Study on cyclic blasting failure characteristics and cumulative damage evolution law of tunnel rock mass under initial in-situ stress

Although in-situ stress significantly affects tunnel rock mass excavation blasting, the crack propagation law of the rock mass under both in-situ stress and cyclic blasting load has not been adequately evaluated. The blasting failure mechanism of rock mass and the cumulative damage evolution effect of cyclic blasting load under different ground stress conditions are systematically studied herein through theoretical analyses, laboratory tests, and numerical analyses. First, the Riedel–Hiermaier–Thoma (RHT) constitutive model is modified and calibrated, and its reliability is improved via an indoor split Hopkinson pressure bar splitting test. Second, the blasting failure analysis model of the dynamic and static load coupling field is established and verified via numerical simulation. Finally, a numerical simulation of the smooth blasting excavation of a rock tunnel is conducted, and the blasting failure mode of a rock tunnel subjected to ground stress is discussed. Notably, the modified and calibrated RHT model can adequately simulate dynamic crack propagation in limestone specimens. Due to the effect of ground stress, the maximum principal stress side is the most favourable direction for blasting crack propagation. The direction of blasting crack propagation is mainly determined by the loading conditions of ground stress, and the number of blasting cycles does not significantly affect the law of rock crack propagation. Smooth blasting during rock tunnel excavation can effectively reduce the dynamic response of surrounding rock in the unexcavated area. Optimizing the cutting-hole and delayed-blasting parameters can improve the blasting quality of tunnel rock mass under in-situ stress.