During underground mining, the dynamic disturbance such as blasting may accelerate the creep process of rock. In order to ascertain the significant effects that dynamic disturbances may have on the creep behavior of rocks, the failure of sandstone under creep-impact loading was conducted. In this study, a new creep-impact testing machine was employed to test rock under this combined creep and impact loading. The damage evolution process of rock under creep-impact load was examined, and the mechanism of dynamic disturbance on rock creep behavior was revealed. The results showed that the axial strain of the rock specimen was instantaneously increased after the impact, and then it underwent the deceleration creep and the steady creep stages. Even under the impact of the last impact that may trigger the failure, the rock specimen did not fail immediately, showing an evident hysteresis. The instability of rock caused by creep-impact can be divided into two types: the first was that the rock fails during impact, the second was that the rock underwent a short decelerating creep stage, followed by steady creep stage and then entered into accelerating creep stage. Dynamic disturbance increased the sensitivity of axial strain in response to the axial stress, and this tended to increase as the creep stress. The increase of creep stress also changed the failure mode of rock under creep-impact loading. Based on a classical power-law creep equation and elastic damage principle, the constitutive law of rock under creep-impact loading was proposed and implemented into COMSOL Multiphysics to simulate the rock damage and failure under different regimes of creep-impact loading. In this regard, the numerical simulation reproduced well the deformation and failure pattern of rock specimen, thus validating the capability of the numerical model and its implementation.
The long-term instability of rock projects such as tunnel, shaft and rock slope is closely related to the creep behavior of rocks. Creep is defined as the long-term deformation of rock under constant stress below its short-term strength (Griggs, 1939). However, the stress state of rock engineering is not invariable, and it is also affected by dynamic disturbances such as rock blasting, which may greatly reduce the stability of rock engineering and improves the unpredictable occurrence of disasters (Zhu et al., 2016; Zhu et al., 2010). Many scholars have also confirmed that dynamic disturbance is an important external cause of disasters such as rock burst (Huang and Wang, 1999; Mansurov, 2001; Tao, 1996). Fu et al. (2008) used real-time computed tomography (CT) testing techniques to examine the creep damage process and micro-damage evolution of gray-green mudstone under dynamic disturbance. Zhu et al. (2018) developed a rock creep-impact testing machine, and used acoustic emission and strain measurement to quantify the rock failure behavior under the creep load and dynamic disturbance.