Micromechanics Study on Liquefaction-Induced Lateral Flow and Soil-Pile Interaction

点击翻译按钮获取中文摘要

Lateral spreading induced by seismic liquefaction causes the ground to experience large displacement and shear strains, which in turn damage pile foundations due to the drag force. There are two difficulties in simulating this problem ; the evaluation of constitutive model for liquefied soil and the choice of adequate simulation tool suitable for such large deformation problem. The objective of this study is to find a way for these difficulties from a micromechanical standpoint.Firstly, we developed some experimental techniques using high-speed camera and PIV (Particle Image Velocimetry). PIV is a powerful tool to detect a velocity field of various experiments from sequential digital images. We performed two types of experiments : one is a shaking table test of Toyoura sand to observe a surface of small-sized ground model, and the other is a kind of permeability test to keep arbitrary liquefaction state by tuning a fluid injection speed from the bottom of the specimen. In both experime … More nts, a cylindrical pipe is installed to measure the drag force acting on it due to the relative displacement between the specimen and the pipe. It was found that the liquefied soil has both properties as a solid (detected by a stick-slip motion between the soil and the pile) and as a viscous fluid (characterized by the rate dependent response).Further investigation was made by DEM (Discrete Element Method). DEM is a simulation method to compute each solid grains based on Newton's second law of motion, and the interaction between grains is simply modeled by a spring-dashpot-slider system. A series of constant-volume simple shear simulations provided us to observe essential micro-mechanisms up to and after liquefaction. In particular, the re-solidification of liquefied soil was also successfully simulated, which is quite important factor to predict the lateral flow displacement due to liquefaction.Based on the above information, we proposed a constitutive model of granular assembly based on micromechanics, which can be well applied up to shear failure of the assembly.Finally, we studied SPH (Smoothed Particle Hydrodynamics), a particle-based simulation method for continuum, which can be applied both in solid and fluid. It was found that the pile-liquefied soil interaction including the re-solidification regime was successfully simulated by SPH. Less