GEOTECHNICAL INVESTIGATION
2000-2070 Bryant Street
San Francisco, California
Prepared For:
Nick Podell Company
22 Battery Street, Suite 404
San Francisco, California 94111
Prepared By:
Langan Treadwell Rollo
501 14th Street, 3rd Floor
Oakland, California 94612
Blaire L. Banagan, P.E.
Project Engineer
Lori A. Simpson, G.E.
Principal/Vice President
28 March 2014
750615602
28 March 2014
Ms. Linsey Perlov
Nick Podell Company
22 Battery Street, Suite 404
San Francisco, California 94111
Subject:
Geotechnical Investigation
2000- 2070 Bryant Street
San Francisco, California
Langan Project No.: 750615602
Dear Ms. Linsey Perlov:
We are pleased to present our geotechnical investigation report for the proposed residential
development to be constructed at 2000-2070 Bryant Street in San Francisco, California. Hard
copies of this report will be furnished upon request.
The project site is rectangular with plan dimensions of about 200 by about 325 feet. It is bound
by Bryant Street on the east, Florida Street on the west, 18th Street on the north, and a
community garden and two buildings on the south (two-story and three-story structures, both
of wood-framed construction). The location of the project site is shown on the Site Location
Map, Figure 1. The site is occupied by a one- and two-story concrete and brick building, a two-
story wood frame building with a basement, two two-story wood frame buildings, a one-story
metal and wood frame building, asphalt paved areas, concrete paved areas, and lawn areas.
The sidewalk elevation ranges from approximately 23 to 26 feet (San Francisco City Datum,
SFCD) (north to south) along Bryant from approximately 21 to 19 feet SFCD (north to south) on
Florida Street. Interior portions of the existing building have raised floors, ramps, or staircases
to accommodate the grade changes between Bryant and Florida Streets.
Based on our review of architectural plans prepared by BDE Architecture, we understand the
proposed development consists of a six-story residential building comprised of five levels of
light-framed construction over a one-level concrete podium with parking, residential, and retail
uses. We also understand that the new building will encompass the entire footprint of the site
and will be constructed at grade to minimize excavation depths. The planned finished floor
elevation for most of the building is Elevation 21.5 feet SFCD and steps up to match existing
grades along Bryant Street (finished floor at about Elevation 27.5 feet SFCD) and down to
match existing grades on Florida Street (finished floor at about Elevation 19 feet SFCD).
Subsurface conditions at the northern portion of the site consist of poor quality fill containing
weathered serpentinite underlain by a Marsh deposit and the Colma formation. The marsh
deposit contains continuous layers of potentially liquefiable material and is judged to have a
Geotechnical Investigation
2000- 2070 Bryant Street
San Francisco, California
Langan Project No.: 750615602
28 March 2014
Page 2 of 2
high potential for lateral spread during a large earthquake. At the southern portion of the site,
subsurface conditions consist of medium dense to dense sand fill (with debris in the upper
several feet) underlain by medium dense to very dense sands and stiff to very stiff clays and
silts, the Colma formation, and stiff clays and medium dense to very dense sands. Thin,
continuous layers of potentially liquefiable material were encountered; however, the predicted
settlement is small, and we judge the potential for lateral spreading is low. Groundwater was
measured at the site between Elevations 7 and 14½ feet SFCD during our exploration.
We conclude that the proposed development can be supported on a mat foundation bearing on
improved soil or engineered fill. At the northern portion of the site, the mat can be supported
on improved soil that has been treated in place to mitigate the liquefaction/lateral spread
potential. At the southern portion of the site, the mat can be supported on engineered fill or
improved soil that has been designed to improve the fill, as discussed in the report.
The recommendations contained in this report are based on a limited subsurface exploration
program. Consequently, variations between expected and actual soil conditions may be found
in localized areas during construction. We should be retained to observe excavation, ground
improvement, mat subgrade preparation, and compaction of backfill, during which time we may
make any changes to our recommendations, if deemed necessary.
We appreciate the opportunity to assist you with this exciting and challenging project. If you
have any questions, please call.
Sincerely,
Langan Treadwell Rollo
Blaire L. Banagan, PE Lori A. Simpson, GE
Project Engineer Principal
750615602.03_BB_Letter_2000_2070 Bryant Street_SF
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TABLE OF CONTENTS
1.0 INTRODUCTION ............................................................................................................. 1
2.0 SCOPE OF SERVICES .................................................................................................... 2
3.0 FIELD EXPLORATION .................................................................................................... 3
3.1 Borings ............................................................................................................... 3
3.2 Cone Penetration Tests ..................................................................................... 4
3.3 Laboratory Testing ............................................................................................ 5
4.0 SUBSURFACE CONDITIONS ......................................................................................... 5
4.1 Groundwater ...................................................................................................... 6
5.0 GEOLOGY AND SEISMICITY ......................................................................................... 7
5.1 Regional Geology ............................................................................................... 7
5.2 Regional Seismicity and Faulting ..................................................................... 8
5.3 Seismic Hazards ............................................................................................... 10
5.3.1 Fault Rupture ........................................................................................ 10
5.3.2 Liquefaction and Associated Hazards ................................................. 11
5.3.3 Lateral Spreading ................................................................................. 14
5.3.4 Cyclic Densification .............................................................................. 15
6.0 DISCUSSION AND CONCLUSIONS ............................................................................ 15
6.1 Ground Improvement ...................................................................................... 16
6.1.1 Drilled Displacement Columns ............................................................ 16
6.1.2 Deep Soil Mixing (DSM) ....................................................................... 17
6.2 Foundations and Settlement .......................................................................... 17
6.3 Groundwater .................................................................................................... 19
6.4 Floor Slabs ........................................................................................................ 19
6.5 Corrosion Potential .......................................................................................... 19
6.6 Construction Considerations .......................................................................... 20
7.0 RECOMMENDATIONS ................................................................................................. 21
7.1 Site Preparation and Grading ......................................................................... 21
7.1.1 Site Clearing ......................................................................................... 21
7.1.2 Subgrade Preparation .......................................................................... 21
7.1.3 Fill Placement and Compaction ........................................................... 22
7.1.4 Utilities .................................................................................................. 23
7.1.5 Temporary Slopes ................................................................................ 24
7.2 Foundation Support ........................................................................................ 24
7.2.1 Mat Foundation .................................................................................... 24
7.2.2 Ground Improvement .......................................................................... 26
7.3 Below�Grade Walls .......................................................................................... 27
7.4 Floor Slab ......................................................................................................... 29
7.5 Shoring and Underpinning .............................................................................. 31
7.6 Construction Monitoring ................................................................................. 31
7.7 Site Drainage .................................................................................................... 32
7.8 Corrosion Design ............................................................................................. 32
7.9 Seismic Design Criteria ................................................................................... 32
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TABLE OF CONTENTS (Cont.)
8.0 FUTURE GEOTECHNICAL SERVICES ......................................................................... 33
9.0 LIMITATIONS ............................................................................................................... 33
10.0 REFERENCES .............................................................................................................. 34
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LIST OF FIGURES
Figure 1 Site Location Map
Figure 2 Site Plan
Figure 3 Map of Major Faults and Earthquake Epicenters
in the San Francisco Bay Area
Figure 4 Modified Mercalli Intensity Scale
LIST OF APPENDICES
Appendix A Logs of Borings and Cone Penetration Tests
Figures A#1 Logs of Borings B#1 through B#4
through A#4
Figure A#5 Classification Chart
Figures A#6 Logs of Cone Penetration Tests CPT#1 through CPT#7
through A#12
Figure A#13 Classification Chart for Cone Penetration Tests
Appendix B Laboratory Test Results
Figure B#1 Plasticity Chart
Figure B#2 Plasticity Chart
Figure B#3 Consolidation Test Report
Figure B#4 Particle Size Analysis
Figure B#5 Particle Size Analysis
Figure B#6 Particle Size Analysis
Appendix C Corrosivity Test Results
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GEOTECHNICAL INVESTIGATION
2000�2070 Bryant STREET
San Francisco, California
1.0 INTRODUCTION
This report presents the results of the geotechnical investigation performed by Langan
Treadwell Rollo for the proposed development to be constructed at 2000#2070 Bryant Street in
San Francisco, California. We previously performed a geotechnical investigation for the 2070
Bryant Street site and presented our results in a report dated 10 July 2013. We understand
that the 2070 and 2000 Bryant Street sites will be developed as one project. Therefore, this
report combines data generated for both sites and presents conclusions and recommendations
regarding the geotechnical aspects of the proposed development for the entire site.
The project site is rectangular with plan dimensions of about 200 by about 325 feet. It is bound
by Bryant Street on the east, Florida Street on the west, 18th Street on the north, and a
community garden and two buildings on the south (two#story and three#story structures, both
of wood#framed construction). The location of the project site is shown on the Site Location
Map, Figure 1. The site is occupied by a one# and two#story concrete and brick building, a two#
story wood frame building with a basement, two two#story wood frame buildings, a one#story
metal and wood frame building, asphalt paved areas, concrete paved areas, and lawn areas.
The sidewalk elevation ranges from approximately 23 to 26 feet1 (north to south) along Bryant
from approximately 21 to 19 feet (north to south) on Florida Street. Interior portions of the
existing building have raised floors, ramps, or staircases to accommodate the grade changes
between Bryant and Florida Streets.
Based on architectural plans prepared by BDE Architecture titled “Background Set” dated 27
February 2014, we understand the proposed development consists of a six#story residential
building comprised of five levels of light#framed construction over a one#level concrete podium
with parking, residential, and retail uses. We also understand that the new building will
encompass the entire footprint of the site and will be constructed at grade to minimize
excavation depths. The planned finished floor elevation for most of the building is Elevation
================================================1 Elevations in this report are referenced to the San Francisco City Datum and were obtained from a site survey
provided by Martin M. Ron Associates.
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21.5 feet and steps up to match existing grades along Bryant Street (finished floor at about
Elevation 27.5 feet) and down to match existing grades on Florida Street (finished floor at about
Elevation 19 feet).
The structural loads for the new development were unknown at the time of this report.
Based on our discussion with the architect, we also understand that the adjacent site currently
occupied by the community garden is being developed; a six#story building is planned.
2.0 SCOPE OF SERVICES
Our scope of services, outlined in our proposals dated 20 March 2013 and 29 October 2013,
consisted of exploring the subsurface conditions at the site and performing laboratory tests and
engineering analyses to develop conclusions and recommendations regarding:
• soil and groundwater conditions at the site
• site seismicity and seismic hazards, including ground rupture, liquefaction, lateral
spreading, and cyclic densification
• the most appropriate foundation type(s) for the proposed structure
• design criteria for the most appropriate foundation type(s), including values for vertical
and lateral capacities
• estimated foundation settlement
• excavation and shoring (if needed)
• floor slabs
• below#grade walls
• ground improvement
• seismic design criteria in accordance with California Building Code 2013 (CBC)
• development of site#specific response spectra using ground motion response analysis (if
deemed necessary)
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• fill quality and compaction criteria
• construction considerations.
3.0 FIELD EXPLORATION
We explored the subsurface conditions at the combined site by drilling four borings, designated
B#1 to B#4, and advancing seven cone penetration tests (CPTs), designated CPT#1 to CPT#7 at
the locations shown on the Site Plan, Figure 2.
Prior to beginning our field investigation, we obtained drilling permits from the City of San
Francisco Department of Public Health (SFDPH) and multiple street#use permits from the City
of San Francisco Department of Public Works (SFDPW), which allowed us to work in the
streets adjacent to the property. We checked boring and CPT locations for the presence of
underground utilities by contracting with a private utility locating service; we also contacted
Underground Service Alert (USA), as required by law, before commencing our field exploration.
Upon completion, borings were backfilled with cement grout in accordance with SFDPH and
SFDPW requirements.
3.1 Borings
From 18 to 19 April 2013 and on 30 January 2014, Pitcher Drilling Company of Palo Alto,
California drilled three borings, designated as B#1, B#2 and B#4, to depths ranging from about 70
to 91½ feet using truck#mounted, rotary#wash drilling equipment. On 22 April 2013, Clearheart
Drilling of Santa Rosa, California drilled one boring designated B#3, to a depth of about 50 feet
using a limited#access, track#mounted drill rig equipped with hollow stem augers. During
drilling, our field engineer logged the borings and collected representative samples of the soil
encountered for classification and laboratory testing. The boring logs are presented in
Appendix A on Figures A#1 through A#4. The soil encountered was classified in accordance
with the soil classification chart on Figure A#5.
Soil samples were obtained using four samplers:
• Standard Penetration Test (SPT) sampler with a 2.0#inch outside and 1.5#inch inside
diameter, without liners
• Sprague & Henwood (S&H) split#barrel sampler with a 3.0#inch outside diameter and
2.5#inch inside diameter, lined with 2.43#inch inside diameter brass tubes.
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• Dames & Moore piston sampler with 2.5#inch outside diameter and a 2.43#inch
inside diameter brass tubes
• Shelby tube sampler with a 3.0#inch outside diameter and 2.875#inch inside diameter
The SPT and S&H samplers were driven with a 140#pound, downhole safety hammer falling
30 inches. The samplers were driven up to 18 inches, and the hammer blows required to
advance the samplers every six inches of penetration were recorded and are presented on the
boring logs. A “blow count” is defined as the number of hammer blows per six inches of
penetration or 50 blows for six inches or less of penetration. The driving of samplers was
discontinued if the observed (recorded) blow count was 50 for six inches or less of penetration.
The blow counts required to drive the SPT and S&H samplers were converted to approximate
SPT N#values using a factor of 1.2 and 0.7, respectively to account for sampler type and
hammer energy and are shown on the boring logs. The blow counts used for this conversion
were: 1) the last two blow counts if the sampler was driven more than 12 inches, 2) the last
one blow count if the sampler was driven more than six inches but less than 12 inches, and
3) the only blow count if the sampler was driven six inches or less.
The Dames & Moore brass tubes and shelby tube were pushed hydraulically into the soil to
obtain relatively undisturbed samples of the soft cohesive soil. The pressure required to
advance the sampler is shown on the logs, measured in pounds per square inch (psi).
3.2 Cone Penetration Tests
On 16 April 2013, 22 April 2013, 28 January 2014, and 1 February 2014 Gregg Drilling &
Testing, Inc. of Martinez, California, advanced seven CPTs designated CPT#1 through CPT#7.
The CPTs were advanced by hydraulically pushing a 1.4#inch diameter (ten square centimeters),
cone#tipped probe into the ground. The cone on the end of the probe measures tip resistance,
and the friction sleeve behind the cone tip measures frictional resistance. Electrical strain
gauges within the cone measure soil parameters continuously for the entire depth advanced.
Soil data, including tip resistance, was transferred to a computer while conducting each test.
Accumulated data was processed by computer to provide engineering information, such as the
types and approximate strength characteristics of the soil encountered. The CPT logs showing
tip resistance, friction ratio, equivalent SPT N#value, in#situ stress, shear strength, and soil
behavior type as a function of depth are presented in Appendix A on Figures A#6 through A#12.
