基于尺寸为80mm×160mm×30mm的双孔洞裂隙长方体砂岩试样单轴压缩试验结果,分析了双孔洞裂隙砂岩裂纹扩展特征,建立了双孔洞裂隙砂岩宏观应力.应变曲线与裂纹扩展过程的关系.利用颗粒流模拟程序,基于试验结果进行细观参数校准,进一步研究了裂隙倾角对双孔洞裂隙试样力学参数及裂纹扩展特征的影响.与完整砂岩试样相比,双孔洞裂隙试样力学参数显著降低,但降低程度与裂隙倾角密切相关.随着裂隙倾角的增大,双孔洞裂隙试样峰值强度先减小后增大,弹性模量呈逐渐增加的趋势,而峰值应变呈非线性变化.完整试样呈轴向劈裂脆性破坏,而双孔洞裂隙试样首先在孔洞上下边缘及裂隙的尖端附近萌生初始裂纹,裂纹的扩展与贯通导致了试样最终失稳破坏.最后探讨了双孔洞裂隙试样裂纹扩展细观机制:首先在裂隙尖端附近和孔洞边缘形成应力集中区,应力提高导致颗粒间黏结断裂,产生微裂纹;在应力集中区转移过程中不断产生新的微裂纹,微裂纹的汇集形成宏观裂纹.
Uniaxial compression experiments were carried out for the sandstone specimens( the size is 80mm × 160mm × 30mm)containing double holes and a single fissure by the rock mechanics servo-controlled testing system. Discrete element method was adopted in the present study. Based on the experimental and numerical results of complete axial stress-axial strain curves, the effect of fissure angle on the strength and deformation behavior of sandstone specimens was made a detailed analysis. The uniaxial compressive strength, elastic modulus and peak axial strain of sandstone specimens containing double holes and a single fissure were all lower than those of intact specimen, and the reduction extent was closely related to the fissure angle. With the increase of fissure angle, the peak strength of specimens containing double holes and a single fissure firstly decreases and then increases, and the elastic modulus increases gradually, but the peak axial strain has a nonlinear variance. The failure mode of intact specimen is a typical axial splitting fracture;But the specimens containing double holes and a single fissure results from a lot of crack initiation and coalescence at the tips of pre-existing fissures and edges of holes, so as to lead to the ultimate unstable failure. The meso-mechanism of crack coalescence was discussed: Stress concentration was firstly formed at the tips of fissures and edges of holes; The particle bond fracture caused by the increase of stress produces a microcraek. In the stress concentration zone transfer process continue to generate new microcracks, and then the convergence of microcracks forms a macroscopic crack.