DRAFT. Proposed 303 Baldwin Avenue Retail, Office, and Residential Building Prelim

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1 Type of Services Project Name Location Client Geotechnical Preliminary Investigation Proposed 303 Baldwin Avenue Retail, Office, and Residential Building Prelim 303 Baldwin Avenue San Mateo, California Prometheus Real Estate Group Client Address 1900 S. Norfolk Street, Suite 150 San Mateo, CA Project Number Date December 15, 2016 DRAFT Prepared by Maura F. Ruffatto, P.E. Project Engineer Geotechnical Project Manager Scott E. Fitinghoff, P.E., G.E. Principal Engineer Quality Assurance Reviewer

2 TABLE OF CONTENTS SECTION 1: INTRODUCTION Project Description Scope of Services Exploration Program Laboratory Testing Program Environmental Services SECTION 2: REGIONAL SETTING Geological Setting Regional Seismicity Table 1: Approximate Fault Distances... 3 SECTION 3: SITE CONDITIONS Surface Description Subsurface Conditions Plasticity/Expansion Potential In-Situ Moisture Contents Ground Water CORROSION SCREENING Preliminary Soil Corrosion Screening... 6 SECTION 4: GEOLOGIC HAZARDS Fault Rupture Estimated Ground Shaking Liquefaction Potential Background Analysis Summary Ground Rupture Potential Lateral Spreading Page i

3 4.5 Seismic Settlement/Unsaturated Sand Shaking Tsunami/seiche Flooding SECTION 5: CONCLUSIONS Summary Potential Settlement of Compressible Clays below 25½ Feet Potential For Liquefaction-Induced Settlements Ground Improvement to Reduce Settlement Below Foundations Shallow Ground Water, Excavation, and Construction Below the Ground Water Table Hydro-static Uplift Pressures and Water Proofing for Buildings with Basements Below the Ground Water Table Differential Movement At On-grade to On-Structure Transitions Design-Level Geotechnical Investigation SECTION 6: EARTHWORK Anticipated Earthwork Measures Below-Grade Excavations Temporary Shoring...14 SECTION 7: FOUNDATIONS Summary of Recommendations Seismic Design Criteria Table 4: CBC Site Categorization and Site Coefficients Shallow Foundations Mat Foundations Mat Foundation Construction Considerations Mat Foundations With Ground Improvement Hydrostatic Uplift and Waterproofing SECTION 10: LIMITATIONS...19 SECTION 11: REFERENCES...20 FIGURE 1: VICINITY MAP FIGURE 2: SITE PLAN Page ii

4 FIGURE 3: REGIONAL FAULT MAP FIGURE 4A TO 4C: LIQUEFACTION ANALYSIS SUMMARY CPT-01 TO CPT-03 APPENDIX A: FIELD INVESTIGATION APPENDIX B: LABORATORY TEST PROGRAM Page iii

5 Type of Services Project Name Location Preliminary Geotechnical Investigation Proposed 303 Baldwin Avenue Retail, Office, and Residential Building 303 Baldwin Avenue San Mateo, California SECTION 1: INTRODUCTION This geotechnical feasibility evaluation was prepared for the sole use of Prometheus Real Estate Group for the proposed 303 Baldwin Avenue Retail, Office, and Residential Building project in San Mateo, California. The location of the site is shown on the Vicinity Map, Figure 1. The purpose of this study was to evaluate the existing subsurface conditions and develop an opinion regarding potential geotechnical concerns that could impact the proposed development. The preliminary geotechnical recommendations contained in this report are for your forward planning, cost estimating, and preliminary project design. 1.1 PROJECT DESCRIPTION We understand that a three- to five-story retail/office/residential building with a two- to threelevel below-grade garage is planned for the site. We understand the planned development will be of concrete-framed construction for the below-grade parking and at-grade podium and wood and steel frame construction for the portion of the structure above grade. Appurtenant parking, utilities, landscaping and other improvements necessary for site development are also planned. Structural loads are not known at this time; however, loads are anticipated to be typical for these types of structures. Grading for site development is anticipated to consist of excavation of 20 feet for two levels below-grade and cuts on the order of 25 feet for mat foundations, shoring, ramps drainage, and mat subgrade stabilization. Grading for site development is anticipated to consist of excavation of 30 feet for three levels below-grade and cuts on the order of 35 feet for mat foundations, shoring, ramps, drainage, and mat subgrade stabilization. 1.2 SCOPE OF SERVICES Our scope of services was presented in our proposal dated November 2, 2016 and consisted of field and laboratory programs to evaluate physical and engineering properties of the subsurface soils, engineering analysis to prepare recommendations for site work and grading, building Page 1

6 foundations, flatwork, retaining walls, and pavements, and preparation of this report. Brief descriptions of our exploration and laboratory programs are presented below. 1.3 EXPLORATION PROGRAM Field exploration consisted of one boring drilled on November 16, 2016 with truck-mounted, hollow-stem auger drilling equipment and three Cone Penetration Tests (CPT s) advanced on November 14, The boring was drilled to a depth of approximately 50 feet; the CPT s were advance to depths of approximately 52½ to 67 feet. Seismic shear wave velocity measurements were collected from CPT s-1 and 3. The boring (Boring EB-1) was advanced adjacent to CPT-2 for direct collection and evaluation of physical samples to correlated soil behavior. The borings and CPT s were backfilled with cement grout in accordance with local requirements; exploration permits were obtained as required by local jurisdictions. The approximate locations of our exploratory boring and CPT s are shown on the Site Plan, Figure 2. Details regarding our field program are included in Appendix A. 1.4 LABORATORY TESTING PROGRAM In addition to visual classification of samples, the laboratory program focused on obtaining data for foundation design and seismic ground deformation estimates. Testing included moisture contents, dry densities, washed sieve analyses, Plasticity Index tests, a consolidation test, and a suite of corrosion tests. Details regarding our laboratory program are included in Appendix B. 1.5 ENVIRONMENTAL SERVICES We understand that environmental services for the project are being provided by others. If environmental concerns are present, the environmental consultant should review our geotechnical recommendations for compatibility with the environmental concerns. SECTION 2: REGIONAL SETTING 2.1 GEOLOGICAL SETTING The San Francisco peninsula is a relatively narrow band of rock at the north end of the Santa Cruz Mountains separating the Pacific Ocean from San Francisco Bay. This represents one mountain range in a series of northwesterly-aligned mountains forming the Coast Ranges geomorphic province of California that stretches from the Oregon border nearly to Point Conception. In the San Francisco Bay area, most of the Coast Ranges have developed on a basement of tectonically mixed Cretaceous- and Jurassic-age (70- to 200-million years old) rocks of the Franciscan Complex. Locally these basement rocks are capped by younger sedimentary and volcanic rocks. Most of the Coast Ranges are covered by still younger surficial deposits that reflect geologic conditions of the last million years or so. Page 2

7 Movement on the many splays within the San Andreas Fault system has produced the dominant northwest-oriented structural and topographic trend seen throughout the Coast Ranges today. This trend reflects the boundary between two of the Earth s major tectonic plates: the North American plate to the east and the Pacific plate to the west. The San Andreas Fault system and its major branch faults are about 40 miles wide in the Bay area and extends from the San Gregorio Fault near the coastline to the Coast Ranges-Central Valley blind thrust at the western edge of the Great Central Valley as shown on the Regional Fault Map, Figure 3. The San Andreas Fault is the dominant structure in the system, nearly spanning the length of California, and capable of producing the highest magnitude earthquakes. Many other subparallel or branch faults within the San Andreas system are equally active and nearly as capable of generating large earthquakes. Right-lateral movement dominates on these faults but an increasingly large amount of thrust faulting resulting from compression across the system is no being identified also. 2.2 REGIONAL SEISMICITY The San Francisco Bay area region is one of the most seismically active areas in the Country. While seismologists cannot predict earthquake events, geologists from the U.S. Geological Survey have recently updated earlier estimates from their 2014 Uniform California Earthquake Rupture Forecast (Version 3) publication. The estimated probability of one or more magnitude 6.7 earthquakes (the size of the destructive 1994 Northridge earthquake) expected to occur somewhere in the San Francisco Bay Area has been revised (increased) to 72 percent for the period 2014 to 2043 (Aagaard et al., 2016). The faults in the region with the highest estimated probability of generating damaging earthquakes between 2014 and 2043 are the Hayward (33%), Rodgers Creek (33%), Calaveras (26%), and San Andreas Faults (22%). In this 30-year period, the probability of an earthquake of magnitude 6.7 or larger occurring is 22 percent along the San Andreas Fault and 33 percent for the Hayward or Rodgers Creek Faults. The faults considered capable of generating significant earthquakes are generally associated with the well-defined areas of crustal movement, which trend northwesterly. The table below presents the State-considered active faults within 25 kilometers of the site. Table 1: Approximate Fault Distances Fault Name Distance (miles) (kilometers) San Andreas (1906) San Gregorio Monte Vista-Shannon Hayward (Total Length) A regional fault map is presented as Figure 3, illustrating the relative distances of the site to significant fault zones. Page 3

