The Bearing Characteristics Of Single Piles In Inhomogeneous Soil

Pile foundations are widely used in engineering practices due to their advantages such as high bearing capacity,small settlement and universal applicability.There have been many studies on the bearing characteristics of pile foundations.However,most of them are aimed at piles embedded in homogeneous soil.The load-transfer mechanism of piles in inhomogeneous soil is basically different with homogeneous soil,and there are few analytical solutions at present.Therefore,this study adopts an inhomogeneous soil model with shear modulus obeying a power law variation with depth.Based on this model,an analytical solution for the displacement and load transfer of axially loaded end-bearing piles,axially load friction piles,and horizontally loaded piles is proposed,and the bearing characteristics of single piles are analyzed.The main contents and achievements of presented paper are:(1)An analytical solution to the load-transfer mechanism of end-bearing piles under vertical load in inhomogeneous soil is proposed.The shear modulus of the soil obeys a power law variation with depth and is controlled by two dimensionless parameters.Ignoring the horizontal displacement of the soil,the balanced differential equation of the vertical displacement is established.The series solution of soil displacement with unknown coefficients is obtained by using the method of separation of variables and the Sturm-Liouville theory.Considering the pile-soil interaction,the unknown coefficients are obtained.Through parameter analysis,the influence of the characteristic parameters of the pile-soil system on the pile head stiffness,pile displacement and axial force distribution is studied.The analysis shows that the soil inhomogeneity would significantly reduce the pile head stiffness in stiff soil.The pilesoil stiffness ratio has a great influence on the bearing capacity of the pile s in inhomogeneous soil.(2)Based on the fictitious soil pile model,analytical formulas of bearing and deformation of single pile in inhomogeneous soil ar e obtained.The effect of the thickness of the underlying soil layer on the bearing capacity of the pile foundation is emphatically analyzed.The analysis shows that the existence of the underlying soil layer will significantly reduce the bearing capacity of the pile foundation,but this effect gradually weakens with the increase of the pile slender ratio and the thickness of the underlying soil layer.(3)This paper presents an analytical solution for the bearing characteristics of horizontally loaded piles with fixed head and pinned tip.Ignoring the vertical displacement,the balance differential equations for the hoop and radial of the soil are established.According to the boundary conditions,the series solution of soil displacement with unknown coefficients is obtained by the method of separated variables and the Sturm-Liouville theory.Generalized Fourier expansion is performed on the displacement of the pile body along the depth to obtain the unknown coefficients.The critical factors that affect the displacement and bending moment distribution of horizontally loaded pile are analyzed.Parameter analysis shows that the displacement and bending moment of the pile top increase with the increase of soil inhomogeneity.The increase in pile modulus will reduce the displacement of the pile top,but will result in an increase in the bending moment.(4)The model in this paper is used to simulate the in-situ test conditions in London clay,and the calculation results are compared with the actua l engineering data.The comparison results show that the pile top settlement calculated by the model is basically consistent with the measured value.This model can be used to estimate the settlement of pile foundation under working load.