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Home My WebLink AboutAppendix C - Soils Engineering Report SOILS ENGINEERING REPORT LITTLE ALAMO 1390 WALKER STREET AND 280-290 PISMO STREET APN: 002-505-005 AND -006 SAN LUIS OBISPO, CALIFORNIA PROJECT SL13900-1 Prepared for Covelop, Inc. 1304 Garden Street San Luis Obispo, California 93401 Prepared by GEOSOLUTIONS, INC. 220 HIGH STREET SAN LUIS OBISPO, CALIFORNIA 93401 (805) 543-8539 © March 7, 2025 SOILS ENGINEERING REPORT Dear Covelop, Inc.: This Soils Engineering Report has been prepared for the proposed mixed-use project referred to as Little Alamo to be located at 1390 Walker Street and 280-290 Pismo Street - APNs: 002-505-005 and -006, San Luis Obispo California. Geotechnically, the site is suitable for the proposed development provided the recommendations in this report for site preparation, earthwork, foundations, slabs, retaining walls, and pavement sections are incorporated into the design. It is anticipated that graded pads will be utilized for construction of the proposed mixed-use development. Given the size of the proposed four-story residential structure and the soil conditions encountered during the field investigation, it is recommended that a deep foundation system be utilized, such as high-capacity helical piles (HCHP). A conventional shallow foundation system may be utilized for the proposed addition to the existing gas works building with foundations excavated into engineered fill. All foundations are to be excavated into uniform material to limit the potential for distress of the foundation systems due to differential settlement. If cuts steeper than allowed by State of California Construction Safety Orders for “Excavations, Trenches, Earthwork” are proposed, a numerical slope stability analysis may be necessary for temporary construction slopes. Thank you for the opportunity to have been of service in preparing this report. If you have any questions, please contact the undersigned at (805) 543-8539. Sincerely, GeoSolutions, Inc. Kraig R. Crozier, PE Principal, C61361 DATE: March 7, 2025 PROJECT NUMBER: SL13900-1 CLIENT: Covelop, Inc. 1304 Garden Street San Luis Obispo, CA 93401 PROJECT NAME: Little Alamo 1390 Walker Street and 280-290 Pismo Street APNs: 002-505-005 and - 006 San Luis Obispo California Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 TABLE OF CONTENTS 1.0 INTRODUCTION .............................................................................................................................. 1 1.1 Site Description ................................................................................................................... 1 1.2 Project Description .............................................................................................................. 1 2.0 PURPOSE AND SCOPE ................................................................................................................. 2 3.0 FIELD AND LABORATORY INVESTIGATION ................................................................................ 2 4.0 HYDROLOGIC SOIL GROUP ......................................................................................................... 5 5.0 SEISMIC DESIGN CONSIDERATIONS .......................................................................................... 5 6.0 LIQUEFACTION HAZARD ASSESSMENT ..................................................................................... 6 7.0 GENERAL SOIL-FOUNDATION DISCUSSION .............................................................................. 6 8.0 CONCLUSIONS AND RECOMMENDATIONS................................................................................ 6 8.1 Preparation of Building Pads .............................................................................................. 7 8.2 Conventional Foundations .................................................................................................. 8 8.3 High Capacity Helical Piles ................................................................................................. 9 8.4 Slab-On-Grade Construction .............................................................................................. 9 8.5 Exterior Concrete Flatwork ............................................................................................... 11 8.6 Retaining Walls ................................................................................................................. 12 8.7 Preparation of Paved Areas .............................................................................................. 15 8.8 Pavement Design .............................................................................................................. 15 9.0 ADDITIONAL GEOTECHNICAL SERVICES ................................................................................. 16 10.0 LIMITATIONS AND UNIFORMITY OF CONDITIONS ................................................................... 17 REFERENCES APPENDIX A Field Investigation Soil Classification Chart Boring Logs CPT Logs APPENDIX B Laboratory Testing Soil Test Reports APPENDIX C Seismic Hazard Analysis Design Map Summary (SEAOC, 2019) APPENDIX D Preliminary Grading Specifications Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 LIST OF FIGURES Figure 1: Site Location Map .......................................................................................................................... 1 Figure 2: Site Plan ......................................................................................................................................... 2 Figure 3: Field Investigation .......................................................................................................................... 3 Figure 4: Regional Geologic Map ................................................................................................................. 4 Figure 5: Sub-Slab Detail ............................................................................................................................ 11 Figure 6: Retaining Wall Detail ................................................................................................................... 13 Figure 7: Retaining Wall Active and Passive Wedges ................................................................................ 13 LIST OF TABLES Table 1: Engineering Properties (Hushmand Associates, Inc., 2015) .......................................................... 4 Table 2: Seismic Design Parameters ............................................................................................................ 6 Table 3: Minimum Footing and Grade Beam Recommendations ................................................................. 8 Table 4: Minimum Slab Recommendations ................................................................................................ 10 Table 5: Retaining Wall Design Parameters ............................................................................................... 12 Table 6: Recommended Pavement Structural Sections ............................................................................. 16 Table 7: Required Special Inspections and Tests of Soils .......................................................................... 17 SOILS ENGINEERING REPORT LITTLE ALAMO 1390 WALKER STREET AND 280-290 PISMO STREET APNS: 002-505-005 AND -006 SAN LUIS OBISPO, CALIFORNIA PROJECT SL13900-1 1.0 INTRODUCTION This report presents the results of the geotechnical investigation for the proposed Little Alamo mixed-use project to be located at 1390 Walker Street and 280-290 Pismo Street - APNs: 002-505-005 and -006, San Luis Obispo California. See Figure 1: Site Location Map for the general location of the project area. Figure 1: Site Location Map was obtained from the website application GIS Surfrider 1.8 (Elfelt, 2016). 1.1 Site Description 1390 Walker Street and 280-290 Pismo Street are located at 35.273043 degrees north latitude and -120.668719 degrees east longitude at a general elevation of 169 feet above mean sea level. The property is approximately rectangular in shape and 0.34 acres in size. The nearest intersection is where Walker Street intersects Pismo Street at the south corner of the property. The project property will hereafter be referred to as the “Site.” See Figure 2: Site Plan for the general layout of the Site. The Site is approximately level with a slight gradient which slopes to north. Surface drainage follows the topography to the south and flows to Pismo Street. Previous activities at the Site have included remedial excavation and removal of impacted soils and replacement with clean fill materials consisting of non-expansive import and cement-slurry materials. Excavation depths at the removal areas varied from 3.0 to 22.0 feet below ground surface, however the removal depths within the proposed building areas appear to be limited to depths between 3.0 feet and 12.0 feet below ground surface. Additional information regarding the remedial operations and backfill materials are presented in the referenced reports by Hushmand Associates Inc. (HAI, 2015 & 2016) 1.2 Project Description The proposed development is anticipated to consist of a 4-story residential building, a remodel of and addition to the existing gas works structure, and site improvements. The proposed 4-story residential building is anticipated to be constructed utilizing reinforced concrete or structural masonry lower floor Figure 1: Site Location Map Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 2 level walls with structural steel and light wood framing residence is to be constructed using light wood framing. The proposed remodel of and addition to the existing gas works building is anticipated to be constructed with light wood framing. It is anticipated that the proposed structures will utilize slab-on-grade lower floor systems. Dead and sustained live loads are currently unknown, but they are anticipated to be relatively light for the proposed addition to the existing gas works building with maximum continuous footing and column loads estimated to be approximately 1.5 kips per linear foot and 15 kips, respectively. Dead and sustained live loads for the proposed residential structure are anticipated to be moderately heavy with maximum continuous footing and column loads estimated to be approximately 4.0 kips per linear foot and 120 kips, respectively. 