Experimental and Numerical Investigation on Crack Propagation and Coalescence in Rock-Like Specimens with Fluid-Infiltrated Parallel Flaws

Underground rock mass conditions are often complex, crack propagation and coalescence results in a reduction in rock strength and can cause brittle failure. We study the influence of the fluid pressure and the lateral pressure on the propagation process of parallel flaws, the failure mechanism of rock bridges and the rock failure modes, respectively. A lateral pressure loading device and a water injection system are designed for experimental analysis. A fracture-damage model is introduced in the continuous discontinuous discrete element method to describe the crack propagation process. The following conclusions are obtained: compared with the specimen without fluid pressure in the flaws, the fluid pressures (0.5 MPa, 1 MPa and 1.5 MPa) affect the rock bridge coalescence modes, strength characteristics and failure forms under uniaxial compression. With the increase of fluid pressure, the failure form of the rock bridge changes from tensile shear failure to tensile failure. Without fluid pressure in the flaws, tensile shear failure occurs in the rock bridge under uniaxial compression. With the increase in the lateral pressure coefficient (30%), wing crack growth is restrained, and shear cracks appear in rock bridges, causing the failure mode of the rock bridge changes from tensile shear failure to shear failure. Compared with the specimen without fluid pressure in the flaws, with the increase of fluid pressure, the tensile stress at the flaw tips increases, and the shear stress at the rock bridges decreases , which promotes the growth of tensile cracks and decreases the peak strength of the specimen. Especially, high-pressure fluid promotes the coalescence of rock bridges and cause tensile failure occurs in the specimen, resulting in more obvious brittle failure characteristics of the specimen than the specimen with low fluid pressure and without fluid pressure.