REPORT OF GEOTECHNICAL INVESTIGATION CUYAMACA COLLEGE BUILDING H RENOVATION EL CAJON, CALIFORNIA. Prepared for

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1 REPORT OF GEOTECHNICAL INVESTIGATION CUYAMACA COLLEGE BUILDING H RENOVATION EL CAJON, CALIFORNIA Prepared for GROSSMONT-CUYAMACA COMMUNITY COLLEGE DISTRICT GAFCON Campus Project Manager 900 Rancho San Diego Parkway El Cajon, California Prepared by GROUP DELTA CONSULTANTS, INC Activity Road, Suite 103 San Diego, California Project No. SD567 June 19, 2018

2 June 19, 2018 Grossmont-Cuyamaca Community College District GAFCON Campus Project Manager 900 Rancho San Diego Parkway El Cajon, CA Attention: Mr. Frank Gonzalez SUBJECT: REPORT OF GEOTECHNICAL INVESTIGATION Cuyamaca College Building H Renovation (Contract C13529) El Cajon, California Mr. Gonzalez: Group Delta Consultants (Group Delta) is submitting this report to present the findings from our geotechnical investigation for the proposed Building H Renovation Project at Cuyamaca College. We prepared this report in accordance with our proposal (Group Delta, 2018) and Grossmont- Cuyamaca Community College District (GCCCD) Project Authorization Letter (GCCCD, 2018). In our opinion, the site is geotechnically suitable for the proposed development. However, remedial earthwork will be needed to provide suitable long-term performance of the new modular building and associated exterior surface improvements. Specific conclusions regarding the potential geotechnical constraints at the site, and geotechnical recommendations for design and construction are provided in the following report. We appreciate this opportunity to be of continued professional service. Feel free to contact the office with any questions or comments, or if you need anything else. GROUP DELTA CONSULTANTS 03/31/2020 Congpu Yao, Ph.D., P.E James C. Sanders, C.E.G Senior Engineer Associate Engineering Geologist Matthew A. Fagan, G.E Senior Geotechnical Engineer Distribution: (1) Addressee, Mr. Frank Gonzalez (fgonzalez@gafcon.com) 9245 Activity Road, Suite 103, San Diego, CA TEL: (858) Anaheim Irvine Ontario San Diego Torrance Vacaville Walnut Creek

3 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page 3 TABLE OF CONTENTS 1.0 INTRODUCTION Scope of Services Site Description Proposed Development FIELD AND LABORATORY INVESTIGATION Field Investigation Infiltration Testing Laboratory Testing GEOLOGY AND SUBSURFACE CONDITIONS Cretaceous Gabbro (Kggb) Undocumented Fill Groundwater GEOLOGIC HAZARDS Ground Rupture Seismicity Liquefaction and Dynamic Settlement Landslides and Lateral Spreads Tsunamis, Seiches and Flooding CONCLUSIONS RECOMMENDATIONS Earthwork Site Preparation Building Area Improvement Areas Fill Compaction Temporary Excavations Surface Drainage Shallow Foundations Settlement Lateral Resistance N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

4 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page Modulus of Subgrade Reaction Seismic Design On-Grade Slabs Moisture Protection for Slabs Pipelines Thrust Blocks Modulus of Soil Reaction Pipe Bedding Reactive Soils Storm Water Infiltration LIMITATIONS REFERENCES TABLES Table CBC Acceleration Response Spectra FIGURES Figure 1 Site Location Map Figure 2 Exploration Plan Figure 3 Proposed Improvements Figure 4A Cross Section Limits A-A & B-B Figure 4B Cross Sections A-A & B-B Figure 5 Local Geologic Map Figure 6 Regional Fault Map Figure Year Flood Map APPENDICES Appendix A Field Exploration Appendix B Laboratory Testing Appendix C Infiltration Assessment N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

5 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page INTRODUCTION The following report presents the results of our geotechnical investigation for the proposed Building H Renovation Project at Cuyamaca College in El Cajon, California. The project is located at the west of the campus behind the existing Building H Science and Mathematics Center, as shown on the Site Location Map, Figure 1. Figure 2 shows the site vicinity in more details. The proposed project improvements consist of a single-story pre-fabricated structure with a building footprint of about 3,400 square feet. Additional improvements at the site include new walkways, trellises, subsurface utilities, landscaping and storm water Best Management Practices (BMPs). Figure 3 presents the proposed project improvements along with existing structures and utilities. Figures 4A and 4B show the two geologic cross sections (A-A and B-B ). 1.1 Scope of Services The purpose of this investigation was to provide geotechnical recommendations for proposed project improvements, as well as any associated underground utilities, retaining walls and surface improvements. This report was prepared in general accordance with the provisions of the referenced proposal (Group Delta, 2018). An outline of the scope of work is provided below: We reviewed available background information, including geologic maps, fault maps, hazard maps, topographic and aerial photographs, and regional groundwater data, as well as as-built drawings for existing Building H, provided by client. We coordinated site access with Cuyamaca College personnel, marked out the proposed boring locations, and notified Underground Service Alert to review the location of the subsurface explorations relative to below-ground utilities. We subcontracted with a drilling subcontractor to complete two hollow-stemauger geotechnical borings and two additional infiltration borings at the selected locations, which were approved by the civil team prior to mobilization. We backfilled the holes with the soil cuttings, and restored the surface to the original condition after drilling. We conducted infiltration testing at the selected depth within the two infiltration borings. We conducted laboratory testing on selected soil samples obtained from the borings to assess the pertinent engineering characteristics of the soils. N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

