Prepared for Newlife Investments, LLC
1350 Ocean Avenue • Emeryville, CA 94608 • (510) 420-5738 www.rockridgegeo.com
FINAL GEOTECHNICAL INVESTIGATION
PROPOSED RAILROAD RESIDENCE DEVELOPMENT
RAILROAD AND S. LINDEN AVENUES
SOUTH SAN FRANCISCO, CALIFORNIA
UNAUTHORIZED USE OR COPYING OF THIS DOCUMENT IS STRICTLY
PROHIBITED BY ANYONE OTHER THAN THE CLIENT FOR THE SPECIFIC
PROJECT
September 18, 2023
Project No. 21-2085
1350 Ocean Avenue • Emeryville, CA 94608 • (510) 420-5738 www.rockridgegeo.com
September 18, 2023
Project No. 21-2085
Newlife Investments, LLC
3646 Maxon Street
Chino, California 91710
ATTN: Ken Cui
Subject: Final Geotechnical Investigation
Proposed Railroad Residence Development
Railroad and S. Linden Avenues
South San Francisco, California
Dear Mr. Cui:
We are pleased to present the results of our final geotechnical investigation report for the proposed residential development and linear park to be constructed on the southern side of Railroad Avenue, between its intersections with S. Spruce and S. Linden avenues in South San Francisco, California. Our geotechnical investigation was performed in accordance with our proposal dated June 27, 2023.
The site consists of two parcels (APNs 014072050 and 014061170) and is bordered by Railroad Avenue to the north, S. Linden Avenue to the east, and commercial properties to the south and west. The site for the proposed residential development is a strip of land along Railroad Avenue that has plan dimensions of approximately 50 by 1,467 feet. The ground surface elevations on the residential development site are close to the grade on Railroad Avenue at the eastern and western ends and up to approximately 20 feet below the Railroad Avenue grade near the center.
Where the grades on the residential development site are lower than Railroad Avenue, the northern portion of the site slopes down towards the south from an existing retaining wall along Railroad Avenue at a gradient as steep as 1.7:1 (horizontal to vertical).
The proposed residential development consists of constructing residential buildings containing 73 townhouse units. The proposed residential buildings will be 3 to 4 stories and of wood-framed construction. The ground level of the residential buildings will have finished floor near Railroad Avenue grade. Some of the buildings will have an accessory dwelling unit (ADU) below the ground floor. Improvements to the residential development site will also include publicly accessible open spaces and a shared rear drive aisle. The existing retaining wall supporting Railroad Avenue will be left in-place and a new retaining wall will be constructed downslope (to the south) of the existing wall.
Other site improvements include constructing a new linear park between existing neighboring commercial properties. The proposed linear park will extend from Railroad Avenue to N. Canal Street.
Newlife Investments, LLC
September 18, 2023
Based on the results of our geotechnical investigation, we conclude there are no major geotechnical issues that would preclude development of the site as proposed. The primary geotechnical issues affecting the proposed development include providing adequate foundation support for the proposed buildings and lateral support for the proposed retaining walls.
The recommendations contained in our final report are based on a limited subsurface exploration.
Consequently, variations between expected and actual subsurface conditions may be found in localized areas during construction. Therefore, we should be engaged to observe site preparation, shoring installation, and foundation installation, during which time we may make changes to our recommendations if deemed necessary.
We appreciate the opportunity to provide our services to you on this project. Should you have any questions, please call.
Sincerely yours,
ROCKRIDGE GEOTECHNICAL, INC.
Krystian P. Samlik, P.E., G.E. Linda H.J. Liang, P.E., G.E.
Senior Project Engineer Principal Engineer
Enclosure
QUALITY CONTROL REVIEWER:
Craig S. Shields, P.E., G.E.
Principal Engineer
TABLE OF CONTENTS
1.0 INTRODUCTION ...............................................................................................................1
2.0 SCOPE OF SERVICES.......................................................................................................2
3.0 FIELD INVESTIGATION AND LABORATORY TESTING...........................................3
3.1 Test Borings.............................................................................................................3
3.2 Dynamic Penetrometer Tests...................................................................................5
3.3 Laboratory Testing...................................................................................................5
4.0 SUBSURFACE CONDITIONS ..........................................................................................6
4.1 Groundwater ............................................................................................................7
5.0 SEISMIC CONSIDERATIONS ..........................................................................................8
5.1 Regional Seismicity and Faulting ............................................................................8
5.2 Geologic Hazards...................................................................................................10
5.2.1 Ground Shaking .........................................................................................10
5.2.2 Ground Surface Rupture ............................................................................10
5.2.3 Liquefaction and Associated Hazards........................................................11
5.2.4 Cyclic Densification...................................................................................12
6.0 DISCUSSIONS AND CONCLUSIONS ...........................................................................12
6.1 Slope Stability Considerations...............................................................................12
6.2 Foundation Support and Settlement.......................................................................13
6.3 Excavation Support................................................................................................13
6.4 Construction Considerations and Monitoring........................................................14
6.5 Soil Corrosivity......................................................................................................14
7.0 RECOMMENDATIONS...................................................................................................15
7.1 Site Preparation and Grading.................................................................................15
7.1.1 Subgrade Preparation.................................................................................16
7.1.2 Fill Quality and Compaction......................................................................16
7.1.3 Utility Trenches .........................................................................................17
7.1.4 Exterior Concrete Flatwork........................................................................17
7.2 Foundation and Settlement ....................................................................................19
7.2.1 Spread Footings .........................................................................................19
7.2.2 Drilled Piers...............................................................................................20
7.3 Concrete Slab-on-Grade Floor...............................................................................21
7.4 Permanent Retaining Walls....................................................................................22
7.5 Temporary Cut Slopes and Shoring.......................................................................24
7.5.1 Cantilevered Soldier Pile and Timber Lagging Shoring System...............24
7.6 Non-Vehicular Concrete Pavers ............................................................................25
7.6.1 Non-Permeable Concrete Pavers for Pedestrian Traffic............................25
7.6.2 Permeable Concrete Pavers for Pedestrian Traffic ....................................26
7.7 Seismic Design.......................................................................................................28
8.0 ADDITIONAL GEOTECHNICAL SERVICES...............................................................28
9.0 LIMITATIONS..................................................................................................................29 REFERENCES ..............................................................................................................................30
FIGURES
APPENDIX A – Boring Logs and Dynamic Penetrometer Test Results APPENDIX B – Laboratory Test Results
LIST OF FIGURES
Figure 1 Site Location Map
Figure 2 Site Plan
Figure 3 Regional Geologic Map
Figure 4 Regional Fault Map
Figure 5 Earthquake Zones of Required Investigation Map Figure 6 Generalized ICPI Permeable Paver Detail
APPENDIX A
Figures A-1 Logs of Borings B-1 through B-13
through A-13
Figure A-14 Classification Chart
Figure A-15 Physical Properties Criteria for Rock Descriptions Figure A-16 Dynamic Penetrometer Test Results
APPENDIX B
Figure B-1 Plasticity Chart
Figure B-2 Particle Size Distribution Report
Figure B-3a Soil Corrosivity Test Result
Figure B-3b Soil Corrosivity Test Result
21-2085 1 September 18, 2023
FINAL GEOTECHNICAL INVESTIGATION
PROPOSED RAILROAD RESIDENCE DEVELOPMENT
RAILROAD AND S. LINDEN AVENUES
South San Francisco, California
1.0 INTRODUCTION
This report presents the results of the final geotechnical investigation performed by Rockridge Geotechnical, Inc. for the proposed residential development and linear park to be constructed on the southern side of Railroad Avenue, between its intersections with S. Spruce and S. Linden avenues in South San Francisco, California, as shown on the Site Location Map, Figure 1. We previously performed a preliminary geotechnical investigation for the project, the results of which were presented in our report dated October 22, 2021.
The site consists of two parcels (APNs 014072050 and 014061170) and is bordered by Railroad Avenue to the north, S. Linden Avenue to the east, and commercial properties to the south and west. The site for the proposed residential development is a strip of land along Railroad Avenue that has plan dimensions of approximately 50 by 1,467 feet, as shown on the Site Plan, Figure 2.
The ground surface elevations on the residential development site are close to the grade on Railroad Avenue at the eastern and western ends and up to approximately 20 feet below the Railroad Avenue grade near the center. Where the grades on the residential development site are lower than Railroad Avenue, the northern portion of the site slopes down towards the south from an existing retaining wall along Railroad Avenue at a gradient as steep as 1.7:1 (horizontal to vertical).
The proposed residential development consists of constructing residential buildings containing 73 townhouse units. The proposed residential buildings will be 3 to 4 stories and of wood-framed construction. The ground level of the residential buildings will have finished floor near Railroad Avenue grade. Some of the buildings will have an accessory dwelling unit (ADU) below the ground floor. Improvements to the residential development site will also include publicly accessible open spaces and a shared rear drive aisle. The existing retaining wall supporting 21-2085 2 September 18, 2023
Railroad Avenue will be left in-place and a new retaining wall will be constructed downslope (to the south) of the existing wall.
Other site improvements include constructing a new linear park between existing neighboring commercial properties. The proposed linear park will extend from Railroad Avenue to N. Canal Street.
2.0 SCOPE OF SERVICES
Our final geotechnical investigation was performed in accordance with our proposal dated June 27, 2023. Our scope of services consisted of exploring subsurface conditions at the site by drilling supplemental borings, performing laboratory testing on selected soil samples, and performing engineering analyses to develop conclusions and recommendations regarding:
• subsurface conditions
• site seismicity and seismic hazards, including the potential for liquefaction, cyclic densification, and seismically-induced landslides
• the most appropriate foundation type(s) for the proposed buildings • design criteria for the recommended foundation type(s), including vertical and lateral capacities for each of the foundation type(s)
• estimates of foundation settlement
• design pressures for permanent walls
• temporary cut slopes and shoring
• site grading, subgrade preparation, and fill quality and compaction • exterior concrete flatwork
• non-permeable and permeable concrete pavers
• 2022 California Building Code (CBC) site class and design spectral response acceleration parameters
• corrosivity of the near-surface soil and groundwater and the potential effects on buried concrete and metal structures and foundations
• construction considerations.
21-2085 3 September 18, 2023
3.0 FIELD INVESTIGATION AND LABORATORY TESTING
We previously performed a preliminary geotechnical investigation for this project, the results of which were presented in our report dated October 22, 2021. Our preliminary investigation consisted of evaluating subsurface conditions at the site by drilling seven test borings, performing five dynamic penetrometer tests (DPTs), and performing laboratory tests on selected soil samples. For our final investigation, we supplemented the subsurface data on the Railroad Avenue retaining wall slope by drilling six borings and performing laboratory tests on selected soil samples. The approximate locations of the borings and DPTs, including those performed for our preliminary investigation, are shown on Figure 2.
Prior to drilling we obtained a drilling permit from the San Mateo County Environmental Health Services Division (SMCEHSD) and contacted Underground Service Alert (USA) to notify them of our work, as required by law. We also retained private utility locators, Precision Locating, LLC and C. Cruz Sub-Surface Locators, to check for buried utilities at the boring locations to reduce the potential of encountering utilities during drilling. Details of the preliminary and final field investigations and laboratory testing are described below.
3.1 Test Borings
Seven borings, designated as B-1 through B-7, were drilled at the approximate locations shown on Figure 2 as part of our preliminary investigation. Borings B-1 through B-4 were drilled on September 8, 2021 by Exploration Geoservices, Inc. of San Jose, California, using a Mobile B61 truck-mounted drill rig equipped with 8-inch-diameter hollow-stem augers. Borings B-5 through B-7 were drilled on September 24, 2021 by Access Soil Drilling, Inc. of San Mateo, California, using a limited access drill rig equipped with 3-inch-diameter solid-stem augers.
Borings B-1 through B-5 were drilled to depths between 7.9 and 21.4 feet below the ground surface (bgs) where the boreholes bottomed in bedrock. Borings B-6 and B-7 were drilled to depths of 11.5 and 13 feet bgs, respectively, where the boreholes bottomed in Bay Mud tidal deposits.
21-2085 4 September 18, 2023
Six additional borings, designated as B-8 through B-13, were drilled at the approximate locations shown on Figure 2 on the sloped portion of the site as part of our final investigation. Borings B-8 through B-13 were drilled on July 17 and 18, 2023 by Access Soil Drilling, Inc. of San Mateo, California, using a limited access drill rig equipped with 3-inch-diameter solid-stem augers.
Borings B-8 through B-13 were drilled to depths between 2.3 and 14.3 feet bgs and bottomed in bedrock.
During drilling, our field engineer logged the soil and bedrock encountered and obtained representative samples of the soil and bedrock for visual classification and laboratory testing.
The logs for borings B-1 through B-13 are presented on Figures A-1 through A-13 in Appendix A. The soil and bedrock encountered in the borings were classified in accordance with the classification systems shown on Figures A-14 and A-15, respectively.
