Study On Micromechanical Damage Model And Numerical Method For Jointed Rock Masses

As a popular material in civil engineering, rock masses consist of two major components:the intact rock matrix and the discontinuities. Different from intact matrix, the existence and complicated behavior of joint govern the mechanical behavior of rock masses. Neglecting the joints often leads to misinterpretation of the rock mass responses to the external loading condition. When the stresses are applied, the jointed rock masses are more deformable than the intact one, and under shear the joints will made the rock masses be anisotropic. In fact the rock masses contain many joints of different size, In engineering problems, large scale joints may extend hundreds meters but in small numbers. Microscopic scale joints are always distributed extensively in rock matrix and in extremely large number.By combining micromechanics and thermodynamic theory, a micromechanics damage model of jointed rock masses is presented.1) The presence of joints can strongly affect the mechanical behavior of a rock masses by providing planes of weakness across which frictional sliding can occur. So a three dimensional joint model is proposed firstly at this thesis. A physically motivated constitutive law for the behavior of geologic discontinuities with dilatancy and contact surface degradation is presented. The asperity surface is idealized as a hyperbolic function which means that the asperity angle will increase first and decrease later while shearing. A tribological model for asperity degration which is capable of replicating the salient features of this type of asperity wear and accounts for the irreversible nature of damage is obtained by assuming that the degration is a function of the plastic tangential work. The constitutive model for the joint is proposed by combining this two effection.2) The joints in rock masses are treated as penny-shaped inclusion in solid not through structural plane by considering joint density, closure effect, joint geometry. The mechanical behavior of the joints is represented by an elasto-plastic constitutive law. Mori-Tanaka method is used to derive the relationship between the joint deformations and macroscopic strains. The incremental stress-strain relationship of rock masses is formulated by taking the volume average of the representative volume element. Implicit constitutive integration algorithm is proposed to achieve the implicit expression of this constitutive model. By implementing the algorithm, the model is applied in non-linear FEM calculation which can reflect the complicate behavior of the rock masses and the joints in it.3) To consider the damage of the jointed rock masses, the mechanical behavior of joint include the coupling between damage and frictional sliding and the occurrence of joint dilatancy is treated as the main object of this model. A joint evolution law is proposed by using thermodynamic theory, and the interaction of sliding and damage evolution is addressed based on it. So with all those feature metioned will be combined together by using equivalent inclusion method. This model will present the joint evolution length and also the sliding displacement. Implicit constitutive integration algorithm is proposed to achieve the implicit expression of this constitutive model. By implementing the algorithm, the model is applied in non-linear FEM calculation which can reflect the complicate behavior of the rock masses and the joints in it.4) The interaction is very difficult to be calculated in micromechanics model. By using TMEM method, the interaction can be macroscopic considered. The reference matrix of equivalent inclusion method is tranisotropic, so the present work is devoted to get the Eshelby Tensor of a penny-shape inclusion with small but nonzero thickness in transversely isotropic elastic solid under uniform stress at infinity. Based on it, the relationship between macroscopic stress and joint displacement can be modified by taking account of interaction of joints.