2.0 PURPOSE AND SCOPE The purpose of this study was to explore and evaluate the surface and sub-surface soil conditions at the Site and to develop geotechnical information and design criteria. The scope of this study includes the following items: 1. A literature review of available published and unpublished geotechnical data pertinent to the project site including geologic maps, and available on-line or in-house aerial photographs. 2. A review of previous field studies performed a the Site along with an additional field study consisting of site reconnaissance and subsurface exploration including exploratory CPT soundings in order to formulate a description of the sub-surface conditions at the Site. 3. A review of laboratory testing performed on representative soil samples that were collected during a previous study by Hushmand Associates Inc. (HAI 2015). 4. Engineering analysis of the data gathered during our literature review, field study, and laboratory testing. 5. Development of recommendations for site preparation and grading as well as geotechnical design criteria for building foundations, retaining walls, pavement sections, underground utilities, and drainage facilities. 3.0 FIELD AND LABORATORY INVESTIGATION The previous field investigation conducted on July 7, 2015 by Hushmand Associates, Inc. was performed using a Hollow Stem Auger drill rig. Eight-inch diameter exploratory borings were advanced to a maximum depth of 60 feet below ground surface (bgs) at the approximate locations indicated on Figure 3: Field Investigation. Sampling methods included the Standard Penetration Test utilizing a Modified California sampler (CA) with liners. Our field investigation was conducted on January 31, 2025 using a CPT Truck provided by Middle Earth Geo Testing, Inc. Four CPT soundings were advanced to a maximum depth of 50.5 feet bgs at the approximate locations indicated on Figure 3: Field Investigation. Figure 2: Site Plan Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 3 Middle Earth Testing of Orange, CA, used a 25-ton CPT rig equipped with an electronic cone to push the CPT’s to depths of approximately 50.5 feet below ground surface (bgs). The electric cone has a 35.7-mm diameter cone-shaped tip with a 60° apex angle, a 35.7-mm diameter by 133.7-mm long cylindrical sleeve, and a pore pressure transducer. The CPT soundings provided a near-continuous soil behavior profile which was used to better characterize the subsurface conditions at the Site. See Appendix A for CPT data and profiles of interpreted soil behavior types. Data gathered during the field investigation suggest that the soil materials at the Site consist of alluvial soils overlying competent formational material. The surface material at the Site generally consisted of light brown silty SAND (SM) with Clay and Light Brown Lean CLAY (CL) encountered in a dry to moist and loose/soft to medium dense/medium stiff conditions. The sub-surface materials consisted of various shades of brown and gray sandy CLAY (CL-CH) and alternating layers of sandy lean CLAY (CL) and silty to poorly graded SANDs (SM-SP) encountered in a moist to saturated and stiff/medium dense to very stiff/very dense conditions. Regional site geology was obtained from United States Geological Survey MapView internet application (USGS, 2013) which compiles existing geologic maps. Figure 4: Regional Geologic Map presents the geologic conditions in site vicinity as mapped on the Geologic Map of the San Luis Obispo Quadrangle (Dibblee, 2004). The majority of all underlying material at the Site was interpreted as Franciscan Complex and will hereafter be referred to as competent formational material. Groundwater was encountered in borings GT-2 and GT-7 (HAI, 2015) at depths of 20.0 and 29.0 feet below ground surface respectively. Groundwater was encountered in all four of the CPT soundings at an approximate depth of 17.0 feet below ground surface. It should be expected that groundwater elevations may vary seasonally and with irrigation practices. Figure 3: Field Investigation Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 4 During the boring operations the soils encountered were continuously examined, visually classified, and sampled for general laboratory testing. A project engineer has reviewed a continuous log of the soils encountered at the time of field investigation. See Appendix A for the Boring Logs from the field investigation. Laboratory tests were performed on soil samples that were obtained from the Site during the previous field investigation. The results of these tests are listed below in Table 1: Engineering Properties (Hushmand Associates, Inc., 2015). Laboratory data reports and detailed explanations of the laboratory tests performed during this investigation are provided in Appendix B. Table 1: Engineering Properties (Hushmand Associates, Inc., 2015) Figure 4: Regional Geologic Map Sample Name Sample Description USCS Specification Plasticity Index Cohesion, c (psf) Angle of Internal Friction, φ (deg.) Fines Content (%) GT-1 5.5-6.0’ Dark Grayish Brown Sandy Lean CLAY CL 21 Medium - - - GT-1 10.5-11.0’ Dark Brown Sand Lean CLAY CL - 60 29.3 - GT-2 5.5-6.0’ Dark Brown Clayey SAND SC - - - 42.0 GT-2 15.5-16.0’ Brown Sandy Fat CLAY CH - - - 50.4 GT-7 5.5-6.0’ Strong Brown Sandy Lean CLAY CL - - - 52.2 Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 5 4.0 HYDROLOGIC SOIL GROUP Based on the Web Soil Survey provided by the Natural Resources Conservation Service, the Site was initially designated as containing Hydrologic Soil Group C & D. Group D soil conditions are less than favorable for infiltration of storm water and runoff due to; very low infiltration rates (high runoff potential), clays with high shrink-swell potential, and soils that are shallow over nearly impervious material. Based on the sub-surface data obtained during the field investigation and the results of the laboratory testing, it is our opinion that the entire Site is best defined as Hydrologic Soil Group D. Based on our understanding of the remedial activities at the Site and the presence of on-site monitoring wells, on-site infiltration of stormwater is not recommended. If utilized, any proposed LID improvements must take into consideration that the on-site soils are expansive with poor infiltration properties. Infiltration of concentrated storm water runoff adjacent to improvements constructed over expansive soils is not recommended as this can result in an increased potential for differential settlement and damage to improvements. Stormwater chambers or basins should be located at a minimum horizontal distance of 10 feet from building foundations, and permeable paver or permeable concrete areas should be located a minimum horizontal distance of 5 feet from building foundations. 5.0 SEISMIC DESIGN CONSIDERATIONS Estimating the design ground motions at the Site depends on many factors including the distance from the Site to known active faults; the expected magnitude and rate of recurrence of seismic events produced on such faults; the source-to-site ground motion attenuation characteristics; and the Site soil profile characteristics. According to section 1613 of the 2022 CBC (CBSC, 2022), all structures and portions of structures should be designed to resist the effects of seismic loadings caused by earthquake ground motions in accordance with the ASCE 7: Minimum Design Loads for Buildings and Other Structures, hereafter referred to as ASCE 7-16 (ASCE, 2016). The Site soil profile classification (Site Class) can be determined by the average soil properties in the upper 100 feet of the Site profile and the criteria provided in Table 20.3-1 of ASCE 7-16. Spectral response accelerations and peak ground accelerations, provided in this report were obtained using the computer-based Seismic Design Maps tool available from the Structural Engineers Association of California (SEAOC, 2019). This program utilizes the methods developed in ASCE 7-16 in conjunction with user-inputted Site location to calculate seismic design parameters and response spectra (both for period and displacement) for soil profile Site Classes A through E. Site coordinates of 35.273043 degrees north latitude and -120.668719 degrees east longitude were used in the web-based probabilistic seismic hazard analysis (SEAOC, 2019). Based on the results from the in- situ tests performed during the field investigation, the Site was defined as Site Class D, “Stiff Soil” profile per ASCE7-16, Chapter 20. Relevant seismic design parameters obtained from the program are summarized in Table 2: Seismic Design Parameters. Sample Name Chloride (mg/kg) Sulphate (mg/kg) pH Resistivity (ohm-cm) Estimated Corrosivity Based on Resistivity Estimated Corrosivity Based on Sulfates GT-1 5.5-6.0’ 20 202 7.3 1,130 Severely Corrosive NA Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 6 Table 2: Seismic Design Parameters Site Class D “Stiff Soil” Seismic Design Category D 1-Second Period Design Spectral Response Acceleration, SD1 (See Note 1) Short-Period Design Spectral Response Acceleration, SDS 0.757g Site Specific MCE Peak Ground Acceleration, PGAM 0.528g Note 1: In accordance with ASCE 7-16, SUPPLEMENT 3, Section 11.4.8.1: A ground motion hazard analysis is not required for structures on Site Class D sites with S1 greater than or equal to 0.2, where the value of the parameter SM1 determined by Eq. (11.4-2) is increased by 50% for all applications of SM1 in this Standard. The resulting value of the parameter SD1 determined by Eq. (11.4-4) shall be used for all applications of SD1 in this Standard. 