非共面双裂隙红砂岩宏细观力学行为颗粒流模拟

通过颗粒流程序(PFC)细观参数敏感性分析与完整红砂岩在常规三轴压缩下的试验结果，获得一组能够真实反映完整红砂岩宏观力学行为的细观参数。在此基础上，对断续双裂隙红砂岩在不同围压作用下进行颗粒流模拟，分析围压以及岩桥倾角对断续双裂隙红砂岩强度破坏特征的影响规律，揭示断续双裂隙红砂岩在不同围压作用下裂纹扩展的细观力学响应机制。研究结果表明：与完整红砂岩相比，断续双裂隙红砂岩峰值强度参数显著降低，且降幅与岩桥倾角?密切相关，黏聚力和内摩擦角均随着岩桥倾角?的增大呈非线性变化。当断续双裂隙红砂岩?= 0°和30°时，两者裂纹扩展模式相近，裂隙①和②之间无贯通；当?= 60°和90°时，两者裂纹扩展模式相近，裂隙①和②之间出现一处贯通；当?= 120°时，在低围压下裂隙①和②之间出现两处贯通，在高围压下只有一处贯通。当应力增大到一定程度之后，颗粒之间黏结断裂，微裂纹不断产生、汇集和贯通，最终形成宏观裂纹，使得试样发生失稳破坏。围压的增加在细观上提高了颗粒之间的接触力，在宏观上表现为强度增大。高围压的存在限制了微裂纹的扩展速率。

PARTICLE FLOW SIMULATION OF MACRO- AND MESO-MECHANICAL BEHAVIOR OF RED SANDSTONE CONTAINING TWO PRE-EXISTING NON-COPLANAR FISSURES

Based on the experimental results of intact red sandstone under conventional triaxial compression，a set of microscopic parameters in particle flow code(PFC) reflecting the macroscopic mechanical behavior of intact red sandstone were obtained by analyzing the sensitivity of microscopic mechanical parameters in PFC. The particle flow simulation was carried out for the red sandstone containing two pre-existing fissures under different confining pressures. The influences of the confining pressure and the ligament angle on the strength failure characteristics of the red sandstone containing two pre-existing fissures were analyzed on the basis of the simulated results and the microscopic mechanical mechanism of crack coalescence of the red sandstone containing two pre-existing fissures was revealed. The parameters of peak strength of red sandstone containing two pre-existing fissures are smaller compared with that of the intact red sandstone，and the extent of reduction is related to the ligament angle β. The cohesion and the internal friction angle varied both nonlinearly with the ligament angle ?. When ? were 0°and 30°，the ultimate failure modes of the red sandstone containing two pre-existing fissures were similar to each other，no coalescence was observed between fissures ① and ②. When ? are 60° and 90°，the ultimate failure modes were similar，one crack coalescence was observed between fissures ① and ②. If ? was 120°，two crack coalescences were observed between fissures ① and ② at lower confining pressure，but only one crack coalescence occurred at higher confining pressure. When stress increased to a certain value，the bonds among grains began to break. The newborn micro-cracks initiate，propagate and coalesce to form the macro-cracks which results in the unstable failure of rock specimens. The increase of confining pressure improves the contact and bond force among grains at the microscopic scale，which leads to the increase of strength at the macroscopic scale. Existence of high confining pressure limits the propagating speed of microscopic cracks.