Simulation of soil-pile-superstructure interaction in the New Madrid Seismic Zone

Deep alluvial soil deposit of the Mississippi Embayment overlies the New Madrid Seismic Zone (NMSZ). The simulation of soil-pile-superstructure interaction (SPSI) at this area has to be divided into two steps. First, the motions at rock base were developed to the interested foundation level and then input for the SPSI analysis.; A new cyclic nonlinear soil model has been developed to take into account the influence of the effective confining pressure on the site response analysis in deep soil deposits. A pore pressure generation model is loosely coupled into the soil model to simulate the possible liquefaction near surface soil layers. The model is implemented into a two-dimensional finite element code in the time domain and calibrated with the recorded motions at typical sites in California. This model was applied into the site response analysis at a Missouri highway bridge site located on the New Madrid rift complex. The results indicate that the influence of the confining pressure is significant for the site response analysis of deep soil sediments and liquefaction could be trigged for M = 6.5 or larger earthquakes in the NMSZ. A coupled SPSI analysis method is then presented to study the seismic response of the highway bridges in the NMSZ. Pile-soil interaction is simulated by the dynamic nonlinear p-y method including the effect of gap and the excess pore water pressure buildup at the pile-soil interface. The presented SPSI approach provided reasonably good agreement with the results the dynamic centrifuge tests. Finally, this method is implemented into the same bridge site for future earthquake scenarios of Mw 7.0. Results indicate that the excess pore water pressure at pile-soil interface significantly influence foundation and superstructure responses.