6 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page 6 We performed engineering analysis to develop recommendations for design of the proposed improvements. We assessed infiltration rate for the design of storm water BMPs. We prepared this report presenting our findings, conclusions and recommendations for design and construction. 1.2 Site Description The approximate centroid of the site is at a latitude of º north and a longitude of º west, as shown in Figure 1. The current Science and Mathematics Center is a twostory building supported by spread footing on compacted fill according to the structural as-built drawings (GCCCD, 2005). The building is surrounded by Portland cement concrete sidewalks, parking, and driveway areas, along with limited landscaping. An existing greenhouse is located about 100 feet west of the existing Building H. The foundation for the greenhouse is unknown, but is assumed to consist of spread footings. The greenhouse is connected to Building H with a concrete pathway. The site is relatively flat, with the surface elevation at about 410 feet above Mean Sea Level (MSL). The northern, western, and southern portions of the property are bordered by a cut slope into the granitic rock. The slope ascends about 15 feet up to a surface elevation of 425 feet MSL. A maintenance road is located at the top of the existing slope. According to the Cuyamaca College Composite Topographic Survey (GCCCD, 2015), there are several underground utilities on the site. Figure 3 presents the estimated location of the 6-inch PVC storm drain, electric line, gas line and irrigation line to the greenhouse. 1.3 Proposed Development The proposed improvements consist of a single-story pre-fabricated structure with a building footprint of about 3,400 square feet located between the existing Building H and greenhouse. The pre-fabricated structure is planned to be 84 feet long and 40 feet wide. We understand that the prefabricated building will be founded on a reinforced concrete slab-on-grade, with continuous perimeter foundations. Additional improvements at the site will also include new walkways, trellises, subsurface utilities, landscaping and storm water BMPs. The project Civil Engineer is considering bio-retention basin BMPs to manage storm water. We have chosen infiltration testing locations based on their input. Figure 3 shows the proposed project improvements. No major grading work is anticipated for this project. The finished grade for the pre-fabricated structure is estimated to be the same as existing grade. The site development will likely begin N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

7 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page 7 with the saw-cutting and removal of the existing pavements and surface improvements in the area of the proposed building. Existing subsurface utilities that will be abandoned or that may otherwise interfere with the new improvements will be relocated, removed or grouted. The general layout of the improvements at the site is shown on Figure FIELD AND LABORATORY INVESTIGATION The field investigation consisted of site reconnaissance, two geotechnical borings and two infiltration test borings as described in the sections below, followed by a discussion of the laboratory testing program. 2.1 Field Investigation A CME-75 truck-mounted drill rig was used to advance two geotechnical borings and two infiltration testing borings, using an 8-inch diameter hollow stem flight auger. The two geotechnical borings were drilled up to 20 feet below ground surface (bgs), while the two infiltration testing borings were drilled up to 5 feet bgs. A Group Delta Engineer was on site to supervise the field investigation, log the borings, and obtain soil samples for laboratory testing using Standard Penetration Test (SPT) and modified California (CAL) samplers. Bulk soil samples were also collected at shallow depths. No groundwater was encountered during drilling. The two geotechnical borings were abandoned with soil cuttings and the ground surface restored. Figure 2 shows the approximate locations of these borings. Appendix A contains the log of the borings. Figures 4A and 4B show the two geologic cross sections. 2.2 Infiltration Testing Immediately following drilling, two borings (A and A ) were prepared for percolation tests by presoaking for at least 20 hours. The tests were conducted in accordance with the percolation tests referenced in the Design Handbook for Low Impact Development Best Management Practices (Riverside, 2011). The infiltration testing was attempted at several depth intervals to assess a variety of soil conditions. Table below presents the summarized infiltration results. According to San Diego County BMP Design Manual (2016), the lower thresholds for full and partial infiltration are 0.5 and 0.05 inches per hour. A Factor of Safety of 2 was adopted using guidance in San Diego County BMP Design Manual (2016). The results from A show the potential for partial infiltration, since the design infiltration rate is 0.30 inches per hour. However, the results from A indicate infiltration is not feasible. N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

8 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page 8 Test Hole Testing Interval Geologic Conditions Design Infiltration Rate inches/hour (with F.S. = 2) A feet ~ 3.8 feet Silty Sand 0.30 A feet ~ 4.2 feet Silty Sand 0.03 Appendix C provides the detailed test results. 2.3 Laboratory Testing Group Delta s San Diego laboratory tested selected soil samples to evaluate the physical properties of the soils, infiltration rate, and subgrade characteristics. The geotechnical testing program included gradation analyses and plasticity index tests to aid in material classification using the unified Soil Classification System (USCS). Index tests were also conducted on the bulk samples to help evaluate the soil expansion and corrosivity potential. A compaction test was assigned to a sample at a shallow depth to obtain the relationship between maximum dry density and optimum water content. Direct shear test was conducted on a remolded sample to aid in strength characterization. Attachment B provides the laboratory test results. 3.0 GEOLOGY AND SUBSURFACE CONDITIONS The site is located within the Peninsular Ranges geomorphic province of southern California. The Peninsular Ranges are characterized by a series of northwest trending mountain ranges separated by valleys, with a coastal plain of subdued landforms. The mountain ranges are underlain primarily by Mesozoic metamorphic rocks that were intruded by plutonic rocks of the southern California batholith, while the coastal plain is underlain by subsequently deposited sedimentary formations. Specifically, the entire site is underlain at depth by Cretaceous Gabbro. The Gabbro is covered with a few feet of undocumented fill soils over the entire site. The United States Geological Survey (USGS) 7.5 Quadrangle Geologic Map for Jamul Mountains is presented in Figure Cretaceous Gabbro (Kggb) Our reconnaissance indicates that the site is underlain at depth by hard igneous rock composed of Cretaceous Gabbro (Map Symbol Kggb). The upper portion of the Gabbro was observed to be heavily decomposed, and weathered into greenish gray medium to coarse grained silty sand (Unified Soil Classification Symbol SM). The rock becomes less weathered at a depth of about 18 feet. The less decomposed Gabbro appears to be dark greenish gray with rock fragments. N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