A classification chart for the CPTs is included as Figure A#13.
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3.3 Laboratory Testing
All samples recovered from the field exploration program were examined for soil classification,
and representative samples were selected for laboratory testing. The laboratory testing
program was designed to correlate and evaluate engineering properties of the soil at the site.
Samples were tested to measure organics, consolidation, moisture content, dry density,
plasticity, and percent fines. Results of the laboratory testing are included on the boring logs
and in Appendix B on Figures B#1 through B#5.
4.0 SUBSURFACE CONDITIONS
The site is approximately 400 feet east of the historical Mission Creek drainage area at the
bottom of Potrero Hill. The adjacent Mission Creek area was reclaimed by placing fill starting in
the 1880s.
The results of the investigation at the proposed project site indicate that the northern portion of
the site is underlain by about 10 to 24 feet of fill. The fill consists of a heterogeneous mix of
gravel, sand, silt, and clay and contains weathered serpentenite with significant rock fragments.
The granular portions of the fill (sand and gravel) are generally loose to medium dense and the
cohesive portions (silt and clay) are soft to medium stiff. At the southern portion of the site, we
encountered 12 to 15 feet of fill generally consisting of medium dense to very dense silty
and/or clayey sand and sand. In boring B#2, about 3 feet of clay fill with varying sand and gravel
content was encountered over the medium dense to very dense sandy fill, and both borings
B#2 and B#3 encountered traces of concrete and brick debris in the upper several feet of the fill.
At the northern portion of the site, the fill is underlain by soft to medium stiff, compressible
sandy clay and sandy/clayey silts and loose to medium dense clayey sand, silty sand, and
clayey silty sand extending to approximate depths between 28 and 44 feet below the ground
surface (bgs). We believe this soil forms a marsh deposit associated with the Mission Creek
drainage. In boring B#4 the marsh consists of two layers; a layer of sandy clay and silty sand is
bound between the upper and lower marsh deposits. Results of consolidation tests performed
on samples of the marsh deposit near and at the project site indicate that the marsh deposit is
normally to over consolidated 2. Laboratory testing performed on the marsh deposit indicates
================================================2 A normally consolidated soil is one that has not historically been subjected to overburden or other pressures
greater than those that are currently present. Additional loading through fill placement or net building load
increase will begin a new cycle of consolidation where reduction in volume of the soil will result as pore
pressures dissipate. An overconsolidated clay has experienced a pressure greater than its current load.
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that the fines content ranges between approximately 33 and 55 percent with the plasticity
index of the fines content ranging between 7 and 19. At the southern portion of the site, the fill
is underlain by medium dense to very dense sand with varying fines content and stiff to very
stiff silts and clays.
The marsh deposit to the north and medium dense to very dense/stiff to very stiff material to
the south are underlain by the Colma formation. The top of the Colma formation was
encountered at depths ranging from 27 to 44 feet below ground surface and extends to the
maximum depths explored of 69 and 49 feet in borings B#1 and B#3, respectively, and to
approximately 67 and 78 feet in B#2 and B#4, respectively. The Colma formation encountered in
our borings consists of medium dense to very dense sand with varying amounts of clay and silt.
According to our CPTs, the upper portion of the Colma formation classifies as very stiff fine#
grained material with very stiff to hard silts and clays and thin layers of medium dense to dense
sands. The Colma deposit typically increases in density with depth, except for an
approximately 4#foot#thick medium dense layer of clayey silty sand encountered in boring B#1 at
a depth of approximately 58 feet. Laboratory testing on this sample indicates a fines content of
about 28 percent with a plasticity index of 7.
Borings B#2 and B#4 in the northern portion of the site were drilled past the Colma formation.
At B#2 a thin layer of very stiff clay was encountered below the Colma formation. The clay is
underlain by about 2½ feet of medium dense clayey silty sand, which is underlain by very
dense sand to the maximum depth explored of about 75 feet bgs. Laboratory testing on a
sample of the medium dense sand indicates a fines content of about 13 percent with a
plasticity index of 4. At the location of boring B#4, the Colma formation is underlain by a five#
foot thick layer of clayey peat underlain by hard, gray clay. The clay is extends to the maximum
depth explored of about 91½ feet bgs.
4.1 Groundwater
Groundwater was encountered during auger drilling prior to switching to rotary wash in borings
B#2 and B#3 at depths of about 12 and 17 feet (Elevations 7 and 7½ feet), respectively.
Groundwater was not measured in B#1 and B#4. Dissipation tests performed in CPT#1,CPT#2,
and CPTs 5 through 7, indicate groundwater is at depths of about 9 and 16 feet (Elevations 14½
and 9 feet) bgs, respectively. Fluctuations in groundwater levels are expected and occur due to
many factors including seasonal fluctuation, tides, underground drainage patterns, regional
fluctuations, and other factors.
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5.0 GEOLOGY AND SEISMICITY
The regional geology and seismicity were evaluated as part of this investigation. The evaluation
was based on our review of published reports, our experience in the project area, and the
results of field investigations.
5.1 Regional Geology
The site is in the northeast portion of the San Francisco peninsula, which lies within the Coast
Ranges geomorphic province. The northwesterly trend of ridges and valleys characteristic of
the Coast Ranges is obscured in San Francisco, except for features such as Russian Hill,
Telegraph Hill, Hunters Point, and Potrero Hill. San Francisco Bay and the northern portion of
the peninsula lie within a down#dropped crustal block bounded by the East Bay Hills and the
Santa Cruz Mountains. The San Francisco Bay depression resulted from interaction between
the major faults of the San Andreas fault zone, particularly the Hayward and San Andreas faults
east and west of the bay, respectively (Atwater, 1979).
San Francisco’s topography is characterized by relatively rugged hills formed by Jurassic# to
Cretaceous#aged bedrock (Schlocker, 1974). The bedrock consists of highly deformed and
fractured sedimentary rocks of the Franciscan complex. The present topography resulted
mainly from east#west compression of coastal California during the late Pliocene and
Pleistocene epochs (Norris and Webb, 1990).
The low#lying areas of the San Francisco peninsula are underlain by Quaternary sediments
deposited on eroded Franciscan bedrock. Sediment deposition within the prehistoric bay
margin was influenced by oscillating late#Quaternary sea levels that resulted from the advance
and retreat of glaciers worldwide. The resulting sequence of alternating estuarine and
terrestrial sediments corresponds to high and low sea#level stands, respectively. In contrast,
Quaternary sediments in the plains landward of the bay are predominantly terrestrial.
By late Pleistocene time, the high sea level associated with the Sangamon (about
125,000 years ago) interglacial resulted in deposition of the Yerba Buena Mud (Sloan, 1992).
The Yerba Buena Mud was deposited in an estuarine environment similar in character and
extent to the present bay. Sea level lowering associated with the onset of Wisconsin glaciation
exposed the bay floor and resulted in terrestrial sedimentation, such as the Colma formation,
on the Yerba Buena Mud. Sea level rose again starting roughly 20,000 years ago, fed by the
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melting of Wisconsin#age glaciers. The sea re#entered the Golden Gate about 10,000 years ago
(Atwater, 1979). Inundation of the present bay resulted in deposition of estuarine sediments,
called Bay Mud, which continue to accumulate.
Historical development of the San Francisco Bay area resulted in placement of artificial fill
material over substantial portions of modern estuaries, marshlands, tributaries, and creek beds
in an effort to reclaim land (Nichols and Wright, 1971).
5.2 Regional Seismicity and Faulting
The major active faults in the area are the San Andreas, San Gregorio and Hayward Faults.
These and other active faults of the region are shown on Figure 3. For each of the active faults
within 50 kilometers (km) of the site, the distance from the site and estimated mean
characteristic Moment magnitude3 [2008 Working Group on California Earthquake Probabilities
(WGCEP) (2008) and Cao et al. (2003)] are summarized in Table 1.
TABLE 1
Regional Faults and Seismicity
Fault Segment
Approximate
Distance from
Site (km)
Direction
from Site
Characteristic
Mean Moment
Magnitude
N. San Andreas – Peninsula 10 West 7.23
N. San Andreas – 1906 Event 10 West 8.05
N. San Andreas – North Coast 15 West 7.51
San Gregorio Connected 17 West 7.50
Total Hayward 19 Northeast 7.00
Total Hayward#Rodgers Creek 19 Northeast 7.33
Mount Diablo Thrust 35 East 6.70
Total Calaveras 36 East 7.03
Rodgers Creek 36 North 7.07
Monte Vista#Shannon 39 Southeast 6.50
Green Valley Connected 40 East 6.80
Point Reyes 42 West 6.90
West Napa 47 Northeast 6.70
================================================3 Moment magnitude is an energy#based scale and provides a physically meaningful measure of the size of a
faulting event. Moment magnitude is directly related to average slip and fault rupture area.
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Figure 3 also shows the earthquake epicenters for events with magnitude greater than 5.0 from
January 1800 through January 1996.
Since 1800, four major earthquakes have been recorded on the San Andreas Fault. In 1836 an
earthquake with an estimated maximum intensity of VII on the Modified Mercalli (MM) scale
(Figure 4) occurred east of Monterey Bay on the San Andreas Fault (Toppozada and Borchardt
1998). The estimated Moment magnitude, Mw, for this earthquake is about 6.25. In 1838, an
earthquake occurred with an estimated intensity of about VIII#IX (MM), corresponding to a Mw
of about 7.5. The San Francisco Earthquake of 1906 caused the most significant damage in the
history of the Bay Area in terms of loss of lives and property damage. This earthquake created
a surface rupture along the San Andreas Fault from Shelter Cove to San Juan Bautista
approximately 470 kilometers in length. It had a maximum intensity of XI (MM), a Mw of about
7.9, and was felt 560 kilometers away in Oregon, Nevada, and Los Angeles. The most recent
earthquake to affect the Bay Area was the Loma Prieta Earthquake of 17 October 1989, in the
Santa Cruz Mountains with a Mw of 6.9, approximately 93 km from the site.
In 1868 an earthquake with an estimated maximum intensity of X on the MM scale occurred on
the southern segment (between San Leandro and Fremont) of the Hayward Fault. The
estimated Mw for the earthquake is 7.0. In 1861, an earthquake of unknown magnitude
(probably a Mw of about 6.5) was reported on the Calaveras Fault. The most recent significant
earthquake on this fault was the 1984 Morgan Hill earthquake (Mw = 6.2).
The 2008 WGCEP at the U.S. Geologic Survey (USGS) predicted a 63 percent chance of a
magnitude 6.7 or greater earthquake occurring in the San Francisco Bay Area in 30 years. More
specific estimates of the probabilities for different faults in the Bay Area are presented in
Table 2.
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TABLE 2
WGCEP (2008) Estimates of 30�Year Probability
of a Magnitude 6.7 or Greater Earthquake
Fault
Probability
(percent)
Hayward#Rodgers Creek 31
N. San Andreas 21
Calaveras 7
San Gregorio 6
Concord#Green Valley 3
Greenville 3
Mount Diablo Thrust 1
5.3 Seismic Hazards
During a major earthquake on a segment of one of the nearby faults, strong to very strong
shaking is expected to occur at the site. Strong shaking during an earthquake can result in
ground failure such as that associated with soil liquefaction4, lateral spreading5, and cyclic
differential compaction6. We used the results of our borings and CPTs to evaluate the potential
for these phenomena to occur at the site. The results of our evaluation are presented below.
5.3.1 Fault Rupture
Historically, ground surface ruptures closely follow the trace of geologically young faults. The
site is not within an Earthquake Fault Zone, as defined by the Alquist#Priolo Earthquake Fault
Zoning Act and no known active or potentially active faults exist on the site. Therefore, we
conclude the risk of fault offset at the site from a known active fault is low. In a seismically
active area, the remote possibility exists for future faulting in areas where no faults previously
existed; however, we conclude the risk of surface faulting and consequent secondary ground
failure is low.
================================================4 Liquefaction is a transformation of soil from a solid to a liquefied state during which saturated soil temporarily
loses strength resulting from the buildup of excess pore water pressure, especially during earthquake#induced
cyclic loading. Soil susceptible to liquefaction includes loose to medium dense sand and gravel, low#plasticity
silt, and some low#plasticity clay deposits.
5 Lateral spreading is a phenomenon in which surficial soil displaces along a shear zone that has formed within an
underlying liquefied layer. The surficial soil is typically displaced in “blocks” that are transported downslope or
in the direction of a free face by earthquake and gravitational forces.
6 Cyclic soil densification is a phenomenon in which non#saturated, cohesionless soil is densified by earthquake
vibrations, resulting in ground surface settlement.
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5.3.2 Liquefaction and Associated Hazards
When a saturated, cohesionless soil liquefies during a major earthquake, it experiences a
temporary loss of shear strength caused by a transient rise in excess pore water pressure
generated by strong ground motion. Flow failure, lateral spreading, differential settlement, loss
of bearing, ground fissures, and sand boils are evidence of excess pore pressure generation
and liquefaction. The site is located within a liquefaction hazard zone as designated by the
California Geological Survey (CGS) seismic hazard zone map for the area titled State of
California Seismic Hazard Zones, City and County of San Francisco, Official Map, dated 17
November 2001. CGS has recommended the content for site investigation reports within
seismic hazard zones be performed in accordance with Special Publication 117A titled
Guidelines for Evaluating and Mitigating Seismic Hazard Zones in California, dated September
11, 2008. Our evaluation of site seismic hazards was performed in general accordance with
these guidelines.
The level of ground shaking that may occur at the site during future earthquakes is uncertain
because the location, recurrence interval, and magnitude of future earthquakes are not known.
A peak ground acceleration (PGA) of 0.58 times gravity was used in our liquefaction analysis.
This PGA was calculated using the procedures specified in the provisions of 2013 California
Building Code (CBC)/ ASCE 7#10 for the Maximum Considered Earthquake, using site class D.
We used a Moment magnitude of 8.05, which is the maximum Moment Magnitude for the San
Andreas Fault, located about 10 kilometers from the site as shown on Table 1. Groundwater
levels used in our liquefaction analysis varied and were based on groundwater level elevations
measured at nearby exploration points.
We used the results of borings B#1, B#2, and B#4 and the CPTs to evaluate the liquefaction
potential at the site. Boring B#3 was not used in our evaluation because it was drilled using
hollow stem auger equipment, which is less reliable in evaluating liquefaction. The liquefaction
analysis was performed in accordance with the methodology presented in the publication titled
Proceedings of the NCEER Workshop on Evaluation of Liquefaction Resistance of Soils,
prepared by the National Center for Earthquake Engineering Research (NCEER), dated 31
December 1997, and in Youd et al. (2001). The susceptibility of sand to liquefaction under
seismic loading was evaluated in general accordance with the procedure presented by Seed
and Idriss (1982). Our liquefaction analysis using the boring and CPT data indicates that the
majority of the relatively shallow, loose material in the fill and marsh deposit that was
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encountered at the northern portion of the site, some thin layers of medium dense material
encountered beneath the fill at the southern portion of the site, and some discontinuous,
isolated medium dense layers encountered at the top, within and below the Colma Formation
at relatively deeper depths are susceptible to liquefaction (FSliq<1.3) during the maximum
considered earthquake, as defined by the provisions of 2013 CBC/ASCE 7#10.
