TRANSMISSION GULLY PROJECT ASSESSMENT OF ENVIRONMENTAL EFFECTS TECHNICAL REPORT No. 3 GEOTECHNICAL ENGINEERING REPORT New Zealand Transport Agency and Porirua City Council Transmission Gully Project Assessment of Environmental Effects Technical Report No.3 Geotechnical Engineering Report July 2011 Prepared by Opus International Consultants Limited P Brabhaharan Wellington Office Principal, Geotechnical Engineering & Risk Level 9, Majestic Centre Geotechnical Team Leader 100 Willis Street, PO Box 12-003 Wellington, New Zealand Telephone: +64 4 471 7000 Reviewed by David Stewart Facsimile: +64 4 471 1397 Senior Geotechnical Engineer Report No GER 2010 / 23 Date: July 2011 Reference: 5C1591.20 Status: Final Opus International Consultants Limited 2011 Technical Report No.3 Geotechnical Engineering Report Contents Executive Summary 1 Introduction .......................................................................................................................... 1 1.1 Overview ...................................................................................................................... 1 1.2 Transmission Gully Main Alignment .............................................................................. 1 1.3 Kenepuru Link Road ..................................................................................................... 2 1.4 Porirua Link Roads ....................................................................................................... 2 1.5 Purpose and Scope of this Report ............................................................................... 2 2 Geotechnical Investigations ................................................................................................ 4 2.1 Present Role ................................................................................................................. 5 2.2 Previous Geotechnical Investigations ........................................................................... 5 2.3 Stage 2 Geotechnical Investigations ............................................................................ 5 3 Characterisation of the Route ............................................................................................. 6 4 Engineering Geology ........................................................................................................... 7 4.1 Overview ...................................................................................................................... 7 4.2 Terrain .......................................................................................................................... 7 4.3 Geology ........................................................................................................................ 9 4.4 Active Faults ............................................................................................................... 12 5 Ground and Groundwater Conditions .............................................................................. 13 5.1 Introduction ................................................................................................................. 13 5.2 Overview of Ground Conditions .................................................................................. 13 5.3 Groundwater Conditions ............................................................................................. 14 6 Material Properties ............................................................................................................. 16 6.1 Rock Mass Properties................................................................................................. 16 6.2 Soil Properties ............................................................................................................ 18 7 Hazards ............................................................................................................................... 21 7.1 Geological Hazards along the Route .......................................................................... 21 7.2 Slope Instability .......................................................................................................... 21 7.3 Debris Floods and Flows ............................................................................................ 22 7.4 Earthquakes and Ground Shaking ............................................................................. 22 7.5 Fault Rupture .............................................................................................................. 22 7.6 Earthquake Induced Landslides ................................................................................. 23 7.7 Liquefaction ................................................................................................................ 23 7.8 Tsunami ...................................................................................................................... 23 8 Seismicity ........................................................................................................................... 24 8.1 Regional Setting ......................................................................................................... 24 8.2 Active Faults ............................................................................................................... 24 5C1591.20 i July 2011: Final Technical Report No.3 Geotechnical Engineering Report 8.3 Ground Shaking ......................................................................................................... 25 9 Design Philosophy ............................................................................................................. 28 9.1 Route Security ............................................................................................................ 28 9.2 Existing State Highway Vulnerabilities ........................................................................ 28 9.3 The Transmission Gully Opportunity .......................................................................... 29 9.4 Geotechnical Design Philosophy ................................................................................ 33 10 Road Form and Engineering Concepts ............................................................................ 