Geotechnical Report

LOS ANGELES • SAN JOSE • FRESNO • STOCKTON • BAKERSFIELD DALLAS • SEATTLE • DENVER GEOTECHNICAL ENGINEERING INVESTIGATION WITH GEOLOGIC-SEISMIC HAZARDS EVALUATION NEW CITY OF MENDOTA CITY HALL AND POLICE STATION RIO FRIO STREET AND 7TH STREET MENDOTA, CALIFORNIA SALEM PROJECT NO. 1-221-0888 OCTOBER 6, 2021 PREPARED FOR: RRM DESIGN GROUP 3765 S. HIGUERA, SUITE 102 SAN LUIS OBISPO, CA 93401 PREPARED BY: SALEM ENGINEERING GROUP, INC. 4729 W. JACQUELYN AVENUE FRESNO, CALIFORNIA 93722 P: (559) 271-9700 F: (559) 275-0827 www.salem.net G EO TE C H N IC A L ● E N VI R O N M EN TA L ● G EO LO G Y ● M A TE R IA LS T ES TI N G & IN SP EC TI O N ● F O R EN SI C ● L A B O R A TO R Y file://fsms022/FSSalem/02%20Geo/2019/Reports%20&%20Data/5-219%20San%20Jose/5_219_0364_7Eleven_Petroleum_Station_Two_Restaurants_Woodland/Report/5-219-0364.GEO 4729 W. Jacquelyn Avenue Fresno, CA 93722 Phone (559) 271-9700 Fax (559) 393-9710 LOS ANGELES

• SAN JOSE • FRESNO • STOCKTON • BAKERSFIELD DALLAS • SEATTLE • DENVER October 6, 2021 Project No. 1-221-0888 Mr. Charles Dellinger RRM Design Group Phone: (805) 543-1794 3765 S. Higuera Suite 102 Email: CADellinger@rrmdesign.com San Luis Obispo, California 93401 Subject: GEOTECHNICAL ENGINEERING INVESTIGATION WITH GEOLOGIC-SEISMIC HAZARDS EVALUATION NEW CITY OF MENDOTA CITY HALL AND POLICE STATION RIO FRIO STREET AND 7TH STREET MENDOTA, CALIFORNIA Dear Mr. Dellinger: With your request and authorization, SALEM Engineering Group, Inc. (SALEM) has prepared this Geotechnical Engineering Investigation report for the proposed City of Mendota City Hall and Police Station building to be located at Rio Frio Street and 7th Street in Mendota, California. The accompanying report presents our findings, conclusions, and recommendations regarding the geotechnical aspects of designing and constructing the project as presently proposed. In our opinion, the proposed project is feasible from a geotechnical standpoint, provided our recommendations are incorporated into the design and construction of the project. We appreciate the opportunity to assist you with this project. Should you have questions regarding this report or need additional information, please contact the undersigned at (559) 271-9700. Respectfully Submitted, SALEM ENGINEERING GROUP, INC. Ken Clark, CEG Dean B. Ledgerwood II, EIT, PG, CEG Senior Engineering Geologist Geotechnical Manager CEG, 1864 PG 8725 /CEG 2613 TABLE OF CONTENTS 1. PURPOSE AND SCOPE ..................................................................................................... 1 2. SITE DESCRIPTION .......................................................................................................... 1 3. HISTORIC SITE DEVELOPMENT AND PREVIOUS REPORTS ................................... 1 4. PROJECT DESCRIPTION .................................................................................................. 2 5. FIELD EXPLORATION ..................................................................................................... 2 5.1 Site Reconnaissance and Test Borings .................................................................................... 2 5.2 Percolation Testing ................................................................................................................. 3 6. LABORATORY TESTING ................................................................................................ 3 7. FINDINGS AND RESULTS ............................................................................................... 3 7.1 Subsurface Soil Conditions and Laboratory Test Results ........................................................ 3 7.2 Groundwater .......................................................................................................................... 4 7.3 Soil Corrosion Screening ........................................................................................................ 4 7.4 Results of Percolation Testing ................................................................................................ 5 8. GEOLOGIC AND SESIMIC HAZARD EVALUATIONS ................................................ 6 12. CONCLUSIONS AND RECOMMENDATIONS............................................................. 12 12.1 General Conclusions and Recommendations ........................................................................ 12 12.2 Surface Drainage .................................................................................................................. 13 12.3 Site Grading .......................................................................................................................... 14 12.4 Soil and Excavation Characteristics ...................................................................................... 17 12.5 Materials for Fill ................................................................................................................... 17 12.6 Foundations-General ............................................................................................................. 19 12.7. Structural Mat Foundations or Quasi-Rigid Structural Slabs............................................... 20 12.8 Shallow Foundations for Non-Habitable Ancillary Structures .............................................. 22 12.9 Cast in Drilled Hole Pier Foundations for Monument Signs ................................................. 23 12.10 Interior Floors ....................................................................................................................... 24 12.11 Exterior Concrete Slabs on Grade ......................................................................................... 25 12.12 Lateral Earth Pressures and Frictional Resistance ................................................................. 26 12.13 Retaining Walls .................................................................................................................... 26 12.14 Temporary Excavations ........................................................................................................ 27 12.15 Underground Utilities ........................................................................................................... 28 12.16 Pavement Design .................................................................................................................. 29 13. PLAN REVIEW, CONSTRUCTION OBSERVATION AND TESTING ........................ 31 13.1 Plan and Specification Review .............................................................................................. 31 13.2 Construction Observation and Testing Services .................................................................... 31 14. LIMITATIONS AND CHANGED CONDITIONS .......................................................... 31 TABLE OF CONTENTS (cont.) FIGURES Figure 1, Vicinity Map Figure 2, Site Plan Figure No.3, Regional Geologic Map Figure No. 4, Regional Fault Map Figure No. 5, Historical Seismicity Map Figure No. 6, Flood Zone Map Liquefaction/Seismic Settlement Analysis APPENDIX A – FIELD INVESTIGATION Figure A1 and A2, Logs of Test Borings B-1 through B-5 Percolation Test Log APPENDIX B – LABORATORY TESTING Gradation Curves Expansion Index Test Result Plasticity Index Test Result Consolidation Test Results Direct Shear Test Result Corrosivity Test Results R-Value Test Results APPENDIX C – EARTHWORK AND PAVEMENT SPECIFICATIONS 4729 W. Jacquelyn Avenue Fresno, CA 93722 Phone (559) 271-9700 Fax (559) 275-0827 Project No. 1-221-0888 - 1 - October 6, 2021 GEOTECHNICAL ENGINEERING INVESTIGATION WITH GEOLOGIC-SEISMIC HAZARDS EVALUATION NEW CITY OF MENDOTA CITY HALL AND POLICE STATION RIO FRIO STREET AND 7TH STREET MENDOTA, CALIFORNIA 1. PURPOSE AND SCOPE This report presents the results of our Geotechnical Engineering Investigation for the proposed City of Mendota City Hall and Police Station building to be located at Rio Frio Street and 7th Street in Mendota, California. The site location is depicted on Figure 1, Vicinity Map. The purpose of this geotechnical engineering investigation was to observe and sample the subsurface conditions encountered at the site, and provide conclusions and recommendations relative to the geotechnical aspects of designing and constructing the project as presently proposed. If project details vary significantly from those described herein, SALEM should be contacted to determine the necessity for review and possible revision of this report. The scope of our investigation included field exploration and soil sampling, laboratory testing, engineering evaluation, and preparation of this report. The conclusions and recommendations presented herein are based on analysis of the data obtained during the investigation and our local experience with similar soil and geologic conditions. 2. SITE DESCRIPTION The site coordinates are 36.75296 degrees north and -120.38265 degrees west. The site is bound by 7th Street to the northwest, Rio Frio Street to the southwest, residential properties to the southeast, an alley and retail and residential properties beyond to the northeast. A sidewalk was noted along the northwest side of the site and a tree was noted near the northernmost corner of the site. At the time of our field investigation, the site was undeveloped and appeared to be relatively flat with elevations of about 167 to 168 feet above mean sea level (AMSL). The surface of the site was mostly dirt with some scattered gravel. Very old and eroded asphaltic concrete pavement was noted in the northern portion of the site. 3. HISTORIC SITE DEVELOPMENT AND PREVIOUS REPORTS Historic aerial photographs of the site area, dated 1937, 1946, 1950, 1957, 1960, 1967, 1973, 1978, 1998, 2006, 2009, 2012, and 2016, were reviewed to assess historic site use. The historic aerial images do not indicate any site development, except a small building located in the north corner of the site. The building appears in the photographs dated 1950 through 2012, and is absent in the 2016 photograph. A street view image, available on-line and dated August 2015, shows a small, single-story brick building with an awning facing 7th Street, at the location of the building image on the historic aerial photographs. No documents pertaining to previous geologic or geotechnical studies were provided to SALEM for review at the time of this investigation. If previous geologic or geotechnical studies reports become available, SALEM should be provided these documents for review. Project No. 1-221-0888 - 2 - October 6, 2021 4. PROJECT DESCRIPTION Based on the Request for Proposal and site schematic drawing provided by RRM Design Group, we understand that the project will include the development of a two-story building. Based on review of the plan provided, the building will have a footprint plan view around 11,000 square feet. The proposed building is anticipated to include wood or steel framed construction with conventional shallow spread foundations, and concrete slab-on-grade. Maximum wall load and column loads are expected to be on the order of 3 to 6 kips per linear foot and about 80 kips, respectively. Maximum total and differential settlement shall be 1 inch and 1⁄2 inch, respectively. Appurtenant construction is anticipated to include asphaltic concrete and Portland cement concrete pavements, underground utilities, and isolated landscape areas. It is our understanding that underground storm water retention may be required under the proposed parking and driveway areas. A site grading plan was not available at the time of preparation of this proposal. As the existing project area is generally flat, we anticipate that cuts and fills during earthwork will be on the order of 1 to 3 feet to providing a level building pad and positive site drainage. The approximate locations of proposed improvements are shown on the Site Plan, Figure 2. 