Study On Bearing Behaviour Of Capped Piles Considering The Interaction Of Pile-soil-cushion

Composite foundation has the advantages of fast treatment speed,good treatment effect and less environmental pollution,and is widely used in the field of foundation treatment.As the main vertical load-bearing component of composite foundation,the bearing behavior of pile has an important value to research.The bearing behavior of the pile with a cap is different compared with the pile without a cap.It is the key problem to be solved about how to consider the influence of pile cap and the coupling effect among pile cap soil and reinforced cushion.In order to solve this problem,this paper analyzes the bearing behavior of capped pile by means of physical model test,theoretical analysis and finite element simulation.The main work and achievements are as follows:(1)The physical model test of soft soil foundation strengthened by cap pile is carried out to study the settlement deformation of model piles with different pile cap sizes under the same load.The hyperbolic model is selected to simulate the load transfer at the pile base and pile shaft,and the load transfer model which can be used to calculate the settlement of capped pile is obtained;The load transfer model of capped pile is established by combining the previous research to define the method of different parameters in single pile model.(2)Based on the load transfer method and circular hole expansion theory,the capped pile in composite foundation is analyzed.The composite foundation is divided into two parts,and the load transfer model of capped pile is adopted,and then the settlement of pile-soil reinforcement area and underlying layer are calculated respectively.The change of friction resistance on vertical face of pile cap edge under different loads is analyzed.Through parameter analysis,the influence of different factors on the settlement of capped pile in composite foundation is studied.(3)Considering the adjustment effect of reinforced cushion formed by Geosynthetics and gravel layer on the plane load of composite foundation pile top,based on the theory of large deflection thin plate,the stress analysis model of reinforced cushion is established.The settlement change of soil between piles in pile-soil reinforcement area is analyzed.The change law of bearing characteristics of pile soil cushion interaction in composite foundation is revealed.The calculation method of soil settlement between piles considering the influence of cushion and pile cap is established.(4)The load transfer model established by the model test is redeveloped,and the analysis model of composite foundation strengthened by cap pile and reinforced cushion is established by the finite element software.The bearing characteristics of composite foundation under different conditions are revealed by changing the pile spacing,pile length and other parameters.