Adaptive time stepping method for seismic liquefaction disasters and its control parameters

Seismic liquefaction of saturated soil is a serious problem in the area of geotechnical earthquake engineering. In the numerical analysis of dynamic process, calculation accuracy and efficiency are the two important indexes to evaluate the numerical method. An adaptive time stepping method is proposed based on a solid-fluid coupled method and an elasto-plastic analysis platform. According to the estimation system of displacement errors, pore water pressure errors and mixed errors, the strategy of time step adjustment and the relevant control parameters are established. Through the sensitivity analysis of control parameters, the error tolerance and proportionality coefficient of pore water pressure errors are identified as the main control parameters, while the initial time step size, lower and upper limits of time step adjustment factor are identified as the assistant parameters. Then, the adaptive stepping method is applied in the numerical analysis of a subway station located in the liquefiable area. The time histories of the uplift displacement and the excess pore water pressure ratio are obtained, which indicates the hazards of underground structure uplift induced by seismic liquefaction. Besides, the fixed stepping and adaptive stepping methods are compared, and it is found that using the adaptive stepping method can save more computational cost without losing the accuracy.