5. FIELD EXPLORATION 5.1 Site Reconnaissance and Test Borings Our field exploration consisted of site surface reconnaissance and subsurface exploration. The results of the site reconnaissance are included in Section 2 of this report. On September 10, 2021, a total of five (5) exploratory test borings (B-1 through B-5) were drilled within the proposed building pad and pavement areas using a truck-mounted CME-55 drill rig equipped with 6- 5/8 inch outside diameter hollow-stem auger and mud-rotary drilling equipment. The borings were drilled to depths ranging from about 5 to 511⁄2 feet below site grade (BSG). In addition, a percolation test (P-1) was conducted at the location of boring B-4. The approximate locations of the test borings and percolation test are shown on Figure No. 2, Site Plan. The materials encountered in the test borings were visually classified in the field, and logs were recorded by a field engineer at that time. Visual classification of the materials encountered in the test borings was generally made in accordance with the Unified Soil Classification System (ASTM D2487). The logs of the test borings and a Unified Soil Classification Chart and key to sampling are presented in Appendix A. Subsurface soil samples were obtained by driving a Modified California sampler (MCS) or a Standard Penetration Test (SPT) sampler. The boring logs include the soil type, color, moisture content, dry density, and the applicable Unified Soil Classification System symbol. The location of the test borings were determined by measuring from site features determined from information provided to us. Hence, accuracy can be implied only to the degree that this method warrants. The actual boundaries between different soil types may be gradual and soil conditions may vary. For a more detailed description of the materials encountered, the boring logs in Appendix A should be consulted. Penetration resistance blow counts were obtained by dropping a 140-pound automated trip hammer through a 30-inch free fall to drive the sampler to a maximum penetration of 18 inches. The number of Project No. 1-221-0888 - 3 - October 6, 2021 blows required to drive the last 12 inches, or less if very dense or hard, was recorded as Penetration Resistance (blows/foot) on the logs of borings. The drilling and soil sampling were performed in accordance with ASTM D1586 and D1587 under the direction of an Engineering Geologist. Soil samples were obtained from the test borings at the depths shown on the logs of borings. The MCS samples were recovered and capped at both ends to preserve the samples at their natural moisture content and SPT samples were recovered and placed in a sealed bag to preserve their natural moisture content. At the completion of drilling and sampling, the test borings were backfilled with soil cuttings, thus some settlement should be anticipated. 5.2 Percolation Testing It is our understanding that underground storm water retention may be required under the proposed parking and driveway areas. Percolation test hole P-1 was installed on September 10, 2021, to a depth of about 5.7 feet BSG in the east portion of the site, at the location shown on the Figure 2 (provided at the end of this report). The test hole was pre-saturated on September 15, 2021, the day before commencement of percolation testing. A hydraulic head of about 2 feet was used for the testing and depth to water readings were made at approximately 30 minute intervals. Water was added to the hole to re-establish the hydraulic head between each reading. The percolation test logs are included in Appendix A of this report. The results of the percolation testing are provided in Section 7.4 of this report. 6. LABORATORY TESTING Laboratory tests were performed on selected soil samples to evaluate their physical characteristics and engineering properties. The laboratory-testing program was formulated with emphasis on the evaluation of natural moisture, density, shear strength, consolidation, gradation, R-value, plasticity index, and expansion index of the materials encountered. In addition, chemical tests were performed to evaluate the corrosivity of the soils to buried concrete. Details of the laboratory test program and the results of laboratory test are summarized in Appendix B. This information, along with the field observations, were used to prepare the final boring logs in Appendix A of this report. 7. FINDINGS AND RESULTS 7.1 Subsurface Soil Conditions and Laboratory Test Results The subsurface conditions encountered appear typical of those found in the geologic region of the site. The near surface soils encountered were medium stiff to stiff and high plasticity sandy lean clays. Undocumented fill soils were encountered from the ground surface and extending to a depth of about 3 feet BSG in boring B-3 in the northernmost portion of the site. A loose to medium dense silty sands was encountered below the lean clays in borings B-1 and B-2. The silty sand extended to the maximum depth explored in boring B-1 at 161⁄2 feet BSG, and to a depth of about 26 feet in boring B-2. The silty sand was underlain by a fat clay extending from depths of about 26 to 30 feet BSG. The fat clay was underlain by a loose to medium dense poorly graded sand with silt extending to a depth of 45 feet BSG. The poorly graded sand with silt was underlain by medium stiff sandy lean clay extending to about 50 feet BSG, underlain by stiff fat clay extending to the maximum depth explored of 511⁄2 feet BSG. The near surface clayey soils appeared to be significantly under optimum moisture content. Project No. 1-221-0888 - 4 - October 6, 2021 The results of two (2) consolidation tests performed on samples obtained from depths of 2 to 31⁄2 feet BSG and 31⁄2 to 5 feet BSG indicated about 4.8 and 5.3 percent consolidation under a normal load of 16 kips per square foot, respectively. The samples from depths of 2 to 31⁄2 feet BSG and 31⁄2 to 5 feet BSG exhibited swell of about 0.7 percent and 0.1 percent, respectively, upon saturation at 0.5 kip per square foot normal load. The result of an expansion index test conducted on a bulk sample collected from depths of 0 to 31⁄2 feet BSG indicated an expansion index of 90 (high expansion potential). The result of an R-value test conducted on a bulk sample collected from depths of 0 to 31⁄2 feet BSG indicated an R-value of 13. Soil conditions described in the previous paragraphs are generalized. Therefore, the reader should consult exploratory test boring logs included in Appendix A for soil type, color, moisture, consistency, and USCS classification of the materials encountered at specific locations and elevations. 7.2 Groundwater Groundwater was encountered in test borings B-2, drilled on September 10, 2021, at a depth of 21 feet BSG. Available groundwater depth records with the Department of Water Resources (www.water.ca.gov./waterlibrary) indicates the closest three (3) wells to the subject site are located approximately 1⁄2 mile feet east and southeast of the project site. Data for these wells included several measurements for each well over the last approximately 20 years. This data indicate relatively consistent measurements corresponding to historic high groundwater depths of about 6 to 13 feet BSG. It should be recognized that water table elevations may fluctuate with time, being dependent upon seasonal precipitation, irrigation, land use, localized pumping, and climatic conditions as well as other factors. Therefore, water level observations at the time of the field investigation may vary from those encountered during the construction phase of the project. The evaluation of such factors is beyond the scope of this report. 7.3 Soil Corrosion Screening Excessive sulfate in either the soil or native water may result in an adverse reaction between the cement in concrete and the soil. The 2011 Edition of ACI 318 (ACI 318) has established criteria for evaluation of sulfate and chloride levels and how they relate to cement reactivity with soil and/or water. A soil sample was obtained from the project site and was tested for the evaluation of the potential for concrete deterioration or steel corrosion due to attack by soil-borne soluble salts and soluble chloride. The water-soluble sulfate concentration in the saturation extract from the soil sample was detected to be 1,433 mg/kg, which is considered moderate sulfate exposure. ACI 318 Tables 4.2.1 and 4.3.1 outline exposure categories, classes, and concrete requirements by exposure class. ACI 318 requirements for site concrete based upon soluble sulfate are summarized in Table 7.3 below. TABLE 7.3 WATER SOLUBLE SULFATE EXPOSURE REQUIREMENTS Boring and Sample Depth Dissolved Sulfate (SO4) in Soil % by Weight Exposure Severity Exposure Class Maximum w/cm Ratio Minimum Concrete Compressive Strength Cementitious Materials Type B-1 @ 0-3.5’ 0.1433 Moderate S1 0.50 4,000 psi Type II http://www.water.ca.gov./waterlibrary Project No. 1-221-0888 - 5 - October 6, 2021 The water-soluble chloride concentration detected in the saturation extract from the soil sample collected from boring B-1 at a depth of 0 to 31⁄2 feet BSG was 72 mg/kg. In addition, resistivity testing performed on the same sample resulted in a minimum resistivity value of 331 ohm-centimeter. Based on the results, these soils would be considered to have an “extremely corrosive” to corrosion potential to buried metal objects (per National Association of Corrosion Engineers, Corrosion Severity Ratings). It is recommended that a qualified corrosion engineer be consulted regarding protection of buried steel or ductile iron piping and conduit or, at a minimum, applicable manufacturer’s recommendations for corrosion protection of buried metal pipe be closely followed. Additional corrosion testing for minimum resistivity may need to be performed if required by the pipe manufacturer. 7.4 Results of Percolation Testing One (1) percolation test was performed on September 16, 2021, in test boring B-4 drilled to a depth of about 68 inches BSG. The percolation test was conducted in the upper soils identified as sandy lean clay. The percolation test hole construction is described in Section 5.2 and is detailed on the percolation test log in Appendix A of this report. The test hole was pre-saturated on the day before the percolation testing commenced. The following table includes a summary of the test results. TABLE 7.4 SUMMARY OF PERCOLATION TEST RESULTS Location Approx. Depth Bottom Test, BSG (feet) Soil Classification (USCS) Gravel Pack Corrected Estimated Unfactored Percolation Rate (minutes per inch) Estimated Unfactored Infiltration Rate (inches/hour) P-1 (B-4) 5.7 Sandy Lean Clay 22 0.2 For assessment of infiltration feasibility and design, appropriate factors of safety should be applied to unfactored infiltration rates and incorporated into basin design. It should be noted that the field percolation tests do not take into account the long term effects of subgrade saturation, silt accumulation, groundwater influence, nor vegetation. Soil bed consolidation, sediment, suspended soils, etc. in the discharge water can result in clogging of the pore spaces in the soil, thus reducing the soil infiltration rate over time. Percolation testing is a relatively small scale test. Variations in soil type and soil density across the infiltration area of the system can influence the infiltration rate. It is our understanding that the results of percolation testing and associated estimate of unfactored infiltration rates may be utilized by the storm water retention system designer to determine sizing of the proposed retention system. The percolation test conducted yielded a low estimated unfactored infiltration rate of 0.2 inches per hour for the lean clay soils. Considering the presence of loose to medium dense granular soils below the site and the potential for liquefaction and significant seismic settlements, on-site infiltration of storm water is not recommended. Project No. 1-221-0888 - 6 - October 6, 2021 8. GEOLOGIC AND SESIMIC HAZARD EVALUATIONS 8.1 Geologic Setting The project site is in San Joaquin Valley, located in the Great Valley Geomorphic Province, which is a topographic and structural basin that is bounded on the east by the Sierra Nevada and on the west by the Coast Ranges. The Sierra Nevada, a fault block dipping gently southwestward, is made up of igneous and metamorphic rocks of pre-Tertiary age that comprise the basement complex beneath the Valley. The Coast Ranges contain folded and faulted sedimentary rocks of Mesozoic and Cenozoic age, which are similar to those rocks that underlie the Valley at depth and non-conformably overlie the basement complex; gently dipping to nearly horizontal sedimentary rocks of Tertiary and Quaternary age overlie the older rocks. The Great Valley Geomorphic province is nearly flat, with sediments as much as 20,000 to 40,000 feet thick. The sediments are derived from the adjacent Sierra Nevada Mountains and Coast Ranges. Based on review of the Geologic Map of California: (Monterey Geologic Sheet1), the area of the subject site is in an area mapped as Quaternary Basin deposits (Qb). A regional geologic map is included as Figure No. 3 at the end of this report. Based on the relatively flat nature of the project and uniform geologic conditions, site specific geologic cross sections are not determined necessary. 