A three-dimensional long-term strength criterion of rocks based on micromechanical method

Rock-like materials are driven not only by applied stresses, but also by time that exhibits creep characteristics. It is significant to establish three-dimensional long-term strength criterion of rocks. In this paper, it is assumed that there exist three-dimensional penny-shaped microcracks in viscoelastic rock matrix. The mode II and mode III stress intensity factors at tips of three-dimensional penny-shaped microcracks in viscoelastic rock matrix are determined. The orientation angle of micro-failure in rock materials is obtained to describe the creep failure of rocks. The relationship between the micro-failure orientation angle and stress components is derived from the creep fracture criterion. Failure characteristic parameters of penny-shaped microcracks under triaxial creep compressive condition are defined, which are an invariant. A three-dimensional long-term strength criterion of rocks is established using micromechanical method, in which the effects of the intermediate principal stress are taken into account. The proposed three-dimensional long-term strength criterion is novel, and never published before. By comparison with the previous experimental data, it is found that the presented three-dimensional long-term strength criterion is in good agreement with the experimental data.