We estimated liquefaction#induced settlement using the procedure outlined in the NCEER
report. The strain potential of any potentially liquefiable layers was estimated in accordance
with the method developed by Tokimatsu and Seed (1984), which relates (N1)60,CS values to
strain potential. For CPTs, the tip resistance (qC1N)CS was converted to an (N1)60,CS value
assuming the ratio (qC1N)CS/(N1)60,CS (blows/foot) is equal to five. This value is consistent with
published values for clean sand. The estimated liquefaction#induced settlement from our
borings and CPTs is summarized in Table 3.
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TABLE 3
Estimated Liquefaction�Induced Settlement
Project Area
Boring / CPT
Approximate
Elevation of
Top of
Liquefiable
Soil Layers
(feet)
Approximate
Thickness of
Liquefiable
Soil Layers
(feet)
Estimated
Settlement
(inches)
Total
Estimated
Settlement
(inches)
Northern
Portion
B#1
1 6 2¼
3 #8 4 ½
#38 4 ¼
B#4 6½ 9½ 1¾ 1¾
CPT#1
2½ 2½ ¾
1¼ #1½ ½ ¼
#3½ 3 ¼
CPT#3
4 12 2¼
2½ #10 1 <¼
#15 ½ <¼
CPT#5 4.5 2½ ¼
¾ #9 3 ½
CPT#6
10 10 1½
2½ #9 2 ½
#14 1 <¼
#17 3½ ½
CPT#7
11 10½ 1¾
3½ #1½ 2 ½
#5 6 1¼
#16 1 <¼
Southern
Portion
B#2 #50½ 2½ ½ ½
CPT#2
½ ½ <¼
¼ #1 ½ <¼
#5½ ½ <¼
CPT#4
4½ 1 <¼
½ #1 1½ <¼
#6 2 <¼
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On the basis of our liquefaction analyses, we conclude that up to about 3½ inches of
liquefaction#induced total and differential settlement may occur at the northern portion of the
project site. The majority of the potentially liquefiable layers are relatively shallow and within
the marsh deposit; however, potentially liquefiable material was also encountered near the top
and near the bottom of the Colma formation. Because of the relatively shallow groundwater
table and shallow liquefiable deposits, we conclude ground failure, such as lurch cracking
and/or the development of sand boils, could occur in the northern portion of the site. The
ground#surface settlement will likely be larger than estimated in areas where these types of
ground failure occur.
At the southern portion of the site, we conclude that about ¼ to ½ inch of liquefaction#induced
total and differential settlement may occur. The majority of the liquefiable layers are thin and
were encountered within the medium dense to very dense/stiff to very stiff material
encountered beneath the fill; however, potentially liquefiable material was also encountered
near the top and near the bottom of the Colma formation. Because the potentially liquefiable
deposits are relatively thin and deep, the potential for ground failure, such as lurch cracking
and/or the development of sand boils at the southern portion of the site is low.
5.3.3 Lateral Spreading
Lateral spreading is a phenomenon in which a surficial soil block displaces along a shear zone
that has formed within an underlying liquefied layer. The surficial blocks are transported
downslope or in the direction of a free face, such as a bay or a channel, by earthquake and
gravitational forces. Lateral spreading is generally the most pervasive and damaging type of
liquefaction#induced ground failure generated by earthquakes.
According to Youd, Hansen, and Bartlett (2002), for significant lateral spreading displacements
to occur, the soils should consist of saturated cohesionless sandy sediments with (N1)60
blowcounts less than 15, where liquefaction of the soils is likely to occur based on standard
liquefaction analysis. At northern portion of the site, we encountered continuous zones (2½ to
10 feet) of potentially liquefiable material with (N1)60 less than 15 blowcounts within the fill and
marsh deposit. If this portion of the site is not mitigated against liquefaction, there are
sufficient zones of liquefiable material present within the fill and marsh deposit to induce lateral
spreading. This has the potential to cause significant damage to shallow or deep foundations.
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Therefore, we conclude the soil beneath the northern portion of the site should be improved to
mitigate the liquefaction and lateral spread potential. The estimated boundary of the zone of
potential lateral spread at the northern portion of the site is shown on the Site Plan, Figure 2.
At the southern portion of the site, we encountered relatively thin, continuous zones of
potentially liquefiable soils with (N1)60 less than 15 blowcounts within the medium dense to
very dense/stiff to very stiff material encountered beneath the fill. However, given that these
potentially liquefiable zones are very thin (< 4 inches) with high fines content, we judge that the
potential for lateral spreading to occur at the southern portion of the site is low.
5.3.4 Cyclic Densification
Cyclic densification refers to seismically-induced differential compaction of non-saturated
granular material (sand and gravel above the groundwater table) caused by earthquake
vibrations. Approximately 13 to 24 feet of loose fill was encountered in our borings and CPTs
at the northern portion of the site during our investigation. Unless mitigated, these non-
saturated granular layers could settle up to one inch due to strong shaking from a large
earthquake.
6.0 DISCUSSION AND CONCLUSIONS
On the basis of the results of our subsurface investigation, laboratory testing and engineering
analyses, we conclude the proposed development is feasible from a geotechnical engineering
standpoint. The primary geotechnical issues associated with the proposed development
include:
presence of shallow, debris-laden fill
presence of potentially liquefiable soils and potential for liquefaction-induced settlement
to occur during a moderate to major earthquake at the site
potential for significant lateral spreading at the northern portion of the site in the event
of liquefaction
construction considerations.
Our discussion and conclusions regarding these and other issues and their impact on the
design and construction of the proposed structure are discussed in the following sections.
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6.1 Ground Improvement
A heterogeneous mix of loose fill overlying marsh deposits blankets the northern portion of the
site. The loose, unsaturated fill is susceptible to cyclic densification, and the loose saturated fill
and marsh deposit has a high liquefaction and lateral spread potential during a large earthquake.
In addition, the soft, compressible sandy clay layers within the marsh deposit could undergo
significant static settlement (consolidation) under the weight of the new development. If not
mitigated, these conditions could cause significant damage to the proposed development,
resulting in poor building performance. Therefore, we recommend mitigating these potential
hazards at the northern portion of the site using ground improvement, which includes deep soil
mixing (DSM) or drilled displacement columns (DDC). Soil improvement methods can also be
used to transfer the support of building loads through the column elements to deeper, more
competent soil.
The approximate area requiring ground improvement, labeled as the zone of potential lateral
spread, at the northern portion of the site is shown on the Site Plan, Figure 2. The delineation
between lateral spread and no lateral spread potential is based on limited exploration within the
footprint of the new building. To better define the portion of the north side of the site that
requires site improvement, additional CPTs should be performed following demolition of the
existing development.
Deep soil mixing (DSM) and drilled displacement columns (DDC) are installed under design#
build contracts by specialty contractors. DSM or DDCs will need to be designed to mitigate the
lateral spreading potential by using a sufficient replacement ratio of cement mixtures to soil.
The ground improvement method should also be designed to adequately transfer the building
loads to a competent bearing layer because of potential settlement between column elements
associated with consolidation and liquefaction. At a minimum, the DSM elements or DDCs
should extend at least three feet below the top of the bearing layer. The estimated elevations
to the top of the bearing layer at the locations explored are shown on the Site Plan, Figure 2.
DDC and DSM are discussed in the following sections.
6.1.1 Drilled Displacement Columns
DDCs are constructed by using a displacement auger to create a soil shaft that is filled with
CLSM (Controlled Low Strength Material) injected under pressure as the displacement auger is
withdrawn from the hole. Because of the installation pressures, DDCs vary between 20 to
24 inches in diameter. Strength of the CLSM is on the order of 500 psi at 28 days, depending
on the foundation load requirements. Installation of DDCs produces minimal soil cuttings
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because the soil is displaced during column installation. The purpose of the drilled
displacement columns is to eliminate the lateral spread potential and transfer building loads to a
deeper bearing stratum. The structure can then be supported on a shallow foundation bearing
on the DDC columns. DDCs can also be constructed to resist uplift loads by drilling them
deeper into the bearing layer and installing a central bar.
Because DDCs inject the CLSM under pressure, there is the potential for soil heave near the
column. To eliminate the potential to damage nearby improvements, DDCs may need to be set
back a horizontal distance from adjacent structures.
6.1.2 Deep Soil Mixing (DSM)
Mechanical deep soil mixing is used to treat soil in#place with cement grout using mixing shafts
consisting of auger cutting heads, discontinuous flight augers, or blades/paddles to create
below ground deep soil elements. Deep soil mixing may be installed in a variety of patterns
including cellular blocks, a grid pattern, or columns/panels. Typical minimum replacement ratios
(ratio of treated soil to building footprint) are on the order of 30 to 50 percent. The structure
can then be supported on a shallow foundation bearing on the improved soil.
The deep soil mixing should be installed in a pattern that will eliminate the potential for
liquefaction and lateral spreading and transfer building loads to a deeper bearing stratum with a
sufficient replacement ratio. A cellular block of continuous DSM walls composed of overlapping
DSM columns or panels may be needed to create an effective buttress for lateral spreading.
Resistance to lateral loads will be developed in friction along the contact area between the soil#
cement shafts and the base of the shallow foundation
The installation of DSM systems typically does not create soil spoils; however, it does transport
cementitious grout spoils and some soil cement mix spoils to the ground surface. DSM
systems typically produce little to no vibrations, such that damage to the adjacent structures
would not be a concern. However, structures should be monitored throughout DSM
installation and DSM operations should cease if unacceptable movement is measured.
6.2 Foundations and Settlement
Once the ground improvement is in place, the northern portion of the building can be supported
on a mat foundation bearing on the improved soil. Based on our experience with sites with
similar soil conditions, we anticipate static settlement of a properly constructed mat foundation
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supported on DDC or DSM will be limited to ¾ inch or less under the weight of the anticipated
building loads with differential settlement dependent upon the loading and rigidity of the mat.
The estimated static settlement should be confirmed by the design#build contractor.
Because the ground improvement will only mitigate the liquefaction/lateral spread potential to
the top of the dense Colma formation, additional seismically#induced total and differential
settlement associated with deeper liquefiable and compressible layers within and below the
Colma formation of up to ½ inch may occur at the northern portion of the site, as discussed in
Section 5.3.2.
The subsurface conditions encountered at the southern portion of the site generally consist of
12 to 15 feet of fill comprised of medium dense to dense sand with varying fines content over
stiff to very stiff silts and clays. In general, this fill appears to be relatively consistent between
points of exploration. However, the upper two to three feet of fill is in poor condition and
contains debris. We judge that the fill is adequate to support the southern portion of the
building bearing on a mat foundation; however, to reduce erratic settlement associated with the
upper portion of the fill, the top three feet of fill beneath the planned foundation elevation
should be overexcavated and recompacted as engineered fill. Also, areas to receive new fill
should be overexcavated to a depth of three feet and recompacted prior to placement of new
fill.
We anticipate static settlement of a properly constructed mat foundation bearing on at least
three feet of engineered fill should be about 1 to 1¼ inches with differential settlement
dependent upon the loading and rigidity of the mat. We estimate about half of these
settlements will occur during construction. In addition to the static settlement, seismically#
induced settlement may occur across the southern portion of the site during a major
earthquake, as discussed in Section 5.3.2.
The subsurface conditions encountered in B#2, B#3, CPT#2, and CPT#4 appear to be
representative of conditions at the southern portion of the site, and we conclude the building in
this area be supported on a mat foundation bearing on at least three feet of engineered fill over
the existing medium dense to dense sand fill. However, we also conclude additional
exploration be performed within the building footprint following demolition of the existing
development to confirm the uniformity of the existing fill.
Alternatively, the mat on the southern portion of the site could also be supported on improved
soil. We understand that there may be environmental costs associated with disturbing and
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excavating the fill. In addition, overexcavation adjacent to existing structures may require
underpinning of adjacent foundations. By improving the fill on the south side of the site with
DDCs or DSM, the need for additional exploration will be eliminated, and the soil is treated in
place to avoid costs associated with, underpinning and exposing the upper portions of the fill.
The replacement ratio and minimum depth of soil improvement methods in areas to improve
the fill are expected to be less than in areas treated to reduce liquefaction and lateral spread
potential. If ground improvement is chosen for this area, the design, pattern, and placement of
soil improvement methods on the southern portion of the site will need to consider the
proximity of the adjacent structures. DDCs displace soil and inject grout which could result in
soil heave near the column. To eliminate the potential to damage nearby improvements, DDCs
may need to be set back a horizontal distance from adjacent structures.
6.3 Groundwater
Groundwater levels were measured during our field investigation at approximate elevations
ranging between 7 and 14½ feet. The measured groundwater is below existing site grades and
the anticipated finished floor of the new building, assuming the building will be constructed to
match existing grades at the site. Therefore, we do not anticipate encountering groundwater
during mass grading of the site. However, groundwater may be encountered in deeper
excavations, such as elevator pits and utilities.
6.4 Floor Slabs
In general, the floor slab will be a mat slab bearing on either improved soil or at least three feet
of engineered fill above the measured groundwater level. Moisture barriers are typically used
in areas where moisture is not desirable including lobby and storage areas. A moisture barrier
may not be necessary in areas beneath the parking areas, provided it is acceptable that
moisture and efflorescence (white powdery calcium or chloride staining) will occur over time.
Although not shown on the plans, we anticipate that elevator pits will be part of the new
development. If the elevator pits extend below the measured groundwater levels, they should
be designed for hydrostatic uplift. The mat foundation for the elevator pits may also need to be
waterproofed.
6.5 Corrosion Potential
Corrosivity testing was performed on a sample from a depth of 5½ feet in Boring B#2 and a
depth of 3 feet in boring B#4. The sample of soil was tested in accordance with Caltrans and
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ASTM protocols by Environmental Technical Services (ETS) of Petaluma, California and CERCO
analytical of Concord, California. The corrosivity test results are presented in Appendix C.
6.6 Construction Considerations
The fill at the site consists mainly of sand, gravel, and clay that can be excavated with
conventional earth#moving equipment such as loaders and backhoes. The granular nature of
the fill will likely make it difficult to maintain neat vertical cuts for utilities and foundation
elements, and prepared subgrade for foundations will likely become disturbed with
construction traffic. Site preparation and grading may be difficult if performed during the rainy
season.
Serpentinite was encountered in the fill. Serpentinite often contains naturally occurring
asbestos, and it may be difficult and costly to dispose of, whether it contains asbestos or not.
The fill may contain heavy metals and petroleum hydrocarbons. Handling and disposal of the fill
material should be performed in accordance with a site mitigation plan (SMP) that includes
health and safety criteria; preparation of an SMP is not within the scope of this investigation.
Although only trace amounts of concrete and brick debris were encountered in our borings,
greater amounts and larger pieces of brick, concrete, and other rubble may be encountered in
the fill. Installation of ground#improvement elements or excavations may be difficult in some
areas of the site.