8 SECTION 3: SITE CONDITIONS 3.1 SURFACE DESCRIPTION The project site is located at 303 Baldwin Avenue in San Mateo, California. The site is currently occupied by a one-story market building and surrounding asphalt concrete parking lot and landscaping areas. The site is bounded by residential and commercial development to the north, North B Street to the east, Baldwin Avenue to the south, and North Ellsworth Avenue to the west. Surface pavements at our exploration location generally consisted of one inch of asphalt concrete over 3 inches of aggregate base. Based on visual observations, the existing pavements are in fair to good condition with minor cracking observed. Based on our review of aerial photographs, geologic maps (Pampeyan, 1994), and experience on adjacent project, we understand that an underground culvert is present along the eastern corner of the site. Based on our review of available maps and photos, it appears the culvert runs along the northeast side parallel to B street and along the southeast side parallel to Baldwin Avenue. The culvert is a concrete box type with an open bottom positioned about 12 to 14 feet below the ground surface. 3.2 SUBSURFACE CONDITIONS Below the surface pavements, our exploratory borings (EB-1 and paired CPT-2) generally encountered very stiff lean clay with varying amounts of sand to a depth of approximately 17 feet. Beneath the lean clay, our boring encountered medium dense silty sand to a depth of 20 feet underlain by dense poorly graded sand with silt and gravel to a depth of approximately 25½ feet. Beneath the sand, our boring encountered medium stiff to stiff lean clay with sand to a depth of 30 feet underlain by medium dense clayey sand to a depth of 34½ feet. Beneath the medium dense clayey sand our boring encountered stiff to very stiff lean clay with varying amounts of sand to a depth of 42½ feet underlain by dense to very dense clayey sand to the maximum boring depth of 50 feet. Below the surface pavements, our CPTs encountered primarily clays with varying amounts of sands and silts with interbedded sand lenses to a depth of approximately 40 feet. Below a depth of approximately 40 feet our CPTs encountered primarily dense to very dense sands with clay and gravel and interbedded silt and clay lenses to the maximum depth explored of approximately 67 feet, or practical refusal Plasticity/Expansion Potential We performed two Plasticity Index (PI) tests on representative samples. Test results were used to evaluate expansion potential of surficial soils, and near the bottom of the proposed excavation. The results of the surficial PI tests indicated a PI of 13 at a depth of 2½ feet and a PI of 23 at a depth of 26 feet, indicating low to moderate expansion potential to wetting and Page 4

9 drying cycles. We anticipate the soils between 20 and 25 feet, and 30 and 35 feet will have low to moderate expansion potential In-Situ Moisture Contents Laboratory testing indicated that the in-situ moisture contents within the upper 25 feet are over the estimated laboratory moisture. The in-situ moisture content is estimated to be approximately 5 percent over in the upper 5 feet, approximately 8 percent over between 5 to 10 feet, approximately 8 percent over between 10 and 15 feet, approximately 6 percent over between 15 and 20 feet, approximately 2 to 7 percent over between 20 and 25 feet, approximately 10 to 15 percent over between 25 and 30, and approximately 20 percent over between 30 and 35 feet. 3.3 GROUND WATER Ground water was encountered in some of our explorations (Boring EB-1 and CPT-2) at depths of approximately 16 to 19 feet below current grades. All measurements were taken at the time of drilling and may not represent the stabilized levels that can be higher than the initial levels encountered. Based on our previous explorations in the area and ground water data reported on GeoTracker, we estimate stabilized levels of groundwater are estimated to be on the order of 14 to 15 feet below existing grade. We recommend a high ground water level of 12 feet be used for design to account for potential fluctuation in ground water levels. Fluctuations in ground water levels occur due to many factors including seasonal fluctuation, underground drainage patterns, regional fluctuations, and other factors. 3.4 CORROSION SCREENING We tested two samples collected at depths of 1½ to 5½ feet for resistivity, ph, soluble sulfates, and chlorides. The laboratory test results are summarized in Table 2. Table 2: Summary of Corrosion Test Results Sample/Test Location Number Depth (feet) Soil ph Minimum Resistivity (1) (ohm-cm) Chloride (mg/kg) Sulfate (% dry wt) EB-1 1½ 7.5 4, EB-1 5½ 7.3 1, Notes: (1) Laboratory resistivity measured at 100% saturation Many factors can affect the corrosion potential of soil including moisture content, resistivity, permeability, and ph, as well as chloride and sulfate concentration. Typically, soil resistivity, which is a measurement of how easily electrical current flows through a medium (soil and/or water), is the most influential factor. In addition to soil resistivity, chloride and sulfate ion concentrations, and ph also contribute in affecting corrosion potential. Page 5

10 3.4.1 Preliminary Soil Corrosion Screening Based on the laboratory test results summarized in Table 2, the soils are considered moderately to severely corrosive to buried metallic improvements (Palmer, 1989). Other corrosion parameters (ph and chloride content) do not indicate a significant contribution to corrosion potential to buried metallic structures. In accordance with the 2013 CBC, Chapter 19, Section 1904A.2, alternative cementitious materials for sulfate exposure shall be in accordance with the following: ACI Table 4.2.1, and Table Based on the laboratory test results, no cement type restriction is required, although, in our opinion, it is generally a good idea to include some sulfate resistance and to maintain a relatively low water-cement ratio. We have summarized applicable design values and parameters from ACI 318, Table below in Table 3 for your information. We recommend the structural engineer and a corrosion engineer be retained to confirm the information provided and for additional recommendations, as required. Table 3: Sulfate Soil Corrosion Design Values and Parameters (1) Category Water-Soluble Sulfate (SO4) in Soil (% by weight) Class Severity Cementitious Materials (2) S, Sulfate < 0.10 S0 not applicable no type restriction Notes: (1) above values and parameters are from on ACI , Table and Table (2) cementitious materials are in accordance with ASTM C150, ASTM C595 and ASTM C1157 SECTION 4: GEOLOGIC HAZARDS 4.1 FAULT RUPTURE As discussed above several significant faults are located within 25 kilometers of the site. The site is not located within a State-designated Alquist Priolo Earthquake Fault Zone. As shown in Figure 3, no known surface expression of fault traces is thought to cross the site; therefore, fault rupture hazard is not a significant geologic hazard at the site. 4.2 ESTIMATED GROUND SHAKING Moderate to severe (design-level) earthquakes can cause strong ground shaking, which is the case for most sites within the Bay Area. A peak ground acceleration (PGA) M was estimated for analysis using a value equal to F PGA x PGA, as allowed in the 2013 and soon to be adopted 2016 editions of the California Building Code. For our liquefaction analysis we used a PGA M of 0.763g. Page 6

11 4.3 LIQUEFACTION POTENTIAL The site is not currently mapped by the State of California, but is within a zone mapped as having a moderate to very high liquefaction potential by the Association of Bay Area Governments (ABAG, 2011). Our field and laboratory programs addressed this issue by sampling potentially liquefiable layers to depths of at least 50 feet, performing visual classification on sampled materials, evaluating CPT correlations, and performing various tests to further classify the soil properties Background During strong seismic shaking, cyclically induced stresses can cause increased pore pressures within the soil matrix that can result in liquefaction triggering, soil softening due to shear stress loss, potentially significant ground deformation due to settlement within sandy liquefiable layers as pore pressures dissipate, and/or flow failures in sloping ground or where open faces are present (lateral spreading) (NCEER 1998). Limited field and laboratory data is available regarding ground deformation due to settlement; however, in clean sand layers settlement on the order of 2 to 3 percent of the liquefied layer thickness can occur. Soils most susceptible to liquefaction are loose, non-cohesive soils that are saturated and are bedded with poor drainage, such as sand and silt layers bedded with a cohesive cap Analysis As discussed in the Subsurface section above, several sand layers were encountered below the design ground water depth of 12 feet. Following the procedures in the 2008 monograph, Soil Liquefaction During Earthquakes (Idriss and Boulanger, 2008) and in accordance with CDMG Special Publication 117A guidelines (CDMG, 2008) for quantitative analysis, these layers were analyzed for liquefaction triggering and potential post-liquefaction settlement. These methods compare the ratio of the estimated cyclic shaking (Cyclic Stress Ratio - CSR) to the soil s estimated resistance to cyclic shaking (Cyclic Resistance Ratio - CRR), providing a factor of safety against liquefaction triggering. Factors of safety less than or equal to 1.3 are considered to be potentially liquefiable and capable of post-liquefaction re-consolidation. The CSR for each layer quantifies the stresses anticipated to be generated due to a designlevel seismic event, is based on the peak horizontal acceleration generated at the ground surface discussed in the Estimated Ground Shaking section above, and is corrected for overburden and stress reduction factors as discussed in the procedure developed by Seed and Idriss (1971) and updated in the 2008 Idriss and Boulanger monograph. The soil s CRR is estimated from the in-situ measurements from CPT s and laboratory testing on samples retrieved from our borings. SPT N values obtained from hollow-stem auger borings were not used in our analyses, as the N values obtained are unreliable in sands below ground water. The tip pressures are corrected for effective overburden stresses, taking into consideration both the ground water level at the time of exploration and the design ground water level, and stress reduction versus depth factors. The CPT method utilizes the soil behavior type index (I C) to estimate the plasticity of the layers. Page 7

