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Abstract 3D fully nonlinear analysis of seismic response of free field in liquefiable site is carried out using the general finite difference program FLAC3D. Compared with the equivalent-linear method，the permanent and irreversible displacements can be modeled automatically in the fully nonlinear method. A proper plastic formulation is used in the soil nonlinear constitutive relation，whereby plastic strain increments are related to stresses. Combined with the pore water pressure model，soil liquefaction under the seismic excitation can be modeled. Soil nonlinearity，pore water pressure build-up process and boundary condition of the model are taken into account in the calculation model. A comparison between the results from the finite difference analysis and those from the shaking table tests is made to validate the effectiveness of the computational model. Numerical results demonstrate that the liquefied soil can filter and isolate vibration. The phenomena of transient minus pore pressure occurr in the test. Pore water pressure does not always dissipate in short time immediately after the excitations，but it may keep on increasing.
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Received: 11 September 2008
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