9 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page Undocumented Fill Localized undocumented fill up to four feet thick was encountered in all borings. The majority of the fill was observed to consist of dark yellowish brown medium dense silty sand (SM). At Boring A , the fill consisted of light gray loose poorly-graded sand with silt. Infiltration testing performed on Boring A shows the potential for partial infiltration on the site. 3.3 Groundwater No seepage or groundwater was encountered in the geotechnical borings. Our previous experience in the site vicinity suggests that the local groundwater table is relatively deep. The USGS Groundwater Watch website indicates that the groundwater depth in nearby borings is greater than 70 feet. However, it should be noted that changes in rainfall, irrigation practices or site drainage may produce seepage or locally perched groundwater conditions at any location within the fill soil or Gabbro units underlying the site. Such conditions are difficult to predict, and are typically mitigated if and where they occur. 4.0 GEOLOGIC HAZARDS The subject site is not located within an area previously known for significant geologic hazards. Evidence of past landslides, liquefaction or active faulting at the site was not encountered in our geotechnical investigation or literature review. We anticipate that the main geologic hazards at the site will be associated with the potential for strong ground shaking due to a seismic event. Each of the potential geologic hazards is described below. 4.1 Ground Rupture Ground rupture is the result of movement on an active fault reaching the ground surface. The site is not located within an Alquist-Priolo Earthquake Fault Zone. The nearest active fault is the Rose Canyon Fault Zone, which is located 19.8 kilometers (km) west of the site. A small concealed local fault is mapped 3 miles east of the site, however it is not considered capable of producing surface rupture. No indications of active faulting at the site were found in our reconnaissance or literature review. Therefore, fault rupture hazard at the site is considered remote. 4.2 Seismicity The proposed addition is located at latitude north and longitude west. The locations of regional faults within a 100-km radius of the site are shown on Figure 6, Regional Fault Map, along with site-to-fault distance (R rup ), Fault Type (Strike Slip or Normal), Caltrans Fault ID (FID) number, and maximum moment magnitude (M MAX ) for the 10 most significant faults contributing to the seismic hazard at the site. N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

10 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page 10 The average shear wave velocity in the upper 100 feet (V S30 ) is estimated to be about 560 meters per second (Soil Type C, Very Dense Soil and Soft Rock) following Caltrans methodology for developing design response spectrum for use in seismic design recommendations (Caltrans, 2012). Seismic design parameters were evaluated in accordance with the 2016 California Building Code (CBC). The seismic design parameters were obtained from the USGS U.S. Seismic Design Maps Tool, and are listed in the table below. Table 1 presents the acceleration response spectra for the site. Site Class Latitude: Longitude: MCE R Spectral Response Acceleration for Short Periods, S s MCE R Spectral Response Acceleration at 1-second Period, S 1 C g g Site Coefficient F a Site Coefficient F V Adjusted MCE R Spectral Response Acceleration at Short Periods, S MS Adjusted MCE R Spectral Response Acceleration at 1-second Period, S M1 Design Spectral Response Acceleration at Short Periods, S DS Design Spectral Response Acceleration at 1-second Period, S D g g g g Since S DS is larger than 0.5g, according to Table of 2016 CBC, the site could be designed as Seismic Design Category D. Site-specific analysis is not required. 4.3 Liquefaction and Dynamic Settlement For liquefaction to occur, three conditions must simultaneously exist: loose to medium dense granular soils, saturation of the soils by groundwater (typically upper 50 feet), and strong earthquake ground motion. Groundwater was not encountered during the exploration. The estimated groundwater depth at the site is more than 50 feet deep. Due to relatively deep groundwater and predominantly very dense nature of subsurface soils/rock below groundwater at the site, the liquefaction potential at the site is considered negligible. Minor seismic compaction (dry sand settlement) is possible, but would not pose a risk of collapse in the extreme event earthquake. 4.4 Landslides and Lateral Spreads Evidence of ancient landslides or slope instabilities was not observed during our literature review or site reconnaissance. It is our opinion that slope instability will not adversely affect the proposed addition, provided that our minimum recommended slope setbacks are implemented for the new building foundations during construction. N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

11 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page Tsunamis, Seiches and Flooding Due to the distance from the coast, and site elevations more than 400 feet above sea level, tsunami risks and seiche risks at the site are considered negligible. The site is not located below any lakes or confined bodies of water, and is not located within a FEMA 100-year flood zone, as shown in Figure 7. Consequently, the potential for earthquake induced flooding is also considered to be negligible. N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

