水力耦合作用下岩体3维裂隙的起裂扩展模式研究

Research on the Initiation and Propagation Modes of 3-D Crack Under Hydro-mechanical Coupling

岩体裂隙在高地应力、强渗透压作用下极易发生扩展、贯通,导致岩体破裂失稳。为研究水力耦合作用下3维裂隙的起裂扩展模式,采用3维断裂分析软件FRANC3D建立水力耦合数值模型,进行数值模拟研究,并开展相应的含裂隙透明树脂类岩石材料室内破裂试验。通过对比模拟与试验结果,分析了不同断裂准则的适用性,验证了数值模型的可靠性。基于数值模拟调查了不同加载条件下裂隙前缘断裂参数的分布特征,获得了水压、侧压等关键因素对裂隙起裂角及扩展长度的影响规律。结果表明:采用优化的能量释放率准则模拟的3维裂隙空间起裂扩展模式与试验现象具有良好的一致性;裂隙长轴端点处的翼裂纹为Ⅰ-Ⅱ(张拉-滑移)型复合裂纹,短轴端点处的平面扩展为Ⅰ-Ⅲ(张拉-撕裂)型复合裂纹,除长、短轴端点外的其余位置发生Ⅰ-Ⅱ-Ⅲ型复合断裂;水压的存在显著改变了裂隙前缘的应力分布状态,水压增大可提高拉应力水平,明显促进张拉断裂的发生,使裂隙倾向于沿原裂隙面方向起裂,并导致裂隙前缘各处扩展速率趋于均衡;侧向压应力增大可显著促进张拉断裂,抑制滑移与撕裂断裂,并使裂隙前缘能量释放率呈降低趋势,从而抑制裂隙扩展,而侧向拉应力起相反作用,由此认为岩体在双向受压状态比拉压受力状态更为安全;侧向压应力与水压共同导致翼裂纹偏转角度明显减小,改变了3维裂隙的空间起裂扩展模式及岩体的宏观破裂形态。

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 theⅠ-Ⅱ(tensile–slip)mixed cracks,whereas the plane extensions at end points of crack short axis are theⅠ-Ⅱ(tensile–tearing)mixed cracks,andⅠ-Ⅱ-Ⅲmixed 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.