Hydraulic fracturing of specimens with holes by using the fluid-solid coupling method based on the continuum-discontinuum method

Using the self-developed fluid-solid coupling method base on the continuum-discontinuum method (which combined the Lagrangian element method and the discrete element method) considering element splitting, the seepage with single fracture and the hydraulic fracturing of specimens with holes are simulated, and the influence of the size of the hole and the preset fracture on the hydraulic fracturing is studied. It is found that for the unsteady seepage with single fracture, under different conditions, the flow of fluid from one end with the high pressure to the other end with the low pressure, and the numerical results are consistent with the theoretical results. For the disc with a hole, the propagation of fractures is obtained. With the increase of time steps, the maximum principal stress near the surface of the hole increases; then these positions creaking; four main fractures form gradually and their direction are almost radial. The number of tensile fracture segments-time steps curves show two stages: the number of tensile fracture segments is zero and the number of tensile fracture segments increases rapidly. The lager of the hole is, the time corresponding to the propagation of fractures is earlier. For the square specimen with a hole, under the hydrostatic pressure, the maximum principal stress is negative at first; with the increase the fluid pressure, fractures occur near the hole and propagate into the specimen; the farther away from the hole, the lower the fluid pressure is. Compared with the results no preset fracture, the fractures are prone to cracking; the propagation of fractures from the preset fractures first, then the propagation of fractures shows a symmetrical trend for the preset fractures specimens.