35 10.1 Road Alignment .......................................................................................................... 35 10.2 Road Form ................................................................................................................. 36 10.3 Geotechnical Enhancements since 2004 Designation ............................................... 37 11 Tunnels ............................................................................................................................... 42 11.1 Location ...................................................................................................................... 42 11.2 Tunnel Form ............................................................................................................... 42 11.3 Cut and Cover Tunnel ................................................................................................ 42 11.4 Underground Excavated Tunnel ................................................................................. 43 11.5 Feasibility of Tunnel Options ...................................................................................... 44 12 Rock Cut Slopes ................................................................................................................ 45 12.1 Design Philosophy ...................................................................................................... 45 12.2 Cut Slope Configuration ............................................................................................. 46 12.3 Stability of Cut Slopes in Rock ................................................................................... 48 12.4 Influence of Defects on Cut Slope Stability ................................................................ 52 12.5 Combined Rock Mass and Defect Controlled Instability ............................................. 56 12.6 Earthquake Stability of Cut Slopes ............................................................................. 58 12.7 Cut Slope Configuration ............................................................................................. 62 12.8 Cut Slope Stabilisation Measures ............................................................................... 63 12.9 Landscaping, Revegetation and Erosion Control ....................................................... 64 12.10 Summary ................................................................................................................... 64 13 Rock Fall Hazards and Management ................................................................................ 65 13.1 Design Philosophy ...................................................................................................... 65 13.2 Cut Slope Design and Effect on Rock Fall Hazards ................................................... 65 13.3 Rock Fall Hazards in the Wellington Region .............................................................. 66 13.4 Assessment of Rock Fall Hazards .............................................................................. 67 13.5 Integrated Rock Fall Management .............................................................................. 69 13.6 Maintenance of Rock fall Protection Measures .......................................................... 76 13.7 Summary .................................................................................................................... 77 14 Soil Cut Slopes................................................................................................................... 79 14.1 Design Philosophy ...................................................................................................... 79 14.2 Proposed Cut Slopes and Geometry .......................................................................... 79 14.3 Precedent Cut Slopes ................................................................................................ 80 14.4 Behaviour in Historical Earthquakes ........................................................................... 81 5C1591.20 ii July 2011: Final Technical Report No.3 Geotechnical Engineering Report 14.5 Stability Analyses ....................................................................................................... 81 14.6 Areas of Existing Landslides ...................................................................................... 83 14.7 Landscaping, Revegetation and Erosion Control ....................................................... 83 14.8 Cut Slope Stabilisation Measures ............................................................................... 83 14.9 Summary .................................................................................................................... 84 15 Embankments .................................................................................................................... 86 15.1 Design Philosophy ...................................................................................................... 86 15.2 Fill Materials ............................................................................................................... 86 15.3 Precedent Embankment Slopes ................................................................................. 87 15.4 Behaviour in Historical Earthquakes ........................................................................... 88 15.5 Stability Analyses ....................................................................................................... 88 15.6 Settlement .................................................................................................................. 89 15.7 Ground Improvement .................................................................................................. 90 15.8 Fill Slope Configuration .............................................................................................. 90 15.9 Reinforced Soil Embankments ................................................................................... 91 15.10 Landscaping and Revegetation ................................................................................. 93 15.11 Summary ................................................................................................................... 