A new stacked ring torsional shear apparatus for multiple liquefaction test of sands

Abstract

Repeated episodes of soil liquefaction during the 2010-2011 New Zealand earthquakes have sparked intense interest in studying multiple liquefaction phenomenon. The present study develops a new stacked ring torsional shear apparatus based on a pressure compensation technique for repeated liquefaction tests on saturated sands. The new stacked ring shear apparatus overcomes some limitations of a similar device using dry sands by the University of Tokyo. To effectively impose lateral constraints on the soil specimen, stainless steel stacked rings are installed on a specially designed bearing system, which minimizes circumferential soil-ring friction. On the other hand, reducing vertical friction between the sample and the ring is a key issue to generate uniform stresses within the sample. In this study, the soil sample is fully saturated, with inner and outer chamber pressure applied to reduce direct contact force between the membrane and rings, such that the effective vertical stress will be much more uniformly distributed along the sample height. Our results indicate that approximately 75% of the applied vertical stress was maintained at the bottom of the specimen by using the pressure compensation. A series of reliquefaction and multiple liquefaction tests were conducted on saturated Toyoura sand using the new stacked ring device, which enables a single specimen to undergo cyclic loading, consolidation, and reloading in multiple liquefaction tests. The test apparatus shows great promise to investigate some fundamental physics of multiple liquefaction, including the effects of relative density, strain history, and fabrics on multiple liquefaction behavior.