8.2 Faulting and Seismicity Numerous active and potentially active faults are located in the site region and contribute to design seismic ground motion estimates. An "active fault" is defined, for the purpose of this evaluation, as a fault that has had surface displacement within the Holocene age (about the last 11,700 years). Based on the distance to active faults in the region, as well as the historic seismic record, the area of the subject site is considered to be subject to moderate seismicity. The project area is not located within an Earthquake Fault Rupture Hazard Zone and a fault rupture hazard investigation is not required. To determine the distance of known active faults within 100 miles of the site, we used the United States Geological Survey (USGS) web-based application 2008 National Seismic Hazard Maps - Fault Parameters, supplemented with the Fault Activity Map of California-web application (Fault Activity Map of California). The ten closest active faults are summarized below in Table 8.2. TABLE 8.2 REGIONAL FAULT SUMMARY Fault Name Distance to Site (miles) Maximum Earthquake Magnitude, Mw Great Valley 11 15.8 6.6 Great Valley 10 17.0 6.5 Great Valley 12 19.1 6.4 Great Valley 9 20.7 6.8 Great Valley 13 (Coalinga) 27.5 7.1 1 Compilation by C.W. Jennings and R.G. Strand, 1958, Geologic Map of California : Santa Cruz Sheet: California Division of Mines and Geology, scale 1:250,000 https://maps.conservation.ca.gov/cgs/fam/app/ https://maps.conservation.ca.gov/cgs/fam/app/ Project No. 1-221-0888 - 7 - October 6, 2021 Fault Name Distance to Site (miles) Maximum Earthquake Magnitude, Mw Ortigalita 28.6 7.1 Great Valley 8 41.0 6.8 San Andreas fault - creeping segment 41.3 N/A Great Valley 14 (Kettlemen Hills) 44.9 7.2 Quien Sabe 46.2 6.6 The faults tabulated above and numerous other faults in the region are sources of potential ground motion. However, earthquakes that might occur on other faults throughout California are also potential generators of significant ground motion and could subject the site to intense ground shaking. 8.3 Geologic Hazards Evaluation The potential geologic hazards of flooding, landslides, and volcanic activity are described in the following subsections 8.4 Flooding Based on FEMA Flood Insurance Rate Map No. 06019C1444H, dated February 18, 2009, the subject site area is labeled as Zone X: “Areas determined to be outside the 0.2% annual chance floodplain.” The flood hazard map is provided as Figure No. 6, attached to this report. Based on review of the Army Corp of Engineers maps (Inundation Areas Below Corps Dams), the site is located in an area of potential flooding due to a breach of Friant Dam. 8.5 Landslides The site vicinity is flat. There are no known landslides at the site, nor is the site in the path of any known or potential landslides. We do not consider the potential for a landslide to be a hazard to this project. 8.6 Volcanic Activity California includes six regions with a history of late Pleistocene and Holocene volcanic eruptions that are subject to hazards from future eruptions (Miller, 1989). Of these six regions, the Mono Lake-Long Valley area is the closest. Based on review of Plate 1, Miller 1989, the subject site is not located within any designated volcanic hazard zones and is outside the zone subject to 5 centimeters or more of compacted ash. The pyroclastic flow hazard zone for this potential volcanic source is indicated to be as close as about 72 miles northeast of the site. Based on the distance of volcanic hazards from the site, the prospect for volcanic hazards to impact the site during the design life of the facility is considered low. Project No. 1-221-0888 - 8 - October 6, 2021 9. OTHER GEOLOGIC HAZARDS 9.1 Expansive Soils One of the potential geotechnical hazards evaluated at this site is the expansion potential of the near surface soils. Expansive soils experience shrink and swell due to moisture content fluctuations throughout the dry and wet season. If not addressed, the potential for shrinkage and heave would have an impact on foundations and lightly loaded slabs. The potential for damage to slabs-on-grade and foundations supported on expansive soils can be reduced by placing non-expansive fill below the slabs-on-grade. Based on the soil types encountered and results of the laboratory tests performed, the near surface soils are considered to have a high expansion potential. This report presents recommendations to reduce the potential impacts of expansive soils on slabs-on-grade. 9.2 Corrosion Protection The risk of corrosion of construction materials relates to the potential for soil-induced chemical reaction. Corrosion is a naturally occurring process whereby the surface of a metallic structure is oxidized or reduced to a corrosion product such as iron oxide (i.e., rust). Testing performed on a near surface soil resulted in a minimum resistivity value of 331 ohm-centimeter. Based on the results, these soils would be considered to have an “extremely corrosive” corrosion potential to buried metal objects (per National Association of Corrosion Engineers, Corrosion Severity Ratings). 9.3 Sulfate Attack of Concrete Excessive sulfate in either the soil or native water may result in an adverse reaction between the cement in concrete and the soil. The 2019 Edition of ACI 318 (ACI 318) has established criteria for evaluation of sulfate levels and how they relate to cement reactivity with soil and/or water. As indicated in Section 7.3 of this report, the exposure class of S1 was determined for a soil sample was obtained from the project site. Thus, the potential for concrete deterioration due to sulfate in soils is considered moderate and Section 7.3 of this report should be referred to for minimum concrete requirements. 10. CONDITIONAL GEOLOGIC HAZARDS Conditional geologic hazards, as identified in Section 31 of California Geological Survey Note 48, are discussed in the following subsections. 10.1 Tsunamis and Seiches The site is not located within a coastal area. Therefore, tsunamis (seismic sea waves) are not considered a significant hazard at the site. Seiches are large waves generated in enclosed bodies of water in response to ground shaking. No major water-retaining structures are located immediately up gradient from the project site. Flooding from a seismically-induced seiche is considered unlikely. 10.2 Hazardous Materials Hazardous materials such as methane gas, hydrogen-sulfide gas and tar seeps are not known to be present in the project area and are not considered to be a concern at the subject site. Project No. 1-221-0888 - 9 - October 6, 2021 10.3 Radon Gas Based on review of the California Geologic Survey Indoor Radon Test Results2 for the area of the site zip code (93640), none (0) of the two (2) test results indicated an indoor radon concentration of greater than or equal to the U.S. EPA action level for radon in air of 4 picocuries per liter. Also, considering that the building is expected to be adequately ventilated with no basement, the potential for indoor radon exposure is not considered a concern for this project. 10.4 Naturally Occurring Asbestos Asbestos commonly occurs in soil and ultramafic rocks such as serpentinite throughout California. Ultramafic rocks are scattered throughout much of the Sierra Nevada Mountain and the Coast Range regions. Based on review of the USGS Open-File Report 2011-1188, Map Sheet 59, titled “Reported Historic Asbestos Mines, Historic Asbestos Prospects, and Other Natural Occurrences of Asbestos in California,” dated 2011, ultramafic rock is identified about 28 miles west of the site. Based on the cited literature and our site observations, it is our opinion that the potential to encounter near surface naturally occurring asbestos containing rock at the site is very low. 10.5 Hydrocollapse Collapsible soils typically consist of loose, dry, low-density soils that, when wetted, will experience settlement/consolidation. Based on the results of testing performed on two (2) relatively undisturbed near surface soil samples, when wetted under a load of 0.5 kips per square foot these soils exhibited swell of approximately 0.7 percent and 0.1 percent. The native clayey near surface soils encountered would not be expected to exhibit collapse. Based on the laboratory test results and the general soil conditions encountered, the potential for hydro-collapse to impact the project is considered very low. 10.6 Regional Subsidence Based on our review of an online map published by California Water Science Center3, the site is located in an area of about 1.2 to 3.6 meters of recorded subsidence due to groundwater pumping between 1926 and 1970. According to USGS Scientific Investigations Report 2013-5142, Lands Subsidence along the Delta-Mendota Canal in the Northern Part of the San Joaquin Valley, California, 2003-10, measurements also indicate about 40 millimeters of subsidence between 2003 and 2008 near the City of Mendota. Regional subsidence due to groundwater pumping in the Central Valley occurs gradually over time and affects large areas. Thus, impacts to structures such as individual buildings are not anticipated to be significant. Regional subsidence due to groundwater withdrawal or other causes is not considered a concern for this project. 11. SEISMIC HAZARDS The potential for fault ground rupture, seismic ground shaking and seismic coefficients/earthquake spectral response acceleration design values, and liquefaction and seismic settlement are described in the following subsections. 2 https://www.cdph.ca.gov/Programs/CEH/DRSEM/CDPH%20Document%20Library/EMB/Radon/Radon%20Test%20Results.pdf 3 https://ca.water.usgs.gov/land_subsidence/california-subsidence-areas.html Project No. 1-221-0888 - 10 - October 6, 2021 11.1 Active Faulting and Surface Fault Rupture The site is not located within a currently established State of California Earthquake Fault Zone for surface fault rupture hazards (Special Studies Zone). The nearest active fault to the project site is Segment 11 of the Great Valley fault (about 15.8 miles west of the site). However, this is a blind thrust fault and does not exhibit surface rupture. The nearest active fault with the potential for surface rupture is the Ortigalita Fault, located about 28.6 miles west of the site. A map depicting the major active faults in the vicinity of the site is included on Figure No. 4 at the end of this report. Considering the distance to the nearest known active fault, the potential for surface fault rupture at the site due to a known active fault is considered low. 11.2 Historic Seismic Activity The general area of the site has experienced recurring seismic activity. Based on historical earthquake data obtained from the U.S. Geological Survey's earthquake database system, approximately 223 historical earthquakes with magnitude 4.5 or greater have been recorded from 1900 through October 4, 2021 within about 100 miles of the site. A map showing the location of the project site with relation to the approximate historical earthquake epicenter locations and magnitude category is presented on Figure No. 5 at the end of this report. The nearest earthquake event (estimated magnitude of 4.8) found during the search occurred on August 29, 1975, approximately 20 miles south of the site and about 2 miles south of Three Rocks, California. The highest magnitude earthquake identified within a 100 mile search radius was the 6.9 magnitude Loma Prieta Earthquake (epicenter about 10 miles northeast of Santa Cruz), which occurred on October 17, 1989, approximately 87 miles northwest of the site. 11.3 Design Seismic Ground Motion Parameters and Site Class Seismic coefficients and spectral response acceleration values were developed based on the 2019 California Building Code (CBC). The CBC methodology for determining design ground motion values is based on the Office of Statewide Health Planning and Development (OSHPD) Seismic Design Maps, which incorporate both probabilistic and deterministic seismic ground motion. A site specific ground motion hazard analysis was not included in this