Excavations below the measured groundwater level should be dewatered as needed to install
utilities and compact soil. Because the fill is granular, there is a potential for significant water
inflow into any excavation. Prior to dewatering, the groundwater should be tested to evaluate if
it can be discharged directly to the storm drain system or if it must be treated on#site prior to
discharge.
If ground improvement is performed in the southern portion of the site, the ground#
improvement design#build contractor should consider the neighboring structures when
designing the appropriate ground#improvement method. If overexcavation and recompaction of
the fill is performed adjacent to existing structures, underpinning or design of shoring to
support the excavation and loads from adjacent structures will be required. A pre#construction
survey and monitoring program should be undertaken prior
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to construction to monitor any effects to the surrounding buildings during construction. The
survey should include documenting the condition of the surrounding structures, including a
crack survey, prior to, during, and following ground#improvement installation or underpinning or
shoring installation.
7.0 RECOMMENDATIONS
Recommendations regarding site preparation, foundation design, ground improvement, floor
slabs, below#grade walls, and seismic design are presented in the following sections.
7.1 Site Preparation and Grading
This section presents earthwork recommendations for site preparation and grading.
7.1.1 Site Clearing
Site demolition should include the removal of all slabs, foundations, retaining walls, pavements,
utilities, and other below#grade improvements that will interfere with the proposed
construction. Where utilities that are removed extend off site, they should be capped or
plugged with grout at the property line. It may be feasible to abandon utilities in#place by filling
them with grout, provided they will not impact future utilities or building foundations. The utility
lines, if encountered, should be addressed on a case#by#case basis.
If an excavation extends below the groundwater during demolition activities, the portion of the
resulting excavation below the groundwater level should be filled with ¾#inch crushed rock. If
fine#grained soil is exposed at the base of the excavation, it may be necessary to place a
reinforcement fabric (Mirafi 500X or equivalent) over the base of the excavation prior to
placement of the rock to prevent the rock from being pushed into the fine#grained soil. Once a
firm base is established above the groundwater level, compacted fill can be placed on the
crushed rock. The crushed rock should be wrapped in filter fabric, such as Mirafi 140NC (or
equivalent) to reduce the potential fines infiltrating into the voids between the crushed rock
particles.
7.1.2 Subgrade Preparation
At the northern portion of the site, the mat will be supported on improved ground. In the case
DDC is the chosen ground improvement option, the mat should bear on at least 12 inches of
Class 2 aggregate base over the DDC columns and be compacted to 95 percent relative
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compaction7. In the case DSM is the chosen ground improvement option, the mat can bear
directly on DSM ground, provided the soil subgrade between the DSM columns is stable and
suitable for a working surface. 12 inches of Class 2 AB compacted to at least 95 percent
relative compaction or a rat slab should be placed if the unimproved soil subgrade is weak and
unstable.
At the southern portion of the site, the mat foundation should bear on improved ground or at
least 3 feet of engineered fill. To provide 3 feet of properly compacted fill, the upper 2½ feet
beneath the mat subgrade should be overexcavated, and the material exposed at the bottom of
the overexcavation should be scarified to a depth of at least 6 inches, moisture conditioned to
near the optimum moisture content, and compacted to at least 95 percent relative compaction.
If soft areas are encountered at the bottom of the overexcavation, the soft material should be
removed and replaced with either crushed rock or engineered fill. If the material is wet, the
upper 12 inches should be scarified and aerated to reduce its moisture content so that it can be
compacted to the required compaction. The remaining 2½ feet of fill should be placed in 8#
inch#loose lifts, moisture conditioned to near the optimum moisture content, and compacted to
at least 95 percent relative compaction. Also, in areas to receive new fill beneath the mat, the
existing fill should be overexcavated as stated above prior to placement of the new fill. After
recompaction of fill or improvement of soil, the subgrade should be proof rolled to provide a
smooth, non#yielding surface.
7.1.3 Fill Placement and Compaction
From a geotechnical standpoint, concrete generated by demolition may be crushed and reused
as fill provided it is free of organic material and rocks or lumps greater than three inches in
greatest dimension. Where crushed concrete is used, particles between 1½ and 3 inches in
greatest dimension should comprise no more than 30 percent of the fill by weight.
Alternatively, concrete may be crushed to meet the requirements of Caltrans Class 2 aggregate
base (“recycled AB); in this case, the recycled AB may be used where AB is recommended.
Onsite fill is suitable for reuse as backfill, provided it is acceptable from an environmental
standpoint and meets the requirements for general fill. All material to be used as fill, including
on#site soil, should be non#corrosive, free of organic matter or other deleterious material,
contains no rocks or lumps larger than four inches in greatest dimension, has a liquid limit of
less than 40 and a plasticity index lower than 12, and is approved by the Geotechnical Engineer.
================================================7 Relative compaction refers to the in#place dry density of soil expressed as a percentage of the maximum dry
density of the same material, as determined by the latest ASTM D1557 laboratory compaction procedure.
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Fill should be placed in horizontal lifts not exceeding 8 inches in uncompacted thickness,
moisture#conditioned to moisture conditioned to near the optimum moisture content, and
compacted to at least 95 percent relative compaction.
It should be noted that if earthwork occurs in city streets, fill placement and compaction should
be in accordance with City and County of San Francisco Standard Specifications; however,
jetting should not be permitted.
The Geotechnical Engineer should approve all sources of fill at least three days before use at
the site. The grading contractor should provide analytical test results or other suitable
environmental documentation indicating the imported fill is free of hazardous materials at least
three days before use at the site. If this data is not available, up to two weeks should be
allowed to perform analytical testing on the proposed import material. A bulk sample of
approved fill should be provided to the geotechnical engineer at least three working days before
use at the site so a compaction curve can be prepared.
7.1.4 Utilities
All trenches should conform to the current OSHA requirements for work safety.
The thickness and type of bedding material required for utility conduits will depend on the soil
conditions at the utility trench bottom. As a minimum, bedding should have a thickness of at
least D/4 (with D equal to the outside pipe diameter) below the bottom of the pipe, and a
minimum thickness of four inches. Clean sand, rod mill, or pea gravel bedding material are
acceptable for use as bedding materials. Below the groundwater level, bedding material should
consist of either Caltrans Class 2 permeable rock or ¾#inch crushed rock wrapped in filter fabric
(Mirafi 140NC or equivalent). Underground utilities should be located above an imaginary plane
inclined downward at 1.5:1 (horizontal to vertical) from the bottom edge of shallow foundation
elements, or foundations will need to be deepened.
Backfill for utility trenches and other excavations is also considered fill, and it should be
compacted according to the recommendations presented in Section 7.1.3. If imported clean
sand or gravel is used as backfill, however, it should be compacted to at least 95 percent
relative compaction. Jetting of trench backfill should not be permitted. Special care should be
taken when backfilling utility trenches in pavement areas. Poor compaction may cause
excessive settlements, resulting in damage to the pavement section.
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Where utility trenches extend from the exterior to the interior limits of a building, lean concrete
should be used as backfill material for a distance of two feet laterally on each side of the
exterior building line to reduce the potential for the trench to act as a conduit for external water
to enter the building footprint.
Utilities should be designed to accommodate the predicted settlement and differential
settlement where they connect into new structures. Flexible connections and hangers should
be considered.
7.1.5 Temporary Slopes
Excavations deeper than five feet entered by workers should be shored or sloped for safety in
accordance with the Occupational Safety and Health Administration (OSHA) standards (29 CFR
Part 1926). Inclinations of temporary slopes should not exceed those specified in local, state or
federal safety regulations. As a minimum, the requirements of the current OSHA Health and
Safety Standards for Excavations (29 CFR Part 1926) should be followed. The Contractor
should determine temporary slope inclinations based on the subsurface conditions exposed at
the time of construction. However, temporary slopes less than 10 feet high should be inclined
no steeper than 1½:1 (horizontal to vertical).
If temporary slopes are open for extended periods of time, exposure to weather and rain could
result in sloughing and erosion. In addition, we recommend all vehicles and other surcharge
loads be kept at least 10 feet away from the tops of temporary slopes and the slopes be
protected from either excessive drying or saturation during construction.
7.2 Foundation Support
7.2.1 Mat Foundation
The proposed mat should gain support on improved ground or engineered fill. At the southern
portion of the site, where the proposed mat may bear on at least three feet of engineered fill,
we recommend an average allowable bearing pressure of 2,000 pounds per square foot (psf)
for dead plus live loads. Concentrated stresses may occur at interior columns and at the edges
of the mat. Mat foundations may be designed to impose a maximum dead plus live load
pressure equivalent to an allowable bearing capacity of 4,000 psf. The allowable bearing
pressures can be increased by one#third for total design loads, including wind and seismic
loads. The allowable bearing pressures for dead plus live and total design loads include factors
of safety of about 2.0 and 1.5, respectively. To design the mat at the southern portion of the
site bearing on engineered fill using the modulus of subgrade reaction method, we recommend
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a modulus of 22 kips per cubic foot (kcf). After the mat analysis is completed, we should
review the computed settlement and bearing pressure profiles to check that the modulus value
is appropriate. It may be necessary to perform additional analysis and refine the modulus value.
For a mat bearing on improved soil, (at the northern portion of the site and possibly the
southern portion) we cannot provide specific design recommendations or settlement estimates
because soil improvement is typically performed by design#build contracts by specialty
contractors. However, the mat on improved soil will have a greater allowable bearing capacity
and a higher modulus than the mat on engineered fill. On the basis of our experience we
estimate DDC or DSM can provide an improved allowable bearing capacity of between 3,000
and 6,000 pounds per square foot (psf), depending on the soil type pattern, and spacing. Once
a soil improvement technique has been chosen, the design capacity should be verified by test
sections. Ground improvement recommendations are provided in Section 7.2.2.
The allowable bearing pressure can be increased by one#third for total design loads, including
wind and seismic loads. The allowable bearing pressures for dead plus live and total design
loads include factors of safety of about 2.0 and 1.5, respectively. To design a mat bearing on
improved soil using the modulus of subgrade reaction method, we recommend a modulus on
the order of 70 to 80 kcf. The values are based on the estimated allowable bearing pressures
and the settlement we anticipate based on our experience with this type of foundation system.
The actual value should be confirmed by the design#build contractor.
Lateral loads may be resisted by friction along the base and by passive pressures against the
embedded vertical faces of the mat. For calculating the lateral resistance, we recommend an
allowable equivalent fluid pressure (triangular distribution) of 250 pounds per cubic foot (pcf) be
used for design. Because we understand a vapor mitigation system will be installed, we
recommend a coefficient of base sliding of 0.2 against the bottom of the mat. The values
include a factor of safety of 1.5 and may be used in combination without reduction.
In general, the mat excavation should be free of standing water, debris, and disturbed materials
prior to placing concrete. Except where DDC or DSM are supporting the mat, if loose or soft
soil is encountered at the mat subgrade, the weak soil should be overexcavated to expose
more competent material. The excavated material should be replaced with engineered fill,
structural concrete, or sand#cement slurry with a minimum 28#day compressive strength of at
least 50 pounds per square inch (psi). The bottoms and sides of excavations should be wetted
following excavation and maintained in a moist condition. We should check foundation
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excavations prior to placement of reinforcing steel to confirm suitable bearing material is
present. We should recheck the condition of the excavations just prior to concrete placement
to confirm the excavations have not become disturbed and are sufficiently moist.
7.2.2 Ground Improvement
A qualified, design#build, specialty contractor, who has previously successfully performed
ground improvement in similar subsurface soil conditions, should perform the ground
improvement. We recommend they be presented with our report and they design the ground
improvement system, including installation method, the depth, size and spacing of the DDC or
DSM elements within the recommended improvement zone limits, the strength of the
element, and the quality control requirements. We should be retained to provide technical
input and review the design prior to construction.
On the northern portion of the site, we recommend that the ground improvement be designed
to mitigate the lateral spreading potential and adequately transfer the building loads to a
competent bearing layer. The approximate elevations to the top of the soil improvement
bearing layer at the northern portion of the site are shown on the Site Plan, Figure 2. At a
minimum, the ground improvement in the northern portion should extend at least three feet
into the bearing layer. If ground improvement is selected on the southern portion of the site,
we recommend the ground improvement methods be designed to improve the fill. We
recommend the soil improvement in the southern portion extend a minimum of 10 feet bgs.
DDC or DSM should have a compressive strength of at least 400 pounds per square inch (psi)
and be designed using a factor of safety of at least 2 for the compressive strength. To mitigate
the effects of liquefaction and thus the potential for lateral spreading, we judge a replacement
ratio between 40 and 50 percent should be used in the northern portion of the site. To improve
the fill in the southern portion of the site, we judge a replacement ratio of about 30 percent
should be used.
To confirm that lateral spreading has been mitigated and the fill has been improved using
DDCs, we recommend a preliminary study with test sections be implemented. For DDCs, Pre#
and post#improvement borings (using SPT sampling) or CPTs should be advanced between
columns to confirm the ground has been sufficiently improved. The CPTs or borings should be
performed at least two weeks following installation of the test section to allow for pore
pressure dissipation and soil improvement.
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The improved soil between columns should have minimum and average SPT blow counts
[(N1)60,CS] , over three consecutive SPTs, of at least 20 and 30 blows per foot, respectively. If
CPTs are used for quality control (QC), the improved soil should have minimum and average tip
resistances [(qc1N) CS] , over an interval of 3 feet, of at least 80 and 120 tons per square foot
(tsf), respectively. The acceptance criteria may need to be reevaluated depending on the soil
types encountered. Improvement of the fill and liquefiable material should be verified at the
test sections prior to continuing improvement throughout the site.
DSM does not densify the soil, but rather improves the soil in place, such that CPTs or SPTs
are not a recommended QC measure. For QC of a DSM#improved zone, we recommend
monitoring the grout pumping and mixing/penetration rate and obtaining wet samples of the in#
situ soil#cement mixed material for laboratory testing. We recommend a minimum unconfined
compressive of 200 psi for the soil#cement mix. In addition, at least two columns should be
cored. Continuous coring should be performed within the outer third of the element.
We should be involved throughout the ground improvement contractor bidding and selection
process and provide additional detailed recommendations and input on specifications and
procedures.
7.3 Below�Grade Walls
The walls of below#grade structures should be designed as restrained walls. The walls should
be designed to resist both static lateral earth pressures and lateral pressures caused by
earthquakes. We used the procedures outlined in (Sitar, et. al., 2012) to compute the seismic
active pressure. The more critical condition of either at#rest pressure or active pressure plus a
seismic increment (total pressure) should be checked. At#rest and total equivalent fluid
pressure for the Design Earthquake (DE) level of shaking for the site, both for level backfill, are
presented in Table 4 for fully drained and undrained conditions.
