Understanding Liquefaction Triggering Risk – An Australian Geotechnical Design Perspective

Resilience is the ability to quickly recover during an adverse event. Following an earthquake the resilience of a community can be directly related to working infrastructure. Geotechnical resilience design must consider liquefaction from future large earthquakes.

Although Australia is considered a stable continental region with relatively low seismic hazard, earthquakes do occur and where susceptible geological conditions exist, liquefaction can occur. In fact, liquefaction has been documented in Australia on at least three occasions. In 1897, liquefaction was observed during a large (Ms 6.5) earthquake near Beachport, south-eastern South Australia (Collins et al., 2004); in the 1903 Warrnambool, Victoria (Ml 5.3) earthquake (Mitchell and Moore, 2007); and in 1968, numerous “sand blows” were observed following the Ms 6.8 earthquake at Meckering in Western Australia (Collins et al., 2004).

Liquefaction is a credible geohazard considered in current Australian geotechnical engineering practice, and infrastructure planning desk studies in Australia commonly identify liquefaction as a geohazard where susceptible soils exist within the project footprint. Further assessments are required in subsequent feasibility and detailed design phases. Accurately assessing the liquefaction triggering potential is an essential part of geotechnical design considerations.

The low seismicity of Australia creates a situation where liquefaction triggering is marginal at design hazard levels. This low level of seismic hazard makes the liquefaction trigger assessment very sensitive to the derivation of the seismic inputs. The lack of guidance on liquefaction from AS1170.4 requires interpretation of the basis seismic hazard inputs.

This paper explored the sensitivity to seismic inputs in low seismicity hazard Australia, to better understand liquefaction triggering risk in Australian geotechnical design. The components of the seismic hazard inputs are reviewed. A case study is presented showing that for liquefaction assessments in low seismicity regions, liquefaction triggering is sensitive to the selection of design magnitude and the calculation of the ground motions through the soil profile.