The effect of initial damage induced by stress on the time-dependent behaviour of Beishan granite

To understand the time-dependent fracture behaviour of hard rock in the excavation damage zone, a series of stress paths are designed to obtain the same initial damage extent induced by excavation. The influence of initial damage under different stress states on the creep process of Beishan granite is investigated experimentally. A unified indicator, i.e., the time-dependent fracture potential index ( ξ TFPI ), is proposed to conveniently describe the effect of applied stress on the creep process. The results show that the time-dependent strain increases with increasing initial damage extent and is significantly affected by the applied stress at a given initial damage extent. Under the same initial damage extent, with the increase in ξ TFPI , the larger the primary creep strain rate and secondary creep strain rate are, and this phenomenon is more obvious in the lateral creep results. The secondary creep strain rate increases with increasing ξ TFPI , and the increasing trend of the axial secondary creep strain rate with ξ TFPI is greater with a higher initial damage. Finally, a quantitative relationship of the secondary creep strain rate with the initial damage and ξ TFPI is established and validated against the experimental results.