Study On Bear-deformation Mechanism Of Composite Foundation In Reinforced With Encased Stone Columns

Rushed stone pile composite foundation has been widely used to treat the soft soil in the construction building、traffic civil engineering、aerodrome engineering、port engineering and etc. The bearing capacity of gravel pile mainly depends on its radial confinement from the soil to make gravel and other bulk materials are capable of forming the pile to withstand the vertical loads. In the engineering, gravel pile can easily happen lateral deformation, because of that soil around the pile can’t provide adequate lateral binding, which lowers the bearing capacity of gravel pile foundation and significantly increases settlement and finally fails to get the expected reinforcement effect. Given such a pile of soil failure mode, geotextile is often used to parcel gravel pile with its high tensile strength, we calls this new foundation treatment method as geotextile encased stone columns composite foundation.The theoretical researches of this new type of reinforcement is at an early stage, Therefore,this paper combining with the characteristics of geotextile encased stone columns composite foundation explores pile-soil stress ratio and deformation calculation methods.Firstly, based on the deformation characteristic of composite foundation reinforced with encased stone columns under vertical loads, a new calculation formula to estimate the pile-soil stress ratio of encased stone columns was proposed with consideration of pile-geosynthetic-soil interactions. In the derivation process, the initial stresses in the soil and column were taken into account, the column was considered as an elastic-plastic material with constant dilatancy angle and satisfying both the Mohr-Coulomb yield criterion and a non-associated flow rule, the soil and the geosynthetic encasement were considered as linear-elastic materials. The validity of the proposed formula was validated by the comparison with the verified elastic-plastic finite element analyses. Finally, a parametric study was conducted to investigate various parametric, such as encasement stiffness, deformation modulus of soil, and the replacement ratio on the behavior of the pile-soil stress ratio.Secondly, this paper can obtain the radial and vertical deformation formula of composite foundation reinforced with encased stone columns. The proposed formula was validated by the comparison with the verified elastic-plastic finite element analyses.and then, a parametric study was conducted to investigate various parametric,such as encasement stiffness, the radial of pile and deformation modulus of soil on the behavior of the deformation.Finally, By comparing the experimental results on the field and the results of proposed formula in this paper, the reasonable and feasible of the geotextile encased stone columns composite foundation formula of deformation analysis method can be verified.It can provide useful reference for practical engineering.