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TABLE 4
Lateral Earth Pressures
Below Grade Wall
Level Backslope
Drainage Condition
Drained Undrained
Static
Pressure
At�rest
Pressure
(pcf)
Total Pressure
Active plus Seismic
Pressure Increment
(pcf)
Static
Pressure
At�rest
Pressure
(pcf)
Total Pressure
Active plus Seismic
Pressure Increment
(pcf)
65 70 95 100
If surcharge loads are present above an imaginary 30#degree line (from the horizontal) projected
up from the bottom of a retaining wall, a surcharge pressure should be included in the wall
design. Where vehicular traffic will pass within 10 feet of retaining walls, traffic loads should
be considered in the design of the walls. Traffic loads may be modeled by a uniform pressure
of 100 psf applied in the upper 10 feet of the walls.
A backdrain can be provided behind below#grade walls to prevent the buildup of hydrostatic
pressure. One acceptable method for backdraining basement and retaining walls is to place a
prefabricated drainage panel against the backside of the newly cast wall. If temporary shoring
is used, the panel may be placed directly on the shoring prior to casting the wall. The panel
should extend down to a perforated PVC collector pipe or an equivalent “flat” pipe (such as
AdvanEdge) at the base of the wall or shoring; where walls are above the groundwater level,
the drain should extend to a pipe at the design groundwater level. The PVC pipe should be
bedded on and covered by at least 4 inches of Class 2 permeable material (per Caltrans
Standard Specifications) or drain rock, and the aggregate material should be surrounded by filter
fabric (Mirafi 140NC or equivalent). If a flat pipe surrounded by a filter fabric is used, it is not
necessary to surround it with rock. A closed collector pipe should be sloped to drain to a
suitable outlet. If water is collected in a sump, a pumping system may be required to carry the
water to the storm drain system. We should review the manufacturer's specifications for
proposed prefabricated drainage panel material and drain pipe to verify they are appropriate for
the intended use.
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To protect against moisture migration, below#grade walls should be waterproofed, and water
stops should be placed at all construction joints.
Wall backfill should be compacted to at least 95 percent relative compaction. If heavy
equipment is used, the wall should be appropriately designed to withstand loads exerted by the
equipment and/or temporarily braced.
7.4 Floor Slab
The floor slab will be a mat slab that will extend across the entire site and bear on subgrade
prepared in accordance with our recommendations in Section 7.1.
Moisture is likely to condense on the underside of the mat slab, even though it will be above
the measured groundwater levels. Consequently, a moisture barrier should be installed
beneath the slabs if movement of water vapor through the slabs would be detrimental to its
intended use. A typical moisture barrier consists of a capillary moisture break and a water
vapor retarder. In general, a moisture barrier is not required beneath parking garage slabs,
provided it is acceptable that moisture and efflorescence (white powdery calcium or chloride
staining) will occur over time. Moisture barriers are typically used in areas where moisture is
not desirable. Parking garage slabs may be underlain by at least 6 inches of Class 2 aggregate
base compacted to at least 95 percent relative compaction.
If the depths of the elevator pits are within 30 inches of the measured groundwater, the
elevator pits should be waterproofed. We recommend a waterproofing consultant be retained
to determine the most appropriate system for this project and to provide input regarding
waterproofing details. Installation of waterproofing should be performed in accordance with
the manufacturer’s requirements.
The capillary moisture break should consist of at least four inches of clean, free#draining gravel
or crushed rock. The vapor retarder should meet the requirements for Class C vapor retarders
stated in ASTM E1745#97. The vapor retarder should be placed in accordance with the
requirements of ASTM E1643#98. These requirements include overlapping seams by
six inches, taping seams, and sealing penetrations in the vapor retarder. The vapor retarder
should be covered with two inches of sand to aid in curing the concrete and to protect the
vapor retarder during slab construction. The particle size of the gravel/crushed rock and sand
should meet the gradation requirements presented in Table 5.
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TABLE 5
Gradation Requirements for Capillary Moisture Break
Sieve Size Percentage Passing Sieve
Gravel or Crushed Rock
1 inch 90 – 100
3/4 inch 30 – 100
1/2 inch 5 – 25
3/8 inch 0 – 6
Sand
No. 4 100
No. 200 0 – 5
=
The sand overlying the membrane should be dry at the time concrete is cast. Excess water
trapped in the sand could eventually be transmitted as vapor through the slab. If rain is forecast
prior to pouring the slab, the sand should be covered with plastic sheeting to avoid wetting. If
the sand becomes wet, concrete should not be placed until the sand has been dried or
replaced.
Concrete mixes with high water/cement (w/c) ratios result in excess water in the concrete,
which increases the cure time and results in excessive vapor transmission through the slab.
Therefore, concrete for the floor slab should have a low w/c ratio # less than 0.50. If approved
by the project structural engineer, the sand can be eliminated and the concrete can be placed
directly over the vapor retarder, provided the w/c ratio of the concrete does not exceed 0.45
and water is not added in the field. If necessary, workability should be increased by adding
plasticizers. In addition, the slab should be properly cured. Before the floor covering is placed,
the contractor should check that the concrete surface and the moisture emission levels (if
emission testing is required) meet the manufacturer’s requirements.
We understand a liquid boot may be installed under the floor slab. If a liquid boot is installed as
part of the environmental program, the need for a capillary break/vapor retarder system is
eliminated.
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7.5 Shoring and Underpinning
Excavations will be required in areas where the fill is removed and replaced with engineered fill.
If temporary slopes are used for the excavation, they may be constructed no steeper than 1½
to 1 (horizontal to vertical). Where space does not permit an open#cut excavation with sloped
sides, the temporary excavation faces can be retained using cantilevered soldier#pile#and#
lagging walls. Cantilevered shoring should be designed to resist an equivalent fluid weight of
65 pounds per cubic feet (pcf). Passive resistance may be calculated using an equivalent fluid
pressure of 300 pcf. Passive pressures include a factor of safety of 1.5. Penetration of soldier
piles should be deep enough to maintain lateral stability. At#rest pressures should be assumed
to act over one pile diameter; passive pressures may be assumed to act over three diameters.
The shoring system should be designed by a licensed civil engineer experienced in the design
of retaining systems, and installed by an experienced shoring specialty contractor. The shoring
engineer should be responsible for the design of temporary shoring in accordance with
applicable regulatory requirements. Control of ground movement will depend as much on the
timeliness of installation of lateral restraint as on the design. We should review the shoring
plans and a representative from our office should observe the installation of the shoring.
If hand#excavated, end bearing piers are used to underpin the adjacent buildings, the piers
should be designed using a minimum allowable bearing pressure of 2,000 pounds per square
foot (psf) for dead plus live loads. We should observe the underpinning pier excavations to
check that the exposed soil can support the design bearing pressures. Piers should extend at
least two feet below the bottom of the excavation and below loose fill and debris. Piers should
be designed to resist an at#rest soil pressure caused by soil against the underpinning; an
equivalent fluid pressure of 65 pcf should be applied against the embedded portion of the pier.
Passive resistance may be calculated using an equivalent fluid pressure of 300 pcf which
includes a factor of safety of 1.5.
7.6 Construction Monitoring
A monitoring program should be established to evaluate the effects of the construction on the
adjacent buildings and improvements. The conditions of the existing buildings and
improvements within 50 feet of the site should be photographed and surveyed prior to start of
construction and monitored periodically during construction. A thorough crack survey of the
adjacent buildings, especially those surrounding the proposed excavation should be performed
by a surveyor prior to start of construction and immediately after its completion.
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7.7 Site Drainage
Drainage control design should include provisions for positive surface gradients so that surface
runoff is not permitted to pond, particularly adjacent to structures, or on roadways or
pavements. Surface runoff should be directed away from foundations and below#grade walls.
7.8 Corrosion Design
All below grade improvements should be properly protected against corrosion. A corrosion
expert should be consulted during the design phase for the most economical and effective
corrosion protection.
7.9 Seismic Design Criteria
As previously mentioned in Section 5.3, potentially liquefiable soils where encountered at the
site during our investigation. According to the 2013 California Building Code (CBC), seismic
design should be based on a site#specific response analysis for sites underlain by potentially
liquefiable soils. However, we evaluated the average shear wave velocities within the top
75 feet at the site taking into account the approximate shear wave velocities of the liquefied
soil layers and found that the average shear wave across the site fell within the range of a site
class D site. Also, we are recommending ground improvement to mitigate the lateral spread
potential at the northern portion of the site, which will further increase the average shear wave
velocity across the site. Therefore, for seismic design in accordance with the provisions of
2013 CBC/ASCE 7#10, we recommend the following:
• Risk Targeted Maximum Considered Earthquake (MCER) SS and S1 of 1.500g and
0.653g, respectively.
• Site Class D
• Site Coefficients FA and FV of 1.0 and 1.5, respectively
• Maximum Considered Earthquake (MCE) spectral response acceleration parameters at
short periods, SMS, and at one#second period, SM1, of 1.500g and 0.979g, respectively.
• Design Earthquake (DE) spectral response acceleration parameters at short period, SDS,
and at one#second period, SD1, of 1.000g and 0.653g, respectively.
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8.0 FUTURE GEOTECHNICAL SERVICES
Prior to construction, we should review the project plans and specifications to check their
conformance to the intent of our recommendations. During construction, the Geotechnical
Engineer should observe excavation, ground improvement, mat subgrade preparation, and
compaction of backfill. These observations will allow us to compare the actual with the
anticipated subsurface conditions and check that the contractor's work conforms to the
geotechnical aspects of the plans and specifications.
9.0 LIMITATIONS
The conclusions and recommendations presented in this report result from limited engineering
studies and are based on our interpretation of the geotechnical conditions existing at the site at
the time of investigation. Actual subsurface conditions may vary. If any variations or
undesirable conditions are encountered during construction, or if the proposed construction will
differ from that described in this report, Langan Treadwell Rollo should be notified to make
supplemental recommendations, as necessary.
=
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10.0 REFERENCES
Atwater, B.F., (1979), “Ancient Processes at the Site of Southern San Francisco Bay:
Movement of the Crust and Changes in Sea Level, published in San Francisco Bay: The
Urbanized Estuary; Investigations into the Natural History of San Francisco Bay and Delta with
Reference to the Influence of Man,” Pacific Division, American Association for the
Advancement of Science, San Francisco, California, Conomos, T.J, ed., pp. 31#45.
Bonilla, M.C., (1998), “Preliminary Geologic Map of the San Francisco South 7.5#Minute
Quadrangle and part of the Hunters Point 7.5#Minute Quadrangle, San Francisco Bay Area,
California.”
California Division of Mines and Geology, (1996), “Probabilistic Seismic Hazard Assessment for
the State of California.” DMG Open#File Report 96#08.
California Division of Mines and Geology, (1997), “Fault Rupture Hazard Zones in California,”
CDMG Special Publication 42.
California Division of Mines and Geology, (1997), “Guidelines for Evaluating and Mitigating
Seismic Hazards in California,” California Department of Conservation, Division of Mines and
Geology, Special Publication 117.
California Division of Mines and Geology, (2001), “Seismic Hazard Zone Report for the City and
County of San Francisco,” California Department of Conservation, Division of Mines and
Geology, Seismic Hazard Zone Report 043.
Cao, T., Bryant, W. A., Rowshandel, B., Branum D. and Wills, C. J., (2003), “The Revised 2002
California Probabilistic Seismic Hazard Maps.”
Helley, E.J., and Herd, D.G., (1977), Map showing faults with Quaternary displacement,
northwestern San Francisco Bay region, California: U.S. Geological Survey Miscellaneous Field
Studies map MF#881, scale 1:125,000.
Jennings, C.W., (1994), “Fault Activity Map of California and Adjacent Areas,” California
Division of Mines and Geology Geologic Data Map No. 6, scale 1: 750,000.
Lienkaemper, J. J., (1992), “Map of Recently Active Traces of the Hayward Fault, Alameda and
Contra Costa counties, California.” Miscellaneous Field Studies Map MF#2196.
Nichols, D.R., and Wright, N.A., (1971), “Preliminary Map of Historic Margins of Marshland,
San Francisco Bay, California,” U.S. Geological Survey Open File Report OFR#71#216.
Norris, R.M., and Webb, R.W., (1990), “Geology of California,” John Wiley & Sons, Inc.
San Francisco Building Code, (2010).
Geotechnical Investigation 28 March 2014
2000�2070 Bryant Street 750615602
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=
Schlocker, J., (1974), “Geology of the San Francisco North Quadrangle, California.”
Sloan, D., (1992), “The Yerba Buena Mud � Record of the Last Interglacial Predecessor of
San Francisco Bay, California,” Geological Society of America Bulletin, v. 104, pp. 716#727.
Sitar, et al, (2012), “Seismically Induced Lateral Earth Pressures on Retaining Structures and
Basement Walls.” Geotechnical Engineering State of the Art and Practice Keynote Lectures
GeoCongress 2012 Geotechnical Special Publication No. 226.
Toppozada, T. R. and Borchardt G., (1998), “Re#Evaluation of the 1836 “Hayward Fault” and the
1838 San Andreas Fault earthquakes.” Bulletin of Seismological Society of America, 88(1), 140#
159.
Townley, S. D. and Allen, M. W., (1939), “Descriptive Catalog of Earthquakes of the Pacific
Coast of the United States 1769 to 1928.” Bulletin of the Seismological Society of America,
29(1).
Tokimatsu, K. and Seed, H.B., (1984). “Simplified Procedures for the Evaluation of Settlements
in Clean Sands,” Earthquake Engineering Research Center Report UCB/EERC#84/16, University
California, Berkeley.
Treadwell & Rollo, Inc., (2005), “Final Geotechnical Investigation, Alabama Street Housing,
San Francisco, California.” 23 August.
Wesnousky, S. G., (1986), “Earthquakes, Quaternary Faults, and Seismic Hazards in California,”
Journal of Geophysical Research, 91(1312).
Working Group on California Earthquake Probabilities (WGCEP), (2008), “The Uniform California
Earthquake Rupture Forecast, Version 2,” Open File Report 2007#1437.
Yanev, P., (1974), “Peace of Mind in Earthquake Country,” Chronicle Books, San Francisco,
California.
Youd, L.T., Hansen, C.M., and Bartlett, S.F., (2002), “Revised Multilinear Regression Equations
for Prediction of Lateral Spread Displacement,” Journal of Geotechnical and Environmental
Engineering, Vol. 128, No. 12, December 1.
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FIGURES
0 1/2 Mile
Approximate scale
1/4
Project No. FigureDate 75061560203/25/14 1
SITE LOCATION MAP
SITE
Base map: The Thomas Guide San Francisco County 2002
2000-2070 BRYANT STREETSan Francisco, California
CPT-3
[-18']
CPT-4
[-8']
B-1
[-12']
B-2
[-8']
B-3
[-18']
CPT-2
[-23']
CPT-1
[-15']
CPT-6
[-20]
B-4
[-23]
CPT-5
[-15]
CPT-7
[-20]
Approximate scale
0 40 Feet
Reference: Base map from a drawing titled "Site Survey of a Portion of Assessor's Block No. 4022 for Nick Podell Company,by Martin M. Ron Associates, dated 06-28-13.