6.0 LIQUEFACTION HAZARD ASSESSMENT Liquefaction occurs when saturated cohesionless soils lose shear strength due to earthquake shaking. Ground motion from an earthquake may induce cyclic reversals of shear stresses of large amplitude. Lateral and vertical movement of the soil mass combined with the loss of bearing strength can result from this phenomenon. Liquefaction potential of soil deposits during earthquake activity depends on soil type, void ratio, groundwater conditions, the duration of shaking, and confining pressures on the potentially liquefiable soil unit. Fine, poorly graded loose sand, shallow groundwater, high intensity earthquakes, and long duration of ground shaking are the principal factors leading to liquefaction. Based on the consistency and relative density of the in-situ soils interpreted from the CPT soundings, the potential for seismic liquefaction of soils at the Site is low. Assuming that the recommendations of the Soils Engineering Report are implemented, the potential for seismically induced settlement and differential settlement at the Site is considered to be low. 7.0 GENERAL SOIL-FOUNDATION DISCUSSION It is anticipated that graded pads will be utilized for construction of the proposed mixed-use development. Given the size of the proposed four-story residential structure and the soil conditions encountered during the field investigation, it is recommended that a deep foundation system be utilized, such as high-capacity helical piles (HCHP). A conventional shallow foundation system may be utilized for the proposed addition to the existing gas works building with foundations excavated into engineered fill. All foundations are to be excavated into uniform material to limit the potential for distress of the foundation systems due to differential settlement. If cuts steeper than allowed by State of California Construction Safety Orders for “Excavations, Trenches, Earthwork” are proposed, a numerical slope stability analysis may be necessary for temporary construction slopes. 8.0 CONCLUSIONS AND RECOMMENDATIONS The Site is suitable for the proposed development provided the recommendations presented in this report are incorporated into the project plans and specifications. The primary geotechnical concerns at the Site are: 1. The presence of non-uniform backfill materials from the remedial activities within the proposed building areas. Excavations ranging from 3.0 feet to 12.0 feet were backfilled with compacted non-expansive import materials or sand cement slurry. Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 7 2. The presence of potentially expansive material. Influx of water from irrigation, leakage from the structures, or natural seepage could cause expansive soil problems. Foundations supported by expansive soils should be designed by a Structural Engineer in accordance with the 2022 California Building Code. 3. The potential for differential settlement occurring between foundations supported on two soil materials having different settlement characteristics, such as native soil, imported fill/slurry, and engineered fill. Therefore, it is important that all of the foundations are founded in equally competent uniform material in accordance with this report. 8.1 Preparation of Building Pads 1. It is anticipated that graded pads will be developed for the proposed mixed-use project with the proposed remodel of/addition to the gas works building supported by a conventional shallow foundations and the proposed 4-story residential structure supported by a deep foundation system consisting of high-capacity helical piles (HCHP). 2. For preparation of a graded pad for the proposed 4-story residential structure to be supported by HCHP, the native material should be over-excavated a minimum of 12 inches below existing grade, to the bottom elevation of the perimeter foundation, or to competent material; whichever is deeper. The exposed surface should be scarified to a depth of 6 inches, and moisture conditioned to 3% over optimum moisture content, and compacted to a minimum relative density of 90 percent (ASTM D1557-12). The over- excavated material, cleared of debris, organics, and oversize materials may then be processed as engineered fill. Refer to Figure 5: Sub-Slab Detail for under-slab drainage material and Appendix D for more details on fill placement. 3. For the preparation of a graded fill pad for the remodel of/addition to the gas works building, the native material should be over-excavated at least 24 inches below existing grade, 12 inches below the bottom of the footings, or to competent material; whichever is deeper. The limits of over-excavation should extend a minimum of 5 feet beyond the perimeter foundation, to property lines, or existing improvements, whichever is least. The exposed surface should be scarified to a depth of 6 inches; moisture conditioned to 3% over optimum moisture content, and compacted to a minimum relative density of 90 percent (ASTM D1557-12). The over-excavated material, cleared of debris, organics and oversize materials may then be processed as engineered fill. Refer to Figure 5: Sub-Slab Detail for under-slab drainage material and Appendix D for more details on fill placement. 4. The ground immediately adjacent to the foundation shall be sloped away from the building at a slope of not less than one unit vertical in 20 units horizontal (5 percent slope) for a minimum distance of 10 feet measured perpendicular to the exterior of the structure per Section 1804.3 of the 2022 CBC. 5. Imported non-expansive material may also be used as engineered fill. All material to be used as non-expansive engineered fill must be observed and approved by a representative of GeoSolutions, Inc. prior to its delivery to the Site). 6. There is potential that soils encountered at the required over-excavation depths may exhibit soft, compressible conditions. If pumping soils are encountered at the bottom of the excavation, stabilization will be necessary and may require the installation of a Tensar BX1100 (woven geotextile fabric, such as Mirafi HP570) or equivalent, on the prepared bottom of the excavation. If the soil within the excavation is not stable enough for proper installation of the geotextile fabric, rock stabilization of the exposed sub-grade may be required, with the placement and compaction of 3-inch to 8-inch diameter (gabion) crushed stone into the soft sub-grade, until stability is achieved, as observed Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 8 and approved by a representative of this firm. Alternative recommendations may be prepared based on the conditions encountered. 7. The recommended soil moisture content should be maintained during construction and following construction of the proposed development. Where soil moisture content is not maintained, desiccation cracks may develop which indicate a loss of soil compaction, leading to the potential for damage to foundations, flatwork, pavements, and other improvements. Soils that have become cracked due to moisture loss should be removed sufficient depth to repair the cracked soil as observed by the soils engineer, and the removed materials should then be moisture conditioned to approximately 3 percent over optimum value, and compacted. 8.2 Conventional Foundations 1. Conventional continuous and spread footings with grade beams may be used for support of the proposed remodel of/addition to the existing gas works structure. Isolated pad footings are not permitted. Spread footings should be a minimum of two feet square and connected to the perimeter foundation by grade beams. 2. Minimum footing and grade beam sizes and depths in engineered fill should conform to the following table, as observed and approved by a representative of GeoSolutions, Inc. Table 3: Minimum Footing and Grade Beam Recommendations Perimeter Footings Grade Beams Minimum Width 12 inches (one or two story) 12 inches Embedment Depth 24 inches 18 inches Minimum Reinforcing* 4 #5 bars (2 top / 2 bottom) 4 #4 bars (2 top / 2 bottom) Spacing - 19 feet on-center each way * Steel should be held in place by stirrups at appropriate spacing to ensure proper positioning of the steel (see WRI Design of Slab-on-Ground Foundations and ACI 318, Section 26.6.6 – Placing Reinforcement). 3. Minimum reinforcing for footings should conform to the recommendations provided in Table 3: Minimum Footing and Grade Beam Recommendations which meets the specifications of Section 1808.6 of the 2022 California Building Code for the soil conditions at the Site. Reinforcing steel should be held in place by stirrups at appropriate spacing to ensure proper positioning of the steel in accordance with WRI Design of Slab- on-Ground Foundations, and ACI 318, Section 26.6.6 – Placing Reinforcement. 4. A representative of this firm should observe and approve all foundation excavations for required embedment depth prior to the placement of reinforcing steel and/or concrete. Concrete should be placed only in excavations that are free of loose, soft soil and debris and that have been maintained in a moist condition with no desiccation cracks present. 5. An allowable dead plus live load bearing pressure of 1,500 psf may be used for the design of footings founded in engineered fill. 6. Allowable bearing capacities may be increased by one-third when transient loads such as wind or seismicity are included. Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 9 7. A total settlement of less than 1 inch and a differential settlement of less than 1 inch in 30 feet are anticipated. 8. Lateral forces on structures may be resisted by passive pressure acting against the sides of shallow footings and/or friction between the engineered fill and the bottom of the footings. For resistance to lateral loads, a friction factor of 0.30 may be utilized for sliding resistance at the base of footings extending a minimum of 24 inches into engineered fill. A passive pressure of 250-pcf equivalent fluid weight may be used against the side of shallow footings in engineered fill. If friction and passive pressures are combined to resist lateral forces acting on shallow footings, the lesser value should be reduced by 50 percent. 