12 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page CONCLUSIONS The proposed building appears to be feasible from a geotechnical perspective, provided that appropriate measures are implemented during construction. Several geotechnical conditions will need to be addressed during fine grading of the site. We anticipate that the proposed building will be entirely underlain by fill over Gabbro. We recommend that the subgrade soils be observed by the geotechnical consultant once the existing concrete pavements are saw-cut and removed from the areas of the planned addition. As a minimum, we have recommended that the upper 12-inches of exposed soil be scarified, brought to above optimum moisture content, and then compacted prior to construction. However, isolated pockets of fill may remain below some portions of the new building pad area that may require additional remedial earthwork. If fill soils are observed during grading, additional remedial grading recommendations may be provided. Laboratory tests indicate that the near surface soils at the site primarily consist of sand and gravel mixtures with a very low expansion potential. However, potentially expansive clays may exist in some portions of the site, particularly within landscaping areas. Additional testing should be conducted during grading of the site to characterize the finish grade soils. The on-site soils should be suitable for reuse as compacted fill, except for soils with deleterious materials, expansive soils, or soils that GCCCD considers to be contaminated. Environmental sampling and testing was not within our scope of work. Based on our current understanding of the proposed addition, we anticipate that the foundation excavations will generally expose very dense decomposed Gabbro overlain by a few feet of compacted fill. These soils will provide relatively good bearing capacity for the conventional shallow foundations proposed for the new building. In general, excavations at the site should be achievable using standard heavy earthmoving equipment. However, excavations within the bedrock may generate large blocks of rock, or boulders that may need to be hauled off site for disposal. Alternatively, over-size materials may or broken down less than 6-inches in maximum dimension and incorporated into compacted fill. There are no known active faults located beneath the subject site, and the potential for ground rupture to adversely impact the development is remote. Other geologic hazards that may impact site development are primarily associated with the potential for strong shaking from an earthquake on the distant Rose Canyon fault zone. The shaking hazard may be mitigated by structural design in accordance with the applicable building code. N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

13 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page RECOMMENDATIONS This section presents recommendations for earthwork, foundation design, and storm water infiltration. These recommendations are based on empirical and analytical methods typical of the standards of practice in southern California. If these recommendations do not to appear to cover a specific feature of the project, please contact our office for additions or revisions. 6.1 Earthwork Grading and earthwork should be conducted in general accordance with the applicable requirements of California Building Code. The following recommendations are provided for specific aspects of the proposed earthwork construction. These recommendations should be considered subject to revision based on the conditions observed by the geotechnical consultant during earthwork Site Preparation General site preparation should begin with the removal of deleterious materials from the site. Deleterious materials include existing structures, foundations, slabs, trees, vegetation, trash, contaminated soil and demolition debris. Areas of the subgrade disturbed by demolition should be restored to the satisfaction of the geotechnical consultant during earthwork. Existing subsurface utilities that will be abandoned should be removed and the excavations backfilled and compacted as described in the Fill Compaction Section of this report. Alternatively, abandoned pipes may be grouted with a two-sack sand-cement slurry under our observation Building Area All existing undocumented fill beneath the proposed building should be excavated and replaced as a uniformly compacted fill. The cut portion of the building pad should also be over-excavated to a minimum depth of 3-feet below finish pad grade. The remedial grading should extend at least 5-feet beyond the perimeter of the proposed structure. All fill placed within the building pad area should have a very low expansion potential (Expansion Index <20) Improvement Areas Two feet of material with an expansion index of 20 or less is recommended beneath all new concrete sidewalks, exterior flatwork areas and building slabs-on-grade. In order to accomplish this objective, the upper 12-inches of soil below the slab subgrade elevations should be scarified immediately prior to constructing the pavements, brought to slightly above optimum moisture, and compacted to at least 90 percent of the maximum dry density per ASTM D1557. If soil with N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

14 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page 14 an expansion index above 20 is encountered, the soil should be excavated and replaced with very low expansion material. Exterior slabs and sidewalks subjected to pedestrian traffic should be at least 4 inches thick. Crack control joints should be placed on a maximum spacing of 10-foot centers, each way, for slabs, and on 5-foot centers for sidewalks. The potential for differential movements across the control joints may be reduced by using steel reinforcement. Typical reinforcement for exterior slabs would consist of 6x6 W2.9/W2.9 welded wire fabric placed at mid-height of the slab Fill Compaction All fill and backfill should be placed at slightly above optimum moisture content using equipment that can produce a uniformly compacted product. The minimum recommended relative compaction is 90 percent of the maximum dry density based on ASTM D1557. Rocks or concrete fragments greater than 6 inches in maximum dimension should not be used in structural fill. A two-sack sand and cement slurry may also be used for structural fill as an alternative to compacted soil. It has been our experience that slurry is often useful in confined areas which may be difficult to access with typical compaction equipment. Samples of the slurry should be fabricated and tested for compressive strength during construction. A minimum 28-day compressive strength of 100 pounds per square inch (psi) is recommended for the sand and cement slurry. Three-quarter inch gravel completely wrapped in filter fabric (Mirafi 140N, or equivalent) may also be used as backfill in confined areas Temporary Excavations Temporary excavations are anticipated for the construction of the proposed underground utilities. All excavations should conform to Cal-OSHA guidelines. Temporary slopes should be inclined no steeper than 1:1 for heights up to 10 feet. Higher slopes, or excavations that encounter seepage, should be evaluated by the geotechnical consultant on a case-by-case basis Surface Drainage Foundation and slab performance depends greatly on how well surface runoff drains from the site. The ground surface should be graded so that water flows rapidly away from the structures and tops of slopes without ponding. The surface gradient needed to achieve this may depend on the prevailing landscaping. Planters should be built so that water will not seep into the foundation, slab, or pavement areas. If roof drains are used, the drainage should be channeled by pipe to storm drains, or discharge at least 10 feet from buildings. Irrigation should be limited to the minimum needed to sustain landscaping. Excessive irrigation, surface water, water line breaks, or rainfall may cause perched groundwater to develop within the underlying soil. N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

