Research And Application On Damage Constitutive Model For Rock Mass Containing Multi-cracks

The damage constitutive model, which is established through the combination of micromechanics and macroscopical phenomenology, can both reflect the micro-structures of the material, and explain its macroscopic mechanical behaviors. Based on micromechanical Gibbs free energy function, as well as fracture mechanics, classic plastic mechanics and continuum thermodynamics, an elastic damage constitutive model and an elastic-plastic constitutive model coupled with damage are obtained. The specific work including:â‘ From research on geological structure of QiXiaShan mine by using equatorial horizon projection principle, the dips of ground stress are determined through the judgment of the X failure. Thus, specimen was picked up in the main roadway in 625 meters depth below ground level according to the determination. And the original ground stress was tested through Kaiser acoustic emissional experiments. In addition, indoor conventional experiments provided necessary parameters to numerical simulations.â‘¡Helmholtz free energy function in the strain space is deduced through Legendre transformation from Gibbs energy function. Three dimensional elastic damage constitutive equations are acquired based upon orthogonality principle. Meanwhile, the elastic damage evolution laws are given for both parallel and uniformly distributed microcracks under both tension and compression respectively by using fracture criterion.â‘¢The pre-peak stress-strain relationship is divided into three stages: Firstly, the elastic damage constitutive equations given in chapter three are adopted for elastic stage only with initial damage. Secondly, by taking classic plastic mechanics and continuum thermodynamics into account, the elastic-plastic strain energy including initial damage and plastic multiplicator are derived for elastic-plastic stage. Then, the elastic-plastic constitutive equations considering initial damage are gained by importing plastic flow rule and isothermal assumption. Threshold value is determined according to the kink expanding of microcracks. Lastly, the total stress rate and strain rate are resolved into three parts as elastic, plastic and damage ones. According to consistent condition, plastic and damage multiplicators are calculated by introducing plastic flow rule and damage evolution equation denoted by conjugated force. The three dimensional nonlinear incremental constitutive equations for the stage of elastic-plastic coupled with damage are developed.â‘£The elastic-plastic constitutive model coupled with damage under plane strain condition is obtained. Identifications, both on uniaxial and bioaxial compressions, have shown good consistency with the experimental curves of stress-strain. The main roadway in 625 meters depth below ground level under plane strain condition is studied through numerical simulation using ANSYS 9.0. Comparison is drawn between the elastic-plastic constitutive model coupled with damage and the ideal elastic-plastic one, and the former is more accord with actual situation.