Numerical Simulation Study On The Whole Process Of XCC Pile Penetration-Consolidation And Set-up Effect Of Bearing Capacity

Soft soil foundation is widely distributed in China.Pile foundation has been proved to be very effective in dealing with soft soil foundation and has been widely used in urban construction.Pile foundation can control the settlement deformation of the building,improve the foundation bearing capacity,and ensure the safety of the building by transferring the load to the deep soil layer.The X-section cast-in-place concrete pile(hereinafter referred to as XCC pile)is a new type of non-circular cross-section shaped pile developed in recent years,which was developed by the research team of Professor Liu Hanlong of Chongqing University.Compared with the traditional circular and square piles,the advantages of the XCC piles are mainly to increase the bearing capacity of the pile foundation by increasing the lateral friction of the piles and to give full play to the potential of the pile body materials.When constructing XCC piles,the X-section steel mold and the X-shaped valve pile boots are inserted into the foundation to form an X-shaped cavity through the static pressure sinking pipe.After that,the concrete is poured into the cavity and the tube is vibrated.The concrete is filled with X-shaped space and the XCC piles are formed.Although the XCC pile is a cast-in-place concrete pile,its static pressure sinking process is similar to that of a static pressure pile.After the pile is piled,the consolidation and bearing capacity change is similar to that of the static pressure pile.Therefore,reference can be made to the static pressure pile.Conduct research analysis.In order to simplify the description and unify with the static pressure pile,this paper describes the XCC pile static pressure sink pipe as “XCC pile penetration”,and the soil consolidation after sinking pile is described as “XCC pile consolidation”.During the process of the XCC pile penetration,the soil around the pile will generate and accumulate a large amount of excess pore pressure.After the end of the pile penetration stage,the excess pore pressure will gradually dissipate as the soil around the pile enters the consolidation stage.As a result,the strength and effective stress of the soil around the pile will increase,and the bearing capacity of the pile will be greatly improved.Therefore,it is very important to study the variation of pore pressure field and stress field during the penetration process and consolidation process of XCC piles to predict and evaluate the long-term bearing capacity of pile foundation.In this paper,the finite element large deformation analysis method of "mixed Euler-Lagrangian" is used to simulate the penetration and consolidation process of piles in natural saturated clay and the long-term bearing capacity variation characteristics.The corresponding contents are as follows:The finite element large deformation analysis method of "mixed Euler-Lagrangian" is used to reproduce the penetration process and consolidation dissipation process of piles in natural saturated clay,and the penetration resistance and pore pressure dissipation results obtained by simulation analysis were compared with the centrifuge test data to verify the rationality and correctness of analytical methods and numerical models.The distribution and development of pore pressure and stress in soil around the pile during XCC pile and round pile penetration were simulated and analyzed,and the difference between the numerical simulation results and the theoretical solution of the circular pile is compared.Compared with the circular pile,the XCC pile penetration process will cause a larger pore pressure influence range and shear stress area in the soil around the pile.The three-dimensional numerical analysis of the change of pore pressure field and stress field of XCC pile and circular pile in the consolidation stage was carried out.It is found that the dissipation rate of the excess pore pressure is related to the initial pore pressure.The higher the initial pore pressure,the faster it dissipates.The radial effective stress in the range of about 10 r from the pile body has been greatly improved.The increment of radial effective stress decreases with the increase of distance from pile.Two groups of XCC piles and circular piles with different cross section areas were compared and studied,and it was found that the change of pile bearing capacity has significant timeliness.When the difference in section circumference is large,the XCC pile with equal cross-sectional area has a very obvious improvement in bearing capacity compared with the circular pile;when the difference in section circumference is smaller,the bearing capacity is not improved significantly.The results show that the section circumference of unit area is of great significance to the post-bearing capacity of XCC piles.