A Simulation Of Installation Of Stone Column And Subsequent Consolidation

Stone column composite foundation is widely used in projects with its excellent treatment, but owing to complexity of stress condition and environment, its loading mechanism and design method have not matured. The research on stress condition of soil around stone column before and after loading is still rarely covered, the effect of installation and subsequent consolidation to soil is far from qualitatively recognized. A lot of model and in situ test research on jacked piles at home and abroad revealed that excess pore pressure ,residual stress induced in the process of installation and subsequent consolidation can largely influence performance of piles. People began to have the concept that a complete and rational pile design should include installation, consolidation and loading process.Installation of stone column has been modeled as undrained expansion of a cylindrical cavity. Based on modified Cam-clay model, the elastic-plastic solution of cavity expansion considering stress history is obtained, including effective stress field, excess pore pressure and radial deformation. However the radial distribution of excess pore pressure is get through a sophisticated numerical method. Two analytical functions are fitted for normally consolidated and overconsolidated clay separately, which are compared with numerical results.The governing equation of consolidation is derived based on elastic deformation of soil skeleton. Combing pre-established initial condition and boundary condition, a solution of radical dissipation of excess pore pressure is obtained through variable separation approach, and a parametric study is made considering the effect of stress history and rigidity index.(3)Fast Lagrangian Code Flac 2D(5.0) is used to simulate pile installation and subsequent consolidation in boston blue clay considering one dimensional compression which is completely different from isotropic compression assumed before. Parameters such as initial stress condition and shear modulus of different stress history chosen for Flac code is discussed from different perspective. Effective stress field and excess pore pressure of different overconsolidation ratio around pile after installation is obtained ,which is compared with results deduced from ideal elastic-plastic hypotheses by early works. After completely dissipation of excess pore pressure ,effective stress field around pile is again generated.Undrained shear strength of soil with different stress history at regions around stone column is also compared. The effect of initial water content ,initial shear modulus to undrained shear strength after consolidation is investigated, and the influence of soil structure to pile installation and consolidation is also discussed. In-situ effective stress around pile increases with depth ,which has similar stress path in the process of expansion and subsequent consolidation, and three dimensional nature of this problem is considered.