Soil samples were obtained using the following samplers:
• Modified California (MC) split-barrel sampler with a 3.0-inch outside diameter and 2.5- inch inside diameter, lined with 2.43-inch inside diameter stainless steel tubes. • California (CA) split-barrel sampler with a 2.5-inch outside diameter and a 2.0-inch inside diameter, lined with 1.875-inch diameter liners. • Standard Penetration Test (SPT) split-barrel sampler with a 2.0-inch outside and 1.5-inch inside diameter; the sampler can accommodate liners, but liners were not used.
The SPT, CA, and MC samplers were driven with a 140-pound hammer falling 30 inches per drop. For the borings drilled by Exploration Geoservices, Inc., a downhole wireline hammer on a Mobile B61 rig was used. For the borings drilled by Access Soil Drilling, Inc., a rope-andcathead safety hammer on the limited access rig was used. The samplers were driven up to 18 or 24 inches and the hammer blows required to drive the samplers were recorded every 6 inches and are presented on the boring logs. A “blow count” is defined as the number of hammer blows per 6 inches of penetration or 50 blows for 6 inches or less of penetration. The blow counts required to drive the MC and SPT samplers were converted to approximate SPT N-values using factors of
0.63 and 1.08, respectively, for the Mobile B-61 rig to account for sampler type, approximate hammer energy, and the fact that the SPT sampler was designed to accommodate liners, but 21-2085 5 September 18, 2023
liners were not used. Factors of 0.7, 0.9, and 1.2 were used to convert the blow counts for MC, CA, and SPT samplers to approximate SPT N-values, respectively, for the limited access rig to account for sampler type, approximate hammer energy, and the fact that the SPT sampler was designed to accommodate liners, but liners were not used. The blow counts used for this conversion were: 1) the last two blow counts if the sampler was driven more than 12 inches, or 2) the last blow count if the sampler was driven less than 12 inches. The converted SPT N-values are presented on the boring logs.
Upon completion, the boreholes were backfilled with neat cement grout in accordance with SMCEHSD requirements. The soil cuttings generated during drilling were spread in landscape areas onsite.
3.2 Dynamic Penetrometer Tests
Subsurface conditions of the slope along Railroad Avenue were also investigated by performing five DPTs, designated as DPT-1 through DPT-5, at the approximate locations shown on Figure 2 during our preliminary investigation. The DPTs were performed following the methodology presented in the technical paper titled A Portable Dynamic Penetrometer for Geotechnical Investigations, prepared by J.R. Triggs and P.D. Simpson. The DPTs consist of manually driving a 1.4-inch-diameter, cone-tipped probe with a 35-pound hammer falling 15 inches. The blow counts required to drive the probe were recorded at 10-centimeter intervals and converted to SPT N-values for use in our engineering analyses. The DPTs were advanced to practical refusal, defined as more than 50 blows per 10-centimeter interval, at depths ranging from approximately
1.6 to 4.6 feet bgs. The DPT results are presented on Figure A-16.
3.3 Laboratory Testing
We re-examined each soil sample in the office to confirm the field classification and selected representative samples for laboratory testing. Soil samples were tested by B. Hillebrandt Soils Testing, Inc. of Alamo, California to measure moisture content, fines content, and Atterberg limits (plasticity index). Near-surface soil samples were tested by Project X Corrosion 21-2085 6 September 18, 2023
Engineering in Murrieta, California. The laboratory test results are presented on the boring logs and in Appendix B.
4.0 SUBSURFACE CONDITIONS
The Regional Geologic Map (Figure 3) for the site vicinity indicates the proposed residential development portion of the site (along Railroad Avenue) is underlain by slope debris and ravine fill (Qsr), Colma formation (Qc), and sandstone and shale bedrock (KJs). The geology map shows the proposed linear park area as being underlain by slope debris and ravine fill (Qsr), Colma formation (Qc), sandstone and shale bedrock (KJs), and artificial fill over tidal flats (Qaf/tf).
The results of our borings and DPTs indicate the proposed residential development site is underlain by slope debris overlying Colma formation overlying residual soil and bedrock. Where explored, the slope debris consists of dense to very dense clayey sand and hard sandy clay; the Colma formation consists of very stiff to hard sandy silt/clay and dense to very dense clayey sand; and the residual soil consists of medium dense to very dense sand and silty sand and very stiff to hard clay with sand and gravel. Top of bedrock was encountered at depths between of 1 and 23 feet bgs. The bedrock consists of sandstone and shale that has low hardness and is friable to weak and deeply to moderately weathered.
The results of borings indicate the proposed linear park area site is underlain by fill consisting of stiff to very stiff sandy clay and medium dense to dense clayey sand with gravel and gravel with varying amounts of silt and sand to depths of 3 to 8 feet bgs; the thickness of the fill increases towards the south. The fill on the northern portion of the proposed linear park site (i.e., Boring B-5) is underlain by about 2 feet of residual soil consisting of very dense silty sand with gravel overlying bedrock. The fill on the southern portion of the proposed linear park site (i.e., borings B-6 and B-7) extends to depths of about 7 to 8 feet bgs and is underlain by Bay Mud tidal deposits consisting of medium stiff to stiff clay and silty clay. The Bay Mud tidal deposits extend to the maximum depths explored in borings B-6 and B-7 of 11.5 and 13 feet bgs, respectively. 21-2085 7 September 18, 2023
4.1 Groundwater
Groundwater was measured at depths of approximately 16 and 11.5 feet bgs in borings B-4 and B-7, respectively, during drilling. Groundwater was not present in borings B-1, B-2, B-3, B-5, B6, and B-8 through B-13 during drilling. It should be noted the groundwater level in the borings was likely not given adequate time to stabilize at the time of drilling and groundwater level measurements.
In the California Geologic Survey (CGS) report Seismic Hazard Zone Report for the San Francisco South 7.5-Minute Quadrangle, San Mateo County, California, Plate 1.3 shows the historic high groundwater at the site is approximately 10 feet bgs near the proposed residential development area and approximately 2 feet bgs near the southern end of the proposed linear park area.
To further evaluate depth to groundwater at the site, we reviewed groundwater data on the State of California Water Resources Control Board GeoTracker website (http://geotracker.waterboards.ca.gov). At a site approximately 400 feet east of the site, located at 7 S. Linden Avenue, groundwater monitoring wells were monitored from February 2004 to December 2018; the groundwater readings showed that the groundwater generally fluctuated from 3 to 11 feet bgs. Another site, approximately 650 feet north of the site, located at 123 Linden Avenue, presents groundwater level readings taken periodically between March 1999 and March 2013; groundwater readings showed that the groundwater fluctuated between 1.5 to 11 feet bgs. A third site, approximately 1000 feet south of the residential portion of the site, located at 114 S. Maple Avenue, had groundwater monitoring wells monitored from December 1998 to March 2015; the groundwater readings showed that the groundwater generally fluctuated from
1.7 to 6.4 feet bgs.
The groundwater level at the site is expected to fluctuate several feet seasonally with potentially larger fluctuations annually, depending on the amount of rainfall. Based on the available groundwater information for the site and vicinity, we conclude a groundwater depth of 10 feet bgs should be used for the residential portion of the site along Railroad Avenue, with the 21-2085 8 September 18, 2023
groundwater depth decreasing to approximately 2 feet bgs at the southern end of the linear park portion of the site.
5.0 SEISMIC CONSIDERATIONS
5.1 Regional Seismicity and Faulting
The site is located within the Coast Ranges Geomorphic Province of California, which is characterized by northwest-trending valleys and ridges. These topographic features are controlled by folds and faults that resulted from the collision of the Farallon and North American plates and subsequent strike-slip faulting along the San Andreas Fault system. The San Andreas Fault is more than 600 miles long and extends from Point Arena in the north to the Gulf of California in the south. The Coast Ranges Geomorphic Province is bounded on the east by the Great Valley and on the west by the Pacific Ocean.
The major active faults in the area are the San Andreas, San Gregorio, and Hayward faults.
These and other faults in the region are shown on Figure 4. For these and other active faults within a 50-kilometer radius of the site, the distance from the site and estimated characteristic moment magnitude1 [Petersen et al. (2014) & Thompson et al. (2016)] are summarized in Table
1. These references are based on the Third Uniform California Earthquake Rupture Forecast (UCERF3), prepared by Field et al. (2013).
1 Moment magnitude (Mw) 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. 21-2085 9 September 18, 2023
TABLE 1
Regional Faults and Seismicity
Fault Segment
Approximate
Distance from
Site (km)
Direction
from Site
Characteristic
Moment
Magnitude
Total North San Andreas
(SAO+SAN+SAP+SAS) 4.2 Southwest 8.04
North San Andreas (Peninsula, SAP) 4.2 Southwest 7.38
San Gregorio (North) 13 West 7.44
Monte Vista - Shannon 21 Southeast 7.14
Total Hayward + Rodgers Creek
(RC+HN+HS+HE) 25 East 7.58
Hayward (South, HS) 25 East 7.00
Hayward (North, HN) 25 Northeast 6.90
North San Andreas (North Coast, SAN) 35 Northwest 7.52
Butano 39 South 6.93
Total Calaveras (CN+CC+CS+CE) 39 East 7.43
Calaveras (North, CN) 39 East 6.86
Mount Diablo Thrust 41 Northeast 6.67
Mount Diablo Thrust North CFM 42 Northeast 6.72
Concord 46 Northeast 6.45
Mount Diablo Thrust South 47 East 6.50
Damaging earthquakes have occurred along many of these faults in recorded history, as depicted on Figure 4 (USGS, 2021). Notable historic earthquakes which have impacted the Bay Area in recorded history include:
• 1838 San Andreas Earthquake, Mw = 7.4 (estimated)
• 1865 San Andreas Earthquake, Mw = 6.5 (estimated)
• 1868 Hayward Earthquake, Mw = 7.0 (estimated)
• 1906 Great San Francisco Earthquake (San Andreas Fault), Mw = 7.9 (estimated) • 1989 Loma Prieta Earthquake (San Andreas Fault), Mw = 6.9 • 2014 West Napa Earthquake, Mw = 6.0
As a part of the UCERF3 project, researchers estimated the probability of at least one Mw ≥ 6.7 earthquake occurring in the greater San Francisco Bay Area during a 30-year period (starting in 2014) is 72 percent. The highest probabilities are assigned to sections of the Hayward (South), 21-2085 10 September 18, 2023
Calaveras (Central), and San Andreas (Santa Cruz Mountains) faults. The respective probabilities are approximately 25, 21, and 17 percent.
5.2 Geologic 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 project site. Strong shaking during an earthquake can result in ground failure such as that associated with ground shaking, ground surface rupture, liquefaction, 2 lateral spreading,
3 and cyclic densification.4 The results of our evaluation are presented in this section.
5.2.1 Ground Shaking
The seismicity of the site is governed by the activity of the San Andreas Fault, although ground shaking from future earthquakes on other faults will also be felt at the site. The intensity of earthquake ground motion at the site will depend upon the characteristics of the generating fault, distance to the earthquake epicenter, and magnitude and duration of the earthquake. We judge that strong to severe ground shaking could occur at the site during a large earthquake on one of the nearby faults.
5.2.2 Ground Surface Rupture
Historically, ground surface displacements 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 probability of fault offset at the site from a known active fault is very low. In a seismically active area, the remote possibility exists for future faulting in areas where no faults 2 Liquefaction is a phenomenon where loose, saturated, cohesionless soil experiences temporary reduction in strength during cyclic loading such as that produced by earthquakes. 3 Lateral spreading is a phenomenon in which surficial soil displaces along a shear zone that has formed within an underlying liquefied layer. Upon reaching mobilization, the surficial blocks are transported downslope or in the direction of a free face by earthquake and gravitational forces. 4 Cyclic densification is a phenomenon in which non-saturated, cohesionless soil is compacted by earthquake vibrations, causing ground-surface settlement.
21-2085 11 September 18, 2023
previously existed; however, we conclude the probability of surface faulting and consequent secondary ground failure from previously unknown faults is also very low.
5.2.3 Liquefaction and Associated Hazards
When a saturated, cohesionless soil liquefies, it experiences a temporary loss of shear strength created by a transient rise in excess pore pressure generated by strong ground motion. Soil susceptible to liquefaction includes loose to medium dense sand and gravel, low-plasticity silt, and some low-plasticity clay deposits. Flow failure, lateral spreading, differential settlement, loss of bearing strength, ground fissures and sand boils are evidence of excess pore pressure generation and liquefaction.
As presented on Figure 5, the proposed residential development area and the northern portion of the proposed linear park area are not within a designated zone of liquefaction potential on the map titled Earthquake Zones of Required Investigation, South San Francisco South Quadrangle, prepared by the California Geological Survey (CGS), dated September 23, 2021. The southern portion of the proposed linear park is mapped within a designated zone of liquefaction potential.
The results of our subsurface investigation indicate the proposed residential development area and the northern portion of the proposed linear park area are underlain very stiff to hard clayey soil, dense to very dense sandy soil, and bedrock. We judge the clayey and sandy soils beneath these two areas are not susceptible to liquefaction due to their cohesion and/or relative density.
Therefore, we conclude the potential for liquefaction to occur in these two areas is very low.
