Shear creep characteristics and constitutive model analysis of jointed rock mass

The geo-environment of deep rock mass is complex,and the development of deep earth engineering project is restricted by the uncertainty of failure mechanism of joint rock mass. In order to study the shear failure of deep joint rock mass,especially the deformation failure of plastic shear fracture zone,a study on the test process for the graded shear creep of bolt discontinuous rock under different normal stresses is implemented by the adoption of similar materi- al simulation test combined with micro CT scanning technology. A new element is introduced to modify the original model and the pore volume fraction in the composite rheological model is solved through the shear creep test and the 3D macro-meso reconstruction. It can be found from the study that:① In the shear creep test of jointed rock mass,the instantaneous creep deformation is negatively related to the normal stress,and the decay creep time is positively related to the normal stress;② It is found that the ratio time factor M of the steady-state creep time to the failure time of the test piece does not vary with the increase of the normal stress,which is regarded as the inherent property of rock mass; in the test,the time factor M of the test piece is more than 84% ,which means that the steady-state creep time accounts for a high proportion in the whole failure process of test piece. Through the statistical analysis of time factor M and pore volume fraction f under different rock strengths,it can be found that time factor M increases with the increase of rock strength,and pore volume fraction f increases linearly with the increase of time factor M,so as to realize the quantita- tive characterization of fracture degree of jointed rock by using time factor M;③ The traditional Nishihara model can accurately describe the decay stage and steady stage of shear and creep for jointed rock mass,but the description of ac- celerating stage doesn’t match the reality. In order to accurately describe the whole process of shear creep of jointed rock mass,GTN model is introduced to modify the traditional Nishihara model,and a composite rheological model is obtained to describe the whole process of shear creep of anchored jointed rock mass. Through the verification of the composite rheological model and the test curve,it is shown that the composite rheological model is better than tradi- tional Nishihara model when describing the accelerating stage of shear creep curve of joint rock mass.