Liquefaction Deformation Analysis Of A Large Reservoir Embankment Foundation And Reinforcement Measures

There are many countries in which ground shakings are most dangerous, and unfortunately China is among them. Many hydraulic structures including levees were destroyed during Tang shan quake in 1976. Deadly "5.12 Wen chuan 8.0-magnitude quake" in 2008 caused severe casualties and also many hydraulic structure failures including swelling earthquake-induced lakes,crack on levees top,levee break as a result of ground soil liquefaction.So researches on levee ground soil behaviors in the saturated soil during the earthquake loading and searches for Liquefied zones and their distribution pattern are the main choices with the motive to select the optimum method to reinforce levees against earthquake. Based on the above, ground soil dynamic response is analyzed and reinforcement measures are compared by the use of FEM software FLAC, the whole work is as follows:(1) Definitions of soil liquefaction prevailing in China and abroad are summarized in this thesis. Types of mechanism for saturated soil liquefaction, analysis methods, present researches on ground soil liquefaction of levee and reinforcement mechanism are discussed and summarized.(2) The nonlinear, large-strain characteristics of ground soil under earthquake can be simulated by the use of FLAC, which is based on the theory of finite difference method. Numerical simulation is done on the whole process including three phases:initial equilibrium, free field and embankment with levee. The view that levee foot adjacent to upper stream is the weak point for anti-seism of embankment is primarily put up with based on the phenomenon that certain extent of shear stress concentration exist near it. During the stage of seismic action, dynamic response characteristics such as ratio of excess pore water pressure and effective stress path of levee ground soil are analyzed. Responses of vertical displacement and acceleration for reference points and responses of vertical stress, effective stress and excess pore water pressure for typical elements are monitored to confirm that levee foot adjacent to upper stream and surface ground inferior-side aeration of levee top center are the weakest points. Three anti-seism methods are put up with to counter against these weak points.(3) The optimum reinforcement method will be chosen among vibro-replacement stone column, rock riprap and plastic concrete wall combined with soil replacement cushion layer. Reinforcement mechanism, the way how to do simulation numerically and physical parameters are described. Three factors of contour map for vertical residual deformation, time history curve of vertical residual deformation for reference points and time history curve of excess pore water pressure for typical elements are used to evaluate the reinforcement effects. Economy, construction feasibility, reinforcement effect and construction quality are considered to determine the optimum reinforcement measure.