investigation. Based on our understanding of the proposed project the project Structural Engineer will utilize code exceptions listed in ASCE 7-16 section 11.4.8 for design of planned foundations. Therefore, Site Specific Ground Motion Hazard Analysis is not required. Based on the 2019 California Building Code (CBC), Site Class E was selected for the site based on soil conditions with standard penetration resistance, N-values, with a weighted average of less than 15 blows per foot. The proposed building is determined to be in Seismic Design Category D. Table 12.6.2 includes design seismic coefficients and spectral response parameters for project foundation design, based on the 2019 CBC. Based on Office of Statewide Health Planning and Development (OSHPD) Seismic Design Maps, the estimated design peak ground acceleration adjusted for Site Class effects (PGAM) was determined to be 0.551g. Project No. 1-221-0888 - 11 - October 6, 2021 11.4 Liquefaction and Seismic Settlement Soil liquefaction is a state of soil particles suspension caused by a complete loss of strength when the effective stress drops to zero. Liquefaction normally occurs under saturated conditions in soils such as sand in which the strength is purely frictional. Primary factors that trigger liquefaction are: moderate to strong ground shaking (seismic source), relatively clean, loose granular soils (primarily poorly graded sands and silty sands), and saturated soil conditions (shallow groundwater). Due to the increasing overburden pressure with depth, liquefaction of granular soils is generally limited to the upper 50 feet of a soil profile. The site is not located within an area which has been mapped by the State of California as a Liquefaction Hazard Zone. The near surface soils encountered were medium stiff to stiff and high plasticity sandy lean clays. A loose to medium dense silty sands was encountered below the lean clays in borings B-1 and B-2 and the silty sand extended to the maximum depth explored in boring B-1 at 161⁄2 feet BSG, and to a depth of about 26 feet in boring B-2. The silty sand was underlain by a fat clay extending from depths of about 26 to 30 feet BSG. The fat clay was underlain by a loose to medium dense poorly graded sand with silt extending to a depth of 45 feet BSG. The poorly graded sand with silt was underlain by medium stiff sandy lean clay extending to about 50 feet BSG, underlain by stiff fat clay extending to the maximum depth explored of 511⁄2 feet BSG. Based on groundwater data presented in Section 7.2 of this report, an historic high groundwater depth of 6 feet BSG was used for the analysis. A liquefaction/seismic settlement evaluation was performed using LiquefyPro computer program (version 5.9c) developed by Civiltech. Input parameters included a maximum earthquake magnitude of 5.5 Mw (based on deaggregation of the 2 percent probability in 50 year seismic event using the USGS Unified Hazard Tool, Dynamic Conterminous U.S. 2014 v4.2.0), a design peak horizontal ground surface acceleration of 0.551g (PGAM), an historic groundwater depth of 5 feet BSG, and SPT (N-value) and soil data obtained from test boring B-2 (see the test boring log for B-2 in Appendix A of this report). Based on our analysis, liquefaction/seismic settlement is expected to occur as a result of the design level earthquake shaking, with total seismic induced settlement estimated to be 6.5 inches and differential seismic settlement estimated to be 4 inches over 40 feet. The analysis output and graphic results are included in Appendix A of this report. The above seismic settlement values, to be considered in foundation design, exceed tolerable limits for conventional shallow foundations. Mitigation measures are discussed in Section 12.1.2 of this report. Granular soils susceptible to liquefaction were encountered as shallow as about 13 feet. Considering the depth of the granular soils and the anticipated relatively small building foundation loads and footing sizes, loss of bearing capacity due to liquefaction of the granular soils is not considered a concern for this project. 11.5 Lateral Spreading Lateral spreading is a phenomenon in which soils move laterally during seismic shaking and is often associated with liquefaction. The amount of movement depends on the soil strength, duration and intensity of seismic shaking, topography, and free face geometry. Due to the clayey nature of the near surface soils, lack of groundwater near the surface, depth to potentially liquefiable soils, and relatively flat nature of the site, we judge the likelihood of lateral spreading to be low. Project No. 1-221-0888 - 12 - October 6, 2021 12. CONCLUSIONS AND RECOMMENDATIONS 12.1 General Conclusions and Recommendations 12.1.1 Based upon the data collected during this investigation, from a geotechnical engineering standpoint, it is our opinion that the site is suitable for construction of the proposed improvements at the site as planned, provided the recommendations contained in this report are incorporated into the project design and construction. Conclusions and recommendations provided in this report are based on our review of available literature, analysis of data obtained from our field exploration and laboratory testing program, and our understanding of the proposed development at this time. 12.1.2 The primary geotechnical concern identified by our investigation is the magnitude of seismic settlement predicted as a result of the design level earthquake. Our investigation indicates that the site has loose to medium dense granular soils, shallow groundwater, and moderate levels of predicted design seismicity. Liquefaction analyses indicate about 6.5 inches of total seismic settlement and 4 inches of differential seismic settlement over 40 feet would occur as a result of the design level earthquake. These settlements exceed typical design tolerances for conventional shallow foundation. However, quasi rigid structural slabs, and/or structural mat foundations may be suitable options to support the building structure and interior floors. Support of the building on deep foundations such as driven pre-stressed concrete piles may be considered. However, because these deep foundations (piles) would need to extend below the liquefiable soils, it appears that mat foundations and/or quasi-rigid foundation with interconnected grade beams may be the most economical method of construction. If based on consultation with the project structural engineer, the seismic settlements exceed tolerable limits for mat foundations and/or quasi-rigid foundations with interconnected grade beams, a deep foundation system or deep ground improvement (e.g DDC, stone columns, etc.) in conjunction with structural mitigation may be required. 12.1.3 The percolation test conducted yielded a low estimated unfactored infiltration rate for the lean clay soils of 0.2 inches per hour. Considering the presence of loose to medium dense granular soils below the site and the potential for liquefaction and significant seismic settlements, on-site infiltration of storm water is not recommended. 12.1.4 Based on the laboratory tests performed, the near surface soils have a high expansion potential and poor pavement support characteristics. 12.1.5 The high expansion potential of the near surface clayey soils is a concern and recommendations are provided in this report to mitigate potential impacts of expansive soils. Due to the expansive nature of the near surface soils encountered, this report recommends to support slabs on grade on a uniform layer of imported non-expansive engineered fill. As an alternative, mitigation of the expansion potential may be achieved by chemical treatment of on-site soils with high calcium quicklime. Chemical suitability testing was not included within the scope of this investigation. If desired, SALEM should be contacted to provide supplemental laboratory testing to determine the suitability of on-site soils for chemical treatment. 12.1.6 Undocumented fill soils and possible buried foundations and buried utility lines, etc., in the former building area located in the north portion of the site are a concern. These features should be located, removed, and properly backfilled with engineered fill. SALEM should be retained to observe, test, and document the removal of these features and subsequent placement of Project No. 1-221-0888 - 13 - October 6, 2021 engineered fill. SALEM should be retained to observe the removal of the undocumented fill soils. Also, existing improvements, such as slabs, foundations, utilities, pavements, etc., will be required to be removed and backfilled with compacted engineered fill. SALEM should be retained to test any and all backfill placed. 12.1.7 Groundwater was encountered in test boring B-2, drilled on September 10, 2021, at a depth of about 21 feet BSG. Based on groundwater data presented in Section 7.2 of this report, a historic high groundwater depth of 6 feet BSG was used for the liquefaction analysis. 12.1.8 Based on the subsurface conditions at the site and the anticipated structural loading, the proposed structures may be supported using conventional shallow foundations provided that the foundations are designed for the static and seismic settlement values given in this report and the recommendations presented herein are incorporated in the design and construction of the project. 12.1.9 To minimize the potential soil movement due to settlement, and provide uniform support for new foundations, the building pad areas and over-build zones should be prepared as recommended under Section 12.3 of this report. 12.1.10 All references to relative compaction and optimum moisture content in this report are based on ASTM D 1557 (latest edition). 12.1.11 SALEM should be retained to review the project plans as they develop further, provide engineering consultation as-needed, and perform geotechnical observation and testing services during construction. 12.1.12 SALEM should be retained to observe demolition activities and provide compaction testing of any and all backfill placed during demolition or site grading. If during demolition or grading soil conditions are not consistent with those identified as part of this investigation, SALEM (if retained) will provide additional recommendations as needed. 12.2 Surface Drainage 12.2.1 Proper surface drainage is critical to the future performance of the project. Uncontrolled infiltration of irrigation excess and storm runoff into the soils can adversely affect the performance of the planned improvements. Saturation of a soil can cause it to lose internal shear strength and increase its compressibility, resulting in a change to important engineering properties. Proper drainage should be maintained at all times. 12.2.2 Barren ground immediately adjacent to foundations shall be sloped away from the building at a slope of not less than 5 percent for a minimum distance of 10 feet. Impervious surfaces within 10 feet of the building foundation shall be sloped a minimum of 1 percent away from the buildings and drainage gradients maintained to carry all surface water to collection facilities and off site. These grades should be maintained for the life of the project. Ponding of water should not be allowed adjacent to the structure. Over-irrigation within landscaped areas adjacent to the structure should not be performed. 12.2.3 Roof drains should be installed and connected to the storm drain system for the development. Grading and drainage design should prevent ponding of surface water. 12.2.4 On-site storm water infiltration is not recommended for this site due to the potential to saturate loose sandy soils which may become susceptible to liquefaction and seismic settlement in the event of an earthquake. Storm water retention facilities should be lined to prevent infiltration Project No. 1-221-0888 - 14 - October 6, 2021 12.3 Site Grading 12.3.1 A representative of our firm should be present during all site clearing and grading operations to test and/or observe earthwork construction. This testing and observation is an integral part of our service as acceptance of earthwork construction is dependent upon compaction of the material and the stability of the material. The Geotechnical Engineer may reject any material that does not meet compaction and stability requirements. Further recommendations of this report are predicated upon the assumption that earthwork construction will conform to recommendations set forth in this section as well as other portions of this report. 