12 In estimating post-liquefaction settlement at the site, we have implemented a depth weighting factor proposed by Cetin (2009). Following evaluation of 49 high-quality, cyclically induced, ground settlement case histories from seven different earthquakes, Cetin proposed the use of a weighting factor based on the depth of layers. The weighting procedure was used to tune the surface observations at liquefaction sites to produce a better model fit with measured data. Aside from the better model fit it produced, the rationale behind the use of a depth weighting factor is based on the following: 1) upward seepage, triggering void ratio redistribution, and resulting in unfavorably higher void ratios for the shallower sublayers of soil layers; 2) reduced induced shear stresses and number of shear stress cycles transmitted to deeper soil layers due to initial liquefaction of surficial layers; and 3) possible arching effects due to nonliquefied soil layers. All these may significantly reduce the contribution of volumetric settlement of deeper soil layers to the overall ground surface settlement (Cetin, 2009). The results of our CPT analyses (CPT-1, CPT-2, and CPT-3) are presented on Figures 4A to 4C of this report Summary Our analyses indicate that several layers could potentially experience liquefaction triggering that could result in soil softening and post-liquefaction total settlement ranging from approximately ½ to 1½ inches based on the Ishihara and Yoshimine (1990) method. Total post-liquefaction settlement will be reduced to approximately ½ to 1 inch for the upper 20 feet removed for a twolevel below-grade basement. Total post-liquefaction settlement will be reduced to approximately ¼ to 1 inch for the upper 30 feet removed for a three-level below-grade basement. As discussed in SP 117A, differential movement for level ground sites over deep soil sites will be up to about two-thirds of the total settlement between independent foundation elements. In our opinion, differential settlements are anticipated to be on the order of 1 inch or less for at-grade, and ⅔-inch or less for two- to three-levels below-grade over a horizontal distance of 30 feet Ground Rupture Potential The methods used to estimate liquefaction settlements assume that there is a sufficient cap of non-liquefiable material to prevent ground rupture or sand boils. For ground rupture to occur, the pore water pressure within the liquefiable soil layer will need to be great enough to break through the overlying non-liquefiable layer, which could cause significant ground deformation and settlement. The work of Youd and Garris (1995) indicates that the 12-foot thick layer of non-liquefiable cap for at-grade construction is sufficient to prevent ground rupture. For belowgrade excavations, the non-liquefiable caps over the thin potentially liquefiable layers below the basement foundations are sufficient to prevent ground rupture; therefore the above total settlement estimates are reasonable. 4.4 LATERAL SPREADING Lateral spreading is horizontal/lateral ground movement of relatively flat-lying soil deposits towards a free face such as an excavation, channel, or open body of water; typically lateral Page 8

13 spreading is associated with liquefaction of one or more subsurface layers near the bottom of the exposed slope. As failure tends to propagate as block failures, it is difficult to analyze and estimate where the first tension crack will form. There are no open faces within a distance considered susceptible to lateral spreading; therefore, in our opinion, the potential for lateral spreading to affect the site is low. 4.5 SEISMIC SETTLEMENT/UNSATURATED SAND SHAKING Loose unsaturated sandy soils can settle during strong seismic shaking. Because the soils encountered at the site above the expected minimum basement cuts of 20 feet were predominantly stiff to very stiff clays and medium dense to dense sands, in our opinion, the potential for significant differential seismic settlement affecting the proposed improvements is low. 4.6 TSUNAMI/SEICHE The terms tsunami or seiche are described as ocean waves or similar waves usually created by undersea fault movement or by a coastal or submerged landslide. Tsunamis may be generated at great distance from shore (far field events) or nearby (near field events). Waves are formed, as the displaced water moves to regain equilibrium, and radiates across the open water, similar to ripples from a rock being thrown into a pond. When the waveform reaches the coastline, it quickly raises the water level, with water velocities as high as 15 to 20 knots. The water mass, as well as vessels, vehicles, or other objects in its path create tremendous forces as they impact coastal structures. Tsunamis have affected the coastline along the Pacific Northwest during historic times. The Fort Point tide gauge in San Francisco recorded approximately 21 tsunamis between 1854 and The 1964 Alaska earthquake generated a recorded wave height of 7.4 feet and drowned eleven people in Crescent City, California. For the case of a far-field event, the Bay area would have hours of warning; for a near field event, there may be only a few minutes of warning, if any. A tsunami or seiche originating in the Pacific Ocean would lose much of its energy passing through San Francisco Bay. Based on the study of tsunami inundation potential for the San Francisco Bay Area (Ritter and Dupre, 1972), areas most likely to be inundated are marshlands, tidal flats, and former bay margin lands that are now artificially filled, but are still at or below sea level, and are generally within 1½ miles of the shoreline. The site is approximately 1 mile inland from the San Francisco Bay shoreline, and is approximately 26 to 29 feet above mean sea level. Therefore, the potential for inundation due to tsunami or seiche is considered low. 4.7 FLOODING Based on our internet search of the Federal Emergency Management Agency (FEMA) flood map public database, the site is located within Zone X, an area determined to be outside the 2% Page 9

14 annual chance flood. We recommend the project civil engineer be retained to confirm this information and verify the base flood elevation, if appropriate. SECTION 5: CONCLUSIONS 5.1 SUMMARY From a geotechnical viewpoint, the project is feasible provided the concerns listed below are addressed in the project design and construction. The preliminary recommendations that follow are intended for conceptual planning and preliminary design. A design-level geotechnical investigation should be performed once site development plans are prepared indicating the depth and location of proposed structures. The design-level investigation findings will be used to confirm the preliminary recommendations and develop detailed geotechnical recommendations for design and construction. Descriptions of each geotechnical concern with brief outlines of our preliminary recommendations follow the listed concerns. Potential settlement of compressible clays below 25½ feet Potential for liquefaction-induced settlements Ground improvement to reduce settlement below foundations Shallow ground water, excavation, and construction below the ground water table Hydro-static uplift pressures for buildings with basements below the ground water table Differential movement at on-grade to on-structure transitions Potential Settlement of Compressible Clays below 25½ Feet As discussed in the Subsurface section, moderately compressible clays were encountered at a depth of approximately 25½ to 30 feet in our boring EB-1 and correlated with CPT-2. Depending on the foundation loads and bottom of mat foundation, their presence may require ground improvement to reduce total and differential settlement. For planning purposes, due to the presence of the high ground water table, potentially compressible clays, and anticipated static and seismic settlement, support of the structure on a mat foundation is recommended on a preliminary basis provided the estimated settlement is tolerable from a structural standpoint. Ground improvement beneath the mat foundation may be needed to mitigate potentially compressible soils and potentially liquefiable soils as discussed below. Alternatively, support of the structure on a deep foundation system consisting of auger cast piles or drilled piers or micro piles could be considered as an alternative to a mat foundation system to control settlement and uplift. Preliminary foundation recommendations are presented in the Foundations section of the report Potential For Liquefaction-Induced Settlements As discussed, our liquefaction analysis indicates that there is a potential for liquefaction of localized sand layers during a significant seismic event. Although the potential for liquefied sands to vent to the ground surface through cracks in the surficial soils is low, our analysis indicates that liquefaction-induced settlement at the ground surface on the order of ½ to 1½ inch Page 10

15 could occur, resulting in differential settlement up to 1-inch. Total post-liquefaction settlement will be reduced to approximately ½ to 1 inch for the upper 20 feet removed for a two-level below-grade basement and total post-liquefaction settlement will be reduced to approximately ¼ to 1 inch for the upper 30 feet removed for a three-level below-grade basement, resulting in differential settlement on the order of ⅔-inch over a horizontal distance of 30 feet. Foundations should be designed to tolerate the anticipated total and differential settlements. Preliminary foundation recommendations are presented in the Foundations section Ground Improvement to Reduce Settlement Below Foundations Based on the subsurface soil conditions encountered at the site and if the mat foundation cannot be designed tolerate the anticipated total and differential settlement, ground improvement may be used to reduce the estimated total and differential settlement due to static loading and liquefaction. The intent of the ground improvement design would be to increase the density of the loose to medium dense sands and reduce the compressibility of the clay soil by laterally displacing and/or densifying the existing in-place soils and reinforcing the clays. The degree to which the density is increased will depend on the improvement method and spacing. In addition to increasing the density, the methods listed above, could provide an additional increase in bearing capacity and soil stiffness at the individual improvement locations, which could be taken into consideration during evaluation of the post-construction settlement. Further details and recommendations are provided in the Foundations section below Shallow Ground Water, Excavation, and Construction Below the Ground Water Table Shallow ground water was measured at depths ranging from approximately 16 to 19 feet below the existing ground surface and high ground water in the area is estimated to be on the order of 12 feet. Our experience with similar sites in the vicinity indicates that shallow ground water could significantly impact grading and underground construction. Obviously, constructing a twoto three-level below grade basement needs to be designed to withstand hydrostatic pressure. In our experience, supporting the below-grade structure on a mat foundation designed to resist uplift hydrostatic pressures, static and seismic settlements appears to be feasible for the subsurface conditions encountered at the site provided the estimated settlement can be tolerated from a structural viewpoint. Depending on the weight of the structure providing resistance to uplift, drilled and post grouted anchors may need to be incorporated into the foundation to resist uplift. Further discussion of this issues is presented in the Foundations section of this report. Dewatering and shoring of the basement excavation will be required at the site during construction and should be anticipated. Carefully planned and implemented temporary dewatering should be anticipated for the construction of this project. Typically, permanent dewatering of the below grade basement is not desired due to potential construction complications such as settlement of adjacent structures and long term maintenance and costs of the site. Page 11