The results of our subsurface investigation indicate the southern portion of the proposed linear park is underlain by fill overlying Bay Mud tidal deposits. The fill may contain lenses of medium dense clayey sand that is susceptible to liquefaction. The Bay Mud tidal deposits may also contain lenses of silty sand and sandy silt that may be susceptible to liquefaction Based on subsurface conditions encountered in borings B-6 and B-7, we estimate liquefactioninduced settlement will be less than 3/4 inch and less than 1/2 inch across a horizontal distance of 30 feet. The non-liquefiable soil overlying the potentially liquefiable soil layers is sufficiently thick and the potentially liquefiable layers are sufficiently thin such that the potential for surface 21-2085 12 September 18, 2023
manifestations of liquefaction, such as sand boils, is low. Considering the potentially liquefiable layers are not continuous, we conclude the risk of lateral spreading is low.
5.2.4 Cyclic Densification
Cyclic densification (also referred to as differential compaction) of non-saturated sand (sand above groundwater table) can occur during an earthquake, resulting in settlement of the ground surface and overlying improvements. Based on the subsurface data from our field investigation, we conclude the soil above the groundwater table is not susceptible to cyclic densification because of its cohesion and/or relative density.
6.0 DISCUSSIONS AND CONCLUSIONS
We conclude that from a geotechnical engineering standpoint, the site can be developed as planned, provided the recommendation presented in this report are incorporated into the project plans and specifications and implemented during construction. The primary geotechnical issues affecting the proposed development are providing adequate foundation support for the proposed buildings and lateral support for the existing and proposed retaining walls. These and other geotechnical issues as they pertain to the proposed development are presented in this section.
6.1 Slope Stability Considerations
The site for the proposed residential development is a strip of land along Railroad Avenue that has plan dimensions of approximately 50 by 1,467 feet. The ground surface elevations on the residential development site are close to the grade on Railroad Avenue at the eastern and western ends and up to approximately 20 feet below the Railroad Avenue grade near the center. Where the grades on the residential development site are lower than Railroad Avenue, the northern portion of the site slopes down towards the south from an existing retaining wall along Railroad Avenue at a gradient as steep as 1.7:1 (horizontal to vertical).
Based on the results of our investigation, we judge the existing slope is stable in its current condition. The project includes constructing retaining walls to provide lateral support for the existing retaining wall, new fill that will be placed on the slope, and new buildings and 21-2085 13 September 18, 2023
improvements on the slope. We conclude the existing slope along the proposed improvements will be stable under static and seismic conditions, provided the proposed improvements, including new retaining walls, and foundation elements are designed and constructed following the recommendations presented in this report, and surface water are prevented from being discharged onto slopes.
6.2 Foundation Support and Settlement
The site for the proposed residential development is underlain by firm native soil that can provide adequate foundation support for light to moderate building loads. Therefore, we judge the proposed buildings may be supported on spread footings where the ground is relatively level.
Where the ground is steeper than 3:1, we recommend the proposed building be supported on drilled piers.
We estimate total and differential static settlements for properly designed and constructed spread footings will be less than 3/4 inch and 1/2 inch over a horizontal distance of 30 feet, respectively.
We also estimate total and differential settlement of properly constructed drilled piers designed based on the recommendations presented in this report will be less than 1/2 inch and 1/4 inch over a horizontal distance of 30 feet, respectively.
6.3 Excavation Support
Excavations that will be entered by workers should be sloped or shored in accordance with the Occupational Safety and Health Administration (OSHA) standards (29 CFR Part 1926). Where space permits, the sides of the temporary excavation can be sloped. Where space does not permit sloping of the excavation perimeter, a shoring system will be required to support the sides of the proposed excavation. The contractor should be responsible for the construction and safety of temporary slopes and shoring. The shoring designer should be responsible for the shoring design.
We judge that a cantilevered soldier pile and lagging shoring system is appropriate for support of excavations that are less than 12 feet deep. Where cuts exceed about 12 feet in height, soldier pile-and-lagging systems are typically more economical if they include tieback anchors; 21-2085 14 September 18, 2023
however, tieback anchors will likely extend beneath the streets, which will require an encroachment agreement with the City of South San Francisco. Where it is not feasible to install tiebacks, then internal bracing of the shoring will be required. If tiebacks or internal bracing are required, we can provide recommendations upon request.
6.4 Construction Considerations and Monitoring
The soil to be excavated consists predominantly of sand and clay, which can be excavated with conventional earth-moving equipment such as loaders and backhoes. Excavations will also likely extend into bedrock and, therefore, contractors should be prepared to use equipment capable of excavating and drilling into rock. Removal of existing on-site improvements, including pavements and buried foundations will require equipment capable of breaking concrete.
Special care should be taken to not undermine the existing retaining wall along Railroad Avenue during construction. Where there are existing structures nearby, heavy equipment should not be used within 10 horizontal feet from existing structures, including the existing retaining wall.
Jumping jack or hand-operated vibratory plate compactors should be used for compacting fill within this zone.
The contractor should establish survey points on the shoring, adjacent streets, and adjacent buildings to monitor the movement during and immediately after excavation. Further, because adjacent streets (i.e., Railroad Avenue) and buildings may experience settlement during construction of the proposed project, a crack survey should be performed on adjacent streets prior to the start of excavation.
6.5 Soil Corrosivity
Corrosivity tests were performed by Project X Corrosion Engineering of Murrieta, California on soil samples obtained from borings B-1, B-3, B-4, and B-8 at a depths between 1 and 6 feet bgs.
The corrosivity test results are presented in Appendix B of this report.
Many factors can affect the corrosion potential of soil including, but not limited to, resistivity, pH, and chloride and sulfate concentrations. Based on the minimum soil resistivity 21-2085 15 September 18, 2023
measurements ranging from 1,876 to 5,025 ohm-cm, we conclude the soil is “moderately to highly corrosive” to buried metal (Roberge, 2018). Accordingly, all buried iron, steel, cast iron, galvanized steel, and dielectric-coated steel or iron should be protected against corrosion depending upon the critical nature of the structure. If it is necessary to have metal in contact with soil, a corrosion engineer should be consulted to provide recommendations for corrosion protection.
The results of the pH tests (7.8 to 8.4) indicate the near-surface soil is “negligibly corrosive” to buried metallic and concrete structures. The chloride ion concentration (11.7 to 100.3 mg/kg) indicates the chlorides in the near-surface soil are “mildly to negligibly corrosive” to buried metallic structures and reinforcing steel in concrete structures below ground. The results also indicate the sulfate ion concentration (32.1 to 96.6 mg/kg) is sufficiently low such that sulfates do not pose a threat to buried concrete and mortars.
7.0 RECOMMENDATIONS
Our recommendations for site preparation and grading, temporary shoring design, retaining wall design, foundation design, seismic design, and other geotechnical aspects of the project are presented in this section.
7.1 Site Preparation and Grading
Any vegetation and organic topsoil should be stripped and disposed of off-site. Site demolition should include the removal of all existing foundation elements and underground utilities, if any.
In general, abandoned underground utilities should be removed to the property line or service connections and properly capped or plugged with concrete. Where existing utility lines are outside of the proposed building footprints and/or will not interfere with the proposed construction, they may be abandoned in-place provided they are filled with lean concrete or cement grout to the property line. Voids resulting from demolition activities should be properly backfilled with engineered fill under the observation of our field engineer and in accordance with our compaction recommendations provide in this section. 21-2085 16 September 18, 2023
If grading is performed during the rainy season, the contractor may find the subgrade material too wet to compact to the recommended relative compaction and will have to be scarified and aerated to lower its moisture content so the recommended compaction can be achieved. Material to be dried by aeration should be scarified to a depth of at least 8 inches; the scarified soil should be turned at least twice a day to promote uniform drying. Once the moisture content of the aerated soil has been reduced to acceptable levels, the soil should be compacted in accordance with our recommendations. Aeration is typically the least costly method used to stabilize the subgrade soil; however, it generally takes the most time and favorable weather conditions to complete. Other soil stabilization alternatives include over-excavating the wet soil and replacing or mixing it with drier soil, and chemical treatment.
7.1.1 Subgrade Preparation
The soil subgrade in areas that will receive improvements (i.e., slab-on-grade floors or exterior concrete flatwork) or fill should be scarified to a depth of at least 8 inches, moisture-conditioned to near optimum moisture-content, and compacted to at least 90 percent relative compaction. 5 If
bedrock is exposed at subgrade elevation, it is not necessary to scarify or compact the bedrock.
Where the building pad will have a crawl space and will not have a slab-on-grade floor, the subgrade does not need to be scarified and recompacted. However, if there will be a crawl space, we recommend a 2- to 3-inch-thick concrete rat slab be placed on the subgrade.
7.1.2 Fill Quality and Compaction
Engineered fill may consist of on-site soil or imported fill that is free of organic matter and contains no rocks or lumps larger than 3 inches in greatest dimension. If imported fill (select fill) is required, it should also have a liquid limit less than 40 and plasticity index less than 12, and be approved by the Geotechnical Engineer. Samples of proposed select fill material should be submitted to the Geotechnical Engineer at least three business days prior to 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 5 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 ASTM D1557 laboratory compaction procedure. 21-2085 17 September 18, 2023
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 imported material.
Fill should be placed in lifts not exceeding 8 inches in loose thickness, moisture-conditioned to near optimum moisture content, and compacted to at least 90 percent relative compaction. Fill consisting of clean sand or gravel (defined as poorly-graded soil with less than 5 percent fines by weight) or more than 5 feet thick should be compacted to at least 95 percent relative compaction.
Fill placed within 8 inches of pavement soil subgrade that will be subjected to vehicular traffic should also be moisture-conditioned to near optimum moisture content, and compacted to at least 95 percent relative compaction and be non-yielding.
7.1.3 Utility Trenches
Excavations for utility trenches should conform to the current CAL-OSHA requirements. To provide uniform support, pipes or conduits should be bedded on a minimum of 4 inches of sand or fine gravel. After the pipes and conduits are tested, inspected (if required), and approved, they should be covered to a depth of 6 inches with sand or fine gravel, which should be mechanically tamped. Backfill for utility trenches and other excavations is also considered fill, and should be placed and compacted as according to the recommendations previously presented. Jetting of trench backfill should not be permitted.
Spread footings should be bottomed below an imaginary line extending up at a 1.5:1 (horizontal to vertical) inclination from the base of utility trenches running parallel to the footings.
Alternatively, the portion of the utility trench (excluding bedding) that is below the 1.5:1 line can be backfilled with controlled low-strength material (CLSM) with a 28-day unconfined compressive strength of at least 100 pounds per square inch (psi).
7.1.4 Exterior Concrete Flatwork
We recommend a minimum of 4 inches of Class 2 aggregate base be placed beneath exterior concrete flatwork (i.e., sidewalks and patios). The soil subgrade should be scarified to a depth of at least 8 inches, moisture-conditioned to near optimum moisture content, and compacted to at 21-2085 18 September 18, 2023
least 90 percent relative compaction. If bedrock is exposed at subgrade elevation, it is not necessary to scarify or compact the bedrock. Class 2 aggregate base beneath concrete flatwork should also be compacted to at least 90 percent relative compaction.
7.1.5 Surface Drainage and Bioswales
Positive surface drainage should be provided around the buildings to direct surface water away from the foundations and slopes. Grades around the building should be determined by the Civil Engineer and conform to the requirements of the 2022 CBC, which will help minimize stormwater accumulation adjacent to foundations. In addition, roof downspouts should be discharged into controlled drainage facilities to keep water away from the foundations and slopes. The use of water-intensive landscaping around the perimeter of the building should be avoided to reduce the amount of water introduced to the soil subgrade.
Care should be taken to minimize the potential for subsurface water to collect beneath pavements and pedestrian walkways, and to be discharged onto slopes. Where landscape beds and tree wells are immediately adjacent to pavements and flatwork, we recommend vertical cutoff barriers be incorporated into the design to prevent irrigation water from saturating the subgrade and aggregate base. These barriers may consist of either flexible impermeable membranes or deepened concrete curbs.
Stormwater treatment systems (infiltration basins, rain gardens, bio-retention systems, vegetated swales, flow-through planters, etc.) should be provided with subdrains. Within 5 feet of the proposed buildings, excavations for stormwater treatment systems should have an impermeable liner in addition to the subdrain. Due to the relatively low estimated permeability of the nearsurface soil, these systems should be designed for partial exfiltration. The drainage layer beneath the “treatment” soil should consist of a minimum 12-inch-thick layer of Caltrans Class 2 Permeable drainage material and include a minimum 4-inch-diameter perforated drain pipe (perforations facing down).
21-2085 19 September 18, 2023
7.2 Foundation and Settlement
We conclude the proposed townhome buildings may be supported on conventional spread footings or drilled piers. Recommendations for spread footings and drilled piers are presented in this section.
7.2.1 Spread Footings
Spread footings should bottom at least 24 inches below the ground surface and bear on firm native soil or bedrock. Spread footings situated near a slope should be setback at least 5 feet horizontally from the top of slope. Alternatively, the footings may be deepened, such that there is at least 7 feet of horizontal distance between the bottom edge of the footing and the face of the slope. Footings adjacent to utility trenches should bear below an imaginary 1.5:1 (horizontal to vertical) plane projected upwards from the bottom edge of the utility trench.
