Soil-Bridge Pile Interaction In A Liquefiable Site Under Strong Earthquake

Prvious seismic hazards verified that pile and ground failure are the main forms ofbridge damage caused by soil liquefaction. Earthquake induced liquefaction and lateralspreading is a major cause of failure of civil structures during seismic events. Collapseand severe damages to pile-supported structures and soil strata belong to the category ofsoil-pile-structure interaction. Therefore, it is very necessary to investigate soil-bridgepile interaction under strong earthquake. In view of the above, the main research workand achievements are as follows:1. A series of scaled shaking table model tests were performed to study thebehavior of a single pile in a soil profile comprised of a nonliquefied clay layer over aloose saturated sand layer over a nonliuqefied clay layer. The input earthquake motionsare compressed0.15g El Centro wave,0.15g El Centro wave and0.15g El Centro wave.Detailed instrumentation and data processing procedures enabled fundamentalmeasurements of the soil-pile interaction behavior in the shaking table tests. Themeasurements include the first available time histories of excess pore water pressures,accelerations of the soil and accelerations and dynamic strains of the pile under realisticearthquake shaking motions. Additionally, the bending moment of the pile is obtainedbased on the bending theory of the column. These shake table tests are performed toreveal the soil and pile response in liquefiable ground under different shakingfrequencies and amplitudes.2. A three-dimensional dynamic finite element model was established forstructures supported on pile foundations in a three-layer liquefiable soil. The modelincludes the dynamic couple response of soil and water, the nonlinear responses of soiland pile, and the soil-pile interaction. Results of the shake table testing on a sing pile inliquefiable soil are used to demonstrate the capability of the model for the reliableanalysis of piles under earthquake loading. The root mean square error is introduced toquantatitively evaluate the accuracy of the model. The proposed coupled soil-brige pilemodel was shown to be an effective tool to investigate the interaction response of a pilefoundation in a liquefiable site.3. A verified model was used for a parametric study. The parametric study was carried out by varying the relative density of the liquefying soil layer, the pile diameter,the superstructure mass and the shaking amplitude. The excess pore water pressure andexcess pore water pressure ratio, the stress and strain, the acceleration, the displacementand the bending moment responses, the distribution of sectional forces and thedeformation at different times were investigated. The effects of the soil relative density,the pile diameter, the superstructure mass and the shaking amplitude are clarified on thesoil and pile responses in a three-layer liquefiable site.4. Based on the above parametric studies, the pile failure modes in a liquefible soilwere obtained for different soil densities, pile diameters, superstructure masses, anddifferent amplitudes. Then, the potential failure mechanism for a pile in a three-layerliquefiable site was postulated under strong earthquake based on the pile bendingmechanism. Furthermore, the effects of overlying clayey layer on the pile internal forcesand deformations are evaluated. Finally, Earthquake relief measurements for pile inliquefiable site were subsequently provided.