16 As the planned basement excavation will extend below the current ground water level, we anticipate the need for stabilization of the excavation bottom where construction activities are planned. Further details are provided in the Anticipated Earthworks section of this report. Based on the site conditions encountered during our investigation, the cuts may be supported by shoring with tie-backs, braced excavations, or potentially other methods such as soil mixed columns or cut-off walls with H-beams or auger assisted installed sheet piles. Because of the groundwater table depth, shoring combined with temporary dewatering may be needed to control the water inflow for some shoring systems. And some shoring methods such as the use of wooden lagging may be problematic for installation because of the water seepage and potential flowing sands and may not be feasible below the water table. Where excavations will extend more than about 10 feet, restrained shoring will most likely be required to limit detrimental lateral deflections and settlement behind the shoring. In addition to soil earth pressures, the shoring system will need to support adjacent loads such as construction vehicles and incidental loading, existing structure foundation loads, and street loading. Underpinning of the adjacent structures may be need depending on the proximity of the excavation to the property line. We recommend that the contractor implement a monitoring program to monitor the effects of the construction on nearby improvements, including the monitoring of cracking and vertical movement of adjacent structures, nearby streets, sidewalks, parking and other improvements. In critical areas, we recommend that inclinometers or other instrumentation be installed as part of the shoring system to closely monitor lateral movement. A discussion of the general shoring issues are provided in the Earthwork section of this report Hydro-static Uplift Pressures and Water Proofing for Buildings with Basements Below the Ground Water Table As previously discussed, it is our opinion that ground water could be encountered during construction at depths ranging from approximately 14 to 15 feet below current grades. However, for design purposes including hydrostatic uplift and waterproofing, we recommend a design depth to ground water to be 12 feet based on available data. Where portions of the mat foundation and related basement structures extend below the design ground water level, including bottoms of mat foundations, they should be water proofed and designed to resist potential hydrostatic uplift pressures. Further recommendations are provided in the Hydrostatic Uplift and Waterproofing section below Differential Movement At On-grade to On-Structure Transitions Proposed improvements, including the driveway into the below-grade basement levels, will transition from on-grade support to on-structure support. On-grade to on-structure transition areas may experience increased differential movement due to a variety of causes, including difficulty in achieving compaction of retaining wall backfill closest to the wall. We recommend consideration be given to where engineered fill is placed behind retaining walls extending to near finished grade, and that subslabs be included beneath flatwork or pavers that can Page 12

17 cantilever at least 3 feet beyond the wall. If surface improvements are included that are highly sensitive to differential movement, additional measures may be necessary. 5.2 DESIGN-LEVEL GEOTECHNICAL INVESTIGATION The preliminary recommendations contained in this feasibility study were based on limited site development information and limited exploration. As site conditions may vary significantly between the small-diameter boring and CPT s performed during this investigation, and more detailed design information will become available as development plans are finalized, we also recommend that we be retained to 1) perform a design-level geotechnical investigation, once detailed site development plans are available; 2) to review the geotechnical aspects of the project structural, civil, and landscape plans and specifications, allowing sufficient time to provide the design team with any comments prior to issuing the plans for construction; and 3) be retained to provide geotechnical observation and testing during earthwork and foundation construction. SECTION 6: EARTHWORK 6.1 ANTICIPATED EARTHWORK MEASURES On a preliminary basis, we recommend that any existing foundations, slabs and/or abandoned underground utilities be removed entirely and the resulting excavations backfilled with engineered fill. As a two- to three-level below grade parking is currently planned for the site, we expect all undocumented fills will be removed during basement excavation and geotechnically they will not be an issue with this project. On-site soils below the paved surface layer appear to be suitable for use as fill at the site. As discussed in the Subsurface section in this report, the in-situ moisture contents are up to about 8 percent over the estimated laboratory optimum in the upper 25 feet of the soil profile. Additionally, the in-situ moisture contents increase to about 10 to 15 percent over the estimated laboratory optimum between 25 and 30 feet and up to about 20 percent over the estimated laboratory optimum between 30 and 25 feet. The contractor should anticipate drying the soils prior to reusing them as fill, and this includes the material from the basement excavation. In addition, repetitive construction loading may de-stabilize the soils which is why subgrade stabilization at the bottom of the basement excavation is recommended. Imported fill material for use as general fill should be predominantly granular with a Plasticity Index of 15 or less. All fill as well as scarified soils in those areas to receive fill or slabs-ongrade should be compacted to at least 90 percent relative compaction as determined by ASTM Test Designation D-1557, latest edition; and be at least 2 percent above optimum. Areas of fill placed behind basement or retaining walls where surface improvements are planned and/or where improvements will transition from on-grade support to overlying the basements should be compacted to 95 percent. The upper 6 inches of subgrade in pavement areas and all aggregate base materials should be compacted to at least 95 percent relative compaction (ASTM D-1557, latest edition). Utility trench backfill should be compacted to at least 95 percent relative compaction (ASTM D-1557, latest edition) by mechanical means only. Page 13

18 As the planned basement excavation will extend below the current ground water level, we recommend that the contractor plan for stabilization of the excavation bottom to provide a working platform upon which to construct the foundation. This may include excavating an additional 12 to 18 inches below subgrade, placing a layer of stabilization fabric (Mirafi 500X or approved equivalent) at the bottom, and backfilling with clean, crushed rock. The crushed rock should be consolidated in place with vibratory equipment. Rubber tired and heavy track equipment should not be allowed to operate on the exposed subgrade; the crushed rock should be stockpiled and pushed out over the stabilization fabric. Because of the water table, we anticipated that chemically treating the bottom with lime treatment may not be feasible due to the concern of additional water inflow during the time frame needed for the mixing, curing and compaction. We anticipate a significant amount of soil off haul will be required for this project. Off haul soils are anticipated to consist of primarily clays with interbedded sand layers that are above optimum moisture content. Analytical testing of soils will be required prior to off haul of soil. This should be anticipated in the budgeting for this project. Some poorly graded sands were encountered in our exploratory boring EB-1 around 20 to 25½ feet below the surface. Depending on the final depth of basement excavation, the sands may slough during excavation, trenching, and shoring. Deeper utility excavation trenches and basement excavations will need to be shored and/or dewatered. Surface water runoff should not be allowed to pond adjacent to building foundations, slabs-ongrade, or pavements. Hardscape surfaces adjacent to structures should slope at least 2 percent towards suitable discharge facilities; landscape areas adjacent to structures should slope at least 3 percent away from buildings. 6.2 BELOW-GRADE EXCAVATIONS Below-grade excavations on the order of 8 to 10 feet deep, if considered, may be constructed with temporary slopes in accordance with OSHA requirements if space allows. Alternatively, temporary shoring may support the planned cuts up to 35 feet. The choice of shoring method should be left to the contractor s judgment based on experience, economic considerations and adjacent improvements such as utilities, pavements, and foundation loads. Temporary shoring should support adjacent improvements without distress and should be the contractor s responsibility. A pre-condition survey including photographs and installation of monitoring points for existing site improvements should be included in the contractor s preliminary cost estimate Temporary Shoring Based on the site conditions encountered during our investigation, the cuts may be supported by shoring with tie-backs, braced excavations, or potentially other methods such as soil mixed columns or cut-off walls with H-beams or auger assisted installed sheet piles. Because of the groundwater table depth, shoring combined with temporary dewatering may be needed to control the water inflow for some shoring systems. And some shoring methods such as the use Page 14

19 of wooden lagging may be problematic for installation because of the water seepage and potential flowing sands and may not be feasible below the water table. Where excavations will extend more than about 10 feet, restrained shoring will most likely be required to limit detrimental lateral deflections and settlement behind the shoring. It is noted that the use of tiebacks will need to be coordinated with avoiding the existing culvert in the city right of way and the feasibility of installation of tie-backs outside of the property needs to be verified. In addition to soil earth pressures, the shoring system will need to support adjacent loads such as construction vehicles and incidental loading, existing structure foundation loads, and street loading. Underpinning of the adjacent buildings may be needed as part of the shoring plan for the project depending on the proximity of the basement excavation to the property line. We performed our borings with hollow-stem auger drilling equipment and as such were not able to evaluate the potential for caving soils, which can create difficult conditions during soldier beam, tie-back, or soil nail installation; caving soils can also be problematic during excavation and lagging placement. The contractor is responsible for evaluating excavation difficulties prior to construction. Where relatively clean sands were encountered during our exploration, pilot holes performed by the contractor may be desired to further evaluate these conditions prior to the finalization of the shoring budget. As previously mentioned, we recommend that a monitoring program be developed and implemented to evaluate the effects of the shoring on adjacent improvements. All sensitive improvements should be located and monitored for horizontal and vertical deflections and distress cracking based on a pre-construction survey. The above considerations are for the use of the design team during conceptual planning and preliminary design. Additional subsurface exploration and engineering analysis should be performed during the design-level geotechnical investigation to develop shoring design parameters, as needed. A California-licensed civil or structural engineer must design and be in responsible charge of the temporary shoring design. SECTION 7: FOUNDATIONS 7.1 SUMMARY OF RECOMMENDATIONS In our opinion and on a preliminary basis, due to proximity of ground water to the basement bottom, the proposed structures may be supported on a mat foundation or a mat foundation overlying ground improvement provided the estimated settlement is tolerable from a structural viewpoint. In our opinion, spread footings are not feasible because they are estimated to settle more than the structure can tolerate and the basement will be subject to hydrostatic uplift pressures. Hold-Down anchors may be necessary to resist hydrostatic uplift pressures. Deep foundations are also feasible but are judged to be more costly so we have not included recommendations in this report for them. This assumption should be verified by the construction estimators assisting the owner in providing preliminary costs for the project. Preliminary recommendations for mat foundations are discussed in the following sections. Page 15

