Dynamic Responce And Simplified Analysis Method For Bridge Pile Foundations In Liquefiable Sloping Ground

Earthquake damage investigation indicates that the failures of bridge pilefoundations are caused by liquefaction-induced large ground deformation during strongearthquake, which is also the underlying cause of bridge hazards for pile foundations.For almost twenty years, the bridge construction in China has been rapidly developingand employing the pile foundation in most cases. China is a country of quake-proneareas with damages widely distributed; and the bridge is usually constructed on gentlysloping, large ground and horizontal ground near the coast causing liquefaction-induced. Therefore, seismic responses and stability of bridge pile foundations slopingliquefiable ground under strong earthquake is one of the essential issues urgentlysolved encompassing seismic bridge for pile foundations in China. In the past, theresearches on liquefaction-induced lateral deformation under strong earthquake wasmainly concentrated on the prediction of lateral displacement and many predictionmodels of lateral displacement were proposed successively. In recent years, the studiespay more attention to seismic responses of bridge pile foundations in liquefaction-induced lateral spreading ground. However, there is few literatures on the seismic pilefoundations for bridge at sloping ground with liquefaction-induced lateral spreading.From the previous discussions, the dynamic responses of bridge pile foundations areresearched in liquefiable gently sloping ground by analyzing the dynamic soil-pileinteraction in this paper. Meanwhile, the physical and mechanical components ofdynamic soil-pile interaction is investigated and simplified analyses procedure ofbridge pile foundations were established gently sloping liquefiable ground.Firstly, three-dimensional (3D) finite element numerical model of dynamic soil-pileinteraction is implemented considering the coupled fluid and solid for saturated sand ingoverning equation of u-p formulation and adopting multi-yield surface plasticconstitutive model based on the shaking table tests. Herein, the mentioned numericalmodel verified was extended to the3D numerical model of dynamic soil-pile-bridgestructure interaction in gently sloping liquefiable ground and the related procedureswere formed. Furthermore, the parametric study on dynamic soil-pile-bridge structureinteraction was performed in gently sloping liquefiable ground. The effects of pile- existence, earthquake motion and multiple direction were investigated. The fundamentalcharacteristic of dynamic soil-pile interaction was gained.Secondly, the numerical simulation was performed under sinusoidal wave usingthe established3D finite element analysis model and related procedures based ondynamic soil-pile-bridge structure interaction. And dynamic p-y curves of soil-pileinteraction were obtained under sinusoidal wave with different amplitudes inliquefiable gently sloping ground. The effects of some factors on the dynamic p-ycurves of sand were investigated. These factors includes pile diameter, and length,permeability, ground inclination angle, relative density, water table depth, thickness ofliquefiable and non-liquefiable soil, multi-directional motion, soil profile, and others.Thirdly, according to the results of dynamic p-y, curves maximum lateral soilpressure of sand corresponding to different pore pressure ratios were obtained bydividing pore pressure ratio time histories into several segments. And then, the simplifiedformula of p-y curve of sand taking pore pressure ratio as a control factor was proposedby adopting the factor of ground inclination angle. An impact factor formula of pilediameter, which influences the lateral soil pressure, was established based on theresponse of0.2m pile diameter from3D finite element model. The mentioned formulawas modified, which makes the effect of pile diameter to be considered in the simplifiedformula of p-y curve of sand. Considering the need for engineering design, the ultimateresistance of saturated sand under cyclic loading from API was selected as the ultimateresistance of simplified model.Finally, by considering the effect of sand liquefaction on soil spring of dynamicsoil-pile interaction in gently sloping ground, the simplified numerical model andnonlinear quasi-static procedure of dynamic soil-pil interaction in liquefiable gentlesloping ground based on nonlinear Winkler foundation beam model and simplifiedmodel of p-y curve for liquefiable soil. The simplified analysis procedure has beenverified by the results of finite element method. The influences of pile diameter, porepressure ratio, ground inclination angle, and pile head restraint on the dynamic soil-pileinteraction were studied by the simplified analysis procedure.In view of discussions previously described, this paper will undoubtedly help tofurther enhance the seismic designs of bridge pile foundations and track theinternational development to ensure the safety of seismic performance of bridge engineering in China. It is an important and positive role that the technical details willbe provided in seismic design of pile foundations for seismic design code of bridgeengineering in liquefaction-induced lateral spreading ground in this paper.