Experimental and theoretical investigation of coupled damage of rock under combined disturbance

Cyclic loading and confining pressure unloading are two common types of disturbance effects in rock engineering. In this study, a series of triaxial tests under combined disturbance consisting of cyclic loading and confining pressure unloading was conducted, and the mechanical characteristics of rock during this process were obtained. A damage constitutive model of rock under combined disturbance was established on the basis of statistical meso damage mechanics. This model modifies the porosity by plastic deviated strain, so it can reflect the evolution law of coupling damage in the combined disturbance more accurately. Results show that if the dynamic modulus decay rate of the first stage cyclic loading is greater than 0.01, then the rock undergoes less than 3 cycles before failure. The final relative confining pressure and the stress ratio K show a linear relationship. In terms of the damage constitutive model, the results of the conventional triaxial tests and combined disturbance tests match well with the results calculated with the model, and m0 and F0 have a linear relationship with the initial confining pressure approximately. Under combined disturbance, the deviatoric strain-damage curve is in the shape of "S". The relationship between damage and disturbance cycle number is stepped when the initial stress ratio is low, whereas the relationship is exponential when the initial stress ratio is high.