Fracture Mechanism of Unstable Rock With Double-Crack Control Discontinuity Subjected to High Earthquake Intensities

Abstract

Unstable rock in the limestone area has typical characteristics of quasimasonry structure and control discontinuity, where the failure essence is the fracture propagation under loads. The unstable rock control discontinuity in the limestone zone was analyzed, and the geological model for a doublecrack unstable rock mass was obtained according to the theory of geomorphologic evolution. The mechanical model and fracture mechanical model for the complex control discontinuity were constructed. Based on the rock weight, the fissure water pressure and the earthquake load, the formula of the fracture stability coefficient was obtained under the maximum circumferential stress criterion. The fracture stability coefficient expression for the unstable rock is rational according to the verifying case analysis. The fracture stability coefficient corresponding to each intensity decreases with the crack length ratio. Under earthquake intensities Ⅷ and Ⅸ, the unstable rock will collapse; the stability of the unstable rock is liable to the coupling effects of the crack length ratio of the main control discontinuity and the earthquake intensity. The critical crack length ratio decreases with the earthquake intensity. Under earthquake intensity Ⅶ, the theoretical value of the critical crack length ratio is 25.8%, which is slightly less than the actual value of 27.7%, and on the slightly safer side. The fracture stability coefficient expression has good applicability. The research results provide an important theoretical support for the treatment of such unstable rock masses.