Numerical Analysis Of Composite Foundation With Capped PTC Piles Under A Freeway Embankment In Shallow Sea

Prestressed concrete thin wall(PTC)pipe pile with cap has been widely used in the reinforcement of soft soil subgrade.The design and analysis of this kind of composite foundation mainly including three aspects:settlement calculation,bearing capacity calculation and stability analysis.At present,settlement calculation and bearing capacity calculation are mainly based on the theory of rigid pile composite foundation,and the stability analysis usually adopt the limit equilibrium method to simplify the composite structure of pile and soil to a simple shear failure.Compared with the actual results,the calculation and analysis results tend to have large and even significant differences,and the present method is difficult to reveal the working mechanism of this kind of composite foundation.With the development of computer and computing technology,the numerical solution especially the finite element method is more and more applied to the design and calculation of capped PTC pile composite foundation.However,it is still based on the plane calculation and the fluid-structure coupling is not considered.The real three-dimensional numerical calculation is still rarely.Thus,based on shallow sea embankment under capped PTC pile composite foundation of Putian Meizhou Island section of Putian-Yongding Freeway in Fujian Province,The main content or conclusions of this article is summarized as follows:(1)The Modified Cam-Clay model(MCC)was introduced in this paper.In the case of considering fluid-structure coupling and time effect,there was study on the reliability of the PTC pile composite foundation,which was analyzed by the ABAQUS.A reliable numerical simulation method was obtained.(2)Based on the engineering practice and the previous research,the reinforcement mechanism of the capped PTC pile composite foundation,the failure mode of the common embankment and the principle,method and application of limit equilibrium method and finite element strength reduction method for embankment stability were described.A more practical method for settlement calculation of PTC pile composite foundation and a more reliable and accurate finite element strength reduction method for analysis of embankment failure was proposed.(3)ABAQUS,a finite element program,was selected to carry on the numerical.simulation of the stability of reinforced embankment with capped PTC pile composite foundation.Study on the deformation and failure characteristics of reinforced embankment with capped PTC pile composite foundation,the anti sliding mechanism of PTC pile and the failure mode of pile.Flow around the pile and the reliability?applicability of the three dimensional reinforced embankment was equivalent to the plane model that were further analyzed.(4)The numerical analysis method was used to analyze the influence of different pile position,pile length and cushion on the stability of capped PTC pile composite foundation.The reasons of deference occur on the effect of reinforcement was analyzed,and the reasonable reinforcement structure of reinforced embankment with capped PTC pile composite foundation was discussed.(5)Take the above support project as an example,the three-dimentional finite element program(ABAQUS)was employed to analyze the structural behavior of the embankment on soft soils improved by the capped PTC piles.The FEM results included settlement,horizontal displacement,excess pore pressure,stress level and pile internal force,they were compared with the same problem with sand compaction piles and without treatment measures.Some useful conclusions had been obtained through the comparison.