Liquefaction Risk Assessment for the State Highway 2: Dowse to Petone Upgrade Project

The site of the proposed realignment of State Highway 2 from Petone overbridge through to the Dowse intersection, Hutt Valley, New Zealand is in a region of high seismicity. The alignment is subject to very large seismic design loadings (1000 year Return Period PGA of 0.65g, Maximum Credible Earthquake PGA 1.0g) due to its proximity to the active Wellington Fault (Mw 7.4). Following a site-specific seismic hazard assessment, the geotechnical assessment of the site included a liquefaction analysis addressing likely magnitude of induced ground subsidence and effects on bridge piles, MSE abutments/ ramps, and nearby commercial properties at Dowse. Results of the seismic assessment present significant challenges to bridge and MSE wall designers for this project in achieving compliance with Transit New Zealand design philosophy requirements. This paper discusses methodologies adopted for the liquefaction assessment, results, and implications for the design of the structures on the project.