15 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page Shallow Foundations Shallow foundations that bear directly within compacted fill soil prepared in accordance with Section may be used to support the proposed building. The existing fill depth beneath the proposed structure is estimated to be 4 feet or less. The following preliminary geotechnical parameters are provided for design: Allowable Bearing: 2,500 lbs/ft 2 (allow a ⅓ increase for short-term wind or seismic loads). Minimum Footing Width: 12 inches Minimum Footing Depth: 18 inches below lowest adjacent soil grade (with minimum embedment into Gabbro materials described above). Minimum Reinforcement: Per structural engineer Settlement We estimate that the total and differential settlement of the new building foundations will be less than ½ inch and ¼ inch in 40 feet, respectively Lateral Resistance Lateral loads against the structure may be resisted by friction between the bottoms of footings and slabs and the soil, and passive pressure from the portion of vertical foundation members embedded into compacted fill or Gabbro materials. A coefficient of friction of 0.35 and a passive pressure of 350 lbs/ft 2 per foot of embedment may be used Modulus of Subgrade Reaction For the preliminary evaluation of settlement under spread footing loads, a modulus of subgrade reaction for a one-foot square footing may be assumed to 300 pounds per cubic inch (k 1 ). This value assumes shallow footings are constructed in accordance with the recommendations provided above. Note that k1 should be adjusted for footing sizes wider than one foot using the following equation: k B = k 1 [(B +1) / 2B] 2 where: k B = the modulus of subgrade reaction for footing of width B B = footing width in feet N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

16 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page Seismic Design Structures should be designed in general accordance with the seismic provisions of the 2016 California Building Code (CBC) for Seismic Design Category D. Based on our understanding of the site conditions and the findings of the previous subsurface explorations, it is our opinion that a 2016 CBC Site Class C would apply to the general site conditions. The USGS mapped spectral ordinates S S and S 1 equal and 0.328, respectively. For Site Class C, the acceleration and velocity coefficients F a and F v equal and 1.472, respectively. The spectral design parameters S DS and S D1 equal and 0.322, respectively. The MCE peak ground acceleration from the 2016 CBC is 0.359g. The recommended 2016 CBC Design and Maximum Considered Earthquake (MCE) spectra for a Site Class C are shown in Table On-Grade Slabs Building slabs should be at least 5 inches thick, and should be reinforced with at least No. 3 bars on 18-inch centers, each way. Slab thickness, control joints, and reinforcement should be designed by the structural engineer and should conform to the requirements of the current CBC. The site soils are anticipated to be predominately granular with a very low expansion potential (EI<20). However, some expansive clays may exist. If expansive soils are encountered in the building pad, the clayey soil should be over-excavated two feet, and two feet of non-expansive soils (EI<20) should be placed directly beneath the heave sensitive concrete slabs on-grade Moisture Protection for Slabs Concrete slabs constructed on grade ultimately cause the moisture content to rise in the underlying soil. This results from continued capillary rise and the termination of normal evapotranspiration. Because normal concrete is permeable, the moisture will eventually penetrate the slab. Excessive moisture may cause mildewed carpets, lifting or discoloration of floor tiles, or similar problems. To decrease the likelihood of problems related to damp slabs, suitable moisture protection measures should be used where moisture sensitive floor coverings, equipment, or other factors warrant. The Architect should specify an appropriate moisture barrier based on the allowable moisture transmission rate for the flooring. This may require a vapor barrier or a vapor retarder. The American Concrete Institute (ACI) provides detailed recommendations for moisture protection systems (ACI 302.1R-04). ACI defines a vapor retarder as having a minimum thickness of 10- mil, and a water transmission rate of less than 0.3 perms when tested per ASTM E96. ACI defines a vapor barrier as having a water transmission rate of 0.01 perms or less (such as a 15 mil StegoWrap). The vapor membrane should be constructed in accordance with ASTM E1643 and E1745 guidelines. All laps or seams should be overlapped at least 6 inches or per the manufacturer recommendations. Joints and penetrations should be sealed with pressure sensitive tape, or the manufacturer s adhesive. The vapor membrane should be protected from puncture, and repaired per the manufacturer s recommendations if damaged. N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