Spread footings may be designed using allowable bearing pressures of 5,000 pounds per square foot (psf) for dead-plus-live loads and 6,650 psf for total design loads, which includes wind or seismic forces; these values include factors of safety of at least 2.0 and 1.5, respectively.
Lateral loads may be resisted by a combination of passive pressures on the vertical faces of the footings and friction between the bottoms of the footings and the supporting soil. To compute lateral resistance, we recommend using an equivalent fluid weight of 300 pounds per cubic foot (pcf); the upper foot of soil should be ignored for lateral resistance unless confined by a slab.
Where the footing is situated near a sloped surface, the depth where the soil can be relied upon for lateral resistance is beneath where there is at least 7 feet of horizontal distance between the edge of the footing and the face of the slope. Frictional resistance should be computed using a base friction coefficient of 0.35 or 0.4 for footings bearing on native soil or bedrock, respectively. The passive pressure and frictional resistance values include a factor of safety of at least 1.5 and may be used in combination without further reduction.
The bottoms and sides of the footing excavations should be moistened following excavation and maintained in a moist condition until concrete is placed. Footing excavations should be free of 21-2085 20 September 18, 2023
standing water, debris, and disturbed materials prior to placing concrete. We should check footing excavations prior to placement of reinforcing steel to confirm the excavations are bottomed on suitable bearing material and have been properly prepared.
7.2.2 Drilled Piers
Drilled piers should be spaced at least three diameters on center. Drilled piers should be at least 8 feet long or extend at least 4 feet into bedrock, whichever is deeper.
Drilled piers should be designed to derive their axial capacity from skin friction in native soil and bedrock starting at a depth of 2 feet below bottom of the grade beam. To compute axial capacity for dead-plus-live loads acting in compression, we recommend using an allowable skin friction 500 psf in native soil and 1,000 psf in bedrock. Skin friction from the upper 2 feet of pier and end bearing should be ignored for vertical support. These skin friction values may be increased by one-third for total load conditions. To compute uplift resistance for the piers, the same skin friction values provided for dead-plus-live loads may be used.
Drilled piers situated on slopes steeper than 3:1 (horizontal to vertical) should be designed to resist downslope creep movement. The piers should be designed for a “creep load” that would act on the piers using an equivalent fluid weight of 51 pcf acting over one pier diameter and to the upper 8 feet of pier where the pier is situated near top of slope (i.e., near northern portion of site, adjacent to Railroad Avenue); and decreasing to 2 feet at base of slope (i.e., at southern limit of residential development site). Piers should be tied together with well-reinforced grade beams running perpendicular to the slope contours. Isolated piers should not be used.
To compute lateral resistance, we recommend using an equivalent fluid weight of 300 pcf; the upper foot of soil should be ignored for lateral resistance unless confined by a slab. Where the pier is near a sloped surface, the depth where the soil can be relied upon for lateral resistance is beneath where there is at least 7 feet of horizontal distance between the pier and the face of the slope. The passive pressure value includes a factor of safety of at least 1.5. The passive pressure may be assumed to act over a width of two pier diameters, or center-to-center spacing between piers, whichever distance is shorter. Passive pressure should not be used for lateral resistance 21-2085 21 September 18, 2023
below a depth of about 8 feet. Below this depth, excessive deflections of the pier head would be required to mobilize the passive pressure.
Drilled piers should be installed by a qualified contractor with demonstrated experience in this type of foundation and subsurface conditions, including drilling into bedrock. The bottoms of the pier holes should be free of debris and water before placement of concrete. If groundwater is encountered during pier drilling, the pier hole should be pumped dry prior to placement of concrete. If the hole cannot be pumped dry prior to placement of concrete, then the concrete should be placed by tremie methods.
Concrete used for pier construction should be discharged vertically using a hose to tremie fill the drilled holes to reduce aggregate segregation. Under no circumstances should concrete be allowed to free-fall against either the steel reinforcement or the sides of the excavation during pouring. Concrete should be placed in the pier holes within 24 hours of completion of drilling if groundwater is encountered.
7.3 Concrete Slab-on-Grade Floor
Where the proposed buildings will have a crawl space underneath the floor, the recommendations below may be ignored. However, we recommend a 2- to 3-inch-thick concrete rat slab be placed on the soil subgrade of the crawl space.
The subgrade for the concrete slab-on-grade floor should be prepared in accordance with our recommendations in Section 7.1.1. We recommend installing a capillary moisture break and water vapor retarder beneath the floor slab. A capillary moisture break consists of at least 4 inches of clean, free-draining gravel or crushed rock. The particle size of the capillary break material should meet the gradation requirements presented in Table 2. 21-2085 22 September 18, 2023
TABLE 2
Gradation Requirements for Capillary Moisture Break
Sieve Size Percentage Passing Sieve
1 inch 90 – 100
3/4 inch 30 – 100
1/2 inch 5 – 25
3/8 inch 0 – 6
The vapor retarder should meet the requirements for Class B vapor retarders stated in ASTM E1745. The vapor retarder should be placed in accordance with the requirements of ASTM E1643. These requirements include overlapping seams by 6 inches, taping seams, and sealing penetrations in the vapor retarder.
Concrete mixes with high water/cement (w/c) ratios result in excess water in the concrete, which increases the cure time and can result in excessive vapor transmission through the slab. Where the concrete is poured directly over the vapor retarder, we recommend the w/c ratio of the concrete not exceed 0.45. Water should not be added to the concrete mix 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 moisture emission levels (if emission testing is required) meet the manufacturer’s requirements.
7.4 Permanent Retaining Walls
Permanent retaining walls, including site retaining walls and basement walls, should be designed to resist lateral earth pressures imposed by the retained soil, as well as surcharge pressures from nearby foundations and traffic, where appropriate. In addition, because the site is in a seismically active area, retaining walls that retain more than 6 feet of soil should be designed to resist pressures associated with seismic forces.
21-2085 23 September 18, 2023
For static conditions, we recommend restrained and unrestrained walls be designed for the following lateral earth repressures:
• Restrained Wall - At-rest earth pressure using an equivalent fluid weight of 51 pcf for drained conditions
• Unrestrained Wall - Active earth pressure using an equivalent fluid eight of 33 pcf for drained conditions
Walls that will retain more than 6 feet of soil will need to be designed for the more critical of static (presented above) or the following seismic conditions. • Restrained Wall - Active earth pressure using an equivalent fluid weight of 33 pcf plus a seismic increment of 47 pcf for drained conditions
• Unrestrained Wall - Active earth pressure using an equivalent fluid weight of 33 pcf plus a seismic increment of 21 pcf for drained conditions
The recommended lateral earth pressures above are based on a level backfill conditions with no additional surcharge loads. If the backfill behind the retaining walls will not be level, we can provide sloped pressures upon request. Where the retaining/below-grade wall is subject to traffic loading within a horizontal distance equal to 1.5 times the height of the wall, the wall should be designed for vehicular surcharge of 100 psf over the entire height of the wall. This surcharge pressure assumes the vehicular traffic on Railroad Avenue is at least 5 feet from the face of the existing wall.
The design pressures recommended above are based on fully drained walls. Although new retaining walls will be above the groundwater level, water can accumulate behind the walls from other sources, such as rainfall, irrigation, and broken water lines. One acceptable method for backdraining retaining walls is to place a prefabricated drainage panel against the shoring or the back of the walls. The drainage panel should extend down to a perforated PVC collector pipe at the base of the wall. The pipe should be surrounded on all sides by at least 4 inches of Caltrans Class 2 permeable material or 3/4-inch drain rock wrapped in filter fabric (Mirafi 150N or equivalent). Where shoring is installed and there is insufficient room to install a perforated pipe between the shoring and the back of the retaining/below-grade wall, the drainage panel should 21-2085 24 September 18, 2023
extend down to a proprietary, prefabricated collector drain system, such as Tremdrain Total Drain or Hydroduct Coil (or equivalent), designed to work in conjunction with the drainage panel and may be used in lieu of the perforated pipe surrounded by gravel described above. The pipe should be connected to a suitable discharge point.
Retaining walls may be supported by spread footings or drilled piers designed using the recommendations presented in Section 7.2 of this report. If backfill is required behind retaining walls, the walls should be braced or hand compaction equipment used to prevent unacceptable surcharges on walls (as determined by the structural engineer).
7.5 Temporary Cut Slopes and Shoring
Excavations that will be entered by workers should be sloped or shored in accordance with the Occupational Safety and Health Administration (OSHA) standards (29 CFR Part 1926). Where space permits, the sides of the temporary excavation can be sloped. We recommend temporary slopes not exceed an inclination of 1.5:1 (horizontal to vertical) in sand or silty/clayey sand (OSHA Type C soil) or 3/4:1 in bedrock.
7.5.1 Cantilevered Soldier Pile and Timber Lagging Shoring System For design of a cantilevered soldier pile and timber lagging shoring system, we recommend using an at-rest earth pressure equivalent to a fluid weight of 51 pcf where there is a structure within a horizontal distance equal to 1.5 times the retained soil height and using an active earth pressure equivalent to a fluid weight of 33 pcf where there are no structures within that horizontal distance. The recommended lateral earth pressures above are based on a level backfill condition with no additional surcharge loads. If the backfill behind the shoring system will not be level, we can provide sloped pressures upon request.
Where there will be vehicular traffic behind the top of the shoring system within a horizontal distance equal to 1.5 times the height of the wall, the wall should be designed for vehicular surcharge of 100 psf acting over the upper 10 feet. Shoring should be designed for surcharge loads from construction equipment and/or stockpiled soil within a horizontal distance of 1.5 21-2085 25 September 18, 2023
times the excavation height from the edge of excavation, and from adjacent foundations that are not underpinned and are located above an imaginary line that extends at an inclination of 1.5:1 (horizontal to vertical) projected upward from the bottom edge of the proposed excavation. We can provide recommendations for surcharge pressures once surcharge loads are known Passive resistance at the toe of the soldier piles should be computed using an equivalent fluid weight of 300 pcf with a maximum pressure of 3,000 psf. The upper foot of soil should be ignored when computing passive resistance. Passive pressure can be assumed to act over an area of three soldier pile widths, assuming the toe of the soldier pile is filled with structural concrete.
If lean concrete is placed in the soldier pile shaft, the passive pressure can be assumed to act over two pile diameters. These passive pressure values include a factor of safety of at least 1.5.
Soldier piles should be placed in pre-drilled holes backfilled with concrete. Soldier piles will likely extend into bedrock, so contractors should be prepared to use equipment capable of drilling in bedrock.
A structural/civil engineer knowledgeable in this type of construction should be retained to design the shoring. The shoring designer should design the shoring system for lateral deformation of less than 1/2 inch at any location on the shoring where there is a structure or improvements within a horizontal distance equal to 1.5 times the retained soil height and 1 inch where there are no structures or improvements within that horizontal distance. We should review the final shoring plans and calculations to check that they are consistent with the recommendations presented in this report.
7.6 Non-Vehicular Concrete Pavers
The section presents our recommendations for non-permeable and permeable concrete pavers for pedestrian traffic.
7.6.1 Non-Permeable Concrete Pavers for Pedestrian Traffic Non-permeable concrete pavers for pedestrian traffic may be 60 millimeters (2.375 inches) thick and should be underlain by at least 4 inches of Class 2 aggregate base compacted to at least 90 21-2085 26 September 18, 2023
percent relative compaction. The soil subgrade beneath the aggregate base should be scarified to a depth of at least 8 inches, moisture-conditioned to near optimum moisture content, and compacted to at least 90 percent relative compaction.
7.6.2 Permeable Concrete Pavers for Pedestrian Traffic
We recommend permeable interlocking concrete pavements (ICP) be designed in accordance with the guidelines presented by the Interlocking Concrete Pavement Institute (ICPI 2017).
These guidelines include specific recommendations for permeable aggregate subbase, base, and bedding courses to be placed beneath ICP pavements. We recommend permeable pavements for pedestrian traffic be designed for partial exfiltration of water into the subgrade soil. This requires installing a subdrain system at the base of the pervious aggregate materials, which are underlain by a filter fabric. ICPI’s generalized paver section for pedestrian traffic is presented on Figure 6.
Where partial exfiltration is installed, some movement should be anticipated if this results in drying and wetting of the subgrade soil.
The soil subgrade beneath ICP pavements should be scarified to a depth of at least 8 inches, moisture-conditioned to near optimum moisture content, and compacted to at least 90 percent relative compaction, prior to placing the filter fabric and aggregate materials. The soil subgrade at the bottom of the permeable section should slope down toward the drain pipe trench at a gradient of at least 2 percent. The perforated pipe should slope down to a suitable outlet at a minimum gradient of 1 percent. The pipe should be placed with the perforations down on a minimum of 2 inches of permeable subbase.
ICPI’s guidelines call for 2 inches of bedding material consisting of ASTM No. 8 crushed aggregate directly below the pavers. This material is also recommended for fill material between the pavers. As shown in Table 3 below, this material consists of fine gravel with 10 to 30 percent sand.