9. Foundation excavations should be observed and approved by a representative of this firm prior to the placement of formwork, reinforcing steel and/or concrete. 10. Foundation design should conform to the requirements of Chapter 18 of the latest edition of the CBC (CBSC, 2022). 11. The base of all grade beams and footings should be level and stepped as required to accommodate any change in grade while still maintaining the minimum required footing embedment and slope setback distance. 8.3 High Capacity Helical Piles 1. High-capacity helical piles may be utilized to support the proposed structure. The piles are advanced by rotation, without vibration and with virtually no spoils. An 8-inch diameter helical pile foundation system has been used successfully on similar projects. However, the structural engineer may consider other helical type systems. Prior to final design one (1) test pile should be installed and load tested. 2. Based on our experience, the helical piles will extend to approximately 50 to 60 feet below land surface. The helical piles should be connected by footings and grade beams that extend a minimum of 24 inches below finished grade. A maximum spacing of 19 feet on center is recommended for grade beams beneath slab-on-grade areas. Minimum reinforcing should be as directed by the project Structural Engineer. 3. An equivalent fluid weight of 250 pounds per cubic foot acting on two times the pile diameter may be used to evaluate passive resistance, starting at a depth of 2.0 feet below ground surface. The passive pressure may be increased by 1/3 for transient loads such as wind or seismic. 4. Lateral forces on structures may be resisted by passive pressure acting against the sides of shallow footings and/or friction between the native material and the bottom of the footings and slab. For resistance to lateral loads, a friction factor of 0.30 may be utilized for sliding resistance at the base of footings and the slab. 5. Foundation excavations should be observed and approved by a representative of this firm prior to the placement of reinforcing steel and/or concrete. Foundation design should conform to the requirements of Chapter 18 of the latest edition of the California Building Code. 8.4 Slab-On-Grade Construction 1. Concrete slabs-on-grade and flatwork should not be placed directly on unprepared native materials. Preparation of sub-grade to receive concrete slabs-on-grade and flatwork should be processed as discussed in the preceding sections of this report. Concrete Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 10 slabs should be placed only over sub-grade that is free of loose, soft soil and debris and that has been maintained in a moist condition with no desiccation cracks present. 2. Concrete slabs-on-grade should be in conformance with the recommendations provided in Table 4: Minimum Slab Recommendations. Reinforcing should be placed on-center both ways at or slightly above the center of the structural section. Reinforcing bars should have a minimum clear cover of 1.5 inches. Where lapping of the slab steel is required, laps in adjacent bars should be staggered a minimum of every five feet (see WRI Design of Slab-on-Ground Foundations, Steel Placement). The recommended reinforcement may be used for anticipated uniform floor loads not exceeding 200 psf. If floor loads greater than 200 psf are anticipated, a Structural Engineer should evaluate the slab design. Table 4: Minimum Slab Recommendations Minimum Thickness 4 inches Reinforcing* #3 bars at 12 inches on-center each way * Where lapping of the slab steel is required, laps in adjacent bars should be staggered a minimum of every five feet (see WRI/CSRI-81 recommendations for Steel Placement, Section 2). 3. Concrete for all slabs should be placed at a maximum slump of less than 5 inches. Excessive water content is the major cause of concrete cracking. If fibers are used to aid in the control of cracking, a water-reducing admixture may be added to the concrete to increase slump while maintaining a water/cement ratio, which will limit excessive shrinkage. Control joints should be constructed as required to control cracking. 4. Where concrete slabs-on-grade are to be constructed for interior conditioned spaces, the slabs should be underlain by a minimum of four inches of clean free-draining material, such as a ¾-inch coarse aggregate mix, to serve as a cushion and a capillary break. Where moisture susceptible storage or floor coverings are anticipated, a 15-mil Stego Wrap membrane (or equivalent installed per manufacturer’s specifications) should be placed between the free-draining material and the slab to minimize moisture condensation under the floor covering. See Figure 5: Sub-Slab Detail for the placement of under-slab drainage material. It is suggested, but not required, that a two-inch thick sand layer be placed on top of the membrane to assist in the curing of the concrete, increasing the depth of the under-slab material to a total of six inches. The sand should be lightly moistened prior to placing concrete. Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 11 Figure 5: Sub-Slab Detail 5. It should be noted that for a vapor barrier installation to conform to manufacturer’s specifications, sealing of penetrations, joints and edges of the vapor barrier membrane are typically required. As required by the California Building Code, joints in the vapor barrier should be lapped a minimum of 6 inches. If the installation is not performed in accordance with the manufacturer’s specifications, there is an increased potential for water vapor to affect the concrete slabs and floor coverings. 6. The most effective method of reducing the potential for moisture vapor transmission through concrete slabs-on-grade would be to place the concrete directly on the surface of the vapor barrier membrane. However, this method requires a concrete mix design specific to this application with low water-cement ratio in addition to special concrete finishing and curing practices, to minimize the potential for concrete cracks and surface defects. The contractor should be familiar with current techniques to finish slabs poured directly onto the vapor barrier membrane. 7. Moisture condensation under floor coverings has become critical due to the use of water- soluble adhesives. Therefore, it is suggested that moisture sensitive slabs not be constructed during inclement weather conditions. 8.5 Exterior Concrete Flatwork 1. Due to the presence of expansive surface soils within the proposed development areas, there is a potential for considerable soil movement and distress to reinforced concrete flatwork if conventional measures are used, such as the placement of 4 to 6 inches of imported sand materials placed beneath concrete flatwork. Heaving and cracking are anticipated to occur. To reduce the potential for movement associated with expansive soils, we recommend the placement of a minimum of 18 inches of approved non- expansive import material placed as engineered fill beneath the flatwork. 2. Minimum flatwork for conventional pedestrian areas should be a minimum of 4 inches thick and consist of No. 3 (#3) rebar spaced at 24 inches on-center each-way at or slightly above the center of the structural section. Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 12 3. Flatwork should be constructed with frequent joints to allow for movement due to fluctuations in temperature and moisture content in the adjacent soils. Flatwork at doorways, driveways, curbs and other areas where restraining the elevation of the flatwork is desired, should be doweled to the perimeter foundation by a minimum of No. 3 reinforcing steel dowels, spaced at a maximum distance of 24 inches on-center. 4. As an alternative, interlocking concrete pavers may be utilized for exterior improvements in lieu of reinforced concrete flatwork. Concrete pavers, when installed in accordance with manufacturers’ recommendations and industry standards (ICPI), allow for a greater degree of soil movement as they are part of a flexible system. If interlocking concrete pavers are selected for use in the driveway area, the structural section should be underlain by a woven geotextile fabric, such as Mirafi HP570 or equivalent, to function as a separation layer and to provide additional support for vehicle tire loads. 8.6 Retaining Walls 1. Retaining walls should be designed to resist lateral pressures from adjacent soils and surcharge loads applied behind the walls. We recommend using the lateral pressures presented in Table 5: Retaining Wall Design Parameters and Figure 6: Retaining Wall Detail for the design of retaining walls at the Site. The Active Case may be used for the design of unrestrained retaining walls, and the At-Rest Case may be used for the design of restrained retaining walls. Table 5: Retaining Wall Design Parameters Lateral Pressure and Condition Equivalent Fluid Pressure, pcf Static, Active Case, Native (γ'KA) 65 Static, At-Rest Case, Native (γ'KO) 80 Static, Passive Case, Engineered Fill (γ'KP) 250 Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 13 2. The above values for equivalent fluid pressure are based on retaining walls having level retained surfaces, having an approximately vertical surface against the retained material, and retaining granular backfill material or engineered fill composed of native soil within the active wedge. See Figure 6: Retaining Wall Detail and Figure 7: Retaining Wall Active and Passive Wedges for a description of the location of the active wedge behind a retaining wall. 3. Proposed retaining walls having a retained surface that slopes upward from the top of the wall should be designed for an additional equivalent fluid pressure of 1 pcf for the active case and 1.5 pcf for the at-rest case, for every degree of slope inclination. 