Liquefaction potential of reconstituted New Zealand loess

Abstract

Loess is an aeolian soil that covers approximately 10% of the South Island of New Zealand. In Canterbury, these materials typically have low plasticity (PI < 12), are silt-dominant (60-75% silt) and are widespread across slopes. Preliminary experimental research indicates that liquefaction of loess below the groundwater table may have been a contributing factor to slope deformation that occurred during the 2010 – 2011 Canterbury Earthquake Sequence. Indeed, cyclic liquefaction of loess has also been observed to be a contributing factor to slope failures that occurred during the 1920 Hauyuan and 1989 Tajikistan Earthquakes. To date the undrained cyclic properties (including pore water pressure generation and cyclic strain development) of loess in New Zealand has not been well understood. Given the region’s seismic environment, the potential for wetter slopes with future climatic change, and the extent of residential development on loess slopes in New Zealand, it is important to better understand the liquefaction resistance of loess and its contribution to future coseismic slope instability. This paper presents results from cyclic triaxial testing of reconstituted loess sampled from Akaroa Harbour, Banks Peninsula. A loess-specific liquefaction resistance curve (CSR-N_c) for reconstituted specimens is shown. Comparison with international data sets is also presented to better understand the liquefaction behavior of these aeolian soils.