Fandamental Study on Liguefaction and Laterel Spread by LAT exporiments and Numerical Simulations

点击翻译按钮获取中文摘要

Since the 1995 Hyogoken-Nanbu earthquake it has been widely recognized that liquefaction-induced lateral spreading may cause severe damage to facilities located in urban coastal areas in Japan. However its mechanism is still unclear because the behavior of liquefied soil is essentially complicated, being controlled by the microscopic behavior of soil particles and the pore water. This research aims to develop both experimental and numerical tools to observe such microscopic behavior of liquefied soils for studying in detail the mechanism of liquefaction-induced lateral spreading.The experimental study consists of three programs. First, a series of hollow-cylindrical torsional shear tests on Toyoura sand was performed under various drainage and loading conditions to show the importance of recovery of shear resistance of liquefied sand. Secondly, a plane-strain compression apparatus, LAT/PSC, was newly developed for visualizing the interior of the specimen using Laser-Aided Tomography technique. Monotonic loading tests using this device brought successfully both macroscopic and microscopic information during shear deformation. Thirdly, visualization of pore fluid motion was attempted by using PIV technique. The combination of LAT and PIV allows us to obtain the information on particle-pore fluid interaction which is essential in liquefaction phenomena.Meanwhile, a series of Discrete Element simulations was also conducted to understand well the deformation mechanism of liquefied sand. Simulations of cyclic simple shear tests under constant volume condition showed that the distributions of both actual and potential contact points characterized the recovery of shear resistance. This implies the necessity for including the evolution law of such contact points in the development of constitutive equation for liquefied sand.