Creeping damage around an opening in rock-like material containing non-persistent joints

The purpose of this study is to investigate experimentally the creeping damage and failure mechanism around an opening in rock-like material containing non-persistent joints. The jointed rock-like specimen is modelled by plaster material, and the underground excavation is simulated by drilling at a certain stress level. In our experimental studies, time evolutions of deformation are recorded at various applied vertical (σ1) and confining (σ3) stress. It is found that with a fixed σ1, tensile mode of creeping failure is dominant when the λ (σ3/σ1) is low (λ=1/3). But when λ is high (≥ 1/2), shear mode of creeping failure is dominant. The creeping failure time decreases with the increased λ and stress ratio of σ1/σ1max(σ1maxis the maximum stress of a jointed rock-like mass). Furthermore, for the excavation in a low stress level (σ1/σ1max≤ 45%), no creeping damage around opening will occur. The stress ratio λ and σ1/σ1maxare the important indices indicating the degree of instability of an opening after excavation.