4. We recommend that the proposed retaining walls at the Site have an approximately vertical surface against the retained material. If the proposed retaining walls are to have sloped surfaces against the retained material, the project designers should contact the Soils Engineer to determine the appropriate lateral earth pressure values for retaining walls located at the Site. Figure 7: Retaining Wall Active and Passive Wedges 5. Retaining wall foundations should be founded a minimum of 24 inches below lowest adjacent grade in engineered fill as observed and approved by a representative of GeoSolutions, Inc. A coefficient of friction of 0.30 may be used between engineered fill Figure 6: Retaining Wall Detail 12” minimum Mirafi 140N or equivalent Ka = 65 pcf Ko = 80 pcf Permeable Drain Rock 4” Dia. Perf. Drainpipe Max Toe Pressure: 1,500 psf Kp= 250 pcf Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 14 and concrete footings. Project designers may use a maximum toe pressure of 1,500 psf for the design of retaining wall footings founded in engineered fill. 6. For earthquake conditions, retaining walls greater than 6 feet in height should be designed to resist an additional seismic lateral soil pressure of 18 pcf equivalent fluid pressure for unrestrained walls (active condition). The pressure resultant force from earthquake loading should be assumed to act a distance of 1/3H above the base of the retaining wall, where H is the height of the retaining wall. Seismic active lateral earth pressure values were determined using the simplified dynamic lateral force component (SEAOC 2010) utilizing the design peak ground acceleration, PGAM, discussed in Section 4.0 (PGAM = 0.528g). The dynamic increment in lateral earth pressure due to earthquakes should be considered during the design of retaining walls at the Site. Based on research presented by Dr. Marshall Lew (Lew et al., 2010), lateral pressures associated with seismic forces should not be applied to restrained walls (at-rest condition). 7. Seismically induced forces on retaining walls are considered to be short-term loadings. Therefore, when performing seismic analyses for the design of retaining wall footings, we recommend that the allowable bearing pressure and the passive pressure acting against the sides of retaining wall footings be increased by a factor of one-third. 8. In addition to the static lateral soil pressure values reported in Table 5: Retaining Wall Design Parameters, the retaining walls at the Site should be designed to support any design live load, such as from vehicle and construction surcharges, etc., to be supported by the wall backfill. If construction vehicles are required to operate within 10 feet of a retaining wall, supplemental pressures will be induced and should be taken into account in the design of the retaining wall. 9. The recommended lateral earth pressure values are based on the assumption that sufficient sub-surface drainage will be provided behind the walls to prevent the build-up of hydrostatic pressure. To achieve this we recommend that a granular filter material be placed behind all proposed walls. The blanket of granular filter material should be a minimum of 12 inches thick and should extend from the bottom of the wall to 12 inches from the ground surface. The top 12 inches should consist of moisture conditioned, compacted, clayey soil. Neither spread nor wall footings should be founded in the granular filter material used as backfill. 10. A 4-inch diameter perforated or slotted drainpipe (ASTM D1785 PVC) should be installed near the bottom of the filter blanket with perforations facing down. The drainpipe should be underlain by at least 4 inches of filter type material and should daylight to discharge in suitably projected outlets with adequate gradients. The filter material should consist of a clean free-draining aggregate, such as a coarse aggregate mix. If the retaining wall is part of a structural foundation, the drainpipe must be placed below finished slab sub- grade elevation. 11. The filter material should be encapsulated in a permeable geotextile fabric. A suitable permeable geotextile fabric, such as non-woven needle-punched Mirafi 140N or equal, may be utilized to encapsulate the retaining wall drain material and should conform to Caltrans Standard Specification 88-1.03 for underdrains. 12. For hydrostatic loading conditions (i.e. no free drainage behind retaining wall), an additional loading of 45-pcf equivalent fluid weight should be added to the active and at- rest lateral earth pressures. If it is necessary to design retaining structures for submerged conditions, the allowed bearing and passive pressures should be reduced by 50 percent. In addition, soil friction beneath the base of the foundations should be neglected. Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 15 13. Precautions should be taken to ensure that heavy compaction equipment is not used adjacent to walls, so as to prevent undue pressure against, and movement of the walls. 14. The use of water-stops/impermeable barriers should be used for any basement construction, and for building walls that retain earth. Damproofing and waterproofing shall meet the minimum standards of Section 1805 of the 2022 California Building Code. 8.7 Preparation of Paved Areas 1. Pavement areas should be excavated to approximate sub-grade elevation or to competent material; whichever is deeper. The exposed surface should be scarified an additional depth of 12 inches, moisture conditioned to slightly above optimum moisture content, and compacted to a minimum relative density of 95 percent (ASTM D1557-12 test method). 2. The top 12 inches of sub-grade soil under all pavement sections should be compacted to a minimum relative density of 95 percent based on the ASTM D1557-12 test method at slightly above optimum. 3. Sub-grade soils should not be allowed to dry out or have excessive construction traffic between moisture conditioning and compaction, and placement of the pavement structural section. 4. Due to the expansive potential of the soils at the Site, the base courses beneath un- reinforced pavement sections may fail, causing cracking of the pavement surfaces, as the sub-grade materials move laterally during expansive shrink-swell cycles. 5. Therefore, in order to minimize the potential for the failure of pavement sections at the Site, GeoSolutions, Inc. recommends that a Type 2 laterally-reinforcing geotextile grid, such as Tensar BX1200, Syntec SBX12, ADS BX124GG, Mirafi BXG120 or equivalent, be installed between the prepared sub-grade and base materials at the Site. 6. GeoSolutions, Inc. should be contacted prior to the design and construction of pavement sections at the Site in order to assist in the selection of an appropriate laterally-reinforcing biaxial geogrid product and to provide recommendations regarding the procedures for the installation of geogrid products at the Site. 8.8 Pavement Design 1. All paving construction and materials used should conform to applicable sections of the latest edition of the State of California Department of Transportation Standard Specifications. 2. As indicated previously, the top 12 inches of sub-grade soil under asphaltic concrete pavement sections should be compacted to a minimum relative density of 95 percent based on the ASTM D1557-12 test method at slightly above optimum moisture content. Aggregate bases and sub-bases should also be compacted to a minimum relative density of 95 percent based on the aforementioned test method. 3. The following table provides the recommended Hot Mix Asphalt (HMA) pavement sections based on an estimated R-Value of 5 for the native soil and an improved R- Value of 25 for pavement sections reinforced with a Type 2 laterally-reinforcing geotextile grid, in accordance with the referenced Subgrade Enhancement Geosynthetic Design and Construction Guide (CADOT, 2013). 4. All pavement sections should be crowned for good drainage. All pavement construction Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 16 and materials used should conform to Sections 25, 26 and 39 of the latest edition of the State of California Department of Transportation Standard Specifications. 5. GeoSolutions, Inc. should be contacted prior to the design and construction of the pavement sections to provide recommendations regarding the selection of and installation of an appropriate laterally-reinforcing biaxial geogrid product Table 6: Recommended Pavement Structural Sections Traffic Index Pavement Section Thickness in Inches Unreinforced Pavement Section Thickness in Inches Reinforced with Type 2 Geogrid HMA AB HMA AB 5.0 3.00 10.0 3.00 6.50 6.0 3.00 14.0 3.00 9.50 7.0 3.00 17.5 3.00 12.5 HMA = Hot Mix Asphalt meeting Caltrans Specification HMA Type A ½ inch mix AB = Aggregate Base meeting Caltrans Specification for Class 2 aggregate base (R-Value = 78 Min) 9.0 ADDITIONAL GEOTECHNICAL SERVICES The recommendations contained in this report are based on a limited number of borings and on the continuity of the sub-surface conditions encountered. GeoSolutions, Inc. assumes that it will be retained to provide additional services during future phases of the proposed project. These services would be provided by GeoSolutions, Inc. as required by the City of San Luis Obispo, the 2022 CBC, and/or industry standard practices. These services would be in addition to those included in this report and would include, but are not limited to, the following services: 1. Consultation during plan development. 2. Plan review of grading and foundation documents prior to construction and a report certifying that the reviewed plans are in conformance with our geotechnical recommendations. 3. Consultation during selection and placement of a laterally-reinforcing biaxial geogrid product. 4. Construction inspections and testing, as required, during all grading and excavating operations beginning with the stripping of vegetation at the Site, at which time a site meeting or pre-job meeting would be appropriate. 5. Special inspection services during construction of reinforced concrete, structural masonry, high strength bolting, epoxy embedment of threaded rods and reinforcing steel, and welding of structural steel. 6. Preparation of construction reports certifying that building pad preparation and foundation excavations are in conformance with our geotechnical recommendations. 