水力耦合作用下岩体3维裂隙的起裂扩展模式研究

It is easy for the cracks in rock masses to propagate and coalesce under the combination of high ground stress and seepage pressure, which leads to the failure of rock masses. In order to investigate the initiation and propagation modes of 3-D crack under hydro-mechanical coupling, a numerical model was established by the 3-D fracture analysis code of FRANC3D. The numerical simulation and the corresponding laboratory failure experiments based on the transparent resin rock-like material were carried out. The applicability of different fracture criteria was analyzed by comparing it with laboratory results, and then the reliability of the model was validated. Based on the numerical simulation, the distribution characteristics of fracture parameters along the crack fronts under different loading conditions were analyzed. The influences of key factors such as water pressure and lateral stress on the angles and lengths of 3-D crack propagation were obtained. The results showed that the numerical results are in good agreement with the test results by using the optimized energy release rate criterion. The wing cracks at end points of crack long axis are the Ⅰ-Ⅱ (tensile-slip) mixed cracks, whereas the plane extensions at end points of crack short axis are the Ⅰ-Ⅱ (tensile-tearing) mixed cracks, and Ⅰ-Ⅱ-Ⅲ mixed fracture occur in the rest of the positions. The existence of water pressure significantly changes the stress distribution of crack fronts. The increase of water pressure can enhance the tensile stress and promote the tensile fracture, resulting in the crack initiation being inclined to the original surface and the propagation rates along the crack fronts tending to be uniform. The increase of lateral compressive stress can significantly facilitate tensile fracture and inhibit slip and tearing fracture. The energy release rates of crack fronts show a decreasing trend under lateral compressive stress, thus restraining the crack propagation, while the lateral tensile stress has an opposite impact on the energy release rates, which indicates that the fractured rock mass is much safer under the biaxial compressive stress state than the tensile-compressive stress state. The lateral compressive stress and water pressure jointly lead to the decrease of the deflection angle of wing crack, which changes the spatial propagation mode of crack and the macro failure pattern of rock mass.