Using probabilistic seismic hazard analyses to optimize ground improvement

As development across New Zealand continues to spread beyond existing city limits, geologically/geotechnically complex development locations are increasingly selected due to their vicinity to existing population centres. One of the major challenges in many of these locations in New Zealand is seismic risk and associated hazards like liquefaction, cyclic softening, seismic instability including flow failure and lateral spreading. Design seismic loading is routinely obtained from national standards or equivalent documents.

A Probabilistic Seismic Hazard Analysis (PSHA) can be performed to provide seismic input including design seismic loads. A PSHA is usually performed for critical infrastructure, rather than for residential or even industrial development. This paper presents a case study of a residential land development project in Cambridge, New Zealand, where a PSHA was performed based on which the peak ground acceleration for the ULS loading (1-in-500 years event) was reduced from 0.28g to 0.17g. The resultant modelling of the site indicated a significant reduction in calculated lateral spread and slope instability risk, which lead to substantial construction cost savings and reduced carbon emissions associated with the development. This was a critical part of the development design, which ultimately allowed the project to proceed from a feasibility study to construction.