SPECIAL FEATURE Effects of Partial Saturation on Liquefaction Triggering

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Published 01 December 2016
SPECIAL FEATURE Effects of Partial Saturation on Liquefaction Triggering

The simplified liquefaction evaluation methods reasonably predicted the severity and extent of liquefaction in Christchurch during the 2010-2011 Canterbury Earthquake Sequence, however there are important cases where moderate-to-severe liquefaction was predicted yet no liquefaction manifestation was observed. These high levels of conservatism have been identified as a major concern in the application of the simplified liquefaction evaluation methods. Detailed field investigations have indicated that some of these sites contain deposits at approximately 0.50 m to 1.50 m depth below the water table that are partially saturated (i.e. voids contain air bubbles or gas). These soil deposits typically contain layers of fines-containing sandy soils of low plasticity. This ongoing research aims to investigate
the influence of partial saturation on liquefaction triggering including:

  • Correlate liquefaction resistance with degree of saturation (Sr) for characteristic Christchurch soils including clean sands and silty sands.
  • Incorporate the effects of saturation in a simplified procedures for liquefaction assessment.
  • Provide basis for quantifying the effects of partial saturation in advanced seismic analysis.


Above: a) modified triaxial platens and bender elements for Vp measurement; b) An example of Ep measurement (residential red zone sand, Sr = 100%)


Figure 2: Liquefaction resistance curve of tested red zone sand

Three types of typical Christchurch soils have been identified for cyclic triaxial testing at three different levels of Sr (including a fully saturated soils). A laboratory methodology has been developed at the Geomechanics Laboratory, UC, to measure and correlate laboratory and in-situ Sr through P-wave velocity, Vp (Figure 1). The liquefaction resistance curve of a fully saturated (Sr = 100%) red zone sand (Fines content, FC=0%) is presented in Figure 2. For the given soil type and testing condition, this curve will be used as a reference when quantifying liquefaction resistance at partially saturated condition.

The outcomes of this project will help to improve state-of-the-practice in engineering design and evaluation of NZ liquefaction hazard. This project is funded by QuakeCoRE (project #QC009/16013)




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Issue 92
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ISSN 0111-6851