21-2085 27 September 18, 2023
TABLE 3
Gradation Requirements for ASTM No. 8 Crushed Aggregate Sieve Size Percentage Passing Sieve
1/2 inch 100
3/8 inch 85 – 100
No. 4 10 – 30
No. 8 0 – 10
No. 16 0 – 5
The ASTM No. 8 bedding should be underlain by a permeable base course of ASTM No. 57 crushed aggregate. As shown in Table 4, ASTM No. 57 aggregate consists of open-graded gravel with a gradation between that of the 3/4-inch drain rock and the ASTM No. 8 aggregate.
TABLE 4
Gradation Requirements for ASTM No. 57 Crushed Aggregate Sieve Size Percentage Passing Sieve
1-1/2 inch 100
1 inch 95 – 100
1/2 inch 25 – 60
No. 4 0 – 10
No. 8 0 – 5
The No. 57 aggregate should be placed in lifts not exceeding 8 inches in loose thickness and compacted with a smooth-drum roller in vibratory mode with sufficient passes to create an unyielding surface. Placement and compaction of the permeable aggregate base and subbase should be performed under the observation of our field engineer. Following compaction of the No. 57 aggregate, the No. 8 bedding, not exceeding 2 inches in loose thickness, should be placed and screeded to a level, undisturbed surface immediately prior to paver installation.
The required thicknesses of the permeable aggregate base and subbase courses depends on the infiltration and water storage design requirements, as well as the traffic loading demand. Our 21-2085 28 September 18, 2023
recommendations for the minimum permeable ICP pavement sections subject to pedestrian traffic is 2 inches of No. 8 bedding underlain by 6 inches of No. 57 aggregate over soil subgrade.
A thicker base of No. 57 aggregate may be used for additional water storage.
The above recommended ICP pavement sections are based on the ICPI technical guidelines (ICPI 2017). From a geotechnical standpoint, it is also acceptable to use compacted structural planting mix in lieu of the No. 57 base courses in locations where the pedestrian ICP section is adjacent to tree wells and is required for promoting root growth.
7.7 Seismic Design
The latitude and longitude of the site are 37.6527° and -122.4134°, respectively. For design of the proposed buildings in accordance with 2022 CBC (ASCE 7-16), we recommend the following:
• Site Class C (very dense soil and soft rock)
• SS = 2.029, S1 = 0.839g
• Fa = 1.2, Fv = 1.4
• SMS = 2.435g, SM1 = 1.175g
• SDS = 1.623g, SD1 = 0.783g
• Seismic Design Category E for Risk Factors I, II, and III
8.0 ADDITIONAL GEOTECHNICAL SERVICES
Prior to construction, Rockridge Geotechnical should review the project plans and specifications to verify that they conform to the intent of our recommendations. During construction, our field engineer should provide on-site observation and testing during site preparation, placement and compaction of fill, and installation of shoring and building foundations. These observations will allow us to compare actual with anticipated subsurface conditions and to verify that the contractor's work conforms to the geotechnical aspects of the plans and specifications. 21-2085 29 September 18, 2023
9.0 LIMITATIONS
This geotechnical investigation has been conducted in accordance with the standard of care commonly used as state-of-practice in the profession. No other warranties are either expressed or implied. The recommendations made in this report are based on the assumption that the subsurface conditions do not deviate appreciably from those disclosed in the borings and DPTs.
If any variations or undesirable conditions are encountered during construction, we should be notified so that additional recommendations can be made. The foundation recommendations presented in this report are developed exclusively for the proposed development described in this report and are not valid for other locations and construction in the project vicinity. 21-2085 30 September 18, 2023
REFERENCES
Bonilla, M.G. (1998), Preliminary Geologic Map of the San Francisco South 7.5’ Quadrangle and Part of the Hunters Point 7.5’ Quadrangle, San Francisco Bay Area, California, U.S.
Geological Survey.
California Building Code (2022).
California Division of Mines and Geology (1996), Probabilistic seismic hazard assessment for the State of California, DMG Open-File Report 96-08.
California Geological Survey (2021). State of California Seismic Hazard Zone Report, San Francisco South 7.5-Minute Quadrangle, California, Seismic Hazard Zone Report.
California Geologic Survey (2008), Fault Rupture Hazard Zones in California, Special Publication 42.
Field, E.H., Biasi, G.P., Bird, P., Dawson, T.E., Felzer, K.R., Jackson, D.D., Johnson, K.M., Jordan, T.H., Madden, C., Michael, A.J., Milner, K.R., Page, M.T., Parsons, T., Powers, P.M., Shaw, B.E., Thatcher, W.R., Weldon, R.J., II, and Zeng, Y., (2013). Uniform California earthquake rupture forecast, version 3 (UCERF3)—The time-independent model: U.S.
Geological Survey Open-File Report 2013–1165, 97 p.
GeoTracker website, State of California Water Resources Control Board, (https://geotracker.waterboards.ca.gov/), accessed October 1, 2021.
Jennings, C.W., 1994, Fault activity map of California and adjacent areas with locations and ages of recent volcanic eruptions: California Division of Mines and Geology Geologic Data Map No. 6, scale 1: 750,000.
Petersen, M.D., Moschetti, M.P., Powers, P.M., Mueller, C.S., Haller, K.M., Frankel, A.D., Zeng, Y., Rezaeian, S., Harmsen, S.C., Boyd, O.S., Field, E.H., Chen, R., Rukstales, K.S., Luco, N., Wheeler, R.L., Williams, R.A., and Olsen, A.H., (2014). Documentation for the 2014 update of the United States national seismic hazard maps: U.S. Geological Survey Open-File Report 2014–1091, 243 p.
Pradel, D. (1998). “Procedure to Evaluate Earthquake-Induced Settlements in Dry Sandy Soils.” Journal of Geotechnical and Geoenvironmental Engineering, Volume 124, Issue 4.
Thompson, E.M., Wald, D.J, Worden, B., Field, E.H., Luco, N., Petersen, M.D., Powers, P.M., Badie, R. (2016) Shakemap earthquake scenario: Building Seismic Safety Council 2014 Event Set (BSSC2014). U.S. Geological Survey. DOI: 10.5066/F7V122XD Tokimatsu, K. & Seed, H.B. (1984). “Simplified Procedures for the Evaluation of Settlements in Sands Due to Earthquake Shaking,” UCB/EERC Report Series, 1998, No. 16. 21-2085 31 September 18, 2023
U.S. Geological Survey (USGS), 2008, The Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2): prepared by the 2007 Working Group on California Earthquake Probabilities, U.S. Geological Survey Open File Report 2007-1437.
Youd, T.L., and Idriss, I.M. (2001). “Liquefaction Resistance of Soils: Summary Report from the 1996 NCEER and 1998 NCEER/NSF Workshops on Evaluation of Liquefaction Resistance of Soils,” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 127, No. 4.
FIGURES
Date Project No. Figure 1
ROCKRIDGEGEOTECHNICAL
0 2,000 Feet
Approximate scale
1,000
Base map: Google Maps, 2021
SITE
SITE LOCATION MAP
08/30/23 21-2085
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
0Approximate scale160 Feet 08/30/23 21-2085 2 South San Francisco, California SITE PLAN Date Project No. Figure RAILROAD RESIDENCE DEVELOPMENT Base map: maps.conservation.ca.gov EXPLANATION Approximate location of boring by Rockridge Geotechnical, Inc., July 17 and 18, 2023 Approximate location of boring by Rockridge Geotechnical, Inc., September 8 and 24, 2021 Approximate location of dynamic penetrometer test by Rockridge Geotechnical, Inc., October 5, 2021 Project limits B-1 B-1 B-2 B-3 B-4 B-5 B-6 B-7 DPT-1 DPT-1 DPT-2 DPT-3 DPT-4 DPT-5 ROCKRIDGE GEOTECHNICAL B-8 B-8 B-9 B-11 B-10 B-12 B-13
REGIONAL GEOLOGIC MAP
Approximate scale
1,000
Date 3 Project No. Figure
0 2,000 Feet
08/30/23 21-2085
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
ROCKRIDGE
GEOTECHNICAL
Base map: Preliminary Geologic Map of the SF South 7.5’ Quadrangle and part of the Hunters Points 7.5’ Quadrangle, San Francisco Bay Area, California, 1998
SITE
Qc
KJu KJu
Qaf/tf Artificial fill over tidal flat
Qal Alluvium
Qsr Slope debris and ravine fill
Qc Colma Formation
KJs Sandstone and shale
KJu Sheared rocks
1800s shoreline and stream channels
1906, M7.9
1838, M7.4
1868, M7.0
1989, M6.9
2014, M6.0
San Andreas (SAN)
San Andreas (SAP)
Hayward (HN) Hayward (HS)
San Andreas (SAS)
Monte Vista-Shannon
Calaveras (CN)
Calaveras (CC)
Calaveras (CS)
San Gregorio (North)
San Gregorio (South)
Greenville
Green Valley
Rodgers Creek
Maacama
West Napa Concord
Great Valley (Midland)
Reliz
Great Valley (Orestimba)
1865, M6.5
Symbol Magnitude (Mw)
7.5+
7.0 - 7.4
6.5 - 6.9
6.0 - 6.4
5.0 - 5.9
Historic Earthquake Epicenters
Pre-1900 1900-1970 1971-2021
Date Project No. Figure
REGIONAL FAULT AND HISTORIC
SEISMICITY MAP
20 Miles
Approximate scale
0 10
0 16 32 Kilometers
EXPLANATION
Faults (National Seismic Hazard Model)
ROCKRIDGE
GEOTECHNICAL 08/30/23 4
SITE
21-2085
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
0 4,000 Feet
Approximate scale
2,000
ROCKRIDGE
GEOTECHNICAL Date Project No. Figure 5
Reference:
Earthquake Zones of Required Investigation
San Francisco South Quadrangle
Seismic Hazard Zones
Released September 23, 2021
Earthquake-Induced Landslide Zones
Areas where previous occurrence of landslide movement, or local topographic, geological, geotechnical and subsurface water conditions indicate a potential for permanent ground displacements such that mitigation as defined in Public Resources Code Section 2693(c) would be required.
Liquefaction Zones
Areas where historical occurrence of liquefaction, or local geological, geotechnical and ground water conditions indicate a potential for permanent ground displacements such that mitigation as defined in Public Resources Code Section 2693(c) would be required.
EARTHQUAKE ZONES OF REQUIRED
INVESTIGATION MAP
08/30/23 21-2085
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
SITE
Date Project No. Figure 6 Reference: "Permeable Interlocking Concrete Pavements", Third Edition, prepared by Interlocking Concrete Pavement Institute, dated 2005. 4 IN (100 MM) THICK NO. 57 STONE OPEN-GRADED BASE TYP. NO. 8, 89, OR 9 AGGREGATE IN OPENINGS CURB/EDGE RESTRAINT WITH CUT-OUTS FOR OVERFLOW DRAINAGE (CURB SHOWN) CONCRETE PAVERS MIN. 3 18 IN. (80 MM) THICK FOR VEHICULAR TRAFFIC (ASPECT RATIO< 3) BEDDING COURSE 1 12 TO 2 IN. (40 TO 50 MM) THICK (TYP. NO. 8 AGGREGATE) PERFORATED PIPES SPACED AND SLOPED TO DRAIN ALL STORED WATER SOIL SUBGRADE SLOPED TO DRAIN MIN. 6 IN. (150 MM) THICK NO. 2 STONE SUBBASE GEOTEXTILE ON TOP AND SIDES OF SUBBASE UNDER/BEYOND CURB GEOTEXTILE ON SUBGRADE NON-PERFORATED OUTFALL PIPE(S) SLOPED TO STORM SEWER OR STREAM 09/05/23 NOTES: 1. 2 38 IN. (60 MM) THICK PAVERS MAY BE USED IN RESIDENTIAL APPLICATIONS. 2. NO. 2 STONE SUBBASE THICKNESS VARIES WITH DESIGN. CONSULT ICPI PERMEABLE INTERLOCKING CONCRETE PAVEMENT MANUAL.. 3. PERFORATED PIPES MAY BE RAISED FOR WATER STORAGE FROM LARGE RAIN EVENTS WITH OUTLET(S) AT LINER BOTTOM TO DRAIN SMALL RAIN EVENTS. GENERALIZED ICPI PERMEABLE PAVER DETAIL FOR PARTIAL EXFILTRATION ROCKRIDGE GEOTECHNICAL 21-2085 South San Francisco, California RAILROAD RESIDENCE DEVELOPMENT
APPENDIX A
Boring Logs and Dynamic Penetrometer Test Results
Sampler
Type
Sample
Blows/ 6"
SPT
N-Value1
DEPTH
LITHOLOGY
(feet)
Dry Density
Lbs/Cu Ft
Type of
Strength
Test
Shear Strength
Lbs/Sq Ft
Fines
%
Confining
Pressure
Lbs/Sq Ft
Natural
Moisture
Content, %
Sampler:
Boring location:
Date started:
Drilling method:
Logged by:
Drilled by:
Rig:
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
MATERIAL DESCRIPTION
LABORATORY TEST DATA
SAMPLES
Figure:
A-1
PROJECT:
Project No.:
21-2085
PAGE 1 OF 1
Log of Boring B-1
ROCKRIDGE
GEOTECHNICAL
See Site Plan, Figure 2
09/08/2021 Date finished:
Modified California (MC), Standard Penetration Test (SPT) SM
10.3 SILTY SAND with GRAVEL (SM)
brown, dense, dry
SANDY SILT (ML)
red-yellow with brown mottling, hard, moist,
fine sand
CLAYEY SAND (SC)
yellow-brown with yellow and dark brown
mottling, dense, moist, fine gravel
CLAYEY SAND (SC)
light brown with yellow mottling, dense, moist,
fine sand
SILTY SAND (SM)
red-yellow, very dense, slightly moist, fine sand
with occasional coarse sand size fragments
SANDSTONE
yellow-brown to yellow-orange, low hardness,
friable, moderately weathered
light brown with gray mottling, very dense
R. Ford
Exploration Geoservices, Inc.
