Assessment of liquefaction and related ground failure hazards in Palmerston North, New Zealand Dick Beetham John Begg Peter Barker Shaun Levick Jean Beetham GNS Science Consultancy Report 2011/108 July 2011 DISCLAIMER This report has been prepared by the Institute of Geological and Nuclear Sciences Limited (GNS Science) exclusively for and under contract to Palmerston North City Council. Unless otherwise agreed in writing by GNS Science, GNS Science accepts no responsibility for any use of, or reliance on any contents of this Report by any person other than Palmerston North City Council and shall not be liable to any person other than Palmerston North City Council, on any ground, for any loss, damage or expense arising from such use or reliance. BIBLIOGRAPHIC REFERENCE Beetham, R.D.; Begg, J.G.; Barker, P.; Levick, S.; Beetham, J. 2011. Assessment of liquefaction and related ground failure hazards in Palmerston North, New Zealand, GNS Science Consultancy Report CR 2011/108 90 p. Project Number: 430W1434 July 2011 CONTENTS EXECUTIVE SUMMARY ...................................................................................................... IV 1.0 INTRODUCTION ........................................................................................................ 8 1.1 Background ................................................................................................................... 8 1.1.1 Project Objectives ............................................................................................ 8 1.1.2 Project Design .................................................................................................. 9 1.1.3 Timelines ........................................................................................................ 10 1.1.4 Previous GNS Reporting of Liquefaction in the region................................... 10 2.0 THE LIQUEFACTION PROCESS ............................................................................. 11 2.1 Introduction .................................................................................................................. 11 2.2 Definition of liquefaction and related terms ................................................................. 12 2.2.1 Liquefaction .................................................................................................... 12 2.2.2 Cyclic strain softening .................................................................................... 12 2.2.3 Ground failure ................................................................................................. 13 2.3 Liquefaction Background ............................................................................................. 14 2.4 Assessment of liquefaction Potential ........................................................................... 17 3.0 SOILS AND GEOLOGY OF PALMERSTON NORTH .............................................. 18 3.1 Palmerston North Regional Tectonic Setting .............................................................. 18 3.2 General Physiography ................................................................................................. 19 3.2.1 Historical Archived Maps ................................................................................ 19 3.3 General information on Lidar data ............................................................................... 19 3.4 Soils of Palmerston North ............................................................................................ 20 3.5 Geology of Palmerston North ...................................................................................... 20 4.0 EARTHQUAKES ...................................................................................................... 21 4.1 Measuring Earthquake Strength .................................................................................. 21 4.2 Earthquake and liquefaction history of Palmerston North ........................................... 22 4.2.1 Historic earthquakes felt in the Palmerston North area.................................. 22 4.3 Liquefaction opportunity - known seismogenic structures in the PNCC region .......... 22 4.3.1 Estimated fault recurrence intervals ............................................................... 23 4.3.2 Modelled Recurrence Interval of strong ground shaking ............................... 25 5.0 LIQUEFACTION SUSCEPTIBILITY ......................................................................... 25 5.1 Conventional liquefaction map .................................................................................... 26 5.1.1 Zone 5 – Negligible Liquefaction Ground Damage Potential ......................... 27 5.1.2 Zone 4 – Low Liquefaction Ground Damage Potential .................................. 27 5.1.3 Zones 2 – 3, Moderate to High Liquefaction Ground Damage Potential ....... 27 5.1.4 Zones 1 – 3, Moderate to Very High Liquefaction Ground Damage Potential 28 5.2 Liquefaction susceptibility incorporating subsurface information ................................ 28 5.2.1 Horizons Manawatu drillhole database .......................................................... 28 5.2.2 Geotechnical information ................................................................................ 29 5.3 Steps in modelling liquefaction potential using digital datasets .................................. 29 5.4.2 Conclusions from digital liquefaction modelling ............................................. 33 5.4.3 Limitations of our subsurface interpretation ................................................... 34 There are a number of limitations associated with the subsurface interpretations that are mentioned below. .................................................................................................. 34 5.4.3.1 Lidar DEM (digital elevation model) ................................................ 34 5.4.3.2 Drillhole coverage ........................................................................... 35 5.4.3.3 Soil layer ......................................................................................... 35 5.4.3.4 Geotechnical data ........................................................................... 35 5.4.4 General statement of limitations ......................................................................... 35 6.0 POTENTIAL FOR LIQUEFACTION AND GROUND DAMAGE IN PALMERSTON NORTH ..................................................................................................................... 36 6.1 PNC Totara Rd. wastewater treatment plant .............................................................. 36 6.2 Anders Road, Racecourse residential growth option .................................................. 36 6.3 Kelvin Grove residential growth option ........................................................................ 37 GNS Science Consultancy Report 2011/108 i July 2011 7.0 MITIGATION OPTIONS & COST .............................................................................. 38 7.1 PNCC Totara Rd Wastewater Treatment Plant .......................................................... 38 7.2 Anders Road, Racecourse and Kelvin Grove residential growth areas ...................... 38 8.0 CONCLUSIONS AND RECOMMENDATIONS ......................................................... 40 9.0 ACKNOWLEDGEMENTS ......................................................................................... 42 10.0 REFERENCES ......................................................................................................... 42 FIGURES Figure 1 Photos from Christchurch showing evidence of liquefaction in the form of sand boils along ―fissures‖. a) The Avon River right bank at Anzac Bridge. b) Mona Vale gardens in Fendalton. c) This swimming pool was full of water during the Darfield Earthquake and stayed in the ground when the site liquefied. However, it was empty and ―floated‖ when the site liquefied in the Christchurch Earthquake. d) This pumping station caisson floated and moved laterally during both earthquakes. ........................................................................................ 47 Figure 2 These photos provide examples of lateral spreading and settlement adjacent to the Avon River after the Christchurch Earthquake: a) Fitzherbert Terrace near the junction with Avonside Drive; b) Bridge St. bridge near New Brighton showing abutment settlement and rotation; c) the Avondale Rd. bridge with lateral spreading cracks and d) abutment rotation and settlement. ................................................................................................................................ 48 Figure 3 a) Palmerston North City lies close to the boundary between the Pacific (here coloured pink) and Australian (yellow) tectonic plates. The plates are moving across the surface of the globe at differing rates and the relative difference is represented here by convergence rates at specific places at along the boundary (red arrows and numbers). b) The Manawatu region sits behind the outer edge of the Australian Plate at the western margin of a zone where the west-dipping plate interface is locked. Locking of the plate interface, and the relative convergence rates and vectors contribute to the upward bulge in the Australian Plate that is the landmass of the southern North Island. The offshore DEM is derived from bathymetric contours. .........................................................................................................................................