Nonlinear coupling damage constitutive model for multi-jointed rock mass

In order to study the influence of the properties and interaction of joints and intact rock on the constitutive properties of rock mass, the dynamic changes of mechanical parameters of joints and intact rock in the process of loading are considered, and the coupling damage effect of joint deformation on intact rock is quantitatively analyzed.The non-linear constitutive model of multi-jointed rock mass is established by using the method of integrating joints and intact rock mass constitutive equation.Firstly, the normal closure, shear and dilatancy expressions of joints are deduced from the results of single joint laboratory test and then the joint stiffness matrix is combined to establish the dynamic joint constitutive model whose parameters varies with joint deformation and joint stress.Secondly, on the basis of the original damage model, the coupling damage factor is introduced to consider the weakening effect of joint deformation on the intact rock, and the variable dynamic Poisson's ratio of intact rock changing with principal strain is also used to establish a new damage constitutive model of intact rock.Thirdly, according to the spatial distribution of joints and intact rock, the nonlinear coupling damage constitutive model for multi-jointed rock mass is presented through integrating joint and intact rock constitutive model.Finally, a numerical simulation is carried out through a Fortran program so as to analyze the influence of coupling damage factor, dynamic Poisson's ratio and dynamic joint stiffness on the strength and deformation of rock mass.Results demonstrate that the additional damage caused by the coupling damage factor of joints leads to the decrease of the strength of intact rock, which can accurately predict the peak strength-joint dip angle curve obtained through the laboratory test, and weaken the deformation resistance of the rock mass when it is damaged.Dynamic intact rock Poisson's ratio can reflect the dilatancy of rock mass.Compared with joints as linear elastomers, the nonlinear features of stress-strain of rock mass will be informed when considering the dynamic change of joint stiffness under loading.