Analysis On Large Ground Displacement Induced By Seismic Liquefaction And Its Influence On Pile Foundation

Catastrophic damages to structure can be made by lateral permanent displacement, namely large ground displacement, on gently sloping ground induced by liquefaction of saturated soil deposits during earthquake, which is the main type of seismic damages of highways , railways, bridges, docks, embankments, buildings, underground structures and lifeline engineering in liquefied area. In recent ten years, studies on the new type of failure made by liquefaction have been carried out. Because of the complex mechanism and the limited research, progress on this subject is quite limited. The paper is made up of three aspects:1 , In this paper the disadvantages of calculation methods of large ground displacement are discussed, and the new method used to calculate the large ground displacement is presented. Nonlinear earthquake respond analysis of soil is carried out to obtain ground acceleration and yield acceleration time history, in which the law of pore pressure in saturated sand is used to revise the yield strength of soil and the strain-stress relationship of soil is assumed to be rigid plastic in every time-internal. Appling the model of Newmark's rigid slide block, the lateral displacement induced by liquefaction during earthquake is calculated and the possible factors which may influence the large ground displacement are well studied. The numerical results show that the method presented is more reasonable in physical mechanism than empirical methods, which can authentically disclose the mechanism of the large ground displacement and coincide with macroscopic earthquake damages.2, Using ANSYS, a finite element analysis model is established to deal with pile-soil interaction under lateral load, and the model is proved to be correct and realizable. With the reasonable size of element, the results can well coincide with theoretical results. Using the model, nonlinear finite analysis of pile in lateral spreading ground is carried out, in which the nonlinear relationship of pile-soil interaction is considered and lateral displacement is subjected to soil springs to simulate the ground displacement in lateral spreading ground. The numerical results show that the lateral ground displacement is one of factors that cause pile failures in liquefied ground. At the soft-hard interface, pile may overbear the ultimate moment which leads to bending and shearing failures. Therefore, except the effect of large inertial loads from superstructure, the influence of the lateral ground displacement onpile foundation cannot be neglected in a seismic design of pile foundation in lateral spreading ground.3. According to the mechanism of large ground displacement, different measures of ground improvement against large ground displacement suited to different conditions are concluded.