Abstract:
Soft and liquefiable soils are a significant concern in New Zealand (NZ) due to the country's seismicity. NZ experiences approximately one magnitude 7+ and ten magnitude 6+ earthquakes each decade. Some of the events have caused widespread damage to infrastructure due to liquefaction and lateral spreading. The use of deep pile foundations penetrating through liquefiable soil layers into competent materials is very common. On many projects ground improvement rather than pile foundations is used to prevent liquefaction and lateral spreading and increase the strength of soft ground.
In recent years, NZ Ministry of Business, Innovation & Employment (MBIE), NZ Earthquake Commission (EQC) and NZ Transport Agency (NZTA) funded many research projects to develop design guidelines for pile foundations and ground improvement. WSP has been involved in the preparation of NZ Verification Method B1/VM4 Foundations, National Earthquake Resistant Foundation Design Guidelines (Module 4), National Ground Improvement Guidelines (Module 5), MBIE C4 Guidelines for Seismic Assessment of Existing Building Foundations, NZTA Bridge Manual and NZTA Guidelines for Pile Foundations at Liquefiable Sites. A brief history of the development and the status of the relevant NZ regulatory framework are described.
Ground improvement methods used on major NZ infrastructure projects such as Te Kaha Canterbury Multi-Use Arena, Wellington Regional Stadium, CentrePort (Wellington), Lyttelton Port (Christchurch), New Plymouth Rugby Stadium, Museum of New Zealand (Wellington), Sulphur Point Wharf (Port of Tauranga), two Tauranga Wastewater Plants, Taupo and Lower Hutt Water Treatment Plants as well as several major Waka Kotahi NZ transport agency’ s road and bridge projects are described. WSP’ s recent experience with the use of innovative expanding resin injection ground improvement method is shared. An innovative methodology for post-earthquake assessment of damage to pile foundations supporting bridges and multi-storey buildings developed by WSP and used on several projects is described.