12.3.2 A preconstruction conference should be held at the site prior to the beginning of grading operations with the owner, contractor, civil engineer and geotechnical engineer in attendance. 12.3.3 Site demolition activities shall include removal of all surface obstructions not intended to be incorporated into final site design. In addition, undocumented fill, underground buried structures, and/or utility lines encountered during demolition and construction should be properly removed and the resulting excavations backfilled with Engineered Fill. After demolition activities, it is recommended that disturbed soils be removed and/or replaced with compacted engineered fill soils. SALEM should be retained to observe demolition activities and provide compaction testing of any and all backfill placed during demolition and site grading. If during demolition or grading soil conditions are not consistent with those identified as part of this investigation, SALEM (if retained) will provide additional recommendations as needed. 12.3.4 Site preparation should begin with removal of existing surface/subsurface structures, underground utilities (as required), disturbed soil, any existing uncertified/undocumented fill, and debris. Excavations or depressions resulting from site clearing/demolition operations, or other existing excavations or depressions, should be restored with Engineered Fill placed and compacted in accordance with the recommendations of this report. 12.3.5 Surface vegetation consisting of grasses and other similar vegetation should be removed by stripping to a sufficient depth to remove organic-rich topsoil. The upper 2 to 4 inches of the soils containing, vegetation, roots and other objectionable organic matter encountered at the time of grading should be stripped and removed from the surface. Deeper stripping may be required in tilled and localized areas. The stripped vegetation will not be suitable for use as Engineered Fill or within 5 feet of building pads. However, stripped topsoil may be stockpiled and reused in landscape or non-structural areas or exported from the site. 12.3.6 If trees are to be removed, their root balls as well as isolated roots greater than 1⁄4-inch in diameter should be thoroughly cleared. The root system removal may disturb a significant quantity of soil. Following tree removal, all loose and disturbed soil should be removed from the tree wells. Any areas or pockets of soft or loose soils, void spaces made by burrowing animals, undocumented fill, or other disturbed soil (i.e. soil disturbed by root removal) that are encountered, should be excavated to expose approved firm native material. Care should be taken during site grading to mitigate (e.g. excavate and compact as engineered fill) all soil disturbed by demolition and tree removal activities. 12.3.7 The subgrade soil consistency was observed to be sensitive to rainfall. It is anticipated that mitigation measures for aeration or chemical treatment of overly moist soils may be required during grading if conducted during or soon after wet seasons, or if excavations are extended near or below groundwater depths. Earthwork operations may encounter very moist unstable Project No. 1-221-0888 - 15 - October 6, 2021 soils which may require removal to a stable bottom. Native soils exposed as part of site grading operations shall not be allowed to dry out to below optimum moisture content, and should be kept continuously moist prior to placement of subsequent fill. 12.3.8 Undocumented fills should be removed as part of site preparation. In the event fill soils or debris are noted at the base of the planned over-excavations, additional excavation will be recommended to remove the undocumented fill soils. SALEM should be retained to observe the over-excavations and test any and all backfill placed. 12.3.9 Structural building pad areas and the over-build zone should be considered as areas extending a minimum of 5 feet horizontally beyond the outside dimensions of buildings, including footings and non-cantilevered overhangs carrying structural loads. 12.3.10 Areas of the proposed building pad and over-build zone should be over-excavated to a minimum of 24 inches below preconstruction site grade or 12 inches below the bottom of proposed foundations, or to the depth required to remove undocumented fills, whichever is greater (undocumented fill was encountered in boring B-3 to a depth of 3 feet BSG). The horizontal limits of the over-excavation should extend throughout the limits of the building pad and 5 feet beyond foundations and attached concrete slabs on grade. Upon approval, the bottom of excavation should be scarified 12 inches, moisture conditioned to between 1 and 4 percent above optimum moisture content and compacted as engineered fill to achieve a stable bottom prior to placement of engineered fill. 12.3.11 Interior mat slabs should be supported on a minimum of 6 inches of Class 2 aggregate base, over a minimum of 12 inches of imported non-expansive engineered fill (or an additional 12 inches of Class 2 aggregate base) over the depth of engineered fill recommended below foundations. This recommendation is provided to reduce the potential for swell/shrink related damage. As an alternative to import non-expansive engineered fill, alternatives such as chemical treatment of on-site soils may be considered. Chemical suitability testing was not included within the scope of this investigation. If desired SALEM should be contacted to provide a fee estimate for chemical suitability testing. For planning purposes, chemical treatment of on-site soils using high calcium quicklime with an application rate of 6 to 7 percent may be considered. 12.3.12 Areas of exterior concrete slabs on grade located outside the building pad over-build zone, should be prepared by over-excavation to a minimum of 18 inches below existing grade or to the bottom of the recommended 18 inch thick non-expansive section, whichever is greater. The zone of over-excavation should extend a minimum of 3 feet beyond these improvements. Slopes between areas of varying over-excavation depths should be sloped at 2H to 1V or flatter to limit abrupt lateral changes in fill thickness. The exposed bottom of excavation should be moisture conditioned to at least 1 percent above optimum moisture content and compacted as engineered fill to achieve a stable bottom prior to placement of engineered fill. Exterior concrete slabs on grade should be supported on a non-expansive section comprising a minimum of 6 inches of Class 2 aggregate base, over a minimum of 12 inches of imported non-expansive engineered fill (or an additional 12 inches of Class 2 aggregate base). 12.3.13 Areas of lightly loaded foundations such as retaining walls, screen walls, etc., should be prepared by over-excavation to a minimum of 18 inches below preconstruction site grade or to the bottom of proposed foundations, or to the depth required to remove undocumented fills, whichever is greater. The resulting bottom-of footing/over-excavation shall be scarified to a depth of at least Project No. 1-221-0888 - 16 - October 6, 2021 12 inches, moisture-conditioned to at least 1 percent above optimum moisture content and compacted as engineered fill to achieve a stable bottom prior to placement of engineered fill. The horizontal limits of the over-excavation should extend, laterally to a minimum of 3 feet beyond the outer edges of the proposed footings. 12.3.14 Areas of Portland cement concrete pavements and asphaltic concrete pavements should be over- excavated to a minimum of 18 inches below preconstruction site grade, or to the depth required to remove undocumented fills, whichever is greater. The horizontal limits of the over-excavation should extend throughout the entire pavement area and 3 feet beyond the edge of pavements. The bottom of excavation should be scarified 12 inches, moisture conditioned to slightly above optimum moisture content and compacted as engineered fill to achieve a stable bottom prior to placement of engineered fill. The upper 12 inches of subgrade below aggregate base should be compacted to a minimum of 95 percent relative compaction. 12.3.15 Areas to receive engineered fill outside the building pad and over-build zone and pavement areas, should be prepared by over-excavation to a minimum of 12 inches below preconstruction site grade. The bottom of excavation should be scarified 12 inches, moisture conditioned to at least 1 percent above optimum moisture content and compacted as engineered fill to achieve a stable bottom prior to placement of engineered fill. 12.3.16 An integral part of satisfactory fill placement is the stability of the placed lift of soil. If placed materials exhibit excessive instability as determined by a SALEM field representative, the lift will be considered unacceptable and shall be remedied prior to placement of additional fill material. Additional lifts should not be placed if the previous lift did not meet the required dry density or if soil conditions are not stable. 12.3.17 The most effective site preparation alternatives will depend on site conditions prior to grading. SALEM should evaluate site conditions and provide supplemental recommendations immediately prior to grading, if necessary. 12.3.18 We do not anticipate groundwater or seepage to adversely affect construction if conducted during the drier months of the year (typically summer and fall). However, grading during wet inclement periods of the year may result in possible excavation and fill placement difficulties. Project site winterization consisting of placement of aggregate base and protecting exposed soils during construction should be performed. If the construction schedule requires grading operations during the wet season, we can provide additional recommendations as conditions warrant. 12.3.19 In the event of wet weather during construction, the Contractor should anticipate the near surface soils would require drying prior to compaction as engineered fill. Typical remedial measures include: discing and aerating the soil during dry weather; mixing the soil with dryer materials; removing and replacing the soil with an approved fill material or placement of crushed rocks or aggregate base material; or mixing the soil with an approved lime or cement product. The most common remedial measure of stabilizing the bottom of the excavation due to wet soil condition is to reduce the moisture of the soil to near the optimum moisture content by having the subgrade soils scarified and aerated or mixed with drier soils prior to compacting. However, the drying process may require an extended period of time and delay the construction operation. To expedite the stabilizing process, crushed rock may be utilized for stabilization provided this method is approved by the owner for the cost purpose. Project No. 1-221-0888 - 17 - October 6, 2021 If the use of crushed rock is considered, it is recommended that the upper soft and wet soils be replaced by 6 to 24 inches of 2-inch to 3-inch crushed rocks. The thickness of the rock layer depends on the severity of the soil instability. The recommended 6 to 24 inches of crushed rock material will provide a stable platform. It is further recommended that lighter compaction equipment be utilized for compacting the crushed rock. All open graded crushed rock/gravel should be fully encapsulated with a geotextile fabric (such as Mirafi 140N) to minimize migration of soil particles into the voids of the crushed rock. Although it is not required, the use of geogrid (e.g. Tensar BX 1100, BX 1200 or TX 160) below the crushed rock will enhance stability and reduce the required thickness of crushed rock necessary for stabilization. In addition, chemical drying of the bottom of the excavation and engineered fill soils could be considered. For bidding purposes, the Contractor may assume 5 percent high calcium quicklime for chemical stabilization/drying of on-site soils. The actual application rate will need to be adjusted based on conditions encountered during grading. Our firm should be consulted prior to implementing remedial measures to provide appropriate recommendations. 