Mobile B-61
1 inch of old road asphalt
Hammer weight/drop: 140 lbs./30 inches Hammer type: Downhole Safety Hammer 09/08/2021
8-inch-diameter hollow-stem auger
hard drilling
SM
SC
SC
ML
57 10.4
36 SPT
SPT
MC
15 16
19 38
Boring terminated at a depth of 21.4 feet below 1
ground surface.
Boring backfilled with cement grout.
Groundwater not encountered during drilling.
MC and SPT blow counts for the last two increments
were converted to SPT N-Values using factors of 0.63
and 1.08, respectively, to account for sampler type and hammer energy.
13 15
38 33
SPT
18 18
26 48
14 14
21 38
SPT
14 21
30 55
30 50/6” 54/6”
SPT
40 44
50/5”
102/
11”
FILL
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
SPT
SLOPE DEBRIS
AND RAVINE
FILL COLMA FORMATION BEDROCK RESIDUAL SOIL
Soil Corrosivity Test; see Appendix B
Sampler
Type
Sample
Blows/ 6"
SPT
N-Value1
DEPTH
LITHOLOGY
(feet)
Dry Density
Lbs/Cu Ft
Type of
Strength
Test
Shear Strength
Lbs/Sq Ft
Fines
%
Confining
Pressure
Lbs/Sq Ft
Natural
Moisture
Content, %
Sampler:
Boring location:
Date started:
Drilling method:
Logged by:
Drilled by:
Rig:
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
MATERIAL DESCRIPTION
LABORATORY TEST DATA
SAMPLES
Figure:
A-2
PROJECT:
Project No.:
21-2085
PAGE 1 OF 1
Log of Boring B-2
ROCKRIDGE
GEOTECHNICAL
See Site Plan, Figure 2
09/08/2021 Date finished:
Standard Penetration Test (SPT)
SC
41 11.3
CLAYEY SAND with GRAVEL (SC)
brown, medium dense, dry
olive with gray and yellow mottling, very dense
CLAYEY SAND (SC)
yellow-brown with red-brown mottling oxidation,
dense, moist, roots
CLAYEY SAND (SC)
yellow-brown with brown mottling, very dense,
moist
SILTSTONE/SHALE
gray-white with red-brown oxidation, very thin
bedded, low hardness, friable to weak, deeply to
moderately weathered
SANDY CLAY (CL)
brown with red-yellow mottling, hard, moist
Hammer weight/drop: 140 lbs./30 inches Hammer type:
09/08/2021
8-inch-diameter hollow-stem auger
SP
SC
CL
SC
SAND (SP)
light gray, trace yellow-orange oxidation, very
dense, moist, fine sand, cemented weakly
Downhole Safety Hammer
R. Ford
Exploration Geoservices, Inc.
Mobile B-61
LL = 28, PI = 15; see Appendix B
62 14.1
SPT
SPT
12 18
22 43
Boring terminated at a depth of 24.3 feet below 1
ground surface.
Boring backfilled with cement grout.
Groundwater not encountered during drilling.
SPT blow counts for the last two increments
were converted to SPT N-Values using a factor of 1.08
to account for sampler type and hammer energy.
15 23
32 59
SPT
25 30
32 67
14 16
26 45
SPT
15 25
40 70
SPT
14 23
28 55
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
SPT
SPT
25 30
35 70
SPT
18 45
50/4”
103/
10”
SLOPE DEBRIS
AND RAVINE FILL COLMA FORMATION BEDROCK RESIDUAL SOIL
Sampler
Type
Sample
Blows/ 6"
SPT
N-Value1
DEPTH
LITHOLOGY
(feet)
Dry Density
Lbs/Cu Ft
Type of
Strength
Test
Shear Strength
Lbs/Sq Ft
Fines
%
Confining
Pressure
Lbs/Sq Ft
Natural
Moisture
Content, %
Sampler:
Boring location:
Date started:
Drilling method:
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
MATERIAL DESCRIPTION
LABORATORY TEST DATA
SAMPLES
Figure:
A-3
PROJECT:
Project No.:
21-2085
PAGE 1 OF 1
Log of Boring B-3
ROCKRIDGE
GEOTECHNICAL
Logged by:
Drilled by:
Rig:
Downhole Safety Hammer
R. Ford
Exploration Geoservices, Inc.
Mobile B-61
See Site Plan, Figure 2
09/08/2021 Date finished:
Standard Penetration Test (SPT)
SC
46 9.5
CLAYEY SAND (SC)
brown, medium dense, dry
SILTY SAND (SM)
yellow, medium dense, dry, fine gravel
SANDSTONE
yellow with red-yellow mottling, fine grained, low
hardness, friable to weak, deeply to moderately
weathered
Hammer weight/drop: 140 lbs./30 inches Hammer type:
09/08/2021
8-inch-diameter hollow-stem auger
SM
SPT
SPT
9 11
11 24
Boring terminated at a depth of 10.2 feet below 1
ground surface.
Boring backfilled with cement grout.
Groundwater not encountered during drilling.
SPT blow counts for the last two increments
were converted to SPT N-Values using a factor of 1.08
to account for sampler type and hammer energy.
11 12
14 28
SPT
18 28
50/3”
84/9”
50/4” 54/4”
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
SPT
SPT 50/2” 54/2”
FILL BEDROCK RESIDUAL SOIL
Soil Corrosivity Test; see Appendix B
Sampler
Type
Sample
Blows/ 6"
SPT
N-Value1
DEPTH
LITHOLOGY
(feet)
Dry Density
Lbs/Cu Ft
Type of
Strength
Test
Shear Strength
Lbs/Sq Ft
Fines
%
Confining
Pressure
Lbs/Sq Ft
Natural
Moisture
Content, %
Sampler:
Boring location:
Date started:
Drilling method:
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
MATERIAL DESCRIPTION
LABORATORY TEST DATA
SAMPLES
Figure:
A-4
PROJECT:
Project No.:
21-2085
PAGE 1 OF 1
Log of Boring B-4
ROCKRIDGE
GEOTECHNICAL
See Site Plan, Figure 2
09/08/2021 Date finished:
GW
46 15.5
(09/08/2021; 8:20 AM)
GRAVEL with SAND and CLAY (GW)
brown, medium dense, moist
CLAYEY SAND (SC)
olive-brown with dark brown and red-yellow
mottling, dense, moist, rounded corase sand-size
to pea size gravel
SILTSTONE/SHALE
brown to dark gray, very thin bedded, low hardness
to plastic friable, pervasively sheared, deeply to
completely weathered
Hammer weight/drop: 140 lbs./30 inches Hammer type:
09/08/2021
8-inch-diameter hollow-stem auger
SC
Modified California (MC), Standard Penetration Test (SPT) CLAY with SAND and GRAVEL (CL)
yellow-brown with yellow mottling, very stiff to
hard, moist
low hardness to weak with completly weathered
zones
CL
Logged by:
Drilled by:
Rig:
Downhole Safety Hammer
R. Ford
Exploration Geoservices, Inc.
Mobile B-61
medium dense
SLOPE DEBRIS AND RAVINE FILL FILL BEDROCK RESIDUAL SOIL MC
25 15
16 20
Boring terminated at a depth of 21.4 feet below
ground surface.
Boring backfilled with cement grout.
Groundwater encountered at a depth of 16 feet
during drilling.
14 25
50 47
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
MC
MC
12 18
24 26
SPT
11 16
17 36
SPT
18 13
24 40
SPT
12 22
35 62
SPT
22 32
50/5”
89/
11”
1 MC and SPT blow counts for the last two increments
were converted to SPT N-Values using factors of 0.63
and 1.08, respectively, to account for sampler type and hammer energy.
LL = 28, PI = 15; see Appendix B
Soil Corrosivity Test; see Appendix B
Sampler
Type
Sample
Blows/ 6"
SPT
N-Value1
DEPTH
LITHOLOGY
(feet)
Dry Density
Lbs/Cu Ft
Type of
Strength
Test
Shear Strength
Lbs/Sq Ft
Fines
%
Confining
Pressure
Lbs/Sq Ft
Natural
Moisture
Content, %
Sampler:
Boring location:
Date started:
Drilling method:
Logged by:
Drilled by:
Rig:
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
MATERIAL DESCRIPTION
LABORATORY TEST DATA
SAMPLES
Figure:
A-5
PROJECT:
Project No.:
21-2085
PAGE 1 OF 1
Log of Boring B-5
ROCKRIDGE
GEOTECHNICAL
See Site Plan, Figure 2
09/24/2021 Date finished:
Standard Penetration Test (SPT)
CL
SANDY CLAY with GRAVEL (CL)
brown, yellow-brown, and olive-gray, hard,
moist, fine to coarse sand, fine angular to
subangular gravel
SILTY SAND with GRAVEL (SM)
pale yellow and gray, very dense, moist, fine to
coarse sand and gravel, angular to subangular
gravel
3-inch-diameter solid stem auger
J. Pisenti
Access Soil Drilling
Limited Access
Hammer weight/drop: 140 lbs./30 inches Hammer type: Rope & cathead safety hammer 09/24/2021
SANDSTONE
pale yellow to light yellow-brown and gray, low
hardness, moderately weak to weak, moderately
to highly weathered
SM
SPT
SPT
SPT
16 16
15 37
Boring terminated at a depth of 7.9 feet below 1
ground surface.
Boring backfilled with cement grout.
Groundwater not encountered during drilling.
SPT blow counts for the last two increments
were converted to SPT N-Values using a factor of 1.2
to account for sampler type and hammer energy.
32 35
38 88
SPT
19 33
37 84
55 50/5” 60/5”
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
SLOPE DEBRIS
AND RAVINE
FILL BEDROCK
RESIDUAL
SOIL
Sampler
Type
Sample
Blows/ 6"
SPT
N-Value1
DEPTH
LITHOLOGY
(feet)
Dry Density
Lbs/Cu Ft
Type of
Strength
Test
Shear Strength
Lbs/Sq Ft
Fines
%
Confining
Pressure
Lbs/Sq Ft
Natural
Moisture
Content, %
Sampler:
Boring location:
Date started:
Drilling method:
Logged by:
Drilled by:
Rig:
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
MATERIAL DESCRIPTION
LABORATORY TEST DATA
SAMPLES
Figure:
A-6
PROJECT:
Project No.:
21-2085
PAGE 1 OF 1
Log of Boring B-6
ROCKRIDGE
GEOTECHNICAL
See Site Plan, Figure 2
09/24/2021 Date finished:
Standard Penetration Test (SPT)
CL
SANDY CLAY with GRAVEL (CL)
brown mottled with yellow-brown, very stiff, dry to
moist, fine to coarse sand, fine angular to
subangular gravel
SANDY CLAY (CL)
yellow-brown mottled with olive-gray and gray,
very stiff, moist, fine to medium sand
3-inch-diameter solid stem auger
J. Pisenti
Access Soil Drilling
Limited Access
Hammer weight/drop: 140 lbs./30 inches Hammer type: Rope & cathead safety hammer 09/24/2021
CLAYEY SAND with GRAVEL (SC)
gray-brown and red-yellow, medium dense, moist,
fine to medium sand, fine subangular gravel SC
CL
SILTY CLAY (CL-ML)
black, medium stiff to stiff, moist to wet, trace fine
sand
CLAY (CL)
olive-gray and black, medium stiff to stiff, moist to wet CL CLML
SPT
SPT
9 10
14 29
Boring terminated at a depth of 11.5 feet below
ground surface.
Boring backfilled with cement grout.
Groundwater not encountered during drilling.
9 11
13 29
SPT
5 10
13 28
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
SPT
3 4
3 8
SPT
5 3
4 8
BAY MUD
1 SPT blow counts for the last two increments
were converted to SPT N-Values using a factor of 1.2
to account for sampler type and hammer energy.