20 Page 16

21 7.2 SEISMIC DESIGN CRITERIA The project structural design should be based on the 2016 California Building Code (CBC), which provides criteria for the seismic design of buildings in Chapter 16. The Seismic Coefficients used to design buildings are established based on a series of tables and figures addressing different site factors, including the soil profile in the upper 100 feet below grade and mapped spectral acceleration parameters based on distance to the controlling seismic source/fault system. Shear wave velocity measurements performed at CPT-1 and CPT-3 to depths of approximately 52½ and 64 feet, respectively, resulted in an average shear wave velocity of 1024 and 899 feet per second (or 312 and 274 meters per second), respectively. Therefore, we have classified the site as Soil Classification D. The mapped spectral acceleration parameters S S and S 1 were calculated using the USGS computer program Design Maps, located at based on the site coordinates presented below and the site classification, which appear to be valid for the 2016 CBC. The table below lists the various factors used to determine the seismic coefficients and other parameters. Table 4: CBC Site Categorization and Site Coefficients Classification/Coefficient Design Value Site Class D Site Latitude Site Longitude second Period Mapped Spectral Acceleration 1, SS 1.941g 1-second Period Mapped Spectral Acceleration 1, S g Short-Period Site Coefficient Fa 1.0 Long-Period Site Coefficient Fv second Period, Maximum Considered Earthquake Spectral Response Acceleration Adjusted for Site Effects - SMS 1.941g 1-second Period, Maximum Considered Earthquake Spectral Response Acceleration Adjusted for Site Effects SM g 0.2-second Period, Design Earthquake Spectral Response Acceleration SDS 1.294g 1-second Period, Design Earthquake Spectral Response Acceleration SD g 1 For Site Class B, 5 percent damped. 7.3 SHALLOW FOUNDATIONS Based on our preliminary investigation, soils between a depth of approximately 20 and 32 feet vary significantly across the site from compressible medium stiff clays to liquefiable sands. On a preliminary basis, and until a design level investigation can be performed, we have provided two mat foundation options we believe may be feasible for planning and design purposes. Page 17

22 7.3.1 Mat Foundations On a preliminary basis, the proposed residential and commercial structure can potentially be supported on a conventionally reinforced concrete mat foundation. Mats should be designed in accordance with the 2016 California Building Code. As discussed, building loads are not yet known; however, we assumed average preliminary mat contact pressures ranging from 650 to 850 pounds per square foot for a 3 to 5 story building with two levels of below grade parking, and 800 to 1,000 pounds per square foot for a 3 to 5 story building with three levels of below-grade parking. To reduce potential differential movement, on a preliminary basis, mats can likely be designed for a maximum average aerial bearing pressure on the order of 1,000 to 1,200 pounds per square foot (psf) for dead plus live loads; at column or wall loading, the maximum localized allowable bearing pressure should be limited to about 2,000 psf. When evaluating wind and seismic conditions, allowable bearing pressures may be increased by one-third. On a preliminary basis, we estimate that the total static mat foundation post-construction settlement will be on the order of ¾-inch for a below grade mat at a depth of 25 feet below current site grades and on the order of ⅔-inch for a below grade mat at a depth of 35 feet. In addition, estimated seismic differential settlement will be on the order of ⅔-inch or less between across a horizontal distance of 30 feet for both a two- and three-level below grade basement. Therefore, the mat would need to be designed to tolerate total differential settlement up to 1¼ inches between center and edge of mat for a two-level below grade basement and approximately 1-inch of total differential settlement between center and edge of mat for a threelevel below grade basement. Detailed settlement analysis should be performed during the design-level geotechnical investigation to confirm these settlement estimates. Alternatively, recommendations for deep foundations can be provided in the design-level investigation if the estimated settlement is not tolerable from a structural viewpoint for mat foundations. We have not provided recommendations for PT mats because we anticipate that there will not be enough room for post tensioning in the basement excavation Mat Foundation Construction Considerations The mat foundation will be constructed near or below the current ground water level and even if temporary dewatering is included, the soil above the water table will be at near saturated conditions. Subgrade stabilization may be required as discussed in the Earthwork section above Mat Foundations With Ground Improvement Based on the subsurface soil conditions encountered at the site and if the mat foundation cannot be designed tolerate the anticipated differential settlement, ground improvement may be used to reduce the estimated differential settlement due to static and seismic loading to less than 1 inch. The design allowable bearing pressures will be dependent on the final ground Page 18

23 improvement details including the stiffness and spacing of ground improvement elements; however, substantial improvement in bearing capacity would be expected. As discussed above, a mat foundation may be used in combination with ground improvement to reduce the total and differential settlements (seismic and static). Ground improvement, such as impact piers, stone columns, drilled displacement columns, or other similar methods, could be used to improve the subsurface soils such that the combined static and seismic differential settlements are reduced to less than 1 inches, enabling the structure to be supported on a mat foundation, in our opinion. 7.4 HYDROSTATIC UPLIFT AND WATERPROOFING As previously discussed, it is our opinion that ground water could be encountered during construction at depths ranging from approximately 14 to 15 feet below current grades. However, for design purposes including hydrostatic uplift and waterproofing, we recommend a design depth to ground water to be 12 feet based on available data. Where portions of the mat foundation and related basement structures extend below the design ground water level, including bottoms of mat foundations, they should be designed to resist potential hydrostatic uplift pressures by constructing a thicker concrete mat foundation, installing ground anchors, or other methods. Basement walls and the bottom of the mat foundation extending below design ground water should be waterproofed and designed to resist hydrostatic pressure for the full wall height below the design ground water depth. Where portions of the basement walls extend above the design ground water level, a drainage system may be added. It may be necessary to construct a Rat Slab on the stabilized bottom of the basement excavation as part of the water proofing system. In addition, the portions of the structures extending below design ground water should be waterproofed to limit moisture infiltration, including mat foundation/thickened slab areas, all construction joints, and any retaining walls. We recommend that a waterproofing specialist design the waterproofing system. SECTION 10: LIMITATIONS This report, an instrument of professional service, has been prepared for the sole use of Prometheus Real Estate Group specifically to support the design of the 303 Baldwin Avenue Retail, Office, and Residential Building Prelim project in San Mateo, California. The opinions, conclusions, and preliminary recommendations presented in this report have been formulated in accordance with accepted geotechnical engineering practices that exist in Northern California at the time this report was prepared. No warranty, expressed or implied, is made or should be inferred. Preliminary recommendations in this report are based upon the soil and ground water conditions encountered during our limited subsurface exploration. Preparation of a design-level investigation is anticipated to provide additional information and refine the preliminary recommendations presented herein. If variations or unsuitable conditions are encountered Page 19

24 during the construction phase, Cornerstone must be contacted to provide supplemental recommendations, as needed. Prometheus Real Estate Group may have provided Cornerstone with plans, reports and other documents prepared by others. Prometheus Real Estate Group understands that Cornerstone reviewed and relied on the information presented in these documents and cannot be responsible for their accuracy. Cornerstone prepared this report with the understanding that it is the responsibility of the owner or his representatives to see that the recommendations contained in this report are presented to other members of the design team and incorporated into the project plans and specifications, and that appropriate actions are taken to implement the geotechnical recommendations during construction. Conclusions and recommendations presented in this report are valid as of the present time for the development as currently planned. Changes in the condition of the property or adjacent properties may occur with the passage of time, whether by natural processes or the acts of other persons. In addition, changes in applicable or appropriate standards may occur through legislation or the broadening of knowledge. Therefore, the conclusions and recommendations presented in this report may be invalidated, wholly or in part, by changes beyond Cornerstone s control. This report should be reviewed by Cornerstone after a period of three (3) years has elapsed from the date of this report. In addition, if the current project design is changed, then Cornerstone must review the proposed changes and provide supplemental recommendations, as needed. An electronic transmission of this report may also have been issued. While Cornerstone has taken precautions to produce a complete and secure electronic transmission, please check the electronic transmission against the hard copy version for conformity. Recommendations provided in this report are based on the assumption that Cornerstone will be retained to provide observation and testing services during construction to confirm that conditions are similar to that assumed for design, and to form an opinion as to whether the work has been performed in accordance with the project plans and specifications. If we are not retained for these services, Cornerstone cannot assume any responsibility for any potential claims that may arise during or after construction as a result of misuse or misinterpretation of Cornerstone s report by others. Furthermore, Cornerstone will cease to be the Geotechnical- Engineer-of-Record if we are not retained for these services. SECTION 11: REFERENCES Aargard, B.T., Blair, J.L., Boatwright, J., Garcia, S.H., Harris, R.A., Michael, A.J., Schwartz, D.P., and DiLeo, J.S., 2016, Earthquake outlook for the San Francisco Bay Region (ver. 1.1, August 2016): U.S. Geological Survey Fact Sheet , 6 p., Page 20

