Criterion of crack initiation and propagation in rock

In this paper, the criterion and mechanism of crack initiation and propagation under creep condition were investigated using specimens collected from sandstone rock formations outcropping in Emei Mountain, the Sichuan Province of China. Cuboid specimens under three point bending were used in this investigation. All specimens were classified into four sorts and used for Mode-I fracture or creep fracture tests. The experimental result shows that due to creep deformation, rock crack will inevitably initiate and propagate under a load of K-I, which is less than fracture toughness K-IC but not less than a constant (marked as K-IC2) K-IC2 indicates the ability of rock to resist crack initiation and propagation under creep conditions and is less than fracture toughness K-IC, it is defined as creep fracture toughness in this paper. K-IC2 should be considered as an important parameter on design and computation of rock engineering.