GEOTECHNICAL EVALUATION CAJON AIR CENTER AT GILLESPIE FIELD EL CAJON, CALIFORNIA PREPARED FOR: Kimley-Horn and Associates, Inc. 401 B Street, Suite 600 San Diego, California 92101 PREPARED BY: Ninyo & Moore Geotechnical and Environmental Sciences Consultants 5710 Ruffin Road San Diego, California 92123 May 11, 2016 Project No. 108139001 Cajon Air Center at Gillespie Field May 11, 2016 El Cajon, California Project No. 108139001 TABLE OF CONTENTS Page 1. INTRODUCTION ....................................................................................................................1 2. SCOPE OF SERVICES ............................................................................................................1 3. SITE DESCRIPTION ...............................................................................................................3 4. PROJECT DESCRIPTION ......................................................................................................4 5. SUBSURFACE EXPLORATION ............................................................................................4 5.1. Percolation Testing .......................................................................................................5 6. GEOTECHNICAL LABORATORY TESTING .....................................................................6 7. GEOLOGY AND SUBSURFACE CONDITIONS .................................................................7 7.1. Regional Geologic Setting ............................................................................................7 7.2. Site Geology .................................................................................................................8 7.2.1. Fill .......................................................................................................................8 7.2.2. Alluvium .............................................................................................................8 7.2.3. Granitic Rock ......................................................................................................9 7.3. Groundwater .................................................................................................................9 7.4. Flood Hazards .............................................................................................................10 8. GEOLOGIC HAZARDS ........................................................................................................10 8.1. Faulting and Seismicity ..............................................................................................10 8.2. Ground Rupture ..........................................................................................................11 8.3. Strong Ground Motion ................................................................................................11 8.4. Liquefaction and Seismically Induced Settlement .....................................................12 8.5. Landsliding .................................................................................................................12 9. CONCLUSIONS ....................................................................................................................12 10. RECOMMENDATIONS ........................................................................................................13 10.1. Earthwork ...................................................................................................................14 10.1.1. Site Preparation .................................................................................................14 10.1.2. Excavation Characteristics ................................................................................14 10.1.3. Excavation Bottom Characteristics ...................................................................15 10.1.4. Temporary Excavations ....................................................................................15 10.1.5. Construction Dewatering ..................................................................................16 10.1.6. Remedial Grading .............................................................................................16 10.1.7. Materials for Fill ...............................................................................................17 10.1.8. General Compacted Fill ....................................................................................18 10.1.9. Subgrade Compaction – Airfield Pavements ....................................................20 10.1.10. Subgrade Preparation – Hydromodification Vault ............................................21 10.1.11. Lateral Pressures for Thrust Blocks ..................................................................21 10.1.12. Pipe Bedding and Modulus of Soil Reaction (E') .............................................21 10.1.13. Pipe Zone Backfill ............................................................................................22 10.1.14. Utility Trench Zone Backfill .............................................................................22 108139001 R Revised.doc i Cajon Air Center at Gillespie Field May 11, 2016 El Cajon, California Project No. 108139001 10.1.15. Drainage ............................................................................................................23 10.2. Seismic Design Considerations ..................................................................................24 10.3. Underground Structures ..............................................................................................24 10.3.1. Mat Foundations ...............................................................................................24 10.3.2. Lateral Pressures ...............................................................................................25 10.3.3. Uplift Considerations ........................................................................................26 10.3.4. Static Settlement ...............................................................................................27 10.4. Concrete Flatwork ......................................................................................................27 10.5. Corrosion ....................................................................................................................27 10.6. Concrete ......................................................................................................................28 10.7. Pre-Construction Conference ......................................................................................28 10.8. Plan Review and Construction Observation ...............................................................28 11. LIMITATIONS .......................................................................................................................29 12. REFERENCES .......................................................................................................................31 Tables Table 1 – Percolation Test Results ...................................................................................................6 Table 2 – 2013 California Building Code Seismic Design Criteria ...............................................24 Figures Figure 1 – Site Location Figure 2 – Exploration Locations Figure 3 – Fault Locations Figure 4 – Geology Figure 5 – Thrust Block Lateral Earth Pressure Diagram Figure 6 – Lateral Earth Pressures for Underground Structures Figure 7 – Uplift Resistance Diagram for Underground Structures Appendices Appendix A – Excavation Logs Appendix B – Geotechnical Laboratory Testing 108139001 R Revised.doc ii Cajon Air Center at Gillespie Field May 11, 2016 El Cajon, California Project No. 108139001 1. INTRODUCTION In accordance with your request and our proposal dated March 23, 2016, we have performed an additional geotechnical evaluation for the proposed Cajon Air Center at Gillespie Field project in El Cajon, California (Figure 1). We previously prepared a draft geotechnical evaluation report for the proposed project in 2009 (Ninyo & Moore, 2009). The purpose of this study was to update, supplement, and finalize the initial draft report. This report presents data from our previous and recent background, field, and laboratory evaluations, as well as our conclusions regarding the geotechnical conditions at the subject site and our recommendations for the design and construc- tion of the proposed airfield improvements. Additionally, the recent phase of this study was focused on providing supplemental geotechnical information regarding the hydromodification vault to be constructed at the northwest corner of the project site. 2. SCOPE OF SERVICES The scope of our geotechnical services for this project was conducted in two phases. The first phase of work was performed in 2009 and the second phase of work was performed recently, in 2016. The scope of services associated with the 2009 phase of work included the following: Reviewing readily available background materials pertaining to the project including previ- ous geotechnical and environmental evaluations, geologic maps, topographic maps, and in- house information. Performing a geotechnical reconnaissance of the site to observe the existing conditions. Marking the subsurface exploration locations for utility clearance by Underground Service Alert (USA). Retaining a geophysical subcontractor to assist in clearing the locations of the subsurface explorations for conflicts with existing underground utilities. Acquiring boring permit #LMON106263 from the County