1 Malibu Creek Ecosystem Restoration Study 2 3 Los Angeles and Ventura Counties, California 4 5 Appendix D 6 7 Geotechnical Engineering 8 9 10 11 12 U.S. Army Corps of Engineers 13 Los Angeles District 14 15 16 January 2017 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 This page was intentionally left blank for duplex printing. Appendix D –Geotechnical Engineering 1 Table of Contents 2 3 Section Page 4 5 1.0 INTRODUCTION ................................................................................................................ 1 6 1.1 Project Location .......................................................................................................... 1 7 1.2 Background ................................................................................................................ 1 8 1.3 Possible Improvements .............................................................................................. 2 9 1.3.1 Geotechnical Measures Considered ....................................................................... 2 10 1.3.2 Alternatives Considered .......................................................................................... 3 11 1.3.3 Beneficial Reuse and Disposal of Impounded Sediment ......................................... 6 12 1.3.4 “Upland Disposal” of Impounded Sediment ............................................................. 6 13 1.4 Available Information .................................................................................................. 8 14 1.5 Scope of Work ............................................................................................................ 8 15 2.0 FIELD, LABORATORY, AND PREVIOUS STUDIES........................................................... 9 16 2.1 Law Crandall .............................................................................................................. 9 17 2.2 Bureau of Reclamation ............................................................................................... 9 18 2.3 USACE Studies .......................................................................................................... 9 19 2.4 Dam Evaluation .........................................................................................................13 20 3.0 SITE CONDITIONS ...........................................................................................................13 21 3.1 Surface Conditions and Topography ..........................................................................13 22 3.2 Regional Geology ......................................................................................................15 23 3.3 Site Geology ..............................................................................................................16 24 3.3.1 Stratigraphy ...........................................................................................................16 25 3.3.2 Landslides (Qls) .....................................................................................................19 26 3.3.3 Alluvium (Qal) ........................................................................................................19 27 3.4 Groundwater ..............................................................................................................21 28 3.5 Faulting and Seismicity ..............................................................................................21 29 4.0 GEOTECHNICAL AND GEOLOGIC CONSTRAINTS ........................................................22 30 5.0 CONCLUSIONS AND RECOMMENDATIONS...................................................................23 31 5.1 Impounded Sediment Characterization and Potential Application ..............................23 32 5.1.1 Quantity and Gradation ..........................................................................................24 33 5.1.2 Chemical (Contaminant) Characteristics ................................................................24 34 5.2 Sediment Disposal .....................................................................................................25 35 5.3 Impounded Sediment Upland Disposal Sites (Permanent Storage) ...........................26 36 5.3.1 Sites A through D ...................................................................................................26 37 5.3.2 Sites E through M ..................................................................................................29 38 5.3.3 Sites N through U ..................................................................................................30 39 5.4 Sediment Removal, Excavation Considerations, and Transport .................................30 40 5.4.1 Sequencing of Dam and Sediment Removal ..........................................................30 41 5.4.2 Excavation Characteristics .....................................................................................32 42 5.4.3 Sediment Transport Options ..................................................................................33 43 5.4.4 Haul Ramp Construction and Deconstruction ........................................................33 44 5.4.5 In-Situ and Off-site Processing ..............................................................................33 45 5.4.6 Temporary Stockpiles ............................................................................................36 46 5.4.7 Diversion and Dewatering ......................................................................................36 47 5.4.8 Re-Deposition of Sediments ..................................................................................37 48 5.5 Dam Stability during Deconstruction ..........................................................................37 49 5.6 Stability of Canyon Slopes .........................................................................................38 50 5.7 Levees and Floodwalls ..............................................................................................39 Malibu Creek Ecosystem Restoration D-i Draft Report Appendix D –Geotechnical Engineering 1 5.8 Removal of Upstream Barriers ...................................................................................40 2 6.0 RECOMMENDED ADDITIONAL STUDIES ........................................................................40 3 6.1 Beach Compatibility Transect Studies .......................................................................40 4 6.2 Chemical Testing .......................................................................................................40 5 6.3 Permanent and Temporary Sediment Storage Site Investigations .............................41 6 6.4 Detailed Site Investigation and Material Characterization ..........................................41 7 6.5 Upstream Barrier Investigations .................................................................................42 8 6.6 Post Dam Removal ....................................................................................................42 9 6.7 Blasting .....................................................................................................................42 10 7.0 LIMITATIONS AND RISK ...................................................................................................43 11 7.1 General .....................................................................................................................43 12 7.2 Elevation datum used by USACE-Geotechnical ........................................................43 13 7.3 Sediment Processing for Disposal .............................................................................43 14 7.4 Flood Risk to Downstream Properties ........................................................................43 15 7.5 Limited Geotechnical Studies ....................................................................................43 16 7.6 Current Haul Ramp Concept......................................................................................44 17 7.7 Stability of Canyon Slopes .........................................................................................44 18 7.8 Establishment of Final Grades ...................................................................................44 19 7.9 Costs and Constructability .........................................................................................44 20 8.0 REFERENCES ..................................................................................................................46 21 Other Reference Consulted ...................................................................................................47 22 23 LIST OF TABLES 24 25 Table 1.3-1 Alternatives Considered ..........................................................................................5 26 27 LIST OF FIGURES 28 29 Figure 1.3-1 Potential Disposal Sites E through M ..................................................................... 7 30 Figure 2.3-1 Aerial of Impound Area ........................................................................................ 12 31 Figure 3.1-1 Malibu Rindge Impoundment Sediment Profile ..................................................... 14 32 Figure 3.3-1 Geologic Map of Dam and Impound ..................................................................... 18 33 Figure 5.3-1 Potential Upland Disposal Sites A, B and C ......................................................... 28 34 35 36 37 APPENDICES 38 39 Appendix D1 – Boring and Test Pit Logs 40 Appendix D2 - Lab and Environmental