25 Association of Bay Area Governments (ABAG), 2011, Interactive Liquefaction Hazard Map: Boulanger, R.W. and Idriss, I.M., 2004, Evaluating the Potential for Liquefaction or Cyclic Failure of Silts and Clays, Department of Civil & Environmental Engineering, College of Engineering, University of California at Davis. Brabb, E.E. and J.A. Olson, 1986, Map Showing Faults and Earthquake Epicenters in San Mateo County, California: U.S. Geological Survey Map I-1257-F. California Building Code, 2016, Structural Engineering Design Provisions, Vol. 2. California Department of Conservation Division of Mines and Geology, 1998, Maps of Known Active Fault Near-Source Zones in California and Adjacent Portions of Nevada, International Conference of Building Officials, February, California Division of Mines and Geology, 1974, Special Studies Zones, San Mateo Quadrangle. California Division of Mines and Geology (2008), Guidelines for Evaluating and Mitigating Seismic Hazards in California, Special Publication 117A, September. Cetin, K.O., Bilge, H.T., Wu, J., Kammerer, A.M., and Seed, R.B., Probablilistic Model for the Assessment of Cyclically Induced Reconsolidation (Volumetric) Settlements, ASCE Journal of Geotechnical and Geoenvironmental Engineering, Vo. 135, No. 3, March 1, Federal Emergency Management Administration (FEMA), 2015, FIRM City of San Mateo, California, Community Panel # F. Idriss, I.M., and Boulanger, R.W., 2008, Soil Liquefaction During Earthquakes, Earthquake Engineering Research Institute, Oakland, CA, 237 p. Ishihara, K., 1985, Stability of Natural Deposits During Earthquakes: Proceedings Eleventh International Conference on Soil Mechanics and Foundation Engineering, San Francisco. Ishihara, K. and Yoshimine, M., 1992, Evaluation of Settlements in Sand Deposits Following Liquefaction During Earthquakes, Soils and Foundations, 32 (1): Lew, M. et al, 2010, Seismic Earth Pressures on Deep Building Basements, Proceedings, SEAOC Convention, Indian Wells, CA. Pampeyan, E.H., 1994, Geologic map of the Montara Mountain and San Mateo 7.5-minute quadrangles, San Mateo County, California: U.S. Geological Survey Miscellaneous Investigation Series Map I-2390, scale 1:24,000. Portland Cement Association, 1984, Thickness Design for Concrete Highway and Street Pavements: report. Page 21

26 Schwartz, D.P. 1994, New Knowledge of Northern California Earthquake Potential: in Proceedings of Seminar on New Developments in Earthquake Ground Motion Estimation and Implications for Engineering Design Practice, Applied Technology Council Seed, H.B. and I.M. Idriss, 1971, A Simplified Procedure for Evaluation soil Liquefaction Potential: JSMFC, ASCE, Vol. 97, No. SM 9, pp Seed, H.B. and I.M. Idriss, 1982, Ground Motions and Soil Liquefaction During Earthquakes: Earthquake Engineering Research Institute. Seed, Raymond B., Cetin, K.O., Moss, R.E.S., Kammerer, Ann Marie, Wu, J., Pestana, J.M., Riemer, M.F., Sancio, R.B., Bray, Jonathan D., Kayen, Robert E., and Faris, A., 2003, Recent Advances in Soil Liquefaction Engineering: A Unified and Consistent Framework., University of California, Earthquake Engineering Research Center Report Southern California Earthquake Center (SCEC), 1999, Recommended Procedures for Implementation of DMG Special Publication 117, Guidelines for Analyzing and Mitigating Liquefaction Hazards in California, March. State of California Department of Transportation, 2015, Highway Design Manual, December 31, Tokimatsu, K., and Seed, H. Bolton, 1987, Evaluation of Settlements in Sands due to Earthquake Shaking, ASCE Journal of Geotechnical Engineering, Vol. 113, August 1987, pp United States Geological Survey, 2014, U.S. Seismic Design Maps, revision date June 23, available at Working Group on California Earthquake Probabilities, 2015, The Third Uniform Earthquake Rupture Forecast, Version 3 (UCERF), U.S. Geologic Survey Open File Report OF , scale 1: Youd, T.L. and C.T. Garris, 1995, Liquefaction-Induced Ground-Surface Disruption: Journal of Geotechnical Engineering, Vol. 121, No. 11, pp Youd, T.L. and Idriss, I.M., et al, 1997, Proceedings of the NCEER Workshop on Evaluation of Liquefaction Resistance of Soils: National Center for Earthquake Engineering Research, Technical Report NCEER , January 5, 6, Youd et al., 2001, Liquefaction Resistance of Soils: Summary Report from the 1996 NCEER and 1998 NCEER/NSF Workshops on Evaluation of Liquefaction Resistance of Soils, ASCE Journal of Geotechnical and Geoenvironmental Engineering, Vo. 127, No. 10, October, Page 22

27 SITE N Vicinity Map 303 Baldwin Avenue Retail, Office, and Residential Buildings San Mateo, CA Project Number Figure Number Figure 1 Date Drawn By November 2016 RRN

28 Transit Center Way North B Street CPT-3 Approximate Site Boundary CPT-1 EB-1 Baldwin Avenue CPT-2 N North Ellsworth Avenue Legend Approximate location of exploratory boring (EB) Approximate location of cone penetration test (CPT) Base by Google Earth, dated 4/5/2016 Site Plan 303 Baldwin Avenue Retail, Office, and Residential Buildings San Mateo, CA APPROXIMATE SCALE (FEET) Project Number Figure Number Figure 2 Date Drawn By November 2016 RRN

29 Project Number RRN SITE Regional Fault Map Figure Number Figure 3 Date Drawn By November Baldwin Avenue Retail, Office, and Residential Buildings San Mateo, CA N Base by California Geological Survey Fault Activity Map of California (Jennings and Bryant, 2010) APPROXIMATE SCALE (MILES)

30 FIGURE 4A CPT NO Cornerstone Earth Group, Inc. PROJECT/CPT DATA CPT ANALYSIS RESULTS Project Title 303 Baldwin Avenue Prelim DRY SAND SETTLEMENT FROM 12 FEET Project No (Inches) Project Manager MJS/MFR LIQUEFACTION SETTLEMENT FROM 50 FEET 1.45 (Inches) SEISMIC PARAMETERS Controlling Fault Earthquake Magnitude (Mw) 7.9 San Andreas TOTAL SEISMIC SETTLEMENT 1.6 INCHES PGA (Amax) (g) POTENTIAL LATERAL DISPLACEMENT SITE SPECIFIC PARAMETERS LDI L/H 38.6 Ground Water Depth at Time of Drilling (feet) 16 LDI 1 Corrected for Distance 0.44 (4 < L/H < 40) Design Water Depth (feet) 12 EXPECTED RANGE OF DISPLACEMENT Ave. Unit Weight Above GW (pcf) to 0.9 feet Ave. Unit Weight Below GW (pcf) Not Valid for L/H Values < 4 and > LDI Values Only Summed to 2H Below Grade. qcn CSR CRR Factor of Safety Cumulative (Liquefaction) Settlement No Liquefaction Depth (feet) 25 Depth (feet) 25 Depth (feet) 25 Depth (feet)

31 FIGURE 4B CPT NO Cornerstone Earth Group, Inc. PROJECT/CPT DATA CPT ANALYSIS RESULTS Project Title 303 Baldwin Avenue Prelim DRY SAND SETTLEMENT FROM 12 FEET Project No (Inches) Project Manager MJS/MFR LIQUEFACTION SETTLEMENT FROM 50 FEET 1.08 (Inches) SEISMIC PARAMETERS Controlling Fault Earthquake Magnitude (Mw) 7.9 San Andreas TOTAL SEISMIC SETTLEMENT 1.1 INCHES PGA (Amax) (g) POTENTIAL LATERAL DISPLACEMENT SITE SPECIFIC PARAMETERS LDI L/H 80.0 Ground Water Depth at Time of Drilling (feet) 16 LDI 1 Corrected for Distance 0.00 (4 < L/H < 40) Design Water Depth (feet) 12 EXPECTED RANGE OF DISPLACEMENT Ave. Unit Weight Above GW (pcf) to 0.0 feet Ave. Unit Weight Below GW (pcf) Not Valid for L/H Values < 4 and > LDI Values Only Summed to 2H Below Grade. qcn CSR CRR Factor of Safety Cumulative (Liquefaction) Settlement No Liquefaction Depth (feet) 25 Depth (feet) 25 Depth (feet) 25 Depth (feet)

