Research Onpile Tip Penetration Of Pile-Net Composite Foundation In High Speed Railway

As a way of foundation improvement to control settlement, pile-net composite foundation has been widely used in the construction of high-speed railway in soft soil area. However, the theoretical study of settlement deformation of pile-net composite foundation is far behind the engineering practice, especially the research on the pile penetration. The paper intent to research the pile tip penetration through theoretical analysis, model test and numerical analysis.This paper from the high-speed railway embankment pile net composite foundation deformation characteristics, analyzes the causes and influencing factors of pile side friction and end resistance, summarizes the calculation method of pile side friction resistance and end resistance ; According to the law of load transfer, the stress mechanism of single pile composite foundation is analyzed. The calculation equation of pile tip deformation is deduced by using the basic hypothesis.On the basis of theoretical analysis, using the similarity theory to design model test, and the stress and deformation characteristics under different pile diameter is studied, the law of pile tip penetration property with pile diameter is revealed.On the basis of model experiments, a two-dimensional model is established by using ABAQUS software. The calculated results are in good agreement with the experimental data.The two dimensional model can be used to calculate the pile tip penetration of the pile-net composite foundation.Based on the two-dimensional model of ABAQUS, the change law of pile tip deformation with various factors is revealed. The results show that the pile tip penetration increases with the increase of the pile diameter. When the pile tip is acted on the soft soil area, the pile tip penetration increases with the increase of the pile length. When the pile tip acts on the bearing stratum with higher shear strength, the pile tip penetration decreases with the increase of the pile length. The pile tip penetration decreases with the increase of the modulus of elasticity of the soil around the pile, and the internal friction and cohesion of the soil around the pile have little influence on the pile tip penetration. The elastic modulus of the pile tip soil has a great influence on the pile tip penetration, and when the pile tip soil elastic modulus increases, the pile tip penetration decreases obviously. The influence of the internal friction angle of pile tip soil on the pile tip penetration is greater than that of cohesive force, and the cohesive force of pile tip soil has no influence on the pile tip penetration. With the increase of the soil friction angle of the pile tip soil, pile tip penetration decreases.