Study On Action Mechanism Of Cushion Under Horizontal Load Of Rigid Pile Composite Foundation

In this paper,the horizontal displacement of the cap and the top of rigid pile composite foundation under different vertical loads is obtained through field tests.The variation of the ultimate horizontal load and the horizontal load sharing ratio of the top of the pile with the vertical loads is analyzed.Based on field tests,the finite element model of double-pile and multi-pile composite foundation is established by ABAQUS software.The displacement and stress distribution and variation law of cushion are studied,and the influence of design parameters on the mechanism of cushion action is discussed.Finally,the horizontal bearing capacity of the composite foundation design scheme in the engineering example is calculated by using the finite element analysis method,which verifies the safety of the scheme,and puts forward reasonable suggestions for the design.The main research results are as follows:(1)With the increase of horizontal load,the horizontal displacement of the cushion layer decreases gradually along the depth direction,and the cushion layer in front of the pile and above the pile forms a compact area;the cushion layer produces the phenomenon of horizontal stress concentration on the top of the pile,and the horizontal stress transfer direction of the cushion layer before and after the pile changes with the increase of load.(2)The horizontal bearing capacity of composite foundation and the horizontal load-sharing ratio of pile and soil are related to the vertical load,the friction angle of cushion,the thickness of cushion and the modulus of cushion.The horizontal control displacement of foundation and the horizontal load-sharing ratio of pile and soil can be determined according to the engineering environment,and then the material parameters of cushion can be adjusted.(3)In multi-pile composite foundation,with the increase of horizontal load,the cushion layer only forms a compact area in front of the front row of piles,but fluidity is better in the middle row and the top of the back row of piles.The cushion layerforms a stress concentration area at the top of each row of piles,and gradually extends along the direction of horizontal load until it is connected.(4)Along the direction of horizontal load,each row of piles in the composite foundation enters the working state in turn.The horizontal load shared by the back row piles increases rapidly,while the horizontal load of the front row piles increases steadily.Vertical to the direction of horizontal load,the horizontal load shared by side piles and corner piles has little difference.(5)The finite element method is used to calculate and analyze the engineering case.With the increase of filling height,the distribution of internal force and deformation of cushion changes,and the maximum value of horizontal load shared by pile top shifts from the first row to the fifth row.It is suggested that the length and stiffness of the front row piles should be reduced and the length and stiffness of the back row piles should be increased on the premise of satisfying the vertical bearing capacity.