93 16 Earthworks and Construction Materials ........................................................................... 95 16.1 Unsuitable Foundation Materials ................................................................................ 95 16.2 Excavation Characteristics ......................................................................................... 95 16.3 Suitability of Cut Materials .......................................................................................... 97 16.4 Compaction Characteristics ........................................................................................ 97 16.5 On-site Material Sources ............................................................................................ 98 16.6 Developing Aggregate Sources .................................................................................. 99 16.7 Summary .................................................................................................................... 99 17 Disposal Sites .................................................................................................................. 101 17.1 Disposal Philosophy ................................................................................................. 101 17.2 Selection of Potential Disposal Sites ........................................................................ 101 17.3 Geotechnical Issues for Consideration of Disposal Sites ......................................... 102 17.4 Construction Management ....................................................................................... 102 17.5 Summary .................................................................................................................. 103 18 Route Security Performance ........................................................................................... 104 18.1 The Regional Context ............................................................................................... 104 18.2 Route Security Philosophy ....................................................................................... 104 18.3 Route Performance .................................................................................................. 104 19 Geotechnical Engineering Risk Management ................................................................ 106 19.1 Geotechnical Engineering Uncertainties and Risks .................................................. 106 19.2 Risk Management ..................................................................................................... 110 20 Reference ......................................................................................................................... 111 5C1591.20 iii July 2011: Final Technical Report No.3 Geotechnical Engineering Report List of Tables Table 3.1 - Geotechnical Sectors Table 3.2 - Geological Strength Index Characterisation of Rocks along TG Table 3.3 - Fault Rupture Hazard Table 3.4 - Active Fault Earthquake Sources Table 3.5 - Peak Ground Accelerations from NZS 1170.5 Table 3.6 - Peak Ground Accelerations from Site Specific Seismicity Study Table 3.7 - Soil Slope Design Criteria Table 3.8 - Rock Slope Design Criteria Table 3.9 - Retaining Wall Design Requirements Table 3.10 - General Guidance on Selection of Alignment Table 3.11 - Appropriate Road Forms Table 3.12 - Principles for Cut Slope Configuration Table 3.13 - Cut Slope Stabilisation Measures Table 3.14 - Comparison of Rock Fall Management Measures Table 3.15 - Proposed Cut Slopes in Soils Table 3.16 - Precedent Cut Slopes in Pre-Holocene Soils in Wellington Region Table 3.17 - Fill Materials and Embankment Configuration Table 3.18 - Excavation Characteristics Table 3.19 - Key Geotechnical Uncertainties and Risk Management List of Illustrations Illustration 3.1 - Location of Transmission Gully Route Illustration 3.2 - Summary Engineering Geology along the Route Illustration 3.3 - Seepages from Active Splinter Fault on Western Flank South of Wainui Saddle Illustration 3.4 - GSI Characterisation of Greywacke Rock along Transmission Gully Illustration 3.5 - Classification of Soils from Transmission Gully Illustration 3.6 - Soil Compaction Test Results Illustration 3.7 - Active Fault Sources in relation to Transmission Gully Route Illustration 3.8 - Highway destroyed by landslides in the 2008 Wenchuan Earthquake, China Illustration 3.9 - Viaduct / bridges in steep terrain destroyed by landslides in the Wenchuan Earthquake Illustration 3.10 - Important Issues Influencing Design of Cut Slopes Illustration 3.11 - Superimposition of Grant-Taylor (1964) Curves on the Precedent Cut Slope Data Illustration 3.12 - Rosette Plot showing Strike of Shear Surfaces Illustration 3.13 - Frequency Plot showing Dip and Dip Directions of Shear Surfaces in Rock Illustration 3.14 - Comparison of Dip Direction of Cuttings and Shear Illustration 3.15 - Stereonet for Wedge and Planar Failures on S & SE Dipping Cuts Illustration 3.16 - Stereonet for Wedge and Planar Failures on N & NW Dipping Cuts Illustration 3.17 - Typical Analysis of Combined Defect and Rock Mass Failures in Rock Illustration 3.18 - Map showing earthquake-induced landslide susceptibility Illustration 3.19 - Benched Cut Slope in Wellington Greywacke at SH 1 Newlands Interchange Illustration 3.20 - Rock Fall Behaviour on Slopes 5C1591.20 iv July 2011: Final Technical Report No.3 Geotechnical Engineering Report Illustration 3.21 - Rock Fall Protection Netting at SH 2 Kaitoke to Te Marua Illustration 3.22- Typical Cut Slope Configuration Illustration 3.23 - 1950’s Cut Slope in Ngauranga Gorge, Wellington Illustration 3.24 - Cut Slope Configuration with Intermediate Benches Illustration 3.25 - Rock Fall with talus and Vegetation on Benches Illustration 3.26 - Rock Fall Analysis with a Uniform Cutting with No Benches Illustration 3.27 - Rock Cutting with Benches along State Highway 2, after 50 Years Illustration 3.28 - Typical Slope Stability Analysis of Cut Slopes in Soil Illustration 3.29 - Failure of Road Embankments due to Liquefaction in 1931 Hawkes Bay Earthquake Illustration 3.30 - Typical Slope Stability Analysis of Soil Embankment Illustration 3.31 - Typical Analysis of a Reinforced Soil Embankment 5C1591.20 v July 2011: Final