孔洞-多裂隙组合型缺陷岩体破裂及分形演化

为研究洞室裂隙围岩破坏机制,构建含孔洞-多裂隙组合型缺陷岩体模型,在单轴压缩试验的基础上,结合RFPA软件对岩体模型的裂纹扩展进行数值模拟;采用盒维数法计算裂纹扩展数字图像的分形维数,研究加载过程中岩体模型的分形演化特征。结果表明:组合型缺陷加重了岩体模型的应力集中现象,劣化了力学参数,表现为最大压应力和最大拉应力的增幅分别达到20.57% ~ 58.19%、14.29% ~ 136.19%;单轴抗压强度和弹性模量的降幅分别达到55.76% ~ 66.09%、42.57% ~ 59.29%。含孔洞-多裂隙组合型缺陷岩体物理模型和数值模型的裂纹扩展模式大致相同,可划分为弹性阶段(S-Ⅰ)、裂纹萌生、扩展阶段(S-Ⅱ)以及残余强度阶段(S-Ⅲ)3个阶段。分形维数的演化特征与裂纹扩展密切相关,并提出了基于分形维数的裂纹起裂以及整体失稳的判据。

Fracturing and Fractal Evolution of Rock Mass Containing Hole-multiple Fissures Combined Flaws

In order to investigate the failure mechanism of fractured rock mass surrounding the cavern, the rock mass model containing hole-multiple fissures combined flaws was established. The uniaxial compression tests were conducted. The crack propagation process of the rock mass model was further simulated by the RFPA code. The fractal dimensions of the digital images of crack propagation were estimated by the box-counting method to study the fractal evolution characteristics of the rock mass model during loading. The hole-multiple fissures combined flaws exacerbate stress concentration and reduce the mechanical parameters of rock mass model. Compared with rock mass model containing a single hole, the amplitude increments of the maximum compressive stress and tensile stress of combined flaws rock mass model are in the range of 20.57% ~ 58.19% and 14.29% ~ 136.19%, respectively. The amplitude reductions of uniaxial compressive strength and elastic modulus of physical and numerical rock mass model are in the range of 55.76%~ 66.09% and 42.57% ~ 59.29%, respectively. The failure modes of physical rock mass model are consistent with numerical rock mass model. Crack propagation processes can be classified into three stages: elastic stage (S-Ⅰ), crack initiation and propagation stage (S-Ⅱ) and residual strength stage (S-III). The fractal dimension evolution characteristics are closely related to crack propagation, and the criteria for crack initiation and rock mass failure are proposed based on fractal dimension results.