Date Project No. Figure
SITE PLAN
San Francisco, California2000-2070 BRYANT STREET
275061560203/25/14
Approximate location of boring by Langan TreadwellRollo, January 2014
Approximate location of cone penetration test byLangan Treadwell Rollo, January and February 2014
Approximate location of boring by Treadwell & Rollo,April 2013
Approximate location of cone penetration test byTreadwell & Rollo, April 2013
Elevation of top of bearing layer
Site boundary
Zone of potential lateral spread
EXPLANATION
B-1
CPT-1
[-14']
B-4
CPT-5
Project No. Figure Date
MAP OF MAJOR FAULTS ANDEARTHQUAKE EPICENTERS IN
THE SAN FRANCISCO BAY AREA
375061560203/25/14
2000-2070 BRYANT STREETSan Francisco, California
SITE
Project No. FigureDate
I Not felt by people, except under especially favorable circumstances. However, dizziness or nausea may be experienced.Sometimes birds and animals are uneasy or disturbed. Trees, structures, liquids, bodies of water may sway gently, and doors may swing very slowly.
II Felt indoors by a few people, especially on upper floors of multi-story buildings, and by sensitive or nervous persons.As in Grade I, birds and animals are disturbed, and trees, structures, liquids and bodies of water may sway. Hanging objects swing, especially if they are delicately suspended.
III Felt indoors by several people, usually as a rapid vibration that may not be recognized as an earthquake at first. Vibration is similar to that of a light, or lightly loaded trucks, or heavy trucks some distance away. Duration may be estimated in some cases.
Movements may be appreciable on upper levels of tall structures. Standing motor cars may rock slightly.
IV Felt indoors by many, outdoors by a few. Awakens a few individuals, particularly light sleepers, but frightens no one except those apprehensive from previous experience. Vibration like that due to passing of heavy, or heavily loaded trucks. Sensation like a heavy body striking building, or the falling of heavy objects inside.
Dishes, windows and doors rattle; glassware and crockery clink and clash. Walls and house frames creak, especially if intensity is in the upper range of this grade. Hanging objects often swing. Liquids in open vessels are disturbed slightly. Stationary automobiles rock noticeably.
V Felt indoors by practically everyone, outdoors by most people. Direction can often be estimated by those outdoors. Awakens many, or most sleepers. Frightens a few people, with slight excitement; some persons run outdoors.
Buildings tremble throughout. Dishes and glassware break to some extent. Windows crack in some cases, but not generally. Vases and small or unstable objects overturn in many instances, and a few fall. Hanging objects and doors swing generally or considerably. Pictures knock against walls, or swing out of place. Doors and shutters open or close abruptly. Pendulum clocks stop, or run fast or slow. Small objects move, and furnishings may shift to a slight extent. Small amounts of liquids spill from well-filled open containers. Trees and bushes shake slightly.
VI Felt by everyone, indoors and outdoors. Awakens all sleepers. Frightens many people; general excitement, and some persons run outdoors.
Persons move unsteadily. Trees and bushes shake slightly to moderately. Liquids are set in strong motion. Small bells in churches and schools ring. Poorly built buildings may be damaged. Plaster falls in small amounts. Other plaster cracks somewhat. Many dishes and glasses, and a few windows break. Knickknacks, books and pictures fall. Furniture overturns in many instances. Heavy furnishings move.
VII Frightens everyone. General alarm, and everyone runs outdoors.People find it difficult to stand. Persons driving cars notice shaking. Trees and bushes shake moderately to strongly. Waves form on ponds, lakes and streams. Water is muddied. Gravel or sand stream banks cave in. Large church bells ring. Suspended objects quiver. Damage is negligible in buildings of good design and construction; slight to moderate in well-built ordinary buildings; considerable in poorly built or badly designed buildings, adobe houses, old walls (especially where laid up without mortar), spires, etc. Plaster and some stucco fall. Many windows and some furniture break. Loosened brickwork and tiles shake down. Weak chimneys break at the roofline. Cornices fall from towers and high buildings. Bricks and stones are dislodged. Heavy furniture overturns. Concrete irrigation ditches are considerably damaged.
VIII General fright, and alarm approaches panic.Persons driving cars are disturbed. Trees shake strongly, and branches and trunks break off (especially palm trees). Sand and mud erupts in small amounts. Flow of springs and wells is temporarily and sometimes permanently changed. Dry wells renew flow. Temperatures of spring and well waters varies. Damage slight in brick structures built especially to withstand earthquakes; considerable in ordinary substantial buildings, with some partial collapse; heavy in some wooden houses, with some tumbling down. Panel walls break away in frame structures. Decayed pilings break off. Walls fall. Solid stone walls crack and break seriously. Wet grounds and steep slopes crack to some extent. Chimneys, columns, monuments and factory stacks and towers twist and fall. Very heavy furniture moves conspicuously or overturns.
IX Panic is general.Ground cracks conspicuously. Damage is considerable in masonry structures built especially to withstand earthquakes; great in other masonry buildings - some collapse in large part. Some wood frame houses built especially to withstand earthquakes are thrown out of plumb, others are shifted wholly off foundations. Reservoirs are seriously damaged and underground pipes sometimes break.
X Panic is general.Ground, especially when loose and wet, cracks up to widths of several inches; fissures up to a yard in width run parallel to canal and stream banks. Landsliding is considerable from river banks and steep coasts. Sand and mud shifts horizontally on beaches and flat land. Water level changes in wells. Water is thrown on banks of canals, lakes, rivers, etc. Dams, dikes, embankments are seriously damaged. Well-built wooden structures and bridges are severely damaged, and some collapse. Dangerous cracks develop in excellent brick walls. Most masonry and frame structures, and their foundations are destroyed. Railroad rails bend slightly. Pipe lines buried in earth tear apart or are crushed endwise. Open cracks and broad wavy folds open in cement pavements and asphalt road surfaces.
XI Panic is general.Disturbances in ground are many and widespread, varying with the ground material. Broad fissures, earth slumps, and land slips develop in soft, wet ground. Water charged with sand and mud is ejected in large amounts. Sea waves of significant magnitude may develop. Damage is severe to wood frame structures, especially near shock centers, great to dams, dikes and embankments, even at long distances. Few if any masonry structures remain standing. Supporting piers or pillars of large, well-built bridges are wrecked. Wooden bridges that "give" are less affected. Railroad rails bend greatly and some thrust endwise. Pipe lines buried in earth are put completely out of service.
XII Panic is general.Damage is total, and practically all works of construction are damaged greatly or destroyed. Disturbances in the ground are great and varied, and numerous shearing cracks develop. Landslides, rock falls, and slumps in river banks are numerous and extensive. Large rock masses are wrenched loose and torn off. Fault slips develop in firm rock, and horizontal and vertical offset displacements are notable. Water channels, both surface and underground, are disturbed and modified greatly. Lakes are dammed, new waterfalls are produced, rivers are deflected, etc. Surface waves are seen on ground surfaces. Lines of sight and level are distorted. Objects are thrown upward into the air.
75061560203/25/14 4
MODIFIED MERCALLI INTENSITY SCALE2000-2070 BRYANT STREET
San Francisco, California
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APPENDIX A
Logs of Borings and Cone Penetration Tests
20.9
20.6
19.9
GRAB
GRAB
S&H
SPT
S&H
S&H
S&H
D&M
SPT
D&M
S&H
GC
SC
SC
CL
SC-SM
CL
SP-SC
4
6
4
4
2
125psi
2
200psi
28
35.9
44.5
54.5
38.5
33.3
533
232123
014
011
111
121723
4 inches Asphalt Concrete (AC)2 inches Aggregate Base (AB)2 inches concreteCLAYEY GRAVEL with SAND (GC)red-brown, moist, fine- to coarse-grainedangular gravel, fine- to coarse-grained sandgreen-gray [SERPENTINITE FILL]
loose, serpentinite fragments up to 2.5 inches indiameter
limited recovery likely due to rocks in fill largerthan sample diameter
CLAYEY SAND (SC)brown and gray, loose, moist, fine-grainedLL = 25, PI = 10, see Figure B-1
CLAYEY SAND (SC)dark gray, loose, moist to wet, fine-grained sand
SANDY CLAY (CL)dark olive-gray, very soft, wet, fine-grained
CLAYEY SILTY SAND (SC-SM)dark olive-gray, loose, wet, fine-graind
strong hydrocarbon odor
LL = 22, PI = 7, see Figure B-1gray with orange-brown mottling, very looseCLAYEY SILTY SAND (SC-SM) (continued)SANDY CLAY (CL)orange-brown, soft, wet, fine-grained sand
SAND with CLAY (SP-SC)olive-brown with orange-brown mottling, mediumdense, moist, fine-grained
FIL
LM
AR
SH
DE
PO
SIT
S
Typ
e of
Str
engt
hT
est
She
ar S
tren
gth
Lbs/
Sq
Ft
Dry
Den
sity
Lbs/
Cu
Ft
Fin
es%
Nat
ural
Moi
stur
eC
onte
nt,
%
Con
finin
gP
ress
ure
Lbs/
Sq
Ft
Hammer type: Down Hole Safety
Boring location:
Date started:
Drilling method:
Hammer weight/drop: 140 lbs./30 inches
E. Toth
Date finished: 4/18/13
See Site Plan, Figure 2
4/18/13
Rotary Wash with Automatic Trip, 6-inch auger to 15 feet
Sampler:
Ground Surface Elevation: 20 feet2
Sprague & Henwood (S&H), Standard Penetration Test (SPT), Dames & Moore (D&M)
Logged by:
Sam
pler
Typ
e
Sam
ple
Blo
ws/
6"
SP
TN
-Val
ue1
LIT
HO
LOG
Y
DE
PT
H(f
eet)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
SAMPLES
LABORATORY TEST DATA
MATERIAL DESCRIPTION
Log of Boring B-12000-2070 BRYANT STREETSan Francisco, California
Figure:
PAGE 1 OF 3
750615602Project No.:
PROJECT:
A-1a
TE
ST
GE
OT
EC
H L
OG
750
615
602
.GP
J T
R.G
DT
3/3
1/1
4
28.3
SPT
SPT
SPT
SPT
SPT
SPT
SP-SC
SC-SM
37
47
84
91
60/5"
29 28.1
171714
91425
242941
374729
3250/5"
141311
SAND with CLAY (SP-SC) (continued)
dense
olive-brown, very dense
SAND (SP) (continued)
with orange-brown mottling, clay seams
CLAYEY SILTY SAND (SC-SM)olive-gray with red-brown mottling, mediumdense, wet, fine-grained, interbedded lenses ofcemented sand, oxidizedLL = 25, PI = 7, see Figure B-1
CO
LM
A F
OR
MA
TIO
N
Typ
e of
Str
engt
hT
est
She
ar S
tren
gth
Lbs/
Sq
Ft
Dry
Den
sity
Lbs/
Cu
Ft
Fin
es%
Nat
ural
Moi
stur
eC
onte
nt,
%
Con
finin
gP
ress
ure
Lbs/
Sq
Ft
Sam
pler
Typ
e
Sam
ple
Blo
ws/
6"
SP
TN
-Val
ue1
LIT
HO
LOG
Y
DE
PT
H(f
eet)
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
SAMPLES LABORATORY TEST DATA
MATERIAL DESCRIPTION
Log of Boring B-12000-2070 BRYANT STREETSan Francisco, California
Figure:
PAGE 2 OF 3
750615602Project No.:
PROJECT:
A-1b
TE
ST
GE
OT
EC
H L
OG
750
615
602
.GP
J T
R.G
DT
3/3
1/1
4
SPT
SPT
SC-SM
SP
60/6"
60/3"
50/6"
4250/3"
CLAYEY SILTY SAND (SC-SM) (continued)
SAND (SP)olive, very dense, wet, fine-grained, trace fines
CO
LM
A F
OR
MA
TIO
N
Typ
e of
Str
engt
hT
est
She
ar S
tren
gth
Lbs/
Sq
Ft
Dry
Den
sity
Lbs/
Cu
Ft
Fin
es%
Nat
ural
Moi
stur
eC
onte
nt,
%
Con
finin
gP
ress
ure
Lbs/
Sq
Ft
Sam
pler
Typ
e
Sam
ple
Blo
ws/
6"
SP
TN
-Val
ue1
LIT
HO
LOG
Y
DE
PT
H(f
eet)
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
SAMPLES LABORATORY TEST DATA
MATERIAL DESCRIPTION
Log of Boring B-12000-2070 BRYANT STREETSan Francisco, California
Figure:
PAGE 3 OF 3
750615602Project No.:
PROJECT:
A-1c
TE
ST
GE
OT
EC
H L
OG
750
615
602
.GP
J T
R.G
DT
3/3
1/1
4
Boring terminated at a depth of 69.3 feet below ground surface.Boring backfilled with cement grout.Groundwater obscured by drilling method.
1 S&H and SPT blow counts for the last two increments wereconverted to SPT N-Values using factors of 0.7 and 1.2,respectively to account for sampler type and hammer energy.
