The Study On Jacking Pressure And Bearing Capacity Of Jacked-in Pile

Jacked-in pile is being widely used in many region of our country, and its theory study lag behind its application. Domestic experts pay more attention to eliminate the geological environment influence caused by jacked-in pile's soil compacting effect, some beneficial conclusions are obtained by adopting some theories and methods similar to CPT study. The mechanism of pile penetration, simulation and computation of resistance & the ultimate bearing capacity of jacked-in pile are be discussed, as well as their relations. Following are the main results in this paper.First, jacked-in pile penetration characteristic of cohesive soil and the sandy soil are analyzed, then giving the merits and faults between traditional plane Cavity Expansion Method(CEM) and spatial cylindrical CEM , it is put forward that the former reasoning simple, easy to be understood, but the displacement, stress and excess pore pressure obtained do nothing with the z coordinates, it's obviously against with the fact, and the latter considers it as an spatial axisymmetric problem, which considering the change of z value along z axis direction, influence ofτrzand the soil self-weight, but neglecting the discrimination of pile end and the pile side. Taking into the above considerations, a simulation & computation pattern that spherical cavity expansion method and sliding friction are adopted to pile end and pile side respectively are proposed to get the stress field around pile, it's proved to be feasible.The generation and dissipation of excess pore pressure during pile penetration are discussed in this paper, which have great significance of jacked-in pile's installation, soil around pile's reconsolidation and the bearing capacity development of pile. As well as domestic and international experts'study of excess pore pressure caused by pile jacking, including theory analysis, calculation and field survey. Then theoretical analysis of the law of excess pore pressure's radial and vertical distribution in the elastic and plastic zone are given by adopting the spatial stress answer of spatial cylinder cavity expansion, and formula according to Henkel excess pore pressure theory.According to the analysis of the trait of the resistance in the pile side and pile end , it is assumed that the soil is homogeneous , isotropic and perfect material of elasticity and plasticity. Mohr-Cloumb model is adopted in this paper. Then the analytic solve is got based on the cavity expansion method, And considering the sliding friction on the pile side , the calculating formula of pile jacking force is confirmed while the pile is in different depth. At last the process of pile jacking is simulated and calculated by using the displacement penetration method in FEM software Ansys8.0. The analysis result accords well to the project .