Dynamic Response Of Geosynthetic Encased Stone Columns Under Traffic Load

To solve the problem of bulging deformation,low stiffness and bearing capacity of ordinary stone columns(OSC),geosynthetic encased stone columns(GESC)was introduced,wrapping the stone columns with geosynthetic encasement.As a result,the stone columns can be improved with the remarkable increasement of its bearing capacity and stiffness,which should be attributed to the lateral confinement of the encasement.However,the current researches mainly focus on the static field,and the dynamic load deformation characteristics under traffic load still need to be further studied.This research was funded by National Natural Science Foundation of China.The bearing mechanism,load transfer law,drainage effect and micro-characteristic of GESC were studied by model test and 3D numerical simulation with discrete-continuum model coupling.A series of cyclic triaxial tests of the aggregates were performed to investigate the influence of the cell pressure,dynamic stress and loading frequency.In addition,six group of static and cyclic loading tests in a designed model test tank were conducted with different loading parameters(varied loading frequencies),different column types(encased or not,endbearing or not).In these tests,vertical compression,lateral deformation,load transfer mechanism and development of pore pressure are discussed to reveal the bearing mechanism of GESC under dynamic load.The continuous materials of soft clay and geogrid were simulated by continuum model in FLAC3 D,while the discrete materials of aggregates were simulated by discrete model in PFC3 D.Consolidation test of soft clay,static and cyclic triaxial tests of aggregates and tensile test of geogrid was simulated to determine the elasticity modulus of soft clay,contact modulus and friction angle of aggregates and tensile stiffness of geogrid,respectively.Based on these microscopic parameters,a 3D discrete element method(DEM)and the finite difference method(FDM)coupled numerical model of GESC was developed,and validated by laboratory observations.The vertical and radial stress within the column,contact distribution,displacements of the particles,failure model and lateral deformation of the column was discussed based on the numerical model.A detailed parametric study of GESC was carried out to evaluate the relative importance of various parameters(e.g.encasement length,tensile stiffness of geogrid,elastic modulus of supporting layer and amplitude of the cyclic stress)under cyclic response.As a result,the correlation curve and expression between the parameters and the final settlement are presented by fitting.Additionally,the critical and allowable values of these parameters were recommended,which could be a significant reference in design and construction.