7. Preparation of special inspection reports as required during construction. 8. In addition to the construction inspections listed above, section 1705.6 of the 2022 CBC (CBSC, 2022) requires the following inspections by the Soils Engineer for controlled fill thicknesses greater than 12 inches as shown in Table 7: Required Special Inspections and Tests of Soils: Little Alamo -1390 Walker and 280 - 290 Pismo Street March 7, 2025 Project SL13900-1 17 Table 7: Required Special Inspections and Tests of Soils Verification and Inspection Task Continuous During Task Listed Periodically During Task Listed 1. Verify materials below footings are adequate to achieve the design bearing capacity. - X 2. Verify excavations are extended to proper depth and have reached proper material. - X 3. Perform classification and testing of controlled fill materials. - X 4. Verify use of proper materials, densities and lift thicknesses during placement and compaction of controlled fill. X - 5. Prior to placement of controlled fill, observe sub-grade and verify that site has been prepared properly. - X 10.0 LIMITATIONS AND UNIFORMITY OF CONDITIONS 1. The recommendations of this report are based upon the assumption that the soil conditions do not deviate from those disclosed during our study. Should any variations or undesirable conditions be encountered during the development of the Site, GeoSolutions, Inc. should be notified immediately and GeoSolutions, Inc. will provide supplemental recommendations as dictated by the field conditions. 2. This report is issued with the understanding that it is the responsibility of the owner or his/her representative to ensure that the information and recommendations contained herein are brought to the attention of the architect and engineer for the project, and incorporated into the project plans and specifications. The owner or his/her representative is responsible to ensure that the necessary steps are taken to see that the contractor and subcontractors carry out such recommendations in the field. 3. As of the present date, the findings of this report are valid for the property studied. With the passage of time, changes in the conditions of a property can occur whether they are due to natural processes or to the works of man on this or adjacent properties. Therefore, this report should not be relied upon after a period of 3 years without our review nor should it be used or is it applicable for any properties other than those studied. However many events such as floods, earthquakes, grading of the adjacent properties and building and municipal code changes could render sections of this report invalid in less than 3 years. \\192.168.1.100\s\SL13500-SL13999\SL13900-1 - Walker Pismo Pacific SER\Engineering\SL13900-1 Walker Street and 280-290 Pismo SER.doc REFERENCES REFERENCES American Concrete Institute (ACI). Building Code Requirements for Structural Concrete (318-08), Chapter 7, Section 7.5, Placing Reinforcement, ACI Committee 318, 2008. American Society of Civil Engineers (ASCE). Minimum Design Loads and Associated Criteria for Buildings and Other Structures (7-16). 2017. California Building Standards Commission (CBSC). 2022 California Building Code, California Code of Regulations. Title 24. Part 2. Vol. 2. California Building Standards Commission: July 2022. County of San Luis Obispo. Assessor’s Map Book: 005, Page 05. August 15, 2016. <https://assessor.slocounty.ca.gov/assessor/pisa/Search.aspx>. DeLorme. Topo USA 8.0. Vers.8.0.0 Computer software. DeLorme, 2009. Dibblee, Thomas W., Jr.. Geologic Map of the San Luis Obispo Quadrangle. Dibblee Geologic Center Map Number DF-129. Santa Barbara Museum of Natural History: June 2004. Elfelt. GIS Surfer 1.8. Vers.1.8.0 Computer software. Elfelt, 2016. Geotechnical Engineering Support Services for Removal Action, Former San Luis Obispo Manufactured Gas Plant (MGP), San Luis Obispo, San Luis Obispo County, California, by Hushmand Associates, Inc., Project Number TPG-15-002, dated March 7, 2016. Geotechnical Observations and Testing Services, Remedial Action at Former San Luis Obispo Manufactured Gas Plant (MGP), San Luis Obispo, California, by Hushmand Associates, Inc., Project Number TPG-15-002, dated December 29, 2017. Lew, M., Sitar, N., Al Atik, L., Paourzanjani, M., and Hudson, M. “Seismic Earth pressure on Deep Building Basements,” SEAOC 2010 Convention Proceedings, 2010. State of California. Department of Industrial Relations. California Code of Regulations. 2001 Edition. Title 8. Chapter 4: Division of Industrial Safety. Subchapter 4, Construction Safety Orders. Article 6: Excavations. http://www.dir.ca.gov/title8/sub4.html. State of California, Department of Transportation. Standard Specifications, California Department of Transportation, 2015. Structural Engineers Association of California (SEAOC), Seismic Design Maps, accessed February 28, 2025. <https://seismicmaps.org/>. Terzaghi, K. Evaluation of Coefficients of Subgrade Reaction, Getechnique, Vol. 5, No. 4, 41-50, 1955. Tensar. Tensar geogrid foundation solutions in earthquake-susceptible locations. Tensar Information Bulletin, IB/Earthquake Foundation, April 5, 2013. United States Geological Survey. MapView – Geologic Maps of the Nation. Internet Application. USGS, accessed February 28, 2025. <http://ngmdb.usgs.gov/maps/MapView/>. United States Geological Survey. TopoView – Geologic Maps of the Nation. Internet Application. USGS, accessed February 28, 2025. <http://ngmdb.usgs.gov/maps/TopoView/>. Wire Reinforcement Institute, Design of Slab-on-Ground Foundations, A Design, Construction $ Inspection Aid for Consulting Engineers, TF 700-R-03 Update, dated 2003. APPENDIX A Field Investigation Soil Classification Chart Boring Logs CPT Logs FIELD INVESTIGATION The previous field investigation was conducted on July 7, 2015 by Hushmand Associates, Inc. using a Hollow Stem Auger drill rig. The surface and sub-surface conditions within the proposed building areas were studied by advancing nine exploratory borings. This exploration was conducted in accordance with presently accepted geotechnical engineering procedures consistent with the scope of the services authorized to GeoSolutions, Inc. The Hollow Stem Auger drill rig with an eight-inch diameter hollow-stem continuous flight auger advanced nine exploratory borings, three of which were located near the approximate locations indicated on Figure 3: Field Investigation. The soils were classified in accordance with the Unified Soil Classification System. See the Soil Classification Chart in this appendix. The CA sampler is a larger diameter sampler than the standard (SPT) sampler with a two-inch outside diameter and provides additional material for normal geotechnical testing such as in-situ shear and consolidation testing. Either sampler may be used in the field investigation, but the N-values obtained from using the CA sampler will be greater than that of the SPT. The N-values for samples collected using the CA can be roughly correlated to SPT N-values using a conversion factor that may vary from about 0.5 to 0.7. A commonly used conversion factor is 0.67 (2/3). More information about standardized samplers can be found in ASTM D1586 and ASTM D3550. Disturbed bulk samples are obtained from cuttings developed during boring operations. The bulk samples are selected for classification and testing purposes and may represent a mixture of soils within the noted depths. Recovered samples are placed in transport containers and returned to the laboratory for further classification and testing. Logs of the borings showing the approximate depths and descriptions of the encountered soils, applicable geologic structures, recorded N-values, and the results of laboratory tests are presented in this appendix. The logs represent the interpretation of field logs and field tests as well as the interpolation of soil conditions between samples. The results of laboratory observations and tests are also included in the boring logs. The stratification lines recorded in the boring logs represent the approximate boundaries between the surface soil types. However, the actual transition between soil types may be gradual or varied. The current field investigation was conducted on January 31, 2025, using the Middle-Earth Cone Penetration Test (CPT) sounding equipment. The four CPT soundings were advanced to a maximum depth of 50.5 feet bgs. This exploration was conducted in accordance with presently accepted geotechnical engineering procedures consistent with the scope of the services authorized to GeoSolutions, Inc. A 20-ton CPT truck was used to advance an electronic cone which measures tip resistance (qC), sleeve friction (fS), and pore water pressure (u2) at approximately 5-cm intervals. This data can be process to provide a near continuous interpretation of the soil profile. All CPT soundings were performed in general accordance with ASTM D5778 standards. GeoSolutions Inc.ProjectLittle Alamo-1390 Walker, San luis ObispoOperatorAJ-ERFilenameSDF(251).cptJob NumberSL13900-1Cone NumberDDG1587GPSHole NumberCPT-01Date and Time1/31/2025 9:59:42 AMMaximum Depth50.52 ftEST GW Depth During Test17.60 ftNet Area Ratio .8Cone Size 15cm²Soil Behavior Referance*Soil behavior type and SPT based on data from UBC-1983 0 5 10 15 20 25 30 35 40 45 50 0 400 TIPTSF 0 5 FRICTIONTSF 0 10 Fs/Qt%-10 90 PRESSURE U2PSI0121 - sensitive fine grained 2 - organic material 3 - clay 4 - silty clay to clay 5 - clayey silt to silty clay 6 - sandy silt to clayey silt 7 - silty sand to sandy silt 8 - sand to silty sand 9 - sand 10 - gravelly sand to sand 11 - very stiff fine grained (*)12 - sand to clayey sand (*) CPT DATADEPTH(ft)SOILBEHAVIORTYPE GeoSolutions Inc.ProjectLittle Alamo-1390 Walker san luis obispoOperatorAJ-ERFilenameSDF(252).cptJob NumberSL13900-1Cone NumberDDG1587GPSHole NumberCPT-02Date and Time1/31/2025 11:14:24 AMMaximum Depth44.78 ftEST GW Depth During Test17.00 ftNet Area Ratio .8Cone Size 15cm²Soil Behavior Referance*Soil