12.4 Soil and Excavation Characteristics 12.4.1 Based on the soil conditions encountered in our borings, the onsite soils can be generally be excavated with moderate effort using conventional excavation equipment. The near surface clayey soils were significantly under optimum moisture content. These soils will excavate as hard clods. Contractors should anticipate that these soils will require significantly more effort to moisture condition for use as engineered fill than more granular soils elsewhere in the Central Valley. 12.4.2 It is the responsibility of the contractor to ensure that all excavations and trenches are properly shored and maintained in accordance with applicable Occupational Safety and Health Administration (OSHA) rules and regulations to maintain safety and maintain the stability of adjacent existing improvements. Temporary excavations are further discussed in a later Section of this report. 12.4.3 The near surface soils encountered during our field investigation were generally identified as damp to moist. Native soils exposed as part of site grading operations shall not be allowed to dry out and should be kept continuously moist prior to placement of subsequent fill. 12.5 Materials for Fill 12.5.1 On-site soils, free of debris/deleterious matter and rock/cemented soil fragments material larger than 3 inches in maximum dimension, can be used as engineered fill at depths below the aggregate base rock and non-expansive soil sections recommended below slabs and pavements. However, contractors should anticipate that these soils will require significantly more effort to moisture condition for use as engineered fill than more granular soils elsewhere in the Central Valley (see Section 12.4.1). 12.5.2 Imported Non-Expansive Engineered Fill soil, should be well-graded, very low-to-non-expansive and slightly cohesive, such as a silty sand or sandy silt. This material should be approved by the Engineer prior to use and should typically possess the soil characteristics summarized below in Table 12.5.2. Project No. 1-221-0888 - 18 - October 6, 2021 TABLE 12.5.2 IMPORT FILL REQUIREMENTS Percent Passing 3-inch Sieve 100 Percent Passing No.4 Sieve 75-100 Percent Passing No 200 Sieve 15-40 Maximum Plasticity Index 15 Organic Content, Percent by Weight Less than 3% Maximum Expansion Index (ASTM D4829) 10 Prior to importing the Contractor should demonstrate to the Owner that the proposed import meets the requirements for import fill specified in this report. In addition, the material should be verified by the Contractor that the soils do not contain any environmental contaminates as regulated by local, state, or federal agencies, as applicable 12.5.3 All Engineered Fill (including scarified ground surfaces and backfill) should be placed in lifts no thicker than will allow for adequate bonding and compaction (typically 6 to 8 inches in loose thickness). 12.5.4 On-Site soils used as engineered fill soils should be moisture conditioned to between 1 and 4 percent above optimum moisture content, and compacted to at least 90 percent relative compaction (95 percent minimum within 12 inches of aggregate base below pavements). 12.5.5 Import Engineered Fill, if selected, should be placed, moisture conditioned to slightly above optimum moisture content, and compacted to at least 92 percent relative compaction. 12.5.6 The recommended material specification for imported engineered fill are suitable for most applications with the exception of exposure to erosion. Project site winterization and protection of exposed soils during the construction phase should be the sole responsibility of the Contractor, since they have complete control of the project site. 12.5.7 Environmental characteristics and corrosion potential of import soil materials should also be considered. 12.5.8 Proposed import materials should be sampled, tested, and approved by SALEM prior to being transported to the site. 12.5.9 Aggregate base material should meet the requirements of a Caltrans Class 2 Aggregate Base. Aggregate base within the building pad should be non-recycled. The aggregate base material should conform to the requirements of Section 26 of the Standard Specifications for Class 2 material, 3⁄4-inch or 11⁄2-inches maximum size. The aggregate base material should be compacted to a minimum relative compaction of 95 percent based ASTM D1557. The aggregate base material should be spread in layers not exceeding 6 inches and each layer of aggregate material course should be tested and approved by the Soils Engineer prior to the placement of successive layers 12.5.10 Open graded gravel and rock material (i.e. 3⁄4 inch or 1⁄2 inch crushed gravel) should not be used as backfill including utility trenches. If required by local agency or for use in subgrade Project No. 1-221-0888 - 19 - October 6, 2021 stabilization, to prevent migration of fines, open graded materials should be fully encapsulated in a geotextile fabric such as Mirafi 140N or equivalent. Open graded rock should be placed in loose lifts no greater than about 6 to 8 inches, and vibrated in-place to a firm non-yielding condition. 12.6 Foundations-General 12.6.1 The design seismic settlement values provide in this report exceed typical design tolerances for conventional shallow foundation. Thus, shallow foundation recommendations are provided in this report solely for use in design of foundations for not-habitable ancillary structures. Quasi rigid structural slabs, and/or structural mat foundations may be suitable options to support the building structure and interior floors and would likely be more economical that a deep foundation system. If based on consultation with the project structural engineer, the seismic settlements exceed tolerable limits for mat foundations and/or quasi- rigid foundations with interconnected grade beams, a deep foundation system or deep ground improvement (e.g DDC, stone columns, etc.) in conjunction with structural mitigation may be required. 12.6.2 For seismic design of the structures, and in accordance with the seismic provisions of the 2019 CBC, our recommended parameters are shown below. These parameters were determined using California’s Office of Statewide Health Planning and Development (OSHPD) (https://seismicmaps.org/) in accordance with the 2019 CBC. The Site Class was determined based on the soils encountered during our field exploration. TABLE 12.6.2 2019 CBC SEISMIC DESIGN PARAMETERS Seismic Item Symbol Value 2016 ASCE 7 or 2019 CBC Reference Site Coordinates -- Lat. 36.75296° North Long.-120.38265° West -- Site Class -- E ASCE 7 Table 20.3 Soil Profile Name -- Soft Clay Soil ASCE 7 Table 20.3 Risk Category -- II CBC Table 1604.5 Site Amplification Factor at PGA FPGA 1.427 ASCE 7 Table 11.8-1 Peak Ground Acceleration (adjusted for Site Class effects) PGAM 0.551 g ASCE 7 Equation 11.8-1 Seismic Design Category SDC D ASCE 7 Table 11.6-1 & 2 Mapped Spectral Acceleration (Short period - 0.2 sec) SS 0.913 g CBC Figure 1613.3.1(1-8) Mapped Spectral Acceleration (1.0 sec. period) S1 0.326 g CBC Figure 1613.3.1(1-8) Site Class Modified Site Coefficient Fa 1.3 CBC Table 1613.2.3(1) Site Class Modified Site Coefficient Fv 2.128* CBC Table 1613.2.3(2) MCE Spectral Response Acceleration (Short period - 0.2 sec) SMS = Fa SS SMS 1.187 g CBC Equation 16-36 Project No. 1-221-0888 - 20 - October 6, 2021 Seismic Item Symbol Value 2016 ASCE 7 or 2019 CBC Reference MCE Spectral Response Acceleration (1.0 sec. period) SM1 = Fv S1 SM1 0.502 g* CBC Equation 16-37 Design Spectral Response Acceleration SDS=2⁄3SMS (short period - 0.2 sec) SDS 0.791 g CBC Equation 16-38 Design Spectral Response Acceleration SD1=2⁄3SM1 (1.0 sec. period) SD1 0.335 g* CBC Equation 16-39 Short Period Transition Period (SD1/SDS), Seconds TS 0.655 ASCE 7-16, Section 11.4.6 Long Period Transition period (seconds) TL 12 ASCE 7-16, Figures 22- 14 through 22-17 Note: * Determined per ASCE Table 11.4.-2 for use in calculating TS only. Site Specific Ground Motion Analysis was not included in the scope of this investigation. Per ASCE 11.4.8, Structures on Site Class E, with S1 greater than or equal to 0.2 and/or Ss greater than or equal to 1.0 may require Site Specific Ground Motion Analysis. However, a site specific ground motion analysis may not be required based on Exceptions listed in ASCE 11.4.8. The Structural Engineer should verify whether Exceptions listed under ASCE 7-16, Section 11.4.8 are valid for the planned construction. In the event a site specific ground motion analysis is required, SALEM should be contacted for these services. 12.6.3 Conformance to the criteria in the above table for seismic design does not constitute any kind of guarantee or assurance that significant structural damage or ground failure will not occur if a large earthquake occurs. The primary goal of seismic design specified by the building code is to protect life and avoid collapse of structures, not to avoid all damage. 12.7. Structural Mat Foundations or Quasi-Rigid Structural Slabs The following recommendations have been prepared in the event that consultation with the project structural engineer indicates structural mat foundations or quasi-rigid structural slabs are feasible to address total and differential seismic settlement of 6.5 inches and 4 inches over 40 feet, respectively. 12.7.1 The site is suitable for use of structural reinforced concrete “mat” foundations supported on approved engineered fill prepared in accordance with Section 12.3 of this report. Structural mat foundations should be supported on 6 inches of Class 2 aggregate base over 12 inches of imported non expansive fill over the depth of engineered fill specified below building foundations in this report. 12.7.2 The final thickness and reinforcement of the structural slab should be determined by the Structural Engineer. At a minimum the mat foundation should be 12 inches thick with double- mat reinforcing bar spaced at 18 inches on center. The mat slab should have thickened edges extending to 30 inches below the bottom of mat foundation. 12.7.3 At a minimum, structural mat foundations shall have a minimum concrete compressive strength of 4,500 pounds per square inch. Project No. 1-221-0888 - 21 - October 6, 2021 12.7.4 Mat foundations supported on the depth of engineered fill recommended in this report may consider total and differential static settlements of 1 inch total and 1⁄2 inch differential in 40 feet. In addition, heave of approximately 1⁄2 inch should be anticipated. 12.7.5 At the time of this report, distributed loads for the mat foundation were not provided. However, based on our experience with similar construction it is anticipated the proposed building will have a distributed load of no greater than 1,000 pounds per square foot. If the anticipated loads are greater than assumed, SALEM should be allowed to review the planned loading and revise the recommendations included herein accordingly. 12.7.6 Based on a distributed load of 1.0 kip per square foot, and the anticipated static and seismic settlements, structural mat foundations and grade beams may be designed utilizing a modulus of subgrade reaction, K-value of 100 pounds per square inch per inch. 12.7.7 Mat Type Foundations supported on Class 2 aggregate base as recommended in this report may be designed based on an allowable bearing capacity of 1,000 pounds per square foot. This value may be increased by 1/3 for wind and seismic loading. 12.7.8 Resistance to lateral footing displacement can be computed using a coefficient of friction of 0.30 acting between the base of foundations and the supporting subgrade. Lateral resistance for footings can alternatively be developed using an allowable equivalent fluid passive pressure of 275 pounds per cubic foot acting against the appropriate vertical slab faces. 12.7.9 Underground utilities running parallel to footings should not be constructed in the zone of influence of footings. The zone of influence may be taken to be the area beneath the footing and within a 1:1 plane extending out and down from the bottom edge of the footing. 12.7.10 The foundation subgrade should be sprinkled as necessary to maintain a moist condition without significant shrinkage cracks as would be expected in any concrete placement. Prior to placing rebar reinforcement, foundation excavations should be evaluated by a representative of SALEM for appropriate support characteristics and moisture content. Moisture conditioning may be required for the materials exposed at footing bottom, particularly if foundation excavations are left open for an extended period. 