Research Of Elasto-plastic Damage Model Of Rock And Its Applications

The research of rock damage mechanics has made great progress in theory, and rock damage mechanics has become an effective theory and method for stability evaluation of rock engineering such as dam foundation,high-steep slope,underground hydropower building,etc. But the extent of application of rock damage mechanics is still smaller compared with the numerous rock engineering practices, especially, it has not been widely accepted by engineers. The main reason perhaps is that the current rock damage mechanics founds on complicated knowledge of mathematics and mechanics,expensive instruments and too simplified assumptions. In order to combine the damage mechanics with rock engineering, and realize its theoretical value, a damage model suitable to engineering should be developed and should be applied to more practical rock engineering, at which the paper initially aimed , and which are the main contents of the research of the subjects. In the thesis, a method of establishing damage model suitable to engineering is proposed, and the damage model is applied to the study of rock fragments distribution , fragmentation prediction of jointed rock and numerical simulation of block caving.The stress-strain curve under an uniaxial compression can be an reflection of the elasto-plastic damage of a rock sample. Based on the experiment and the assumption that damage only affects elasticity of the brittle materials, and by uncoupling elasticity and plasticity, an one-dimensional (1-D)damage model can be establised. Then, by using twin-shear theory, the 1-D damage model can be generalized to three-dimensional (3D)model.The plasticity of rock results from the friction between the fissure walls. The complicated states and conditions of fissure walls compose the complicated soften-harden specialities. According to the viewpoint above, an 3-D anistropic elasto-plastic damage model can be deduced, which using the plastic displacement along the crack of rock as the harden variable. Comparing with the tranditional variables, this variable has a clearer physic concept , and its parameters can be easily obtained by experiment.One application of the rock damage model is in the study of rock fragments and fragmentation prediction of jointed rock. Usually, the method of fragmentation prediction is fractal value measurement of microcracks or microholes in the rock sample, or is that directly compute the size of fragmentation by searching the possibly crossed cracks, which is based on a simulated joints net . In the thesis, the fragmentation prediction is based on the mechanism of brittle fracture of rock, on which a fractal model of fragment evolution is proposed. The distribution of rock fragmentation under compression is a measurement of its brittleness and the result of the fractal distributed cracks cutting the intact rock. If the fractal dimension of fragmentation is used as a symbol of specific rock, the minimal size in the fragmentation system should decrease with the damage evolution in the rock. In the thesis, according to the principle of conversation of energy, a theoretical formula is established, which represents the relationship between the fragmentation size, the fractal dimension number of fragmentation system, and the damage variable. For the practical engineering using, the formula has been simplified, which has the fragment size and damage as its variables. Because of the characteristics of self-simularity of the fragmentation system, the formula of size-damage can be generalized to the fragmentation prediction of the jointed rock. The prediction of fragmentation of jointed rock can be done by calculating the damage variable by measuring the joint datum from rock mass, and by calculating the minimal size of the fragmentation system according to the size-damage formula. The significance of the formula is that it presents a new method to predict the fragmentation in block caving.As a try, the damage model is applied to numerical simulation of block caving The simulation is done in the environment of ANSYS9.0 , which the ANSYS's Preprocessor, General Postprocessor and linear or nonlinear Solver are used for an routine Finite Element Analysis, and the Initial Stress is used to apply additional force to the damaged material. The whole analysis is finished by using APDL(Ansys Programming Desin Language). The simulation based on damage model can well display the stress distribution and displacements in the block, and this could be a good guidance to the practical production.