2 Elevations based on San Francisco City datum and Site Surveydated 06-28-13.
PP 1,600
16.2
18.9
GRAB
GRAB
S&H
SPT
S&H
D&M
SPT
SPT
CL
SC
CL
SP-SM
36
32
14
300psi
44
41
13.5
122428
111413
6812
81225
151618
6 inches Asphalt Concrete (AC)5 inches concreteSANDY CLAY with GRAVEL (CL)dark brown, moist, fine sand, angular gravel,trace concrete and brick debris
CLAYEY SAND (SC)brown and gray, moist, fine-grained
dense
olive-brown, clayey sand
(04/19/12, 9:00 a.m.)SANDY CLAY (CL)olive-brown with orange-brown mottling, stiff,moist to wet, fine-grained sand
SAND with SILT (SP-SM)olive-gray, dense, wet, fine-grained
FIL
L 110
Typ
e of
Str
engt
hT
est
She
ar S
tren
gth
Lbs/
Sq
Ft
Dry
Den
sity
Lbs/
Cu
Ft
Fin
es%
Nat
ural
Moi
stur
eC
onte
nt,
%
Con
finin
gP
ress
ure
Lbs/
Sq
Ft
Hammer type: Down Hole Safety
Boring location:
Date started:
Drilling method:
Hammer weight/drop: 140 lbs./30 inches
E. Toth
Date finished: 4/19/13
See Site Plan, Figure 2
4/19/13
Rotary Wash with Automatic Trip, 6-inch auger to 13.5 feet
Sampler:
Ground Surface Elevation: 19 feet2
Sprague & Henwood (S&H), Standard Penetration Test (SPT), Dames & Moore (D&M)
Logged by:
Sam
pler
Typ
e
Sam
ple
Blo
ws/
6"
SP
TN
-Val
ue1
LIT
HO
LOG
Y
DE
PT
H(f
eet)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
SAMPLES
LABORATORY TEST DATA
MATERIAL DESCRIPTION
Log of Boring B-22000-2070 BRYANT STREETSan Francisco, California
Figure:
PAGE 1 OF 3
750615602Project No.:
PROJECT:
A-2a
TE
ST
GE
OT
EC
H L
OG
750
615
602
.GP
J T
R.G
DT
3/3
1/1
4
20.1
21.1
SPT
SPT
SPT
SPT
SPT
SP-SM
SP-SC
35
42
35
80
73
10.5
12.7
101415
91421
91019
142938
222734
SAND with SILT (SP-SM) (continued)
SAND with CLAY (SP-SC)olive-brown with orange-brown and blackmottling, dense, wet, fine-grained
very dense
increase clay content
CO
LM
A F
OR
MA
TIO
N
Typ
e of
Str
engt
hT
est
She
ar S
tren
gth
Lbs/
Sq
Ft
Dry
Den
sity
Lbs/
Cu
Ft
Fin
es%
Nat
ural
Moi
stur
eC
onte
nt,
%
Con
finin
gP
ress
ure
Lbs/
Sq
Ft
Sam
pler
Typ
e
Sam
ple
Blo
ws/
6"
SP
TN
-Val
ue1
LIT
HO
LOG
Y
DE
PT
H(f
eet)
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
SAMPLES LABORATORY TEST DATA
MATERIAL DESCRIPTION
Log of Boring B-22000-2070 BRYANT STREETSan Francisco, California
Figure:
PAGE 2 OF 3
750615602Project No.:
PROJECT:
A-2b
TE
ST
GE
OT
EC
H L
OG
750
615
602
.GP
J T
R.G
DT
3/3
1/1
4
PP 2,000
30.9
SPT
SPT
SPT
S&H
SPT
SP-SC
CL
SC-SM
SP
68
60/4"
107/9.5"
19
66
12.9
323027
4650/4"
253950/3.5"
41017
6550
SAND with CLAY (SP-SC) (continued)
dark gray, 4 inch clay lens at 54.5
gray-brown with orange-brown mottling, ironoxide staining
no oxidation
SANDY CLAY (CL)dark gray, very stiff, wet, fine-grained sand,interbedded seams of sand
CLAYEY SILTY SAND (SC-SM)dark gray, medium dense, wet, fine-grainedsandLL = 22, PI = 4, see Figure B-1
SAND (SP)dark gray, very dense, wet, fine-grained,interbedded lenses of sandy clay
CO
LM
A F
OR
MA
TIO
N
Typ
e of
Str
engt
hT
est
She
ar S
tren
gth
Lbs/
Sq
Ft
Dry
Den
sity
Lbs/
Cu
Ft
Fin
es%
Nat
ural
Moi
stur
eC
onte
nt,
%
Con
finin
gP
ress
ure
Lbs/
Sq
Ft
Sam
pler
Typ
e
Sam
ple
Blo
ws/
6"
SP
TN
-Val
ue1
LIT
HO
LOG
Y
DE
PT
H(f
eet)
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
SAMPLES LABORATORY TEST DATA
MATERIAL DESCRIPTION
Log of Boring B-22000-2070 BRYANT STREETSan Francisco, California
Figure:
PAGE 3 OF 3
750615602Project No.:
PROJECT:
A-2c
TE
ST
GE
OT
EC
H L
OG
750
615
602
.GP
J T
R.G
DT
3/3
1/1
4
Boring terminated at a depth of 75 feet below ground surface.Boring backfilled with cement grout.Groundwater encountered at 12.3 feet below ground surface duringdrilling.PP = pocket penetrometer
1 S&H and SPT blow counts for the last two increments wereconverted to SPT N-Values using factors of 0.7 and 1.2,respectively to account for sampler type and hammer energy.
2 Elevations based on San Francisco City datum and Site Surveydated 06-28-13.
23.2
18.8
S&H
SPT
S&H
DIST
SPT
SPT
S&H
SP-SC
SP
CL
SP-SC
SP
CL
SC
22
38
16
26
24
29
30
11.8
16.7
101517
131517
7914
111522
8911131212
111924
8.5 inches concrete
SAND with CLAY (SP-SC)brown, moist, fine-grained, trace concrete debris
medium dense
SAND (SP)brown, dense, moist, fine-grained
SANDY CLAY (CL)olive-brown with red mottling, very stiff, moist,fine-grained sand
(04/22/13, 8:10 a.m.)
SAND with CLAY (SP-SC)olive-brown, medium dense, wet, fine-grained
SAND (SP)olive-brown, medium dense, wet, fine-grained
SAND (SP) (continued)
SANDY CLAY (CL)orange-brown with black mottling, very stiff, wet,fine-grained sand
CLAYEY SAND (SC)orange-brown with black mottling, dense, wet,
FIL
L
Typ
e of
Str
engt
hT
est
She
ar S
tren
gth
Lbs/
Sq
Ft
Dry
Den
sity
Lbs/
Cu
Ft
Fin
es%
Nat
ural
Moi
stur
eC
onte
nt,
%
Con
finin
gP
ress
ure
Lbs/
Sq
Ft
Hammer type: Down Hole Safety
Boring location:
Date started:
Drilling method:
Hammer weight/drop: 140 lbs./30 inches
E. Toth
Date finished: 4/22/13
See Site Plan, Figure 2
4/22/13
Hollow Stem Auger with Automatic Trip
Sampler:
Ground Surface Elevation: 24.5 feet2
Sprague & Henwood (S&H), Standard Penetration Test (SPT), Dames & Moore (D&M)
Logged by:
Sam
pler
Typ
e
Sam
ple
Blo
ws/
6"
SP
TN
-Val
ue1
LIT
HO
LOG
Y
DE
PT
H(f
eet)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
SAMPLES
LABORATORY TEST DATA
MATERIAL DESCRIPTION
Log of Boring B-32000-2070 BRYANT STREETSan Francisco, California
Figure:
PAGE 1 OF 2
750615602Project No.:
PROJECT:
A-3a
TE
ST
GE
OT
EC
H L
OG
750
615
602
.GP
J T
R.G
DT
3/3
1/1
4
SPT
SPT
SPT
SPT
SC
SP-SC
29
28
67
60/4"
101311
41112
203125
3550/4"
fine grained
olive-brown with orange mottling, medium dense
with black mottling
SAND with CLAY (SP-SC)olive-brown with red and black mottling, verydense, wet, fine-grained, iron oxide staining
gray-brown
CO
LM
A F
OR
MA
TIO
N
Typ
e of
Str
engt
hT
est
She
ar S
tren
gth
Lbs/
Sq
Ft
Dry
Den
sity
Lbs/
Cu
Ft
Fin
es%
Nat
ural
Moi
stur
eC
onte
nt,
%
Con
finin
gP
ress
ure
Lbs/
Sq
Ft
Sam
pler
Typ
e
Sam
ple
Blo
ws/
6"
SP
TN
-Val
ue1
LIT
HO
LOG
Y
DE
PT
H(f
eet)
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
SAMPLES LABORATORY TEST DATA
MATERIAL DESCRIPTION
Log of Boring B-32000-2070 BRYANT STREETSan Francisco, California
Figure:
PAGE 2 OF 2
750615602Project No.:
PROJECT:
A-3b
TE
ST
GE
OT
EC
H L
OG
750
615
602
.GP
J T
R.G
DT
3/3
1/1
4
Boring terminated at a depth of 49.3 feet below ground surface.Boring backfilled with cement grout.Groundwater encountered at 17.3 feet below ground surface duringdrilling. by drilling method.
1 S&H and SPT blow counts for the last two increments wereconverted to SPT N-Values using factors of 0.7 and 1.2,respectively to account for sampler type and hammer energy.
2 Elevations based on San Francisco City datum and Site Surveydated 06-28-13.
39.2
20.0
14.4
17.9
25.2
GRAB
S&H
S&H
S&H
SPT
S&H
S&H
ST
SC
SM
GP-GC
GP-GM
CL
7
8
16
22
15
6
41.1
9.5
6.7
7.1
455
347
1311124135
91111
235
0-350psi
6 inches concreteCLAYEY SAND with GRAVEL (SC)red-brown, moist, fine to medium grained sand,subangular to angular gravel, trace wood debris
color change to light brown
orange-brown, loose, moist, decrease clay andgravel content
SILTY SAND with GRAVEL (SM)brown and gray, loose, moist, angular tosubangular gravel, trace sand[crushed serpentinite]LL = 59, PL = 38, PI = 21, see Figure B-2Sieve Analysis, see Figure B-4
gravel up to 2" in diameter observed in cuttingsloss of drilling fluid, advance casing to 15 feet
GRAVEL with CLAY and SAND (GP-GC)gray, olive gray sand with yellow mottling,medium dense, wet, subangular gravelLL = 41, PL = 25, PI = 16, see Figure B-2Sieve Analysis, see Figure B-5
loss of drilling fluid, advance casing to 20 feet
GRAVEL with SILT and SAND (GP-GM)gray-brown, medium dense, wet, subangular toangular gravel[crushed weathered serpentinite]LL = 38, PL = 31, PI = 7, see Figure B-2Sieve Analysis, see Figure B-6
SANDY CLAY (CL)black, medium stiff, wet, trace organics
LL = 36, PL = 17, PI = 19, see Figure B-2
grayConsolidation Test, see Figure B-3
FIL
LM
AR
SH
DE
PO
SIT 100.2
Typ
e of
Str
engt
hT
est
She
ar S
tren
gth
Lbs/
Sq
Ft
Dry
Den
sity
Lbs/
Cu
Ft
Fin
es%
Nat
ural
Moi
stur
eC
onte
nt,
%
Con
finin
gP
ress
ure
Lbs/
Sq
Ft
Hammer type: Automatic Safety
Boring location:
Date started:
Drilling method:
Hammer weight/drop: 140 lbs./30 inches
P. Brady
Sprague & Henwood (S&H), Standard Penetration Test (SPT)
Date finished: 1/30/14
See Site Plan, Figure 2
1/30/14
Rotary Wash
Sampler:
Ground Surface Elevation: 21.5 feet2
Logged by:
Sam
pler
Typ
e
Sam
ple
Blo
ws/
6"
SP
TN
-Val
ue1
LIT
HO
LOG
Y
DE
PT
H(f
eet)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
SAMPLES
LABORATORY TEST DATA
MATERIAL DESCRIPTION
Log of Boring B-42000-2070 BRYANT STREETSan Francisco, California
Figure:
PAGE 1 OF 4
750615602Project No.:
PROJECT:
A-4a
TE
ST
GE
OT
EC
H L
OG
750
615
602
.GP
J T
R.G
DT
3/3
1/1
4
23.7
24.9
S&H
SPT
DIST
SPT
SPT
SPT
SPT
CL
SM
SC
SP
23
28
11
78
95
50
29.8
44.8
81223
7815
245
152736
192950
121933
SANDY CLAY (CL) (continued)yellow-brown, very stiff, wet, trace fine gravel
SILTY SAND (SM)yellow-brown, medium dense, wet, fine grainedsandPI = Non-Plastic, see Figure B-2
CLAYEY SAND (SC)olive gray, medium dense, wet, trace fine tomedium gravel
LL = 24, PL = 16, PI = 8, see Figure B-2
SAND (SP)olive-gray, very dense, wet, trace silt, fine tocoarse grained sand
increase in gravel content
MA
RS
H D
EP
OS
ITC
OL
MA
FO
RM
AT
ION
Typ
e of
Str
engt
hT
est
She
ar S
tren
gth
Lbs/
Sq
Ft
Dry
Den
sity
Lbs/
Cu
Ft
Fin
es%
Nat
ural
Moi
stur
eC
onte
nt,
%
Con
finin
gP
ress
ure
Lbs/
Sq
Ft
Sam
pler
Typ
e
Sam
ple
Blo
ws/
6"
SP
TN
-Val
ue1
LIT
HO
LOG
Y
DE
PT
H(f
eet)
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
SAMPLES LABORATORY TEST DATA
MATERIAL DESCRIPTION
Log of Boring B-42000-2070 BRYANT STREETSan Francisco, California
Figure:
PAGE 2 OF 4
750615602Project No.:
PROJECT:
A-4b
TE
ST
GE
OT
EC
H L
OG
750
615
602
.GP
J T
R.G
DT
3/3
1/1
4
24.2
SPT
SPT
SPT
SPT
SPT
S&H
PT
CL
60/5"
102/10"
114/10"
58
14
33
4.3
3050/6"
3835
50/4"
3545
50/4"
102424
248
102027
SAND (SP) (continued)
color change to yellow-brown
gray
CLAYEY PEAT (PT)black to dark brown, stiff to very stiff, wet, tracefine sand, trace shell, root structureorganic matter = 25.73%
CLAY (CL)gray, hard, wet
CO
LM
A F
OR
MA
TIO
N
Typ
e of
Str
engt
hT
est
She
ar S
tren
gth
Lbs/
Sq
Ft
Dry
Den
sity
Lbs/
Cu
Ft
Fin
es%
Nat
ural
Moi
stur
eC
onte
nt,
%
Con
finin
gP
ress
ure
Lbs/
Sq
Ft
Sam
pler
Typ
e
Sam
ple
Blo
ws/
6"
SP
TN
-Val
ue1
LIT
HO
LOG
Y
DE
PT
H(f
eet)
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
SAMPLES LABORATORY TEST DATA
MATERIAL DESCRIPTION
Log of Boring B-42000-2070 BRYANT STREETSan Francisco, California
Figure:
PAGE 3 OF 4
750615602Project No.:
PROJECT:
A-4c
TE
ST
GE
OT
EC
H L
OG
750
615
602
.GP
J T
R.G
DT
3/3
1/1
4
S&H CL41213029
CLAY (CL) (continued)hard, trace fine grained sand, trace fine angulargravel
Typ
e of
Str
engt
hT
est
She
ar S
tren
gth
Lbs/
Sq
Ft
Dry
Den
sity
Lbs/
Cu
Ft
Fin
es%
Nat
ural
Moi
stur
eC
onte
nt,
%
Con
finin
gP
ress
ure
Lbs/
Sq
Ft
Sam
pler
Typ
e
Sam
ple
Blo
ws/
6"
SP
TN
-Val
ue1
LIT
HO
LOG
Y
DE
PT
H(f
eet)
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
SAMPLES LABORATORY TEST DATA
MATERIAL DESCRIPTION
Log of Boring B-42000-2070 BRYANT STREETSan Francisco, California
Figure:
PAGE 4 OF 4
750615602Project No.:
PROJECT:
A-4d
TE
ST
GE
OT
EC
H L
OG
750
615
602
.GP
J T
R.G
DT
3/3
1/1
4
Boring terminated at a depth of 91.5 feet below ground surface.Boring backfilled with cement grout.Groundwater not measured during drilling.
1 S&H and SPT blow counts for the last two increments wereconverted to SPT N-Values using factors of 0.7 and 1.2,respectively to account for sampler type and hammer energy.
