Experimental study on dynamic and static characteristics of marble considering pre-peak unloading damage

Excavation of tunnels under deep high stress environment will induce unloading damage or even cracking of surrounding rock and, then, the damaged surrounding rock will rupture or fail under static and dynamic loads caused by mining activities. Therefore, it is necessary to study the dynamic and static mechanical behavior of damaged surrounding rock. Pre-peak unloading tests on 72 damaged marble specimens were performed under three confining pressures of 15, 25 and 35 MPa with four unloading points respectively corresponding to 70%, 80%, 90% and 100% of each confining pressure, and then, static and dynamic uniaxial compression tests of the damaged samples were respectively carried out by MTS815 and split Hopkinson pressure bar(SHPB) test system. The test results show that the damage variable of the rock samples increases with increasing the unloading point/confining pressure under the same confining pressure/unloading point. The static and dynamic compressive strength and elastic modulus of the unloading damaged rock samples decrease with the damage variable in a negative exponential function. When the damage variable is lower than the critical value Dc = 0.17, the dynamic enhancement factor keeps stable around 1.5. The dynamic elastic modulus decreases rapidly while the static elastic modulus does not change significantly. When the damage variable is greater than 0.17, the dynamic enhancement factor increases sharply while the dynamic and static elastic moduli tend to be the same. The dynamic and static differences are attributed to the complex coupling of unloading damage effect and strain rate effect. The findings of this research can provide a reference for the selection of the mechanical parameters of the surrounding rock and the optimization of the support scheme. © 2019, Science Press. All right reserved.