17 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page 17 The vapor membrane is typically placed over 4 inches of granular material. The material should consist of a clean, fine graded sandy soil with roughly 10 to 30 percent passing the No. 100 sieve. The sand should not be contaminated with clay, silt, or organic material. The sand should be proof-rolled prior to placing the vapor membrane. Based on current ACI recommendations, the concrete slab should be placed directly over the vapor membrane. The common practice of placing sand over the vapor membrane may increase moisture transmission through the slab, because it provides a reservoir for bleed water from the concrete to collect. The sand placed over the vapor membrane may also move during placement, resulting in an irregular slab thickness. When placing concrete directly on an impervious membrane, it should be noted that finishing delays may occur. Care should be taken to assure that a low water to cement ratio is used, and that the concrete is moist cured in accordance with ACI guidelines. 6.4 Pipelines The development will include a variety of pipelines such as water, storm drain and sewer systems. Geotechnical aspects of pipeline design include lateral earth pressures for thrust blocks, modulus of soil reaction, and pipe bedding. Each of these parameters is discussed separately below Thrust Blocks Lateral resistance for thrust blocks may be determined by a passive pressure value of 350 lbs/ft 2 per foot of embedment, assuming a triangular distribution. This value may be used for thrust blocks embedded into compacted fill soils as well as the Gabbro materials Modulus of Soil Reaction The modulus of soil reaction (E ) is used to characterize the stiffness of soil backfill placed along the sides of buried flexible pipelines. To evaluate deflection due to the load associated with trench backfill over the pipe, a value of 1,500 lbs/in 2 is recommended for the general conditions, assuming granular bedding material is placed around the pipe Pipe Bedding Typical pipe bedding as specified in the Standard Specifications for Public Works Construction may be used. As a minimum, we recommend that pipes be supported on at least 4 inches of granular bedding material such as minus ¾-inch crushed rock or disintegrated granite. Where pipeline or trench excavations exceed a 15 percent gradient, we do not recommend that open graded rock be used for bedding or backfill because of the potential for piping and internal erosion. For sloping utilities, we recommend that coarse sand or sand-cement slurry be used for the bedding and pipe zone. The slurry should consist of a 2-sack mix having a slump no greater than 5 inches. N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

18 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page Reactive Soils To assess the sulfate exposure of concrete in contact with the site soils, samples were tested for water-soluble sulfate content, as shown in Appendix B. The test results indicate that the on-site soils have a negligible potential for sulfate attack based on commonly accepted criteria. The sulfate content of the finish grade soils should be determined during mass grading. In order to assess the reactivity of the site soils with buried metals, the ph and resistivity were also determined (see also Appendix B). These tests suggest that the on-site soils are corrosive to buried metals. Typical corrosion control measures should be incorporated into design, such as providing minimum clearances between reinforcing steel and soil, or sacrificial anodes for buried metal structures. A corrosion consultant may be contacted for specific recommendations. 6.6 Storm Water Infiltration We evaluated the geotechnical aspects of storm water management in accordance with the latest version of the County of San Diego BMP Design Manual. Although the infiltration results from show the potential for partial infiltration, we do not recommend that on-site infiltration be promoted on site due to the impact on the existing and proposed building as well as utilities. The entire site will consist of existing Building H, existing greenhouse, and the proposed onestory pre-fabricated structure. It is considered a congested site. The design BMP should be located at least 20 feet away from any structures. With the current layout, it is not easy to meet this requirement. There are numerous utilities on site as shown in Figure 3. The design BMP will have negative impact on the utility backfill, which might cause settlement issues. Furthermore, the impermeable granitic rock materials were encountered at a depth of about 4 feet below existing grades. Due to this relatively shallow rock condition, there is a potential for infiltrated storm water to pond within the fill soil, and adversely impact the existing and proposed structures. Accordingly, our feasibility screening of the potential for on site infiltration resulted in the no infiltration category. 7.0 LIMITATIONS This report was prepared using the degree of care and skill ordinarily exercised, under similar circumstances, by reputable geotechnical consultants practicing in similar localities. No warranty, express or implied, is made as to the conclusions and professional opinions included in this report. The findings of this report are valid as of the present date. However, changes in the condition of a property can occur with the passage of time, whether due to natural processes or the work of man on this or adjacent properties. In addition, changes in applicable or appropriate standards of practice may occur from legislation or the broadening of knowledge. Accordingly, the findings of this report may be invalidated wholly or partially by changes outside our control. Therefore, this report is subject to review and should not be relied upon after three years. N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

19 Report of Geotechnical Investigation GDC Project No. SD567 Cuyamaca College Building H Renovation June 19, 2018 Grossmont-Cuyamaca Community College District Page REFERENCES American Public Works Association (2006). Standard Specifications for Public Works Construction, Section , Untreated Base Materials, Section 400-4, Asphalt Concrete: BNI, 761 p. American Society for Testing and Materials (2006). Annual Book of ASTM Standards, Section 4, Construction, Volume Soil and Rock (I); Volume Soil and Rock (II); Geosynthetics, ASTM, West Conshohocken, PA, Compact Disk. California Building Standards Commission (2016). California Building Code, California Code of Regulations Title 24, Part 2, based on 2015 International Building Code. California Department of Transportation (2012). Methodology for Developing Design Response Spectrum for Use in Seismic Design Recommendations, November, County of San Diego (2016). BMP Design Manual for Permanent Site Design, Storm Water Treatment and Hydromodification Management. February. Grossmont-Cuyamaca Community College District (2018). Master Agreement for Geotechnical Services Cuyamaca College Building H Renovation, Amendment No. 05, dated March 19, Grossmont-Cuyamaca Community College District (2015). Cuyamaca College Composite Topographic Survey, prepared by NV5, dated February Grossmont-Cuyamaca Community College District (2005). As-Built Drawings for Science and Technology Mall at Cuyamaca College (Building H), dated Jan 25, Group Delta Consultants (2018). Proposal for Geotechnical Investigation Cuyamaca College Building H Renovation, El Cajon, California, Proposal No. SD18-005, Dated January 16, Riverside County Flood Control and Water Conservation District (2011). Design Handbook for Low Impact Development Best Management Practices. Riverside, California, September. United States Geologic Survey (2002). Geologic Map of the Jamul Mountains 7.5 Quadrangle, San Diego County, California, mapping by Siang S. Tan, digital preparation by Sybil Jorgensen and Jonathan Williams. N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