12.7.11 In areas where it is desired to reduce floor dampness where moisture-sensitive coverings, coatings, underlayments, adhesives, moisture sensitive goods, humidity controlled environments, or climate cooled environments are anticipated, construction should have a suitable vapor retarder (a minimum of 15 mils thick, is recommended, polyethylene vapor retarder sheeting, Raven Industries “VaporBlock 15, Stego Industries 15 mil “StegoWrap” or W.R. Meadows Sealtight 15 mil “Perminator”) incorporated into the floor slab design. The water vapor retarder should be a decay resistant material complying with ASTM E96 or ASTM E1249 not exceeding 0.01 perms, ASTM E154 and ASTM E1745 Class A. The vapor retarder should, maintain the recommended permeance after conditioning tests per ASTM E1745. The vapor barrier should be placed between the concrete slab and the compacted granular aggregate subbase material. The water vapor retarder (vapor barrier) should be installed in accordance with ASTM Specification E 1643-18. Project No. 1-221-0888 - 22 - October 6, 2021 12.7.12 The concrete may be placed directly on vapor retarder. The vapor retarder should be inspected prior to concrete placement. Cut or punctured retarder should be repaired using vapor retarder material lapped 6 inches beyond damaged areas and taped. Extend vapor retarder over footings and seal to foundation wall or slab at an elevation consistent with the top of the slab or terminate at impediments such as water stops or dowels. Seal around penetrations such as utilities or columns in order to create a monolithic membrane between the surface of the slab and moisture sources below the slab as well as at the slab perimeter. 12.7.13 Avoid use of stakes driven through the vapor retarder. 12.7.14 The recommendations of this report are intended to reduce the potential for cracking of slabs due to soil movement. However, even with the incorporation of the recommendations presented herein, foundations, stucco walls, and slabs-on-grade may exhibit some cracking due to soil movement. This is common for project areas that contain expansive or loose soils since designing to eliminate potential soil movement is cost prohibitive. The occurrence of concrete shrinkage cracks is independent of the supporting soil characteristics. Their occurrence may be reduced and/or controlled by limiting the slump of the concrete, proper concrete placement and curing, and by the placement of crack control joints at periodic intervals, in particular, where re-entrant slab corners occur. 12.7.15 Proper finishing and curing should be performed in accordance with the latest guidelines provided by the American Concrete Institute, Portland Cement Association, and ASTM 12.8 Shallow Foundations for Non-Habitable Ancillary Structures 12.8.1 The site is suitable for use of conventional shallow foundations for non-habitable ancillary structures such as screen walls, retaining walls, etc. However, damage to these structures should be anticipated as a result of seismic settlement occurring during a large earthquake (total and differential seismic settlement of 6.5 inches and 4 inches over 40 feet, respectively). The shallow foundations consisting of continuous footings and isolated pad footings should be supported on engineered fill prepared in accordance with recommendations under Sections 12.3 and 12.5 of this report. Shallow conventional foundations supported on soils prepared as recommended in this report may be designed based on total static settlement of 1 inch and a differential static settlement of 1⁄2 inch in 40 feet. If damage due to a large earthquake is not acceptable for the non- habitable structure, the foundations should be designed for seismic settlement (total and differential seismic settlement of 6.5 inches and 4 inches over 40 feet, respectively) in accordance with Section 12.7 of this report. 12.8.2 Lightly loaded foundations for screen walls, retaining walls, etc., should have a minimum width of 12 inches and minimum depth of 30 inches below adjacent grade. 12.8.3 Footing concrete should be placed into neat excavations. The footing bottoms shall be maintained free of loose and disturbed soil. 12.8.4 Foundations supported on the depth of engineered fill recommended in this report may be designed base on an allowable bearing capacity of 2,500 pounds per square foot. This value may be increased by one-third due to wind and seismic loading. 12.8.5 Resistance to lateral footing displacement can be computed using an allowable coefficient of friction factor of 0.30 acting between the base of foundations and the supporting native subgrade. Project No. 1-221-0888 - 23 - October 6, 2021 12.8.6 Lateral resistance for footings can alternatively be developed using an allowable equivalent fluid passive pressure of 275 pounds per cubic foot acting against the appropriate vertical native footing faces. The frictional and passive resistance of the soil may be combined without reduction in determining the total lateral resistance. An increase of one-third is permitted when using the alternate load combination in Section 1605.3.2 of the 2019 CBC that includes wind or earthquake loads. 12.8.7 Underground utilities running parallel to footings should not be constructed in the zone of influence of footings. The zone of influence may be taken to be the area beneath the footing and within a 1:1 plane extending out and down from the bottom edge of the footing. 12.8.8 The foundation subgrade should be sprinkled as necessary to maintain a moist condition without significant shrinkage cracks as would be expected in any concrete placement. Prior to placing rebar reinforcement, foundation excavations should be evaluated by a representative of SALEM for appropriate support characteristics and moisture content. Moisture conditioning may be required for the materials exposed at footing bottom, particularly if foundation excavations are left open for an extended period. 12.9 Cast in Drilled Hole Pier Foundations for Monument Signs 12.9.1 Cast in Drilled Hole (CIDH) pier foundations should have a minimum diameter of 24 inches and extend a minimum depth of 10 feet below the lowest adjacent grade. 12.9.2 Casing of the CIDH piers will likely be required to prevent caving if drilling is required below a depth of about 10 feet where sandy soils were encountered in the test borings. The casing should be bedded into the soil unit near the design depth prior to placement of the reinforcing steel and concrete, and casing extraction. 12.9.3 Settlements of the drilled CIDH piers are not expected to exceed 1 inch total and 1⁄2 inch differential between piers, or over a distance of 20 feet, whichever is the higher distortion. In additional total and differential seismic settlement of about 1 inch total and 1⁄2 inch differential in 40 feet should be anticipated due to a design level seismic event. 12.9.4 CIDH piers should be designed neglecting the lateral capacity within the upper two (2) feet or 1 pile diameter, whichever is greater. Below the neglect depth, the allowable lateral capacity can be designed for 275 pounds per square foot per foot of depth below the lowest adjacent grade to a maximum of 2,750 pounds per square foot. This value may be increased by 1/3 for wind and seismic loading. 12.9.5 CIDH pier foundations should have a minimum embedment depth of 10 feet BSG. The upper two (2) feet should be neglected for axial resistance design. The CIDH foundations may be designed based on an allowable skin friction value of 300 pounds per square foot. End bearing support should be neglected for monument sign CIDH pier design. The allowable skin friction value may be increased by one-third for wind and seismic loading. 12.9.6 Uplift design can consider 60 percent of the allowable downward side friction of the pier plus the weight of the pier. Project No. 1-221-0888 - 24 - October 6, 2021 12.10 Interior Floors 12.10.1 Due to the estimated magnitude of seismic settlement recommended in this report for design, the interior floors should be structurally designed to be either mat slabs (see Section 12.7) or to span grade beams (quasi rigid foundation) which are designed for the static and seismic settlements given in this report. 12.10.2 Site preparation and placement of non-expansive fill soils below interior floors should be in accordance with Section 12.3 of this report. Slab thickness and reinforcement should be determined by the structural engineer based on the anticipated loading and design settlements provided in this report. 12.10.3 The spacing of crack control joints for slabs should be designed by the project structural engineer. In order to regulate cracking of the slabs, we recommend that full depth construction joints or control joints be provided at a maximum spacing of 15 feet in each direction for 5-inch thick slabs and 12 feet for 4-inch thick slabs. 12.10.4 Crack control joints should extend a minimum depth of one-fourth the slab thickness and should be constructed using saw-cuts or other methods as soon as practical after concrete placement. The exterior slab should be poured separately in order to act independently of the walls and foundation system. 12.10.5 It is recommended that the utility trenches within the structure be compacted, as specified in our report, to minimize the transmission of moisture through the utility trench backfill. Special attention to the immediate drainage and irrigation around the structures is recommended. 12.10.6 Moisture within the structure may be derived from water vapors, which were transformed from the moisture within the soils. This moisture vapor penetration can affect floor coverings and produce mold and mildew in the structure. To minimize moisture vapor intrusion, it is recommended that a vapor retarder be installed in accordance with manufacturer’s recommendations and/or ASTM guidelines, whichever is more stringent. In addition, ventilation of the structure is recommended to reduce the accumulation of interior moisture. 12.10.7 In areas where it is desired to reduce floor dampness where moisture-sensitive coverings, coatings, underlayments, adhesives, moisture sensitive goods, humidity controlled environments, or climate cooled environments are anticipated, construction should have a suitable vapor retarder (a minimum of 15 mils thick, is recommended, polyethylene vapor retarder sheeting, Raven Industries “VaporBlock 15, Stego Industries 15 mil “StegoWrap” or W.R. Meadows Sealtight 15 mil “Perminator”) incorporated into the floor slab design. The water vapor retarder should be a decay resistant material complying with ASTM E96 or ASTM E1249 not exceeding 0.01 perms, ASTM E154 and ASTM E1745 Class A. The vapor retarder should, maintain the recommended permeance after conditioning tests per ASTM E1745. The vapor barrier should be placed between the concrete slab and the compacted granular aggregate subbase material. The water vapor retarder (vapor barrier) should be installed in accordance with ASTM Specification E 1643-18. Project No. 1-221-0888 - 25 - October 6, 2021 12.10.8 The concrete may be placed directly on the vapor retarder. The vapor retarder should be inspected prior to concrete placement. Cut or punctured retarder should be repaired using vapor retarder material lapped 6 inches beyond damaged areas and taped. Extend vapor retarder over footings and seal to foundation wall or slab at an elevation consistent with the top of the slab or terminate at impediments such as water stops or dowels. Seal around penetrations, such as utilities or columns, in order to create a monolithic membrane between the surface of the slab and moisture sources below the slab, as well as at the slab perimeter. 12.10.9 Avoid use of stakes driven through the vapor retarder. 12.10.10 The recommendations of this report are intended to reduce the potential for cracking of slabs due to soil movement. However, even with the incorporation of the recommendations presented herein, foundations, stucco walls, and slabs-on-grade may exhibit some cracking due to soil movement. This is common for project areas that contain expansive or loose soils since designing to eliminate potential soil movement is cost prohibitive. The occurrence of concrete shrinkage cracks is independent of the supporting soil characteristics. Their occurrence may be reduced and/or controlled by limiting the slump of the concrete, proper concrete placement and curing, and by the placement of crack control joints at periodic intervals, in particular, where re-entrant slab corners occur. 