Geotechnical investigations to address Earthquake Hazards for the Petone to Grenada Link Road, Wellington, New Zealand

The New Zealand Transport Agency is developing a new Petone to Grenada (P2G) link between Hutt Valley and Porirua, to improve road access and reliability in the region. Resilience is a key objective for the project and for the transportation network in the Wellington region. The P2G project crosses land that has complex geotechnical issues and is exposed to significant natural hazards, and consequently a comprehensive programme of site investigation was carried out to characterise the ground conditions and inform the development of robust and resilient options for the road alignment. Particular geotechnical issues investigated for this project were the location of the active Wellington Fault, the liquefaction hazards in Petone, the slope failure hazards in the steep hilly terrain, the properties of the highly fractured and faulted greywacke bedrock and the depth and distribution of deeply weathered material. A comprehensive ground model is presented that incorporates the geomorphology and geology of the site with the geotechnical issues and hazards, and implications for the geotechnical design of the project are discussed. It is noted that the development of this project is in progress, and additional geotechnical investigations are currently being carried out to inform further development of the design.