Settlement Analysis For Pile Groups In Elastic Layer Soils

Although there are many researches about pile groups and pile-raft foundation in elastic half-space, few researches has been carried out in layered elastic half-space. Besides, there is still a big concern over the speed and precision of the calculation for pile groups. Focusing on these problems, a simple theory has been proposed to analyze single pile, pile-pile interaction and pile groups. The theory is based on the stress and displacement solution of axisymmetric problem in the layered elastic half-space, which is carried out by finite difference method. Though example analysis, research on the behaviors of single pile, interaction factor of piles, stiffening effect factor of piles, pile groups and pile raft have been made.The main research work of this paper consists of the following parts:1. The general solution of axisymmetric problem in layered elastic half-space has been deduced in integral transformation and matrix transfer method, which can give stress and displacement solutions of every position in layered elastic half-space. This solution can deal with many load types including concentrated load, round area and annular area distributed load in uniform expressions. Compared with present solutions, numerical results show that the theory in this paper is identical with Mindlin solution in elastic half-space and FEM solution in layered elastic half-space. Good efficiency has been proven.2. Based on the displacement solution in layered elastic half-space, the single pile's settlement equation has been deduced by finite difference method. Compared with the integral equation method, errors reduced by neglecting holes after separation of pile and soil are discussed. After analyzing of the effect of subsection number of pile, comparison has been made with the present results which validate the theory in this paper.3. The definition of interaction factor of pile-pile given by previous researchers is discussed in this paper. Stiffening effect factor of pile-pile is introduced in order to consider the reduction of adjacent pile to current pile. The settlement equations of pile groups with only two piles have been deduced. The expressions of interaction factor of pile-pile and stiffening effect factor of pile-pile are demonstrated. The method in this paper can be used for interaction of both similar piles with same lengths and diameters and dissimilar piles with different lengths and diameters. Numerical results show that the method of this paper is agreeable with the FEM result. Stiffening effect factor can be neglected in the case of similar piles, but can not be neglected in the case of dissimilar piles.4. The expressions for interaction factor of pile-pile, interaction factor of pile-soil, interaction factor of soil-pile and interaction factor of soil-soil are deduced in finite difference method based on the general solution of layered elastic half-space. Analysis equations of pile group and pile raft foundation have been proposed by interaction method. Parameter calculations of pile groups with rigid high cap, pile groups of dissimilar pile lengths and pile raft with rigid cap were carried out to get settlement and load carrying ratio characters. During these calculations, results have been compared with previous researches.