FILL
Sampler
Type
Sample
Blows/ 6"
SPT
N-Value1
DEPTH
LITHOLOGY
(feet)
Dry Density
Lbs/Cu Ft
Type of
Strength
Test
Shear Strength
Lbs/Sq Ft
Fines
%
Confining
Pressure
Lbs/Sq Ft
Natural
Moisture
Content, %
Sampler:
Boring location:
Date started:
Drilling method:
Logged by:
Drilled by:
Rig:
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
MATERIAL DESCRIPTION
LABORATORY TEST DATA
SAMPLES
Figure:
A-7
PROJECT:
Project No.:
21-2085
PAGE 1 OF 1
Log of Boring B-7
ROCKRIDGE
GEOTECHNICAL
See Site Plan, Figure 2
09/24/2021 Date finished:
SC
(09/24/2021; 9:50 AM)
CLAYEY SAND with GRAVEL (SC)
brown to ligh brown with light gray, dense, dry to
moist, fine to coarse sand and gravel, angular to
subangular gravel
GRAVEL with SILT and SAND (GW-GM)
gray and yellow brown, medium dense to dense,
dry to moist, fine to coarse sand and gravel,
angular to subangular gravel
3-inch-diameter solid stem auger
J. Pisenti
Access Soil Drilling
Limited Access
Hammer weight/drop: 140 lbs./30 inches Hammer type: Rope & cathead safety hammer 09/24/2021
Modified California (MC), Standard Penetration Test (SPT) SANDY CLAY with GRAVEL (CL)
yellow brown and olive-gray mottled with gray, stiff,
moist, fine to coarse sand, fine angular gravel CL
GWGM
SILTY CLAY (CL-ML)
dark gray to black, medium stiff, moist, trace fine
sand
CL
CLML
medium stiff, moist to wet
CLAY (CL)
dark gray, medium stiff, wet
SPT
MC
38 31
36 47
Boring terminated at a depth of 13 feet below
ground surface.
Boring backfilled with cement grout.
Groundwater encountered at a depth of 11.5 feet
during drilling.
17 13
12 30
SPT
6 5
7 14
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
SPT
3 3
3 7
SPT
2 2
2 5
1 MC and SPT blow counts for the last two increments
were converted to SPT N-Values using factors of 0.7
and 1.2, respectively, to account for sampler type and
hammer energy.
SPT
2 2
3 6
BAY MUD FILL
MC 32
7 13
17 29
9.7 SPT 86/9”
30 72
50/3”
SPT 131
23 30
40 69
MC 32
21 27
24 21
MC 76
26 36
50/6”
58/6”
CA 93
30 35
52 51
Sampler
Type
Sample
Blows/ 6"
SPT
N-Value1
DEPTH
(feet)
LITHOLOGY
Boring location:
Date started:
Drilling method:
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
MATERIAL DESCRIPTION
SAMPLES LABORATORY TEST DATA
Figure:
A-8
PROJECT:
Project No.: Type of Strength Test Confining Pressure
Lbs/Sq Ft
Shear
Strength
Lbs/Sq Ft
Fines
%
Natural
Moisture
Content,%
Dry
Density
Lbs/Cut Ft
ROCKRIDGE
GEOTECHNICAL
21-2085
Boring terminated at a depth of 14.25 feet below
ground surface.
Boring backfilled with cement grout.
Groundwater not encountered during drilling.
1 See Site Plan, Figure 2
07/17/2023 Date finished: 07/17/2023
Hammer weight/drop: 140 lbs./30 inches Hammer type:
CLAYEY SAND with GRAVEL (SC)
brown, dense, moist, fine to coarse sand, fine
subrounded gravel, roots
CL
SC
Sampler:
Logged by:
Drilled by:
Rig:
PAGE 1 OF 1
Log of Boring B-8
CLAYEY SAND (SC)
yellow-brown mottled with red-brown, dense, moist,
fine to medium sand, roots
SANDY CLAY (CL)
olive-brown, hard, moist
SC
Modified California (MC), California (CA), Standard Penetration Test (SPT) SAND with CLAY (SP-SC)
red-yellow, dense, moist, fine sand
4-inch-diameter solid-stem auger
SLOPE DEBRIS
AND RAVINE FILL
COLMA FORMATION
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
J. Pisenti
Access Soil Drilling
Minuteman
SAND with CLAY (SP-SC)
red-yellow, very dense, moist, fine sand
yellow-brown
yellow, trace fine subangular gravel
yellow-brown
SPSC
SPSC
MC, CA, and SPT blow counts for the last two increments were converted to SPT N-Values using factors of 0.7, 0.9, and 1.2, respectively, to account for sampler type and
hammer energy.
Rope & Cathead Safety Hammer
Soil Corrosivity Test; see Appendix B
MC 24
7 9
9 25
71 SPT 127
18 30
44 62
MC 67
30 28
43 52
CA 97/9”
22 32
58 50/3”
SPT 60/3” 50
50/3”
Sampler
Type
Sample
Blows/ 6"
SPT
N-Value1
DEPTH
(feet)
LITHOLOGY
Boring location:
Date started:
Drilling method:
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
MATERIAL DESCRIPTION
SAMPLES LABORATORY TEST DATA
Figure:
A-9
PROJECT:
Project No.: Type of Strength Test Confining Pressure
Lbs/Sq Ft
Shear
Strength
Lbs/Sq Ft
Fines
%
Natural
Moisture
Content,%
Dry
Density
Lbs/Cut Ft
ROCKRIDGE
GEOTECHNICAL
21-2085
Boring terminated at a depth of 11 feet below
ground surface.
Boring backfilled with cement grout.
Groundwater not encountered during drilling.
1 See Site Plan, Figure 2
07/17/2023 Date finished: 07/17/2023
Hammer weight/drop: 140 lbs./30 inches Hammer type:
CLAYEY SAND (SC)
yellow-brown, medium dense, moist, fine to medium
sand, trace fine subrounded gravel, roots
CL
Sampler:
Logged by:
Drilled by:
Rig:
PAGE 1 OF 1
Log of Boring B-9
SANDY CLAY (CL)
red-yellow, very stiff to hard, moist, fine sand, trace fine subangular gravel
SANDY CLAY (CL)
yellow-brown, hard, moist, fine sand
SC
Modified California (MC), California (CA), Standard Penetration Test (SPT) SAND with CLAY (SP-SC)
yellow, very dense, moist, fine sand
4-inch-diameter solid-stem auger
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
SAND with CLAY (SP-SC)
red-yellow, very dense, moist, fine sand
SILTY SAND (SM)
yellow-brown, very dense, moist fine to medium sand SM
SPSC
MC, CA, and SPT blow counts for the last two increments were converted to SPT N-Values using factors of 0.7, 0.9, and 1.2, respectively, to account for sampler type and
hammer energy.
red-yellow
SPSC
CL
J. Pisenti
Access Soil Drilling
Minuteman
Rope & Cathead Safety Hammer
Particle Size Distribution; see Appendix B
SLOPE DEBRIS
AND RAVINE FILL
RESIDUAL SOIL
MC 11
4 5
5 10
79 MC 59/
11”
14 34
50/5”
CA 45/4” 47
50/4”
SPT 60/3” 50
50/3”
10.5 Sampler
Type
Sample
Blows/ 6"
SPT
N-Value1
DEPTH
(feet)
LITHOLOGY
Boring location:
Date started:
Drilling method:
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
MATERIAL DESCRIPTION
SAMPLES LABORATORY TEST DATA
Figure:
A-10
PROJECT:
Project No.: Type of Strength Test Confining Pressure
Lbs/Sq Ft
Shear
Strength
Lbs/Sq Ft
Fines
%
Natural
Moisture
Content,%
Dry
Density
Lbs/Cut Ft
ROCKRIDGE
GEOTECHNICAL
21-2085
Boring terminated at a depth of 5 feet below
ground surface.
Boring backfilled with cement grout.
Groundwater not encountered during drilling.
1 See Site Plan, Figure 2
07/17/2023 Date finished: 07/17/2023
Hammer weight/drop: 140 lbs./30 inches Hammer type:
SANDY CLAY (CL)
olive-brown, stiff, moist, fine to coarse sand,
trace fine subangular gravel
Sampler:
Logged by:
Drilled by:
Rig:
PAGE 1 OF 1
Log of Boring B-10
CLAYEY SAND (SC)
red-yellow, medium dense, fine sand
SC
Modified California (MC), California (CA), Standard Penetration Test (SPT) SAND with CLAY (SP-SC)
yellow-brown, very dense, moist, fine sand, trace fine
subangular gravel, rootlets
4-inch-diameter solid-stem auger
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
MC, CA, and SPT blow counts for the last two increments were converted to SPT N-Values using factors of 0.7, 0.9, and 1.2, respectively, to account for sampler type and
hammer energy.
red-yellow
SPSC
CL
J. Pisenti
Access Soil Drilling
Minuteman
Rope & Cathead Safety Hammer
Particle Size Distribution; see Appendix B
SLOPE
DEBRIS
AND
RAVINE
FILL
RESIDUAL SOIL
MC 56/9”
2 5
30 50/3”
SPT 125/
6”
104/
6”
Sampler
Type
Sample
Blows/ 6"
SPT
N-Value1
DEPTH
(feet)
LITHOLOGY
Boring location:
Date started:
Drilling method:
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
MATERIAL DESCRIPTION
SAMPLES LABORATORY TEST DATA
Figure:
A-11
PROJECT:
Project No.: Type of Strength Test Confining Pressure
Lbs/Sq Ft
Shear
Strength
Lbs/Sq Ft
Fines
%
Natural
Moisture
Content,%
Dry
Density
Lbs/Cut Ft
ROCKRIDGE
GEOTECHNICAL
21-2085
Boring terminated at a depth of 2.25 feet below
ground surface.
Boring backfilled with cement grout.
Groundwater not encountered during drilling.
1 MC and SPT blow counts for the last two increments
were converted to SPT N-Values using factors of 0.7
and 1.2, respectively, to account for sampler type and
hammer energy.
See Site Plan, Figure 2
07/18/2023 Date finished: 07/18/2023
Hammer weight/drop: 140 lbs./30 inches Hammer type:
CLAYEY SAND with GRAVEL (SC)
brown, very dense, moist, fine to coarse sand, fine
subangular gravel, rootlets
Sampler:
Logged by:
Drilled by:
Rig:
PAGE 1 OF 1
Log of Boring B-11
SANDSTONE
yellow-brown, closely to intensely fractured, low
hardness to moderately hard, weak to moderately
strong, moderately weathered
SC
Modified California (MC), Standard Penetration Test (SPT) 4-inch-diameter solid-stem auger
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
J. Pisenti
Access Soil Drilling
Minuteman
Rope & Cathead Safety Hammer RESIDUAL SOIL BEDROCK
MC 35
12 20
28 22
24 5.6
SPT 118
47 61
49 49
MC 55
16 27
35 43
CA 37
17 17
21 20
CA 189
38 55
72 138
SPT 77
30 36
35 46
Sampler
Type
Sample
Blows/ 6"
SPT
N-Value1
DEPTH
(feet)
LITHOLOGY
Boring location:
Date started:
Drilling method:
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
MATERIAL DESCRIPTION
SAMPLES LABORATORY TEST DATA
Figure:
A-12
PROJECT:
Project No.: Type of Strength Test Confining Pressure
Lbs/Sq Ft
Shear
Strength
Lbs/Sq Ft
Fines
%
Natural
Moisture
Content,%
Dry
Density
Lbs/Cut Ft
ROCKRIDGE
GEOTECHNICAL
21-2085
Boring terminated at a depth of 12 feet below
ground surface.
Boring backfilled with cement grout.
Groundwater not encountered during drilling.
1 See Site Plan, Figure 2
07/18/2023 Date finished: 07/18/2023
Hammer weight/drop: 140 lbs./30 inches Hammer type:
CLAYEY SAND with GRAVEL (SC)
olive-gray, dense, moist, fine to coarse
sand, fine to coarse subangular gravel
Sampler:
Logged by:
Drilled by:
Rig:
PAGE 1 OF 1
Log of Boring B-12
SILTY SAND with GRAVEL (SM)
gray, dense, moist, fine to coarse sand, fine to
coarse angular gravel
SILTSTONE/SHALE
gray, intensely fractured, low hardness, friable, deeply to moderately weathered
SC
Modified California (MC), California (CA), Standard Penetration Test (SPT) 4-inch-diameter solid-stem auger
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
SM
MC, CA, and SPT blow counts for the last two increments were converted to SPT N-Values using factors of 0.7, 0.9, and 1.2, respectively, to account for sampler type and
hammer energy.
trace clay
gray and light gray
J. Pisenti
Access Soil Drilling
Minuteman
Rope & Cathead Safety Hammer
Particle Size Distribution; see Appendix B
SLOPE DEBRIS
AND RAVINE FILLRESIDUAL SOIL BEDROCK
MC 14
1 7
9 11
7 SPT 120/
6”
100/
6”
MC 30
20 21
20 23
MC 55
29 23
43 36
CA 88/9”
22 34
48 50/3”
Sampler
Type
Sample
Blows/ 6"
SPT
N-Value1
DEPTH
(feet)
LITHOLOGY
Boring location:
Date started:
Drilling method:
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
MATERIAL DESCRIPTION
SAMPLES LABORATORY TEST DATA
Figure:
A-13
PROJECT:
Project No.: Type of Strength Test Confining Pressure
Lbs/Sq Ft
Shear
Strength
Lbs/Sq Ft
Fines
%
Natural
Moisture
Content,%
Dry
Density
Lbs/Cut Ft
ROCKRIDGE
GEOTECHNICAL
21-2085
Boring terminated at a depth of 8.25 feet below
ground surface.