32 FIGURE 4C CPT NO Cornerstone Earth Group, Inc. PROJECT/CPT DATA CPT ANALYSIS RESULTS Project Title 303 Baldwin Avenue Prelim DRY SAND SETTLEMENT FROM 12 FEET Project No (Inches) Project Manager MJS/MFR LIQUEFACTION SETTLEMENT FROM 50 FEET 0.54 (Inches) SEISMIC PARAMETERS Controlling Fault Earthquake Magnitude (Mw) 7.9 San Andreas TOTAL SEISMIC SETTLEMENT 0.5 INCHES PGA (Amax) (g) POTENTIAL LATERAL DISPLACEMENT SITE SPECIFIC PARAMETERS LDI L/H 25.0 Ground Water Depth at Time of Drilling (feet) 16 LDI 1 Corrected for Distance 0.03 (4 < L/H < 40) Design Water Depth (feet) 12 EXPECTED RANGE OF DISPLACEMENT Ave. Unit Weight Above GW (pcf) to 0.1 feet Ave. Unit Weight Below GW (pcf) Not Valid for L/H Values < 4 and > LDI Values Only Summed to 2H Below Grade. qcn CSR CRR Factor of Safety Cumulative (Liquefaction) Settlement No Liquefaction Depth (feet) 25 Depth (feet) 25 Depth (feet) 25 Depth (feet)

33 APPENDIX A: FIELD INVESTIGATION The field investigation consisted of a surface reconnaissance and a subsurface exploration program using truck-mounted, hollow-stem auger drilling equipment and 20-ton truck-mounted Cone Penetration Test equipment. One 8-inch-diameter exploratory borings were drilled on November 16, 2016 to a depth of approximately 50 feet. Three CPT soundings were also performed in accordance with ASTM D (revised, 2002) on November 14, 2016, to depths ranging from approximately 52½ to 67 feet. The approximate locations of exploratory borings and CPTs are shown on the Site Plan, Figure 2. The soils encountered were continuously logged in the field by our representative and described in accordance with the Unified Soil Classification System (ASTM D2488). Boring logs, as well as a key to the classification of the soil and bedrock, are included as part of this appendix. Boring and CPT locations were approximated using existing site boundaries, and other site features as references. Boring and CPT elevations were not determined. The locations of the borings and CPTs should be considered accurate only to the degree implied by the method used. Representative soil samples were obtained from the borings at selected depths. All samples were returned to our laboratory for evaluation and appropriate testing. The standard penetration resistance blow counts were obtained by dropping a 140-pound hammer through a 30-inch free fall. The 2-inch O.D. split-spoon sampler was driven 18 inches and the number of blows was recorded for each 6 inches of penetration (ASTM D1586). 2.5-inch I.D. samples were obtained using a Modified California Sampler driven into the soil with the 140-pound hammer previously described. Relatively undisturbed samples were also obtained with inch I.D. Shelby Tube sampler which were hydraulically pushed. Unless otherwise indicated, the blows per foot recorded on the boring log represent the accumulated number of blows required to drive the last 12 inches. The various samplers are denoted at the appropriate depth on the boring logs. The CPT involved advancing an instrumented cone-tipped probe into the ground while simultaneously recording the resistance at the cone tip (q c) and along the friction sleeve (f s) at approximately 5-centimeter intervals. Based on the tip resistance and tip to sleeve ratio (R f), the CPT classified the soil behavior type and estimated engineering properties of the soil, such as equivalent Standard Penetration Test (SPT) blow count, internal friction angle within sand layers, and undrained shear strength in silts and clays. A pressure transducer behind the tip of the CPT cone measured pore water pressure (u 2). Graphical logs of the CPT data is included as part of this appendix. Field tests included an evaluation of the unconfined compressive strength of the soil samples using a pocket penetrometer device. The results of these tests are presented on the individual boring logs at the appropriate sample depths. Attached boring and CPT logs and related information depict subsurface conditions at the locations indicated and on the date designated on the logs. Subsurface conditions at other locations may differ from conditions occurring at these boring and CPT locations. The passage of time may result in altered subsurface conditions due to environmental changes. In addition, Page A-1

34 any stratification lines on the logs represent the approximate boundary between soil types and the transition may be gradual. Page A-2

35 UNIFIED SOIL CLASSIFICATION (ASTM D ) MATERIAL TYPES CRITERIA FOR ASSIGNING SOIL GROUP NAMES GROUP SYMBOL SOIL GROUP NAMES & LEGEND COARSE-GRAINED SOILS >50% RETAINED ON NO. 200 SIEVE GRAVELS >50% OF COARSE FRACTION RETAINED ON NO 4. SIEVE SANDS >50% OF COARSE FRACTION PASSES ON NO 4. SIEVE CLEAN GRAVELS <5% FINES GRAVELS WITH FINES >12% FINES CLEAN SANDS <5% FINES SANDS AND FINES >12% FINES Cu>4 AND 1<Cc<3 Cu>4 AND 1>Cc>3 FINES CLASSIFY AS ML OR CL FINES CLASSIFY AS CL OR CH Cu>6 AND 1<Cc<3 Cu>6 AND 1>Cc>3 FINES CLASSIFY AS ML OR CL FINES CLASSIFY AS CL OR CH GW GP GM GC SW SP SM SC WELL-GRADED GRAVEL POORLY-GRADED GRAVEL SILTY GRAVEL CLAYEY GRAVEL WELL-GRADED SAND POORLY-GRADED SAND SILTY SAND CLAYEY SAND FINE-GRAINED SOILS >50% PASSES NO. 200 SIEVE SILTS AND CLAYS LIQUID LIMIT<50 SILTS AND CLAYS LIQUID LIMIT>50 INORGANIC ORGANIC INORGANIC ORGANIC PI>7 AND PLOTS>"A" LINE PI>4 AND PLOTS<"A" LINE LL (oven dried)/ll (not dried)<0.75 PI PLOTS >"A" LINE PI PLOTS <"A" LINE LL (oven dried)/ll (not dried)<0.75 CL ML OL CH MH OH LEAN CLAY SILT ORGANIC CLAY OR SILT FAT CLAY ELASTIC SILT ORGANIC CLAY OR SILT HIGHLY ORGANIC SOILS Poorly-Graded Sand with Clay Clayey Sand OTHER MATERIAL SYMBOLS Silt PRIMARILY ORGANIC MATTER, DARK IN COLOR, AND ORGANIC ODOR Sand SAMPLER TYPES SPT PT PEAT Modified California (2.5" I.D.) Shelby Tube No Recovery Sandy Silt Well Graded Gravelly Sand Rock Core Grab Sample PLASTICITY INDEX (%) Artificial/Undocumented Fill Gravelly Silt ADDITIONAL TESTS CA - CHEMICAL ANALYSIS (CORROSIVITY) PI - PLASTICITY INDEX Poorly-Graded Gravelly Sand Asphalt CD - CONSOLIDATED DRAINED TRIAXIAL SW SWELL TEST CN - CONSOLIDATION TC - CYCLIC TRIAXIAL Topsoil Boulders and Cobble CU - CONSOLIDATED UNDRAINED TRIAXIAL TV - TORVANE SHEAR DS - DIRECT SHEAR UC - UNCONFINED COMPRESSION Well-Graded Gravel PP - POCKET PENETROMETER (TSF) (1.5) - (WITH SHEAR STRENGTH with Clay (3.0) - (WITH SHEAR STRENGTH IN KSF) - IN KSF) Well-Graded Gravel RV - R-VALUE UU UNCONSOLIDATED with Silt SA - SIEVE ANALYSIS: % PASSING - UNDRAINED TRIAXIAL #200 SIEVE PLASTICITY CHART - WATER LEVEL 80 PENETRATION RESISTANCE (RECORDED AS BLOWS / FOOT) 70 SAND & GRAVEL SILT & CLAY 60 CH 50 RELATIVE DENSITY BLOWS/FOOT* CONSISTENCY BLOWS/FOOT* STRENGTH** (KSF) VERY LOOSE 0-4 VERY SOFT LOOSE 4-10 SOFT MEDIUM DENSE MEDIUM STIFF DENSE STIFF CL OH & MH 20 VERY DENSE OVER 50 VERY STIFF HARD OVER 30 OVER * NUMBER OF BLOWS OF 140 LB HAMMER FALLING 30 INCHES TO DRIVE A 2 INCH O.D. CL-ML (1-3/8 INCH I.D.) SPLIT-BARREL SAMPLER THE LAST 12 INCHES OF AN 18-INCH DRIVE 0 (ASTM-1586 STANDARD PENETRATION TEST) ** UNDRAINED SHEAR 0 STRENGTH IN KIPS/SQ FT. AS DETERMINED BY LABORATORY LIQUID LIMIT (%) TESTING OR APPROXIMATED BY THE STANDARD PENETRATION TEST, POCKET PENETROMETER, TORVANE, OR VISUAL OBSERVATION. "A" LINE LEGEND TO SOIL DESCRIPTIONS Figure Number A-1

