The Research On Load Transfer Mechanism And Settlement Calculation Method Of Pile-supported Embankment

In recent years,the pile-reinforced composite foundation has been widely recognized in engineering field because of its good working performance.The composite foundation of "pile-supported embankment" has the advantages of fast construction and high economic efficiency,so it is widely used in projects with soft soil foundation treatment,such as expressways,intercity railways and the widening project of old roads.The pile-supported embankment is complicitly constructed and can be divided into four parts: embankment,reinforced cushion layer,pile-soil reinforcement area and underlying layer.The load transfer mechanism of the system usually also consists of four parts: a.Soil arching effect in the embankment;b.membrane effect of the Geotextile;c.pile-soil interaction in the reinforcement area;d.the vertical deformation of the subsoil.The current theoretical researches,however,mostly focus on the theoretical study of soil arching and membrane effect.Further research is needed for the interactions among the four parts of the system.Simultaneously,there are some contradictions of the assumptions of existing theories with the actual situation,such as the assumption that the deformation of the soil between piles is uniform at a certain level,and that there is no relative displacement at the pile-soil interface,etc.Therefore,this article starts with the load transfer mechanism of the pile-supported embankment system,and studies the load transfer mechanism and settlement calculation method of the pile-supported embankment through theoretical analysis,model test,and numerical simulation.This study is under the funding of the National Natural Science Foundation of China(Title: "Study on bearing mechanism and deformation analysis method of rigid pile composite foundation under traffic load",number.51078138).To begin with,this paper analyzes the load transfer mechanism in the pile-supported embankment system,and summarizes the current researches and their deficiencies in terms of the soil arching model,tensile membrane effect,and pile-soil interaction.On this basis,the following theoretical methods are proposed: 1.an improved theoretical soil arching method that can consider the influence of the relative displacement of the inner and outer soil columns on the load transfer;2.a theoretical calculation method that can consider the non-uniform deformation of the soil between piles and the pile-soil relative slippage;3.a theoretical calculation method of pile-soil interaction for pile-supported embankment with a conical pile-head;4.a theoretical calculation method of load transfer in subsoil under the pile tip.Considering that the soil arch in embankment varies with the relative displacement between the pile and the soil,trapdoor tests were then designed in the cohesive soil and the sandy soil to study the evolution of the "soil arch structure",respectively.With the help of Video Gauge and soil pressure sensors,the test measured the evolution of the soil arch structure,strain field,displacement field,and soil pressure with the increase of the displacement of the trapdoor.A large-scale shear test of the pile-soil interface was also carried out according to the load transfer mechanism of the pile-soil interface and the functional relationship between the side friction of the pile and the pile-soil relative displacement.A discussion was conducted for the relationship between the ultimate shear stress and ultimate shear displacement of the pile-soil interface under different conditions.Finally,a coupled theorecial model of pile-supported embankment was established to predict the settlement of the system by combining the relashionships among the four parts of the system based on the stress and displacement continuity conditions at the planes of the pile top and the pile tip.Following settlement-stress calculation methods were respectively proposed based on different engineering characteristics: 1.the settlement analysis method of pile-supported embankment based on double-equal settlement surface;2.the settlement calculation method of pile-supported embankment considering the non-uniform deformation of the soil between the piles;3.the settlement-stress calculation method for pile-supported embankment with a conical pile-head.