Method for Fitting of P-S Curve and Mechanism of Friction Pile

The load-settlement curve of a bored and cast-in-place friction pile simulated by the finite element mathod is described in this paper. The development of pile skin friction is interpreted in terms of direct and simple shear tests. On this basis the mathematical model of pile is established, in which the joint elements are introduced between the pile and the surrounding soil to simulate the shear forces and displacements after the occurrence of plastic state on the cylindrical shear surface of soil. In order to approximate the actual vertical stiffness coefficients of the joint elements representing the shear strength of soil, formulas and iteration method are suggested. It is noted that the fitting of the measured P-S curve will yield relationship between the shearing force and displacement through the pile loading test, which would provide a new approach for back calculating the constitutive relation of soil.From the calculated profile of shear stress and vertical displacements in the soil the working behavior and failure mechanism of the friction pile is also analyzed, leading to the conclusion that the bearing capacity of friction pile depends directly upon the shear strength of the surrounding soil.