20 TABLES

21 TABLE CBC ACCELERATION RESPONSE SPECTRA INPUT SPECTRUM CALCULATION OUTPUT S S = g = short period (0.2 sec) mapped spectral response acceleration MCE Site Class B (CBC 2010 Fig (3) or USGS Ground Motion Calculator) Site Latitude: S 1 = g = 1.0 sec period mapped spectral response acceleration MCE Site Class B (CBC 2010 Fig (4) or USGS Ground Motion Calculator) Site Longitude: Site Class= C = Site Class definition based on CBC 2010 Table Seismic Design Category: C F a = = Site Coefficient applied to S s to account for soil type (CBC 2010 Table (1)) F v = = Site Coefficient applied to S 1 to account for soil type (CBC 2010 Table (2)) T L = 8.00 sec = Long Period Transition Period (ASCE 7 05 Figure 22 16) S MS = = site class modified short period (0.2 sec) MCE spectral response acceleration = F a x S s (CBC 2010 Eqn ) S M1 = = site class modified 1.0 sec period MCE spectral response acceleration = F v x S 1 (CBC 2010 Eqn ) S DS = = site class modified short period (0.2 sec) Design spectral response acceleration = 2/3 x S MS (CBC 2007 Eqn ) S D1 = = site class modified 1.0 sec period Design spectral response acceleration = 2/3 x S M1 (CBC 2007 Eqn ) T 0 = sec = 0.2 S D1 /S DS = Control Period (left end of peak) for ARS Curve (Section ASCE 7 05) T S = sec = S D1 /S DS = Control Period (right end of peak) for ARS Curve (Section ASCE 7 05) T Design MCE T Design MCE (seconds) Sa (g) Sa (g) (seconds) Sa (g) Sa (g) Design MCE Period (seconds) Spectral Acceleration (g)

22 FIGURES

23 SITE LAT: N LON: W GROUP DELTA CONSULTANTS, INC. ENGINEERS AND GEOLOGISTS 9245 ACTIVITY ROAD, SUITE 103 SAN DIEGO, CA (858) PROJECT NAME Building H Renovation Project Cuyamaca College, El Cajon, California NO SCALE REFERENCE: Google Maps (2018). PROJECT NUMBER SD-567 DOCUMENT NUMBER FIGURE NUMBER 1 SITE LOCATION MAP

24 A (Infil) A (Geo) A (Geo) A (Infil) A (Geo) Approximate limits of proposed development. Location of borings GROUP DELTA CONSULTANTS, INC. ENGINEERS AND GEOLOGISTS 9245 ACTIVITY ROAD, SUITE 103 SAN DIEGO, CA (858) A (Infil) Location of borings converted to infiltration testing PROJECT NAME Building H Renovation Project Cuyamaca College, El Cajon, California NO SCALE REFERENCE: Google Maps (2018). PROJECT NUMBER SD 567 DOCUMENT NUMBER FIGURE NUMBER 2 EXPLORATION PLAN

25 LEGEND Geotechnical Boring Location Infiltration Testing Location Estimated Location for Existing 6" PVC Storm Drain (sd) Estimated Location for Existing Electric Line (e) Estimated Location for Existing Irrigation Line Estimated Location for Existing Gas Line (g) A Note: 1. The datum presented on the base drawing is unknown. 2. A Existing underground utilities were located based on Cuyamaca College Composite Topographic Survey (Sheets 8&11), dated February A A GROUP DELTA CONSULTANTS, INC. ENGINEERS AND GEOLOGISTS 9245 ACTIVITY ROAD, SUITE 103 SAN DIEGO, CA (858) PROJECT NAME Reference: Base Drawing was provided by Di Donato Associates, Dated March 5, Building H Renovation Project Cuyamaca College, El Cajon, California NO SCALE PROJECT NUMBER SD567 DOCUMENT NUMBER FIGURE NUMBER 3 PROPOSED IMPROVEMENTS

26 LEGEND Geotechnical Boring Location A Infiltration Testing Location A A' Cross Section Note: 1. The datum presented on the base drawing is unknown. B B' A A A A A' GROUP DELTA CONSULTANTS, INC. ENGINEERS AND GEOLOGISTS 9245 ACTIVITY ROAD, SUITE 103 SAN DIEGO, CA (858) PROJECT NAME Building H Renovation Project Cuyamaca College, El Cajon, California Reference: Base Drawing was provided by Di Donato Associates, Dated March 5, NO SCALE PROJECT NUMBER SD567 DOCUMENT NUMBER FIGURE NUMBER 4A CROSS SECTION LIMITS A-A' & B-B'

27 LEGEND Borings? Estimated Geologic Contact A A Projected South A Projected North A Projected North???? Cretaceous Gabbro (Kggb) Artificial Fill (af)? CROSS SECTION A-A' A Projected West A Projected West A Projected East A Projected East? Artificial Fill (af)???? Cretaceous Gabbro (Kggb)? CROSS SECTION B-B' Reference: Base Drawing was provided by Di Donato Associates, Dated March 5, NO SCALE GROUP DELTA CONSULTANTS, INC. ENGINEERS AND GEOLOGISTS 9245 ACTIVITY ROAD, SUITE 103 SAN DIEGO, CA (858) PROJECT NAME Building H Renovation Project Cuyamaca College, El Cajon, California B CROSS SECTIONS A-A' & B-B' PROJECT NUMBER SD567 DOCUMENT NUMBER FIGURE NUMBER

