Accelerated creep model for rock based on statistical damage principle

Aiming at the problems that the existing creep theoretical models cannot describe the accelerated creep characteristics of the viscoplastic phase of rock and how to determine the start conditions of its accelerated creep phase, the triaxial creep tests are carried out on the deep surrounding rocks taken from Hengda Coal Mine of Fuxin. The creep deformation laws of rock are analyzed. In order to make the model describe the creep characteristics of the rock well and correspond to each stage of the classic creep curve, and by defining the index of each segment critical point based on the classical creep deformation, a new visco-elastoplastic creep model for rock considering accelerated creep is established. The results show that on the basis of considering the development of internal defects in rock and soil, the statistical damage theory can be used to formulate the accelerated creep model for rock. It is proved that the proposed model based on the statistical damage principle is correct in reflecting the whole curve of rock creep. The correctness of the critical point index defined by statistical damage variables and classic creep curves is also proved. The loading process of rock creep is also a kind of damage and destruction process of micro-elements inside the rock, which is irreversible in the material microstructure. By dividing the creep curve into stages, the expression form for the damage variable of the segmentation critical point is defined. By combining the statistical damage theory with the Perzyna viscoplastic model, the traditional Nishihara model is appropriately improved so as to establish the nonlinear creep damage model to better reflect the influences of the stress and strain state of the rock and the damage evolution laws.