Damage and fracture evolution of hydraulic fracturing in compression-shear rock cracks

Compression-shear fractured rock under high pore fluid pressure was studied to determine an appropriate model for describing the Initial Cracking Law and the Evolution Law of the stress intensity factor at the tip of a wing crack. Considering the interaction of wing cracks and the additional stress caused by rock bridge damage, this paper proposes an intensity factor Evolution Equation of multiple rock cracks which combines the action of compression-shear stress and pore fluid pressure. The interaction of multiple wing cracks resulting in rock bridge damage makes the stress intensity factor at the crack tip larger than that of a single wing crack, and wing crack propagation under high pore fluid pressure takes a turn from stable expansion to unstable expansion. Based on the rock fracture mechanics criterion, the damage fracture mechanical models of a compression-shear rock mass are established when the rock bridge happens axial transfixion failure, tension-shear combined failure, or wing crack shear connection failure under the combined action of compression-shear stress and high pore fluid pressure. This theory provides the basis for the quantitative investigation of the hydraulic fracturing process.