behavior type and SPT based on data from UBC-1983 0 5 10 15 20 25 30 35 40 45 50 0 400 TIPTSF 0 5 FRICTIONTSF 0 10 Fs/Qt%-10 90 PRESSURE U2PSI0121 - sensitive fine grained 2 - organic material 3 - clay 4 - silty clay to clay 5 - clayey silt to silty clay 6 - sandy silt to clayey silt 7 - silty sand to sandy silt 8 - sand to silty sand 9 - sand 10 - gravelly sand to sand 11 - very stiff fine grained (*)12 - sand to clayey sand (*) CPT DATADEPTH(ft)SOILBEHAVIORTYPE GeoSolutions Inc.ProjectLittle Alamo-1390 Walker san luis obispoOperatorAJ-ERFilenameSDF(253).cptJob NumberSL13900-1Cone NumberDDG1587GPSHole NumberCPT-03Date and Time1/31/2025 12:15:28 PMMaximum Depth41.01 ftEST GW Depth During Test17.00 ftNet Area Ratio .8Cone Size 15cm²Soil Behavior Referance*Soil behavior type and SPT based on data from UBC-1983 0 5 10 15 20 25 30 35 40 45 50 0 400 TIPTSF 0 5 FRICTIONTSF 0 10 Fs/Qt%-10 90 PRESSURE U2PSI0121 - sensitive fine grained 2 - organic material 3 - clay 4 - silty clay to clay 5 - clayey silt to silty clay 6 - sandy silt to clayey silt 7 - silty sand to sandy silt 8 - sand to silty sand 9 - sand 10 - gravelly sand to sand 11 - very stiff fine grained (*)12 - sand to clayey sand (*) CPT DATADEPTH(ft)SOILBEHAVIORTYPE GeoSolutions Inc.ProjectLittle Alamo-1390 Walker san luis obispoOperatorAJ-ERFilenameSDF(255).cptJob NumberSL13900-1Cone NumberDDG1587GPSHole NumberCPT-04Date and Time1/31/2025 1:20:07 PMMaximum Depth49.87 ftEST GW Depth During Test17.00 ftNet Area Ratio .8Cone Size 15cm²Soil Behavior Referance*Soil behavior type and SPT based on data from UBC-1983 0 5 10 15 20 25 30 35 40 45 50 0 400 TIPTSF 0 5 FRICTIONTSF 0 10 Fs/Qt%-10 90 PRESSURE U2PSI0121 - sensitive fine grained 2 - organic material 3 - clay 4 - silty clay to clay 5 - clayey silt to silty clay 6 - sandy silt to clayey silt 7 - silty sand to sandy silt 8 - sand to silty sand 9 - sand 10 - gravelly sand to sand 11 - very stiff fine grained (*)12 - sand to clayey sand (*) CPT DATADEPTH(ft)SOILBEHAVIORTYPE APPENDIX B Laboratory Testing Soil Test Reports (Hushmand Associates, Inc., 2015) LABORATORY TESTING This appendix includes a discussion of the test procedures and the laboratory test results reviewed as part of this investigation. The purpose of the laboratory testing is to assess the engineering properties of the soil materials at the Site. The laboratory tests were performed using the currently accepted test methods, when applicable, of the American Society for Testing and Materials (ASTM). Undisturbed and disturbed bulk samples used in the laboratory tests are obtained from various locations during the course of the field exploration, as discussed in Appendix A of this report. Each sample is identified by sample letter and depth. The Unified Soils Classification System is used to classify soils according to their engineering properties. The various laboratory tests performed are described below: Liquid Limit, Plastic Limit, and Plasticity Index of Soils (ASTM D4318) are the water contents at certain limiting or critical stages in cohesive soil behavior. The liquid limit (LL or WL) is the lower limit of viscous flow, the plastic limit (PL or WP) is the lower limit of the plastic stage of clay and plastic index (PI or IP) is a range of water content where the soil is plastic. The Atterberg Limits are performed on samples that have been screened to remove any material retained on a No. 40 sieve. The liquid limit is determined by performing trials in which a portion of the sample is spread in a brass cup, divided in two by a grooving tool, and then allowed to flow together from the shocks caused by repeatedly dropping the cup in a standard mechanical device. To determine the Plastic Limit a small portion of plastic soil is alternately pressed together and rolled into a 1/8-inch diameter thread. This process is continued until the water content of the sample is reduced to a point at which the thread crumbles and can no longer be pressed together and re-rolled. The water content of the soil at this point is reported as the plastic limit. The plasticity index is calculated as the difference between the liquid limit and the plastic limit. Direct Shear Tests of Soils Under Consolidated Drained Conditions (ASTM D3080) is performed on undisturbed and remolded samples representative of the foundation material. The samples are loaded with a predetermined normal stress and submerged in water until saturation is achieved. The samples are then sheared horizontally at a controlled strain rate allowing partial drainage. The shear stress on the sample is recorded at regular strain intervals. This test determines the resistance to deformation, which is shear strength, inter-particle attraction or cohesion c, and resistance to interparticle slip called the angle of internal friction φ. Particle Size Analysis of Soils (ASTM D422) is used to determine the particle-size distribution of fine and coarse aggregates. In the test method the sample is separated through a series of sieves of progressively smaller openings for determination of particle size distribution. The total percentage passing each sieve is reported and used to determine the distribution of fine and coarse aggregates in the sample. Corrosion Potential (Including pH, minimum resistivity, soluble sulfates and soluble chlorides determinations) in accordance with CAL DOT Standard Test Nos. 643, 532, 417-B and 422. APPENDIX C Seismic Hazard Analysis Design Map Summary (SEAOC, 2019) SEISMIC HAZARD ANALYSIS According to section 1613 of the 2022 CBC (CBSC, 2022), all structures and portions of structures should be designed to resist the effects of seismic loadings caused by earthquake ground motions in accordance with the ASCE 7: Minimum Design Loads for Buildings and Other Structures, hereafter referred to as ASCE7-16 (ASCE, 2016). Estimating the design ground motions at the Site depends on many factors including the distance from the Site to known active faults; the expected magnitude and rate of recurrence of seismic events produced on such faults; the source-to-site ground motion attenuation characteristics; and the Site soil profile characteristics. As per section 1613.2.2 of the 2022 CBC, the Site soil profile classification is determined by the average soil properties in the upper 100 feet of the Site profile and can be determined based on the criteria provided in Table 20.3-1 of ASCE7-16. ASCE7-16 provides recommendations for estimating site-specific ground motion parameters for seismic design considering a Risk-targeted Maximum Considered Earthquake (MCER) in order to determine design spectral response accelerations and a Maximum Considered Earthquake Geometric Mean (MCEG) in order to determine probabilistic geometric mean peak ground accelerations. Spectral accelerations from the MCER are based on a 5% damped acceleration response spectrum and a 1% probability of exceedance in 50 years. Maximum short period (Ss) and 1-second period (S1) spectral accelerations are interpolated from the MCER-based ground motion parameter maps for bedrock, provided in ASCE7-16. These spectral accelerations are then multiplied by site-specific coefficients (Fa, Fv), based on the Site soil profile classification and the maximum spectral accelerations determined for bedrock, to yield the maximum short period (SMS) and 1-second period (SM1) spectral response accelerations at the Site. According to section 11 of ASCE7-16 and section 1613 of the 2022 CBC, buildings and structures should be specifically proportioned to resist design earthquake ground motions. Section 1613.2.4 of the 2022 CBC indicates the site-specific design spectral response accelerations for short (SDS) and 1-second (SD1) periods can be taken as two-thirds of maximum (SDS = 2/3*SMS and SD1 = 2/3*SM1). Per ASCE7-16, Section 21.5, the probabilistic maximum mean peak ground acceleration (PGA) corresponding to the MCEG can be computed assuming a 2% probability of exceedance in 50 years (2475-year return period) and is initially determined from mapped ground accelerations for bedrock conditions. The site-specific peak ground acceleration (PGAM) is then determined by multiplying the PGA by the site-specific coefficient Fh (where Fh is a function of Site Class and PGA). Spectral response accelerations and peak ground accelerations, provided in this report were obtained using the computer-based Seismic Design Maps tool available from the Structural Engineers Association of California (SEAOC, 2022). This program utilizes the methods developed in ASCE 7-16 in conjunction with user-inputted Site location to calculate seismic design parameters and response spectra (both for period and displacement) for soil profile Site Classes A through E. APPENDIX D Preliminary Grading Specifications PRELIMINARY GRADING SPECIFICATIONS A. General 1. These preliminary specifications have been prepared for the subject site; GeoSolutions, Inc. should be consulted prior to the commencement of site work associated with site development to ensure compliance with these specifications. 2. GeoSolutions, Inc. should be notified at least 72 hours prior to site clearing or grading operations on the property in order to observe the stripping of surface materials and to coordinate the work with the grading contractor in the field. 3. These grading specifications may be modified and/or superseded by recommendations contained in the text of this report and/or subsequent reports. 4. If disputes arise out of the interpretation of these grading specifications, the Soils Engineer shall provide the governing interpretation. B. Obligation of Parties 1. The Soils Engineer should provide observation and testing services and should make evaluations to advise the client on geotechnical matters. The Soils Engineer should report the findings and recommendations to the client or the authorized representative. 