Effect of Sand Content on the Liquefaction Potential and Post-Earthquake Behaviour of Coode Island Silt

Traditionally, sandy soils are known to be the only type of soils susceptible to liquefaction. However, liquefaction has also been observed in silty and clayey soils. As one of the most problematic soft soils in the state of Victoria, Australia, Coode Island Silt (CIS) extends from the northern shoreline of Port Phillip Bay to the south and west of Melbourne central business district and contains a considerable and variable amount of sand. Although this material covers an area of more than 20 km(2)at a depth varying from ground level to 30 m below the ground level in the metropolitan region of Melbourne, the effect of sand content on the liquefaction potential and post-earthquake behaviour of CIS has never been studied properly. Through an extensive set of monotonic, cyclic and post-cyclic triaxial tests, this paper explores the earthquake and post-earthquake response of CIS containing variable sand content. Based on the test results, it is found that the sand content up to 60% does not affect the liquefaction potential of CIS under the tested cyclic stress ratio. Also, it is found that although the applied cyclic loading does not considerably alter the internal friction of CIS-sand mixtures, the post-cyclic secant stiffness increases dramatically.