Research Of Hydraulic Fracturing Based On Coupling Model Of Stress-Seepage-Damage By EFM

The element-free method (EFM) has great advantages comparing with the finite element method (FEM) such as simply preprocessing and post-processing and high precision of computation, especially applied in simulation of crack propagation. In this paper, combining with the key project of the academician development fund of Hohai University, the basic theory of EFM and its application for simulating crack propagation are studied deeply. By use of damage theory, a stress - seepage -damage coupling analysis model is put forward, which is used successfully to simulate the hydraulic fracturing of gravity dam. The main contents are as follows:(1) The basic theory and functions of the moving least square method (MLSM) based on orthogonal basis function are introduced. And the principle and mothod for chosing the weight function and adaptive influential radius are discussed.(2) The basic theory of integration of EFM function and the realizing process of simulating crack propagation with EFM, the non-linear iteration of crack and the mothod of calculating stress intensity factor are deeply studied.(3) The seepage characteristic in crack is deeply studied. The hydraulic pressure distribution in crack is obtained by the iteration with the relationship among the width of crack, load of node and displacement of crack node, and the computation program is also developed.(4) The basic theory of coupling analysis of seepage and damage in EFM is deeply studied, and the method of describing the influence of rock damage degree on its permeability coefficient and intensity is put forward. Based on the EFM, the stress-seepage-damage coupling analysis model is established,and the corresponding computation program is developed, which is used to simulate the hydraulic fracturing process. It is shown by some examples that the proposed model is reasonable and the results are conformed to the general law.