Liquefaction of sand under multidirectional shaking table tests

A physical model test using a large biaxial laminar shear box on the shaking table at the National Center for Research on Earthquake Engineering (NCREE), Taiwan was conducted to study the liquefaction behavior of saturated sand under multidirectional earthquake shakings. The laminar shear box is composed of 15 layers of aluminum alloy frames with a specimen size of 1.880 m x 1.880 m in plan and 1.520 m in height. Specimens of clean Vietnam silica sand were prepared by wet sedimentation method. The densely placed instrumentation, including water pressure transducers, accelerometers, displacement transducers, provided a better insight of the mechanism of the pore pressure changes and liquefaction of the sand specimen. It is found that the excess pore water pressures generated during a multidirectional shaking are substantially higher than those generated under the one-dimensional shaking of the same magnitude of acceleration. Due to the rapid water pressure transmission during the shaking tests, the sand liquefied first at the shallower depth in a homogeneous stratum, and a thicker depth of liquefaction was induced by a multidirectional shaking than by a one-direction shaking. The test results also showed that significant settlements occurred only when there is liquefaction of the soil.