Boring backfilled with cement grout.
Groundwater not encountered during drilling.
1 See Site Plan, Figure 2
07/18/2023 Date finished: 07/18/2023
Hammer weight/drop: 140 lbs./30 inches Hammer type:
CLAYEY SAND with GRAVEL (SC)
brown, medium dense, moist, fine to coarse sand,
fine to coarse angular gravel
Sampler:
Logged by:
Drilled by:
Rig:
PAGE 1 OF 1
Log of Boring B-13
olive-brown, medium dense to dense, trace silt
SILTSTONE/SHALE
gray, closely to intensely fractured, low hardness
to moderately hard, weak to moderately strong,
moderately weathered
SC
Modified California (MC), California (CA), Standard Penetration Test (SPT) 4-inch-diameter solid-stem auger
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
MC, CA, and SPT blow counts for the last two increments were converted to SPT N-Values using factors of 0.7, 0.9, and 1.2, respectively, to account for sampler type and
hammer energy.
GRAVEL with SAND and CLAY (GW-GC)
brown, medium dense, moist, fine to coarse sand,
fine to coarse angular gravel
CLAYEY GRAVEL with SAND (GC)
olive-brown mottled with yellow, very dense, moist,
fine to coarse sand, fine to coarse angular gravel,
rootlets
GWGC
GC
J. Pisenti
Access Soil Drilling
Minuteman
Rope & Cathead Safety Hammer
Particle Size Distribution; see Appendix B
SLOPE DEBRIS
AND RAVINE FILL
RESIDUAL
SOIL BEDROCK
CLASSIFICATION CHART
Major Divisions Symbols Typical Names
GW
GP
GM
GC
SW
SP
SM
SC
ML
CL
OL
MH
CH
OH
Highly Organic Soils PT
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 Size
in 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
Coarse-Grained Soils
(more than half of soil > no. 200
sieve size)
Fine -Grained Soils
(more than half of soil
< no. 200 sieve size)
Gravels
(More than half of
coarse fraction >
no. 4 sieve size)
Sands
(More than half of
coarse fraction <
no. 4 sieve size)
Silts and Clays
LL = < 50
Silts and Clays
LL = > 50
Gravel
coarse
fine
3" to No. 4
3" to 3/4"
3/4" to No. 4
No. 4 to No. 200
No. 4 to No. 10
No. 10 to No. 40
No. 40 to No. 200
76.2 to 4.76
76.2 to 19.1
19.1 to 4.76
4.76 to 0.075
4.76 to 2.00
2.00 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
MC Modified California 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 California or Modified California split-barrel sampler. 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
Sample taken with Direct Push sampler
Sonic
Unstabilized groundwater level
Stabilized groundwater level
Date 08/30/23 Project No. Figure A-14 21-2085
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
ROCKRIDGE
GEOTECHNICAL
I FRACTURING
Intensity Size of Pieces in Feet
Very little fractured Greater than 4.0
Occasionally fractured 1.0 to 4.0
Moderately fractured 0.5 to 1.0
Closely fractured 0.1 to 0.5
Intensely fractured 0.05 to 0.1
Crushed Less than 0.05
II HARDNESS
1. Soft - reserved for plastic material alone.
2. Low hardness - can be gouged deeply or carved easily with a knife blade.
3. Moderately hard - can be readily scratched by a knife blade; scratch leaves a heavy trace of dust and is readily visible after the powder has been blown away.
4. Hard - can be scratched with difficulty; scratch produced a little powder and is often faintly visible.
5. Very hard - cannot be scratched with knife blade; leaves a metallic streak.
III STRENGTH
1. Plastic or very low strength.
2. Friable - crumbles easily by rubbing with fingers.
3. Weak - an unfractured specimen of such material will crumble under light hammer blows.
4. Moderately strong - specimen will withstand a few heavy hammer blows before breaking.
5. Strong - specimen will withstand a few heavy ringing hammer blows and will yield with difficulty only dust and small flying fragments.
6. Very strong - specimen will resist heavy ringing hammer blows and will yield with difficulty only dust and small flying fragments.
IV WEATHERING - The physical and chemical disintegration and decomposition of rocks and minerals by natural processes such as oxidation, reduction, hydration, solution, carbonation, and freezing and thawing.
D. Deep - moderate to complete mineral decomposition; extensive disintegration; deep and thorough discoloration; many fractures, all extensively coated or filled with oxides, carbonates and/or clay or silt.
M. Moderate - slight change or partial decomposition of minerals; little disintegration; cementation little to unaffected.
Moderate to occasionally intense discoloration. Moderately coated fractures.
L. Little - no megascopic decomposition of minerals; little of no effect on normal cementation. Slight and intermittent, or localized discoloration. Few stains on fracture surfaces.
F. Fresh - unaffected by weathering agents. No disintegration of discoloration. Fractures usually less numerous than joints.
ADDITIONAL COMMENTS:
V CONSOLIDATION OF SEDIMENTARY ROCKS: usually determined from unweathered samples. Largely dependent on cementation.
U = unconsolidated
P = poorly consolidated
M = moderately consolidated
W = well consolidated
VI BEDDING OF SEDIMENTARY ROCKS
Splitting Property Thickness Stratification
Massive Greater than 4.0 ft. very thick-bedded
Blocky 2.0 to 4.0 ft. thick bedded
Slabby 0.2 to 2.0 ft. thin bedded
Flaggy 0.05 to 0.2 ft. very thin-bedded
Shaly or platy 0.01 to 0.05 ft. laminated
Papery less than 0.01 thinly laminated
Date Project No. Figure A-15
PHYSICAL PROPERTIES CRITERIA
FOR ROCK DESCRIPTIONS
08/24/23 21-2085
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
ROCKRIDGE
GEOTECHNICAL
0 1
2 3
4 5
0 5 10 15 20 25 30 35 40 45 50 55 60
DPT-1
DPT-2
DPT-3
DPT-4
DPT-5
DYNAMIC PENETROMETER
TEST RESULTS
A-16
BLOWS PER 4 INCHES (10 centimeters)
Date Project No. Figure
DEPTH BELOW GROUND SURFACE (feet)
08/24/23 21-2085
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
ROCKRIDGE
GEOTECHNICAL
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 (%)
PLASTICITY CHART
Date B-1 08/30/23 Project No. Figure 21-2085
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
ROCKRIDGE
GEOTECHNICAL
PLASTICITY INDEX (PI)
Ref erence:
ASTM D2487-00
B-2 at 1-2.5 feet
B-4 at 2.0 feet
CLAYEY SAND (SC)
yellow-brown with red-brown mottling
CLAYEY SAND (SC)
olive-brown with dark brown and redyellow mottling
11.3 --
--
--
28 28
15 15
SYMBOL SOURCE DEPTH Material Description USCS (ft.)
SOIL DATA
PERCENT FINER
0 10
20 30
40 50
60 70
80 90
100
GRAIN SIZE - mm.
100 10 1 0.1 0.01 0.001
% +3" Coarse
% Gravel
Fine Coarse Medium
% Sand
Fine Silt
% Fines
Clay
0.0 0.2 0.2 1.5 4.0 23.3 70.8
0.0 0.2 0.2 0.9 5.3 14.2 79.2
0.0 5.0 14.8 17.1 29.9 9.7 23.5
0.0 35.9 29.9 13.1 12.8 1.8 6.5 6 in. 3 in. 2 in.
1½ in.
1 in.
¾ in.½ in.3/8 in.#4#10#20
#30#40
#60
#100
#140#200
B-9 2.3'
B-10 0.8'
B-12 4.0'
B-13 1.0'
PARTICLE SIZE DISTRIBUTION REPORT
ROCKRIDGE
GEOTECHNICAL 08/28/23 21-2085
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
SANDY CLAY, red-yellow
SANDY CLAY, olive-brown
SILTY SAND with GRAVEL, gray
GRAVEL with SAND and CLAY, brown
Date B-2 Project No. Figure
CL
CL
SM
GW-GC
S210924H
Method ASTM
D4972
ASTM
G200
ASTM D4658
ASTM D4327
ASTM D6919
ASTM D6919
ASTM D6919
ASTM D6919
ASTM D6919
ASTM D6919
ASTM D4327
ASTM D4327
Bore# / Description Depth pH Redox Sulfide
S2-
Nitrate
NO3-
Ammonium
NH4+
Lithium
Li+
Sodium
Na+
Potassium
K+
Magnesium
Mg2+
Calcium
Ca2+
Fluoride
F2--
Phosphate
PO43-
(ft) (mg/kg) (wt%) (mg/kg) (wt%) (Ohm-cm) (Ohm-cm) (mV) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) 4 96.6 0.0097 23.0 0.0023 2,881 1,943 8.4 106 <0.01 0.2 2.7 0.05 66.7 0.9 76.1 181.3 3.5 3.4 1-2.5 51.5 0.0051 24.2 0.0024 18,090 5,025 7.8 95 <0.01 0.3 4.8 0.04 46.8 1.4 59.6 153.6 3.2 3.0
1.5 32.1 0.0032 11.7 0.0012 2,010 2,010 8.2 110 <0.01 0.9 2.2 0.03 54.1 2.0 96.5 208.9 4.3 2.2 ASTM
G187
ASTM D4327
ASTM D4327
Resistivity
As Rec'd | Minimum
Sulfates
SO42-
Chlorides
ClCations and Anions, except Sulfide and Bicarbonate, tested with Ion Chromatography mg/kg = milligrams per kilogram (parts per million) of dry soil weight ND = 0 = Not Detected | NT = Not Tested | Unk = Unknown Chemical Analysis performed on 1:3 Soil-To-Water extract PPM = mg/kg (soil) = mg/L (Liquid)
Date 08/28/23 Project No. Figure B-3a
B-1: SANDY SILT (ML) red-yellow with brown mottling
Project X REPORT
Corrosion Engineering
Corrosion Control – Soil, Water, Metallurgy Testing Lab 29990 Technology Dr., Suite 13, Murrieta, CA 92563 Tel: 213-928-7213 Fax: 951-226-1720 www.projectxcorrosion.com
21-2085
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
B-3: SANDY SILT (SM) yellowB-4: GRAVEL with SANDand CLAY (GW), brown
ROCKRIDGEGEOTECHNICAL
SOIL CORROSIVITY
TEST RESULTS
S230728A
Method ASTM
G51
ASTM
G200
SM
4500-D
ASTM D4327
ASTM D6919
ASTM D6919
ASTM D6919
ASTM D6919
ASTM D6919
ASTM D6919
ASTM D4327
ASTM D4327
Bore# /
Description
Depth pH Redox Sulfide
S2-
Nitrate
NO3-
Ammonium
NH4+
Lithium
Li+
Sodium
Na+
Potassium
K+
Magnesium
Mg2+
Calcium
Ca2+
Fluoride
F2--
Phosphate
PO43-
(ft) (mg/kg) (wt%) (mg/kg) (wt%) (Ohm-cm) (Ohm-cm) (mV) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) (mg/kg) B-8 Sample #4 6.0 61.9 0.0062 100.3 0.0100 20,100 1,876 7.8 141 10.8 0.1 11.5 ND 145.5 7.4 94.6 187.7 6.4 98.1 ASTM
G187
ASTM D4327
ASTM D4327
Resistivity
As Rec'd | Minimum
Sulfates
SO42-
Chlorides
ClCations and Anions, except Sulfide and Bicarbonate, tested with Ion Chromatography mg/kg = milligrams per kilogram (parts per million) of dry soil weight ND = 0 = Not Detected | NT = Not Tested | Unk = Unknown Chemical Analysis performed on 1:3 Soil-To-Water extract PPM = mg/kg (soil) = mg/L (Liquid)
Note: Sometimes a bad sulfate hit is a contaminated spot. Typical fertilizers are Potassium chloride, ammonium sulfate or ammonium sulfate nitrate (ASN). So this is another reason why testing full corrosion series is good because we then have the data to see if those other ingredients are present meaning the soil sample is just fertilizer-contaminated soil. This can happen often when the soil samples collected are simply surface scoops which is why it's best to dig in a foot, throw away the top and test the deeper stuff. Dairy farms are also notorious for these items.
Date 08/28/23 Project No. Figure B-3b
Project X REPORT
Corrosion Engineering
Corrosion Control – Soil, Water, Metallurgy Testing Lab 29990 Technology Dr., Suite 13, Murrieta, CA 92563 Tel: 213-928-7213 Fax: 951-226-1720 www.projectxcorrosion.com
21-2085
RAILROAD RESIDENCE DEVELOPMENT
South San Francisco, California
ROCKRIDGEGEOTECHNICAL
SOIL CORROSIVITY
TEST RESULTS