| In recent years stepped cross-section pile composite foundation has been applied in engineering practice as a kind of composite foundation.In order to explore the working characteristics of stepped cross-section pile composite foundation under cyclic loading,this paper relying on the tutor’s scientific research project adopts a method that combines indoor model test and FLAC3D numerical simulation,systematically researches and contrasts the working characteristics of cylindrical pile composite foundation and stepped cross-section pile composite foundation under cyclic loading.The main conclusions are as follows:1.Based on indoor model test,the curves of cylindrical pile and stepped cross-section pile composite foundation settlement,inter-pile soil settlement,pile top settlement and cyclic loading times are obtained.Besides,the influence of pile-soil stress ratio,axial force of pile and pile lateral friction resistance that are caused by number of cyclic loading is discussed.The critical times of cyclic loading are obtained when settlement of composite foundation and pile-soil stress ratio are in a steady state.The results of the study show that: when the times of cyclic loading are less than the critical ones,the settlement of composite foundation increases nonlinearly along with the times of cyclic loading;when the times of cyclic loading are over the critical ones,the settlement keeps stable;the critical times of cyclic loading of cylindrical pile composite foundation are substantially equal to the ones of stepped cross-section pile composite foundation;but the settlement of cylindrical pile composite foundation is significantly greater than the one of stepped cross-section pile composite foundation,and pile-soil stress ratio and axial force of pile of cylindrical pile composite foundation is obviously less than that of stepped cross-section pile composite foundation.2.The finite difference model of composite foundation was established by using FLAC3D software.The model test’s results show that the numerical simulation model is reasonable and reliable.Based on numerical simulation results,the influence of work characteristics of stepped cross-section pile composite foundation that are caused by thickness of cushion,cushion modulus,soil modulus,cyclic loading ratio and pile’s length-diameter ratio under cyclic loading is discussed.The results show that cushion modulus,soil modulus,cyclic loading ratio and pile’s length-diameter ratio have a great influence on the settlement and pile-soil stress ratio of stepped cross-section pile composite foundation.And the thickness of cushion’s effect on the settlement is not obvious,but its effect on pile-soil stress ratio is significant. |