36 DRILLING CONTRACTOR DRILLING METHOD LOGGED BY NOTES DL Exploration Geoservices, Inc. Mobile B-61, 8 inch Hollow-Stem Auger PROJECT NAME DATE STARTED 11/16/16 DATE COMPLETED 11/16/16 GROUND ELEVATION BORING DEPTH 50 ft. LATITUDE GROUND WATER LEVELS: AT TIME OF DRILLING AT END OF DRILLING 303 Baldwin Avenue PROJECT NUMBER PROJECT LOCATION BORING NUMBER EB-1 PAGE 1 OF 2 San Mateo, CA 19 ft. 39 ft. LONGITUDE ELEVATION (ft) DEPTH (ft) 0 SYMBOL This log is a part of a report by Cornerstone Earth Group, and should not be used as a stand-alone document. This description applies only to the location of the exploration at the time of drilling. Subsurface conditions may differ at other locations and may change at this location with time. The description presented is a simplification of actual conditions encountered. Transitions between soil types may be gradual. DESCRIPTION 1 inch asphalt concrete over 3 inches aggregate base Sandy Lean Clay (CL) very stiff, moist, dark brown, fine to coarse sand, some fine subangular to subrounded gravel, low plasticity Liquid Limit = 31, Plastic Limit = 18 N-Value (uncorrected) blows per foot 28 SAMPLES TYPE AND NUMBER MC-1B DRY UNIT WEIGHT PCF 115 NATURAL MOISTURE CONTENT 18 PLASTICITY INDEX, % 13 PERCENT PASSING No. 200 SIEVE UNDRAINED SHEAR STRENGTH, ksf HAND PENETROMETER TORVANE UNCONFINED COMPRESSION UNCONSOLIDATED-UNDRAINED TRIAXIAL CORNERSTONE EARTH GROUP2 - CORNERSTONE 0812.GDT - 11/29/16 08:42 - P:\DRAFTING\GINT FILES\ 303 BALDWIN AVE.GPJ Lean Clay with Sand (CL) very stiff, moist, brown, fine to medium sand, moderate plasticity Sandy Lean Clay (CL) very stiff, moist, brown, fine to medium sand, low plasticity Silty Sand (SM) medium dense, moist to wet, brown, fine to coarse sand, some fine subangular to subrounded gravel Poorly Graded Sand with Silt and Gravel (SP-SM) dense, wet, gray brown, fine to coarse sand, fine to coarse subangular to subrounded gravel Continued Next Page MC MC-3B MC MC-5B SPT SPT-7 SPT

37 PROJECT NAME 303 Baldwin Avenue PROJECT NUMBER PROJECT LOCATION BORING NUMBER EB-1 PAGE 2 OF 2 San Mateo, CA ELEVATION (ft) DEPTH (ft) 25 SYMBOL This log is a part of a report by Cornerstone Earth Group, and should not be used as a stand-alone document. This description applies only to the location of the exploration at the time of drilling. Subsurface conditions may differ at other locations and may change at this location with time. The description presented is a simplification of actual conditions encountered. Transitions between soil types may be gradual. DESCRIPTION Lean Clay with Sand (CL) medium stiff to stiff, moist, brown, fine sand, moderate plasticity Liquid Limit = 40, Plastic Limit = 17 N-Value (uncorrected) blows per foot 15 SAMPLES TYPE AND NUMBER SPT-9B DRY UNIT WEIGHT PCF NATURAL MOISTURE CONTENT 28 PLASTICITY INDEX, % 23 PERCENT PASSING No. 200 SIEVE UNDRAINED SHEAR STRENGTH, ksf HAND PENETROMETER TORVANE UNCONFINED COMPRESSION UNCONSOLIDATED-UNDRAINED TRIAXIAL ST-10 consol 30 increasing sand content Clayey Sand (SC) medium dense, moist, brown, fine to coarse sand, some fine subrounded gravel 35 MC-11B becomes wet 11 SPT CORNERSTONE EARTH GROUP2 - CORNERSTONE 0812.GDT - 11/29/16 08:42 - P:\DRAFTING\GINT FILES\ 303 BALDWIN AVE.GPJ Sandy Lean Clay (CL) very stiff, moist, brown, fine to medium sand, some fine subangular to subrounded gravel, low plasticity Lean Clay with Sand (CL) stiff, moist, brown, fine to medium sand, moderate plasticity Clayey Sand (SC) dense to very dense, moist, brown, fine to coarse sand, some fine subangular to subrounded gravel Bottom of Boring at 50.0 feet " SPT-13 MC-14B MC-15B MC-16B

38 Cornerstone Earth Group Project 303 Baldwin Avenue Building Operator KK-RB Filename SDF(375).cpt Job Number P6803 Cone Number DDG1333 GPS Hole Number CPT-01 Date and Time 11/14/2016 6:44:41 AM Maximum Depth ft EST GW Depth During Test ft Net Area Ratio.8 DEPTH (ft) 0 CPT DATA TIP FRICTION Fs/Qt SPT N 0 TSF TSF 18 0 % SOIL BEHAVIOR TYPE sensitive fine grained 4 - silty clay to clay 7 - silty sand to sandy silt 10 - gravelly sand to sand 2 - organic material 5 - clayey silt to silty clay 8 - sand to silty sand 11 - very stiff fine grained (*) 3 - clay 6 - sandy silt to clayey silt 9 - sand 12 - sand to clayey sand (*) Cone Size 10cm squared *Soil Behavior behavior Referance type and SPT based on data from UBC-1983

39 Cornerstone Earth Group Project 303 Baldwin Avenue Building Operator KK-RB Filename SDF(376).cpt Job Number P6803 Cone Number DDG1333 GPS Hole Number CPT-02 Date and Time 11/14/2016 7:57:20 AM Maximum Depth ft EST GW Depth During Test ft Net Area Ratio.8 DEPTH (ft) 0 CPT DATA TIP FRICTION Fs/Qt SPT N 0 TSF TSF 18 0 % SOIL BEHAVIOR TYPE sensitive fine grained 4 - silty clay to clay 7 - silty sand to sandy silt 10 - gravelly sand to sand 2 - organic material 5 - clayey silt to silty clay 8 - sand to silty sand 11 - very stiff fine grained (*) 3 - clay 6 - sandy silt to clayey silt 9 - sand 12 - sand to clayey sand (*) Cone Size 10cm squared *Soil Behavior behavior Referance type and SPT based on data from UBC-1983

40 Cornerstone Earth Group Project 303 Baldwin Avenue Building Operator KK-RB Filename SDF(377).cpt Job Number P6803 Cone Number DDG1333 GPS Hole Number CPT-03 Date and Time 11/14/2016 9:31:28 AM Maximum Depth ft EST GW Depth During Test ft Net Area Ratio.8 DEPTH (ft) 0 CPT DATA TIP FRICTION Fs/Qt SPT N 0 TSF TSF 18 0 % SOIL BEHAVIOR TYPE sensitive fine grained 4 - silty clay to clay 7 - silty sand to sandy silt 10 - gravelly sand to sand 2 - organic material 5 - clayey silt to silty clay 8 - sand to silty sand 11 - very stiff fine grained (*) 3 - clay 6 - sandy silt to clayey silt 9 - sand 12 - sand to clayey sand (*) Cone Size 10cm squared *Soil Behavior behavior Referance type and SPT based on data from UBC-1983

41 APPENDIX B: LABORATORY TEST PROGRAM The laboratory testing program was performed to evaluate the physical and mechanical properties of the soils retrieved from the site to aid in verifying soil classification. Moisture Content: The natural water content was determined (ASTM D2216) on 12 samples of the materials recovered from the borings. These water contents are recorded on the boring logs at the appropriate sample depths. Dry Densities: In place dry density determinations (ASTM D2937) were performed on 7 samples to measure the unit weight of the subsurface soils. Results of these tests are shown on the boring logs at the appropriate sample depths. Washed Sieve Analyses: The percent soil fraction passing the No. 200 sieve (ASTM D1140) was determined on two samples of the subsurface soils to aid in the classification of these soils. Results of these tests are shown on the boring logs at the appropriate sample depths. Plasticity Index: Two Plasticity Index determinations (ASTM D4318) were performed on samples of the subsurface soils to measure the range of water contents over which this material exhibits plasticity. The Plasticity Index was used to classify the soil in accordance with the Unified Soil Classification System and to evaluate the soil expansion potential. Results of these tests are shown on the boring logs at the appropriate sample depths. Consolidation: One consolidation test (ASTM D2435) was performed on a relatively undisturbed sample of the subsurface clayey soils to assist in evaluating the compressibility property of this soil. Results of the consolidation test are presented graphically in this appendix. Soluble Sulfate: Two soluble sulfate determination (California Test Method No. 417-Modified) was performed on a sample of the subsurface soil to water soluble sulfate content. Results of this test are attached is this appendix. Page B-1

42 60 Plasticity Index ( ASTM D4318) Testing Summary 50 Plasticity Index (%) CL CH A line OH or MH 10 CL-ML OL or ML Liquid Limit (%) Symbol Boring No. Depth (ft) Natural Water Content (%) Liquid Limit (%) Plastic Limit (%) Plasticity Index Passing No. 200 (%) EB EB Group Name ( USCS - ASTM D2487) Sandy Lean Clay (CL) Lean Clay with Sand (CL) Plasticity Index Testing Summary 303 Baldwin Avenue Retail, Office, and Residential Buildings San Mateo, CA Project Number Figure Number Date November 2016 Figure B1 Drawn By FLL

43 Consolidation Test ASTM D2435 Job No.: Boring: EB-1 Run By: MD Client: Cornerstone Earth Group Sample: 10 Reduced: PJ Project: Depth, ft.: 27.0(Tip-4") Checked: PJ/DC Soil Type: Dark Olive Brown Sandy CLAY Date: 12/5/2016 Strain-Log-P Curve Strain, % Effective Stress, psf Assumed Gs 2.75 Initial Final Moisture %: Dry Density, pcf: Void Ratio: % Saturation: Remarks: