13

firm

stiff

firm

stiff

at 6':Liquid Limit = 50%Plasticity Index = 35

BORING DIAMETER 4-inch

DESCRIPTION AND CLASSIFICATION

EXPLORATORY BORING LOG

DE

PT

H(F

EE

T)

DESCRIPTION AND REMARKS

BORING NO.

SFB-1

DRILL RIG Mobile B24 CFA LOGGED BY RAC

DATE DRILLED 06/13/19

SURFACE ELEVATION 337 feet

DEPTH TO GROUND WATER 25 feet

PROJECT NO. DATE

June 2019864-1



EX

PLO

RA

TO

RY

BO

RIN

G L

OG

864

-1.G

PJ

ST

EV

EN

S F

ER

RO

NE

BA

ILE

Y.G

DT

6/

27/1

9

UN

C.

CO

MP

.(K

SF

)

SA

MP

LER

WA

TE

RC

ON

TE

NT

(%

)

DR

Y D

EN

SIT

Y(P

CF

)

SP

TN

-VA

LUE

ELE

VA

TIO

N

335

330

325

320

315

310

305

0

5

10

15

20

25

30

CONSIST SOILTYPE

OTHER

TESTS

CLAY (CL) Continued, change color tograyish-brown, some sand(fine- tocoarse-grained), trace gravel(fine, subangular tosubrounded), moist.

Bottom of Boring = 41.5 feetNotes: Stratification is approximate, variationsmust be expected. Blowcounts converted toSPT N-values. See Report for additional details.

17

15

very stiff

stiff




DE

PT

H(F

EE

T)


BORING NO.

SFB-1

DRILL RIG Mobile B24 CFA LOGGED BY RAC



DEPTH TO GROUND WATER 25 feet

PROJECT NO. DATE

June 2019864-1



EX

PLO

RA

TO

RY

BO

RIN

G L

OG

864

-1.G

PJ

ST

EV

EN

S F

ER

RO

NE

BA

ILE

Y.G

DT

6/

27/1

9

UN

C.

CO

MP

.(K

SF

)

SA

MP

LER

WA

TE

RC

ON

TE

NT

(%

)

DR

Y D

EN

SIT

Y(P

CF

)

SP

TN

-VA

LUE

ELE

VA

TIO

N

300

295

290

285

280

275

270

35

40

45

50

55

60

65

CONSIST SOILTYPE

OTHER

TESTS

FILL: CLAY (CL), dark grayish brown, silty,some gravel(fine, subangular to subrounded),some sand(fine- to coarse-grained), traceorganics (rootlets), dry to damp.Change color to brown with gray mottling, withgravel(fine to course, rounded to subangular),with sand(fine- to coarse-grained), damp.Some gravel(fine to course, rounded tosubangular).CLAY (CL-ML), grayish-brown, silty, sandy(fine-to medium-grained), moist.

SAND (SM), bluish-gray, fine- to coarse-grained,with silt, some gravel(fine to course, rounded tosubangular), some clay, wet.CLAY (CL), greenish-gray, silty, with sand(fine-to medium-grained), trace rootlets, moist.

With interbeded sand (fine- to course-grained)lenses about 6" thick between 16' and 20', wet.

Change color to gray, moist to wet.

Change color to bluish-gray.

Bottom of Boring = 26.5 feetNotes: Stratification is approximate, variationsmust be expected. Blowcounts converted toSPT N-values. See Report for additional details.

19

18

39

95

12

5

7

5

9

9

12

stiff

firm

firm

loose

firm

stiff

At 6':Percent Passing #200Sieve = 65.2%

At 10':Percent Passing #200Sieve = 20.3%




DE

PT

H(F

EE

T)


BORING NO.

SFB-2

DRILL RIG Minuteman, CFA, 70lb. Hammer LOGGED BY RAC



DEPTH TO GROUND WATER 9.5 feet

PROJECT NO. DATE

June 2019864-1



EX

PLO

RA

TO

RY

BO

RIN

G L

OG

864

-1.G

PJ

ST

EV

EN

S F

ER

RO

NE

BA

ILE

Y.G

DT

6/

27/1

9

UN

C.

CO

MP

.(K

SF

)

SA

MP

LER

WA

TE

RC

ON

TE

NT

(%

)

DR

Y D

EN

SIT

Y(P

CF

)

SP

TN

-VA

LUE

ELE

VA

TIO

N

325

320

315

310

305

300

295

0

5

10

15

20

25

30

CONSIST SOILTYPE

OTHER

TESTS

APPENDIX B Laboratory Investigation

Stevens, Ferrone & Bailey Engineering Co., Inc. B-1 3721 Mt. Diablo Blvd., 864-1.rpt June 27, 2019

APPENDIX B Laboratory Investigation

Our laboratory testing program for the proposed development project was directed toward a quantitative and qualitative evaluation of the physical and mechanical properties of the soils underlying the site. The natural water content was determined on eight subsurface soil samples. The water contents are recorded on the boring logs at the appropriate sample depths. Dry density determination was performed on four samples of the subsurface soils to evaluate their physical properties. The results of this test are shown on the boring log at the appropriate sample depths. Atterberg Limit determinations were performed on one soil sample to determine the range of water content over which the soil exhibits plasticity. These values were used to classify the soil in accordance with the Unified Soil Classification System and to indicate the soil's compressibility and expansion potentials. The results of the tests are presented on the boring logs at the appropriate sample depths and are also attached to this appendix. The percent passing the #200 sieve was performed on two soil samples. These tests were performed to assist in the classification of the soil and to determine their grain size distribution. The results of the tests are presented on the boring logs at the appropriate sample depths and are also attached to this appendix. Unconfined compression testing was performed on two relatively undisturbed subsurface soil samples of to evaluate the undrained shear strengths of these materials. Failure was taken as the peak normal stress. The results of the tests are presented on the boring logs at the appropriate sample depths and are also attached to this appendix.

Atterberg Limits Test – ASTM D4318

Project Number: 864-1 Project Name: 3721 Mt. Diablo Boulevard

Boring/Sample No: 1 Depth: 6.0 Date: 06-20-19

Description of Sample: Dark gray brown silty CLAY some sand (CL/CH) Tested By R

Data Summary Liquid Limit 50

Plastic Limit 15

Plasticity Index 35

Natural Water Content 23.5

Liquidity Index 0.243

% Passing #200 Sieve --

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

Plas

ticity

Inde

x (%

)

Liquid Limit (%)

Plasticity Chart

MH or OH

CL-ML

CL or OL

ML or OL

15 20 25 30 35 40 45 5048

49

50

51

52

53

10

Wat

er C

onte

nt (

%)

Number of Blows

Liquid Limit

Plastic Limit Data

Trial 1 2 Ave Water Content (%) 15.3 15.4 15

UNCONFINED COMPRESSIVE STRENGTH – D2166

0

500

1000

1500

2000

2500

3000

0.0 5.0 10.0 15.0

Unc

onfin

ed S

treng

th (l

b/ft2 )

Strain (%)

Project Number: 864-1 Boring #: 1 Depth : 11

Project Name: 3721 Mt. Diablo Boulevard Date: 6/17/2019

Description: Dark gray brown sandy silty CLAY some gravel (CL) Tested By: R

Soil Specimen Initial Measurements

Diameter 2.42 in Initial Area 4.60 in2

Initial Length 5.2 in Volume 0.01384 ft3

Water Content 18.3 % Wet Density 130.0 pcf Dry Density 109.8 pcf

Max Unconfined Compressive Strength

Elapsed Time 12.5 min Vertical Dial 0.625 in

Strain 12.0 % Area 0.03631 ft2

Axial Load 89.8 lbs Compressive Strength 2473 psf

UNCONFINED COMPRESSIVE STRENGTH – D2166

0

500

1000

1500

2000

2500

3000

3500

4000

0.0 5.0 10.0 15.0 20.0

Unc

onfin

ed S

treng

th (l

b/ft2 )

Strain (%)

Depth : 15.5

Date: 6/17/2019

Project Number: 864-1 Boring #: 1

Project Name: 3721 Mt. Diablo Boulevard

Description: Olive gray silty CLAY some sand (CL/CH) Tested By: R

Soil Specimen Initial Measurements

Diameter 2.42 in Initial Area 4.60 in2

Initial Length 5.07 in Volume 0.01350 ft3

Water Content 21.6 % Wet Density 126.2 pcf Dry Density 103.8 pcf

Max Unconfined Compressive Strength

Elapsed Time 15 min Vertical Dial 0.75 in

Strain 14.8 % Area 0.03749 ft2

Axial Load 138.1 lbs Compressive Strength 3684 psf

APPENDIX C ASFE Guidelines

geotechnical feasibility investigation 3721 mt. diablo

Documents