12.10.11 Proper finishing and curing should be performed in accordance with the latest guidelines provided by the American Concrete Institute, Portland Cement Association, and ASTM. 12.11 Exterior Concrete Slabs on Grade 12.11.1 The following recommendations are intended for lightly loaded exterior slabs on grade not subject to vehicular traffic (i.e. flatwork, sidewalks, etc.). Slab thickness and reinforcement should be determined by the structural engineer based on the anticipated loading. We recommend that non-structural slabs-on-grade be at least 4 inches thick and underlain by a minimum of 6 inches of Class 2 aggregate base, over a minimum of 18 inches of imported non-expansive engineered fill (or an additional 12 inches of Class 2 aggregate base), underlain by engineered fill as recommended under Section 12.3 of this report. 12.11.2 The spacing of crack control joints should be designed by the project structural engineer. In order to regulate cracking of the slabs, we recommend that full depth construction joints or control joints be provided at a maximum spacing of 15 feet in each direction for 5-inch thick slabs and 12 feet for 4-inch thick slabs. 12.11.3 Crack control joints should extend a minimum depth of one-fourth the slab thickness and should be constructed using saw-cuts or other methods as soon as practical after concrete placement. 12.11.4 Proper finishing and curing should be performed in accordance with the latest guidelines provided by the American Concrete Institute, Portland Cement Association, and ASTM. Project No. 1-221-0888 - 26 - October 6, 2021 12.12 Lateral Earth Pressures and Frictional Resistance 12.12.1. Active, at-rest and passive unit lateral earth pressures against footings and walls are summarized in the table below: Allowable Lateral Pressure Conditions Soil Equivalent Fluid Pressure Active Pressure, Drained, pcf 40 At-Rest Pressure, Drained, pcf 61 Allowable Passive Pressure, pcf 275 Allowable Coefficient of Friction 0.30 Minimum Wet Unit Weight (lbs/ft3) [γmin] 95 Maximum Wet Unit Weight (lbs/ft3) [γmax] 135 12.12.2. Active pressure applies to walls, which are free to rotate. At-rest pressure applies to walls, which are restrained against rotation. The preceding lateral earth pressures assume sufficient drainage behind retaining walls to prevent the build-up of hydrostatic pressure. The top one-foot of adjacent subgrade should be deleted from the passive pressure computation. 12.12.3. The allowable parameters include a safety factor of 1.5 and can be used in design for direct comparison of resisting loads against lateral driving loads. 12.12.4. If combined passive and frictional resistance is used in design, a 50 percent reduction in frictional resistance is recommended. 12.12.5. For lateral stability against seismic loading conditions, we recommend a minimum safety factor of 1.1. 12.12.6. For dynamic seismic lateral loading the following equation shall be used: Dynamic Seismic Lateral Loading Equation Dynamic Seismic Lateral Load = 3⁄8γKhH2 Where: γ = Maximum In-Place Soil Density (Section 12.12.1 above) Kh = Horizontal Acceleration = 2⁄3PGAM (Section 12.6.1 above) H = Wall Height 12.13 Retaining Walls 12.13.1 Site preparation for retaining walls associated with non-habitable structures should be conducted in accordance with the recommendations under Section 12.3 of this report. Foundation for retaining walls associated with non-habitable structures should be designed using the geotechnical parameters in under section 12.8 of this report and appropriate lateral loads due to any applicable surcharges (see Section 12.12). In the event proposed retaining walls exceed 5 Project No. 1-221-0888 - 27 - October 6, 2021 feet of retained height, SALEM should be notified by the wall designer to review the wall plans prior to submittal for permit and/or construction bidding. 12.13.2 Retaining and/or below grade walls should be drained with either perforated pipe encased in free- draining gravel or a prefabricated drainage system. The gravel zone should have a minimum width of 12 inches wide and should extend upward to within 12 inches of the top of the wall. The upper 12 inches of backfill should consist of native soils, concrete, asphaltic-concrete or other suitable backfill to minimize surface drainage into the wall drain system. The gravel should conform to Class 2 permeable materials graded in accordance with the current Caltrans Standard Specifications. 12.13.3 Prefabricated drainage systems, such as Miradrain®, Enkadrain®, or an equivalent substitute, are acceptable alternatives in lieu of gravel provided they are installed in accordance with the manufacturer’s recommendations. If a prefabricated drainage system is proposed, our firm should review the system for final acceptance prior to installation. 12.13.4 Drainage pipes should be placed with perforations down and should discharge in a non-erosive manner away from foundations and other improvements. 12.13.5 The top of the perforated pipe should be placed at or below the bottom of the adjacent floor slab or pavements. The pipe should be placed in the center line of the drainage blanket and should have a minimum diameter of 4 inches. Slots should be no wider than 1/8-inch in diameter, while perforations should be no more than 1⁄4-inch in diameter. 12.13.6 For retaining walls less than 5 feet in height, the perforated pipe may be omitted in lieu of weep holes on 4 feet maximum spacing. The weep holes should consist of 2-inch minimum diameter holes (concrete walls) or unmortared head joints (masonry walls) and placed no higher than 18 inches above the lowest adjacent grade. Two 8-inch square overlapping patches of geotextile fabric (conforming to the Caltrans Standard Specifications for "edge drains") should be affixed to the rear wall opening of each weep hole to retard soil piping. 12.13.7 During grading and backfilling operations adjacent to any walls, heavy equipment should not be allowed to operate within a lateral distance of 5 feet from the wall, or within a lateral distance equal to the wall height, whichever is greater, to avoid developing excessive lateral pressures. Within this zone, only hand operated equipment ("whackers," vibratory plates, or pneumatic compactors) should be used to compact the backfill soils. 12.14 Temporary Excavations 12.14.1 We anticipate that the majority of the site soils will be classified as Cal-OSHA “Type C” soil when encountered in excavations during site development and construction. Excavation sloping, benching, the use of trench shields, and the placement of trench spoils should conform to the latest applicable Cal-OSHA standards. The contractor should have a Cal-OSHA-approved “Competent Person” onsite during excavation to evaluate trench conditions and make appropriate recommendations where necessary. 12.14.2 It is the contractor’s responsibility to provide sufficient and safe excavation support as well as protecting nearby utilities, structures, and other improvements which may be damaged by earth movements. All onsite excavations must be conducted in such a manner that potential surcharges from existing structures, construction equipment, and vehicle loads are resisted. The surcharge Project No. 1-221-0888 - 28 - October 6, 2021 area may be defined by a 1:1 projection down and away from the bottom of an existing foundation or vehicle load. 12.14.3 Temporary excavations and slope faces should be protected from rainfall and erosion. Surface runoff should be directed away from excavations and slopes. 12.14.4 Open, unbraced excavations in undisturbed soils should be made according to the slopes presented in the following table: RECOMMENDED MAXIMUM EXCAVATION SLOPES Depth of Excavation (ft) Slope (Horizontal : Vertical) 0-5 1:1 5-10 11⁄2:1 10-15 2:1 12.14.5 If, due to space limitation, excavations near existing structures are performed in a vertical position, braced shorings or shields may be used for supporting vertical excavations. Therefore, in order to comply with the local and state safety regulations, a properly designed and installed shoring system would be required to accomplish planned excavations and installation. A Specialty Shoring Contractor should be responsible for the design and installation of such a shoring system during construction. 12.14.6 Braced shorings should be designed for a maximum pressure distribution of 35H, (where H is the depth of the excavation in feet). The foregoing does not include excess hydrostatic pressure or surcharge loading. Fifty percent of any surcharge load, such as construction equipment weight, should be added to the lateral load given herein. Equipment traffic should concurrently be limited to an area at least 3 feet from the shoring face or edge of the slope. 12.14.7 The excavation and shoring recommendations provided herein are based on soil characteristics derived from the borings within the area. Variations in soil conditions will likely be encountered during the excavations. SALEM Engineering Group, Inc. should be afforded the opportunity to provide field review to evaluate the actual conditions and account for field condition variations not otherwise anticipated in the preparation of this recommendation. Slope height, slope inclination, or excavation depth should in no case exceed those specified in local, state, or federal safety regulation, (e.g. OSHA) standards for excavations, 29 CFR part 1926, or Assessor’s regulations. 12.15 Underground Utilities 12.15.1 Underground utility trenches should be backfilled with properly compacted material. The material excavated from the trenches should be adequate for use as final backfill provided it does not contain deleterious matter, vegetation or rock larger than 3 inches in maximum dimension. Trench backfill should be placed in loose lifts not exceeding 8 inches and moisture conditioned and compacted as recommended under Section 12.5 of this report. The upper 12 inches of trench backfill within asphalt or concrete paved areas shall be moisture conditioned and compacted to at least 95 percent relative compaction. Project No. 1-221-0888 - 29 - October 6, 2021 12.15.2 Bedding and pipe zone backfill typically extends from the bottom of the trench excavations to approximately 12 inches above the crown of the pipe. Pipe bedding, haunches and initial fill extending to 1 foot above the pipe should consist of a clean well graded sand with 100 percent passing the #4 sieve, a maximum of 15 percent passing the #200 sieve, and a minimum sand equivalent of 20. 12.15.3 It is suggested that underground utilities crossing beneath new or existing structures be plugged at entry and exit locations to the building or structure to prevent water migration. Trench plugs can consist of on-site clay soils, if available, or sand cement slurry. The trench plugs should extend 2 feet beyond each side of individual perimeter foundations. 12.15.4 The contractor is responsible for removing all water-sensitive soils from the trench regardless of the backfill location and compaction requirements. The contractor should use appropriate equipment and methods to avoid damage to the utilities and/or structures during fill placement and compaction. 12.16 Pavement Design 12.16.1 Pavement subgrade soils should be prepared as recommended under Section 12.5 of this report. 12.16.2 The pavement design recommendations provided herein are based on the State of California Department of Transportation (CALTRANS) design manual and the results of the R-value testing performed. An R-value of 12 was utilized for design of project pavements. 12.16.3 The pavement design recommendations provided herein are based on a 20-year pavement life for traffic indexes ranging from 5.0 to 8.0. Table 10.16.3 presents minimum sections recommended for flexible asphaltic concrete pavements. TABLE 12.16.3 ASPHALT CONCRETE PAVEMENT THICKNESSES Traffic Index Asphaltic Concrete, (inches) Class 2 Aggregate Base, (inches)* Compacted Subgrade, (inches)* 4.0 2.5 5.5 12.0 5.0 2.5 9.5 12.0 6.0 3.0 12.0 12.0 7.0 4.0 13.5 12.0 *95% compaction based on ASTM D1557 Test Method Project No. 1-221-0888 - 30 - October 6, 2021 12.16.4 The following recommendations are for Portland Cement Concrete pavement sections. TABLE 12.16.4 PORTLAND CEMENT CONCRETE PAVEMENT THICKNESSES Traffic Index Portland Cement Concrete, (inches)* Class II Aggregate Base, (inches)** Compacted Subgrade. (inches)** 4.0 6.0 6.0 ...