28 SITE LAT: N LON: W LEGEND: GROUP DELTA CONSULTANTS, INC. ENGINEERS AND GEOLOGISTS 9245 ACTIVITY ROAD, SUITE 103 SAN DIEGO, CA (858) PROJECT NAME Building H Renovation Project Cuyamaca College, El Cajon, California NO SCALE REFERENCE: Geologic Map of the Jamul Mountains 7.5 Quadrangle, San Diego County, California, mapping by Siang S. Tan, digital preparation by Sybil Jorgensen and Jonathan Williams (2002). PROJECT NUMBER SD-567 DOCUMENT NUMBER FIGURE NUMBER 5 LOCAL GEOLOGIC MAP

29 408 SITE Fault ID, Distance, Type, and Maximum Magnitude FID R rup (km) Type M max Km Rose Canyon fault zone (Silver Strand section Downtown Graben fault) SS Km Rose Canyon fault zone (Silver Strand section Silver Strand fault) SS Km Rose Canyon fault zone (San Diego section) SS Km Elsinore (Julian) SS Km Rose Canyon fault zone (Silver Strand section Coronado fault) SS Km Coronado Bank (alt2) SS Km Rose Canyon fault zone (Silver Strand section Spanish Bight fault) SS Km Elsinore (Coyote Mountains) SS Km Elsinore (Temecula) SS Km Point Loma fault zone N 6.3 REFERENCE: CALTRANS ARS Online V , CUYAMACA COLLEGE BUILDING H RENOVATION EL CAJON, CALIFORNIA REGIONAL FAULT MAP 6 SD 567

30 SITE LAT: N LON: W LEGEND: GROUP DELTA CONSULTANTS, INC. ENGINEERS AND GEOLOGISTS 9245 ACTIVITY ROAD, SUITE 103 SAN DIEGO, CA (858) PROJECT NAME Building H Renovation Project Cuyamaca College, El Cajon, California NO SCALE REFERENCE: Flood zones in Southern California: PROJECT NUMBER SD-567 DOCUMENT NUMBER FIGURE NUMBER YEAR FLOOD MAP

31 APPENDIX A FIELD EXPLORATION

32 APPENDIX A FIELD EXPLORATION The subsurface exploration program included a visual and geologic reconnaissance of the site, and the excavation of four exploratory borings (A up to A ) on May 2, All borings were drilled using CME 75 truck-mounted rig, with an 8-inch diameter hollow-stem flight auger. Drive samples were collected from the borings using an automatic hammer with an average Energy Transfer Ratio (ETR) of about 71.2 percent. All holes were terminated at the depths of less than 20 feet below ground surface (bgs). Figures A-1 through A-4 show the logs. Soil samples were collected from the borings using both a Standard Penetration Test (SPT) sampler, and a modified California (CAL) ring sampler at selective depths. For each sample, the number of blows needed to drive the sampler 12 inches was recorded on the logs. The field blow counts (N) were normalized to approximate the standard 60 percent ETR, as shown on the logs (N 60 ). Bulk soil samples were also collected from the borings at shallow depths. The approximate boring elevations were estimated from Google Earth. The boring locations were determined by visually estimating, handheld GPS reading, pacing and taping distances from landmarks shown on the Exploration Plan. The locations shown should not be considered more accurate than is implied by the method of measurement used and the scale of the map. The lines designating the interface between differing soil materials on the logs may be abrupt or gradational. Further, soil conditions at locations between the excavations may be substantially different from those at the specific locations we explored. It should be noted that the passage of time may also result in changes in the soil conditions reported in the logs. N:\Projects\SD\SD567 GCCCD Cuyamaca College Building H Renovation\5. Reports\ \DRAFT\ R.docx

33 SOIL IDENTIFICATION AND DESCRIPTION SEQUENCE HOLE IDENTIFICATION Holes are identified using the following convention: H YY NNN Where: H: Hole Type Code YY: 2-digit year NNN: 3-digit number ( ) Description Sequence Examples: SANDY lean CLAY (CL); very stiff; yellowish brown; moist; mostly fines; some SAND, from fine to medium; few gravels; medium plasticity; PP=2.75. Describe the soil using descriptive terms in the order shown Minimum Required Sequence: USCS Group Name (Group Symbol); Consistency or Density; Color; Moisture; Percent or Proportion of Soil; Particle Size; Plasticity (optional). = optional for non-caltrans projects Where applicable: Cementation; % cobbles & boulders; Description of cobbles & boulders; Consistency field test result REFERENCE: Caltrans Soil and Rock Logging, Classification, and Presentation Manual (2010). Well-graded SAND with SILT and GRAVEL and COBBLES (SW-SM); dense; brown; moist; mostly SAND, from fine to coarse; some fine GRAVEL; few fines; weak cementation; 10% GRANITE COBBLES; 3 to 6 inches; hard; subrounded. Clayey SAND (SC); medium dense, light brown; wet; mostly fine sand,; little fines; low plasticity. Project No. SD567 Cuyamaca College Building H Renovation El Cajon, California BORING RECORD LEGEND #1

34 (2.4 ID, 3 OD) (after drilling, date) REFERENCE: Caltrans Soil and Rock Logging, Classification, and Presentation Manual (2010). Project No. SD567 Cuyamaca College Building H Renovation El Cajon, California BORING RECORD LEGEND #2

35 REFERENCE: Caltrans Soil and Rock Logging, Classification, and Presentation Manual (2010), with the exception of consistency of cohesive soils vs. N 60. Project No. SD567 Cuyamaca College Building H Renovation El Cajon, California BORING RECORD LEGEND #3

36 Project No. SD567 Cuyamaca College Building H Renovation El Cajon, California BORING RECORD LEGEND #4