2 Elevations based on San Francisco City datum and Site Surveydated 06-28-13.
Project No. FigureDate 03/25/14 A-5
CLASSIFICATION CHART
Major Divisions Symbols Typical Names
GW
GP
GM
GC
SW
SP
SM
SC
ML
CL
OL
MH
CH
OH
PTHighly Organic Soils
UNIFIED SOIL CLASSIFICATION SYSTEM
Well-graded gravels or gravel-sand mixtures, little or no fines
Poorly-graded gravels or gravel-sand mixtures, little or no fines
Silty gravels, gravel-sand-silt mixtures
Clayey gravels, gravel-sand-clay mixtures
Well-graded sands or gravelly sands, little or no fines
Poorly-graded sands or gravelly sands, little or no fines
Silty sands, sand-silt mixtures
Inorganic silts and clayey silts of low plasticity, sandy silts, gravelly silts
Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, lean clays
Organic silts and organic silt-clays of low plasticity
Inorganic silts of high plasticity
Inorganic clays of high plasticity, fat clays
Organic silts and clays of high plasticity
Peat and other highly organic soils
Clayey sands, sand-clay mixtures
Range of Grain Sizes
Grain Sizein Millimeters
U.S. Standard Sieve Size
Above 12"
12" to 3"
Classification
Boulders
Cobbles
Above 305
305 to 76.2
Silt and Clay Below No. 200 Below 0.075
GRAIN SIZE CHART
SAMPLER TYPE
Co
arse
-Gra
ined
So
ils(m
ore
than
hal
f of s
oil >
no.
200
siev
e si
ze
Fin
e -G
rain
ed S
oils
(mor
e th
an h
alf o
f soi
l<
no.
200
sie
ve s
ize)
Gravels(More than half ofcoarse fraction >no. 4 sieve size)
Sands(More than half ofcoarse fraction <no. 4 sieve size)
Silts and ClaysLL = < 50
Silts and ClaysLL = > 50
Gravel coarse fine
3" to No. 43" to 3/4"
3/4" to No. 4
No. 4 to No. 200No. 4 to No. 10No. 10 to No. 40
No. 40 to No. 200
76.2 to 4.7676.2 to 19.119.1 to 4.76
4.76 to 0.0754.76 to 2.002.00 to 0.420
0.420 to 0.075
Sand coarse medium fine
C Core barrel
CA California split-barrel sampler with 2.5-inch outside diameter and a 1.93-inch inside diameter
D&M Dames & Moore piston sampler using 2.5-inch outside diameter, thin-walled tube
O Osterberg piston sampler using 3.0-inch outside diameter, thin-walled Shelby tube
PT Pitcher tube sampler using 3.0-inch outside diameter, thin-walled Shelby tube
S&H Sprague & Henwood split-barrel sampler with a 3.0-inch outside diameter and a 2.43-inch inside diameter
SPT Standard Penetration Test (SPT) split-barrel sampler with a 2.0-inch outside diameter and a 1.5-inch inside diameter
ST Shelby Tube (3.0-inch outside diameter, thin-walled tube) advanced with hydraulic pressure
SAMPLE DESIGNATIONS/SYMBOLS
Sample taken with Sprague & Henwood split-barrel sampler with a 3.0-inch outside diameter and a 2.43-inch inside diameter. Darkened area indicates soil recovered
Classification sample taken with Standard Penetration Test sampler
Undisturbed sample taken with thin-walled tube
Disturbed sample
Sampling attempted with no recovery
Core sample
Analytical laboratory sample, grab groundwater
Sample taken with Direct Push sampler
Sonic
Unstabilized groundwater level
Stabilized groundwater level
750615602
2000-2070 BRYANT STREETSan Francisco, California
CONE PENETRATION TEST RESULTSCPT-1
Project No. Figure750615602 A-6Date 03/25/14
Terminated at 43.9 feet.Groundwater encountered at elevation 14.5 feet.Date performed 04/16/13.Ground surface elevation: 23.5 feet, City of San Francisco Datum.
v
v 'E f fect ive vert icals t ress,
T otal vert ical s t ress,
Undrained S hearS t rength, s
u
2000-2070 BRYANT STREETSan Francisco, California
55
45
35
25
15
5
0 200 400 600qc (ts f)
55
45
35
25
15
5
0 1 2 3 4 5 6 7 8 9R f (percen t)
55
45
35
25
15
5
0 20 40 60 80S P T (N )
55
45
35
25
15
5
0 10 20 30 40 50Ø (deg)
55
45
35
25
15
5
0 1 2 3 4 5 6 7 8S u (ts f)
55
45
35
25
15
5
v v, ',
CONE PENETRATION TEST RESULTSCPT-2
Project No. Figure750615602 A-7Date 03/25/14
Terminated at 51.5 feet.Groundwater encountered at elevation 9 feet.Date performed 04/16/13.Ground surface elevation: 25 feet, City of San Francisco Datum.
v
v 'E f fect ive vert icals t ress,
T otal vert ical s t ress,
Undrained S hearS t rength, s
u
2000-2070 BRYANT STREETSan Francisco, California
55
45
35
25
15
5
0 200 400 600qc (ts f)
55
45
35
25
15
5
0 1 2 3 4 5 6 7 8 9R f (percen t)
55
45
35
25
15
5
0 20 40 60 80S P T (N )
55
45
35
25
15
5
0 10 20 30 40 50Ø (deg)
55
45
35
25
15
5
0 1 2 3 4 5 6 7 8S u (ts f)
55
45
35
25
15
5
v v, ',
CONE PENETRATION TEST RESULTSCPT-3
Project No. Figure750615602 A-8Date 03/25/14
Terminated at 44.9 feet.
Date performed 04/22/13.Ground surface elevation: 20 feet, City of San Francisco Datum.
v
v 'E f fect ive vert icals t ress,
T otal vert ical s t ress,
Undrained S hearS t rength, s
u
2000-2070 BRYANT STREETSan Francisco, California
55
45
35
25
15
5
0 200 400 600qc (ts f)
55
45
35
25
15
5
0 1 2 3 4 5 6 7 8 9R f (percen t)
55
45
35
25
15
5
0 20 40 60 80S P T (N )
55
45
35
25
15
5
0 10 20 30 40 50Ø (deg)
55
45
35
25
15
5
0 1 2 3 4 5 6 7 8S u (ts f)
55
45
35
25
15
5
v v, ',
CONE PENETRATION TEST RESULTSCPT-4
Project No. Figure750615602 A-9Date 03/25/14
Terminated at 45.6 feet.
Date performed 04/22/13.Ground surface elevation: 19.5 feet, City of San Francisco Datum.
v
v 'E f fect ive vert icals t ress,
T otal vert ical s t ress,
Undrained S hearS t rength, s
u
2000-2070 BRYANT STREETSan Francisco, California
55
45
35
25
15
5
0 200 400 600qc (ts f)
55
45
35
25
15
5
0 1 2 3 4 5 6 7 8 9R f (percen t)
55
45
35
25
15
5
0 20 40 60 80S P T (N )
55
45
35
25
15
5
0 10 20 30 40 50Ø (deg)
55
45
35
25
15
5
0 1 2 3 4 5 6 7 8S u (ts f)
55
45
35
25
15
5
v v, ',
Project No. FigureDate 03/25/14 A-10750615602
2000-2070 BRYANT STREETSan Francisco, California CONE PENETRATION TEST RESULTS
CPT-5Date performed 01/28/14.Ground surface elevation: 23 feet, City of San Francisco Datum.
Project No. FigureDate 03/25/14 A-11750615602
2000-2070 BRYANT STREETSan Francisco, California CONE PENETRATION TEST RESULTS
CPT-6Date performed 01/28/14.Ground surface elevation: 22 feet, City of San Francisco Datum.
Project No. FigureDate 03/25/14 A-12750615602
2000-2070 BRYANT STREETSan Francisco, California CONE PENETRATION TEST RESULTS
CPT-7Date performed 02/01/14.Ground surface elevation: 22 feet, City of San Francisco Datum.
03/25/14 A-13
CLASSIFICATION CHART FORCONE PENETRATION TESTS
GR
EG
G
Project No. FigureDate
ZONE SOIL BEHAVIOR TYPE
123456789
Reference: Lunne, T., Robertson, P.K., and Powell, J.J.M., 1997.
Sensitive Fine GrainedOrganic Material
SILTY CLAY to CLAYCLAYEY SILT to SILTY CLAYSILTY SAND to SANDY SILT
SANDS to SILTY SANDGRAVELLY SAND to Dense SAND
Very Dense SAND to CLAYEY SANDVery Stiff, Fine Grained
Qt = (qt – svo)/s’vo = Normalized Cone Resistance qt = qc + (1-a)u2 = Corrected Cone Resistance qc = Measured Cone Resistance a = 0.8 = Area Ratio of Cone u2 = Pore Pressure Measured Behind Cone During Test svo = Total Vertical Stress s’vo = Total Effective Vertical Stress F = fs/(qt – svo) x 100% = Normalized Friction Ratio fs = Measured unit Sleeve Friction Resistance
Note Testing Performed in Accordance with ASTM D5778-95
Normalized Friction Ratio, F= x 100%fs
q t vo
f 1
Nor
mal
ized
Con
e R
esis
tanc
e, Q
t
7 8
9
3
2
6
5
4Inc
reasin
g
OCR & ag
e
I = 2.6
c
1000
100
10
1 0.1 1 10
Normally Consolidated
s
Increasin
g
Sensitivity
Increasi
ng
OCR, age,
cementati
on
1
Increasing Ic
750615602
2000-2070 BRYANT STREETSan Francisco, California
=
APPENDIX B
Laboratory Test Results
ML or OL
MH or OH
Symbol Source
Natural
M.C. (%)
Liquid
Limit (%)
CL - ML
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70 80 90 100 110 120
LIQUID LIMIT (LL)
Description and Classification% Passing
#200 Sieve
Plasticity
Index (%)
Project No. FigureDate 03/25/14 B-1
PLASTICITY CHART
PLA
ST
ICIT
Y IN
DE
X (
PI)
Ref erence:
ASTM D2487-00
750615602
2000-2070 BRYANT STREET
San Francisco, California
B-1 at 11 feet
B-1 at 23.5 feet
B-1 at 59 feet
B-2 at 69.5 feet
CLAYEY SAND (SC), brown and gray
CLAYEY SILTY SAND (SC-SM), dark
olive-gray
CLAYEY SILTY SAND (SC-SM), olive-gray
with red-brown mottling
20.9
19.9
28.3
30.9
35.9
33.3
28.1
12.9
25
22
25
22
10
7
7
4CLAYEY SILTY SAND (SC-SM), dark gray
ML or OL
MH or OH
Symbol SourceNatural
M.C. (%)Liquid
Limit (%)
CL - ML
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60 70 80 90 100 110 120
LIQUID LIMIT (LL)
Description and Classification% Passing#200 Sieve
PlasticityIndex (%)
Project No. FigureDate 03/25/14 B-2
PLASTICITY CHART
750615602
2000 BRYANT STREETSan Francisco, California
PLA
ST
ICIT
Y IN
DE
X (
PI)
Ref erence:ASTM D2487-00
B-4 at 11 feet
B-4 at 16.5 feet
B-4 at 21 feet
B-4 at 26 feet
B-4 at 35 feet
B-4 at 42 feet
SILTY SAND with GRAVEL (SM), brown and gray
GRAVEL with CLAY and SAND (GP-GC),gray
GRAVEL with SILT and SAND (GP-GM),gray-brown
SANDY CLAY (CL), black
SILTY SAND (SC), yellow-brown
CLAYEY SAND (SC), olive gray
39.2
14.4
17.9
25.2
23.7
24.9
41.1
6.7
7.1
--
29.8
44.8
59
41
38
36
--
24
21
16
7
19
--
8
Sampler Type: Shelby Tube Condition Before Test After Test Diameter (in) 2.42 Height (in) 1.00 Water Content wo 23.1 % wf 15.8 % Overburden Pressure, po 2,240 psf Void Ratio eo 0.65 ef 0.43 Preconsol. Pressure, pc 3,200 psf Saturation So 96 % Sf 100 % Compression Ratio, Cc 0.125 Dry Density d 102 pcf d 118 pcf LL PL PI Gs (assumed) Classification SANDY CLAY (CL), gray Source B-4 at 27 feet
2000-2070 BRYANT STREETSan Francisco, California
03/25/14 750615602
2.70
CONSOLIDATION TEST REPORT
Date Project No. Figure B-3
0
5
10
15
20
25
0.1 1.0 10.0 100.0Vo
lum
etric
Stra
in (p
erce
nt)
Pressure (ksf)
0
200
400
600
800
1000
0.1 1.0 10.0 100.0
Cv
(ft2
/ yea
r)
0
10
20
30
40
50
60
70
80
90
100
100 10 1 0.1 0.01 0.001GRAIN SIZE (millimeters)
50 5 0.5 0.05 0.005
3 11/2 3/4 3/8 4 8 16 30 40 50 100 200 Ref erence: ASTM D422
U.S. Standard Sieve Size (in.) U.S. Standard Sieve Numbers Hydrometer
% Cobbles % Grav el %Sand % Fines
Symbol
Coarse Fine
Sample Source
ClaySiltFineMediumCoarse
0.00.0 0.00.00.00.0 0.0
Classification
PE
RC
EN
T FI
NE
R B
Y W
EIG
HT
Project No. FigureDate B-4
PARTICLE SIZE ANALYSIS
B-4 at 11 feet SILTY SAND with GRAVEL (SM), brown and gray
03/25/14 750615602
2000-2070 BRYANT STREETSan Francisco, California
0
10
20
30
40
50
60
70
80
90
100
100 10 1 0.1 0.01 0.001GRAIN SIZE (millimeters)
50 5 0.5 0.05 0.005
3 11/2 3/4 3/8 4 8 16 30 40 50 100 200 Ref erence: ASTM D422
U.S. Standard Sieve Size (in.) U.S. Standard Sieve Numbers Hydrometer
% Cobbles % Grav el %Sand % Fines
Symbol
Coarse Fine
Sample Source
ClaySiltFineMediumCoarse
0.00.0 0.00.00.00.0 0.0
Classification
PE
RC
EN
T FI
NE
R B
Y W
EIG
HT
Project No. FigureDate B-5
PARTICLE SIZE ANLYSIS
B-4 at 16.5 feet GRAVEL with CLAY and SAND (GP-GC), gray
03/25/14 750615602
2000 BRYANT STREETSan Francisco, California
0
10
20
30
40
50
60
70
80
90
100
100 10 1 0.1 0.01 0.001GRAIN SIZE (millimeters)
50 5 0.5 0.05 0.005
3 11/2 3/4 3/8 4 8 16 30 40 50 100 200 Ref erence: ASTM D422
U.S. Standard Sieve Size (in.) U.S. Standard Sieve Numbers Hydrometer
% Cobbles % Grav el %Sand % Fines
Symbol
Coarse Fine
Sample Source
ClaySiltFineMediumCoarse
0.00.0 0.00.00.00.0 0.0
Classification
PE
RC
EN
T FI
NE
R B
Y W
EIG
HT
Project No. FigureDate B-6
PARTICLE SIZE ANLYSIS
B-4 at 21 feet GRAVEL with SILT and SAND (GC-GM), gray-brown
03/25/14 750615602
2000-2070 BRYANT STREETSan Francisco, California
=
APPENDIX C
Corrosivity Test Results
DISTRIBUTION
1 copy: Ms. Linsey Perlov
Nick Podell Company
22 Battery Street, Suite 404
San Francisco, California 94111
:
QUALITY CONTROL REVIEWER:
Richard D. Rodgers, G.E.
Managing Principal