2. The client or their authorized representative should be chiefly responsible for all aspects of the project. The client or authorized representative has the responsibility of reviewing the findings and recommendations of the Soils Engineer. During grading the client or the authorized representative should remain on-site or should remain reasonably accessible to all concerned parties in order to make decisions necessary to maintain the flow of the project. 3. The contractor is responsible for the safety of the project and satisfactory completion of all grading and other operations on construction projects, including, but not limited to, earthwork in accordance with project plans, specifications, and controlling agency requirements. C. Site Preparation 1. The client, prior to any site preparation or grading, should arrange and attend a meeting which includes the grading contractor, the design Structural Engineer, the Soils Engineer, representatives of the local building department, as well as any other concerned parties. All parties should be given at least 72 hours’ notice. 2. All surface and sub-surface deleterious materials should be removed from the proposed building and pavement areas and disposed of off-site or as approved by the Soils Engineer. This includes, but is not limited to, any debris, organic materials, construction spoils, buried utility line, septic systems, building materials, and any other surface and subsurface structures within the proposed building areas. Trees designated for removal on the construction plans should be removed and their primary root systems grubbed under the observations of a representative of GeoSolutions, Inc. Voids left from site clearing should be cleaned and backfilled as recommended for structural fill. 3. Once the Site has been cleared, the exposed ground surface should be stripped to remove surface vegetation and organic soil. A representative of GeoSolutions, Inc. should determine the required depth of stripping at the time of work being completed. Strippings may either be disposed of off-site or stockpiled for future use in landscape areas, if approved by the landscape architect. D. Site Protection 1. Protection of the Site during the period of grading and construction should be the responsibility of the contractor. 2. The contractor should be responsible for the stability of all temporary excavations. 3. During periods of rainfall, plastic sheeting should be kept reasonably accessible to prevent unprotected slopes from becoming saturated. Where necessary during periods of rainfall, the contractor should install check-dams, de-silting basins, sand bags, or other devices or methods necessary to control erosion and provide safe conditions. E. Excavations 1. Materials that are unsuitable should be excavated under the observation and recommendations of the Soils Engineer. Unsuitable materials include, but may not be limited to: 1) dry, loose, soft, wet, organic, or compressible natural soils; 2) fractured, weathered, or soft bedrock; 3) non- engineered fill; 4) other deleterious materials; and 5) materials identified by the Soils Engineer or Engineering Geologist. 2. Unless otherwise recommended by the Soils Engineer and approved by the local building official, permanent cut slopes should not be steeper than 2:1 (horizontal to vertical). Final slope configurations should conform to section 1804 of the 2022 California Building Code unless specifically modified by the Soil Engineer/Engineering Geologist. 3. The Soil Engineer/Engineer Geologist should review cut slopes during excavations. The contractor should notify the Soils Engineer/Engineer Geologist prior to beginning slope excavations. F. Structural Fill 1. Structural fill should not contain rocks larger than 3 inches in greatest dimension, and should have no more than 15 percent larger than 2.5 inches in greatest dimension. 2. Imported fill should be free of organic and other deleterious material and should have very low expansion potential, with a plasticity index of 12 or less. Before delivery to the Site, a sample of the proposed import should be tested in our laboratory to determine its suitability for use as structural fill. G. Compacted Fill 1. Structural fill using approved import or native should be placed in horizontal layers, each approximately 8 inches in thickness before compaction. On-site inorganic soil or approved imported fill should be conditioned with water to produce a soil water content near optimum moisture and compacted to a minimum relative density of 90 percent based on ASTM D1557- 12e1. 2. Fill slopes should not be constructed at gradients greater than 2-to-1 (horizontal to vertical). The contractor should notify the Soils Engineer/Engineer Geologist prior to beginning slope excavations. 3. If fill areas are constructed on slopes greater than 10-to-1 (horizontal to vertical), we recommend that benches be cut every 4 feet as fill is placed. Each bench shall be a minimum of 10 feet wide with a minimum of 2 percent gradient into the slope. 4. If fill areas are constructed on slopes greater than 5-to-1, we recommend that the toe of all areas to receive fill be keyed a minimum of 24 inches into underlying dense material. Key depths are to be observed and approved by a representative of GeoSolutions, Inc. Sub-drains shall be placed in the keyway and benches as required. H. Drainage 1. During grading, a representative of GeoSolutions, Inc. should evaluate the need for a sub-drain or back-drain system. Areas of observed seepage should be provided with sub-surface drains to release the hydrostatic pressures. Sub-surface drainage facilities may include gravel blankets, rock filled trenches or Multi-Flow systems or equal. The drain system should discharge in a non- erosive manner into an approved drainage area. 2. All final grades should be provided with a positive drainage gradient away from foundations. Final grades should provide for rapid removal of surface water runoff. Ponding of water should not be allowed on building pads or adjacent to foundations. Final grading should be the responsibility of the contractor, general Civil Engineer, or architect. 3. Concentrated surface water runoff within or immediately adjacent to the Site should be conveyed in pipes or in lined channels to discharge areas that are relatively level or that are adequately protected against erosion. 4. Water from roof downspouts should be conveyed in solid pipes that discharge in controlled drainage localities. Surface drainage gradients should be planned to prevent ponding and promote drainage of surface water away from building foundations, edges of pavements and sidewalks. For soil areas we recommend that a minimum of 2 percent gradient be maintained. 5. Attention should be paid by the contractor to erosion protection of soil surfaces adjacent to the edges of roads, curbs and sidewalks, and in other areas where hard edges of structures may cause concentrated flow of surface water runoff. Erosion resistant matting such as Miramat, or other similar products, may be considered for lining drainage channels. 6. Sub-drains should be placed in established drainage courses and potential seepage areas. The location of sub-drains should be determined after a review of the grading plan. The sub-drain outlets should extend into suitable facilities or connect to the proposed storm drain system or existing drainage control facilities. The outlet pipe should consist of a non-perforated pipe the same diameter as the perforated pipe. I. Maintenance 1. Maintenance of slopes is important to their long-term performance. Precautions that can be taken include planting with appropriate drought-resistant vegetation as recommended by a landscape architect, and not over-irrigating, a primary source of surficial failures. 2. Property owners should be made aware that over-watering of slopes is detrimental to long term stability of slopes. J. Underground Facilities Construction 1. The attention of contractors, particularly the underground contractors, should be drawn to the State of California Construction Safety Orders for “Excavations, Trenches, Earthwork.” Trenches or excavations greater than 5 feet in depth should be shored or sloped back in accordance with OSHA Regulations prior to entry. 2. Bedding is defined as material placed in a trench up to 1 foot above a utility pipe and backfill is all material placed in the trench above the bedding. Unless concrete bedding is required around utility pipes, clean sand should be used as bedding. Sand to be used as bedding should be tested in our laboratory to verify its suitability and to measure its compaction characteristics. Sand bedding should be compacted by mechanical means to achieve at least 90 percent relative density based on ASTM D1557-12. 3. On-site inorganic soils, or approved import, may be used as utility trench backfill. Proper compaction of trench backfill will be necessary under and adjacent to structural fill, building foundations, concrete slabs, and vehicle pavements. In these areas, backfill should be conditioned with water (or allowed to dry), to produce a soil water content of about 2 to 3 percent above the optimum value and placed in horizontal layers, each not exceeding 8 inches in thickness before compaction. Each layer should be compacted to at least 90 percent relative density based on ASTM D1557-12. The top lift of trench backfill under vehicle pavements should be compacted to the requirements given in report under Preparation of Paved Areas for vehicle pavement sub-grades. Trench walls must be kept moist prior to and during backfill placement. K. Completion of Work 1. After the completion of work, a report should be prepared by the Soils Engineer retained to provide such services. The report should including locations and elevations of field density tests, summaries of field and laboratory tests, other substantiating data, and comments on any changes made during grading and their effect on the recommendations made in the approved Soils Engineering Report. 2. Soils Engineers shall submit a statement that, to the best of their knowledge, the work within their area of responsibilities is in accordance with the approved soils engineering report and applicable provisions within Chapter 18 of the 2022 CBC.