双轴加载下断续预置裂纹贯通机制的研究

MECHANISMS OF CRACK COALESCENCE OF PRE- EXISTING FLAWS UNDER BIAXIAL COMPRESSION

通过物理实验和数值模拟,研究双轴作用下不同几何分布和不同围压的断续预置三裂纹的萌生、扩展和贯通机制。结果清楚显示裂纹贯通机制主要受加载条件与预置裂纹几何分布的影响。在双轴加载条件下,裂纹贯通的模式包括拉贯通、剪贯通、压贯通和混合贯通。拉裂纹在双轴加载下, 其扩展速度减慢或停止,且在岩桥间出现剪裂纹,从而形成混合贯通或剪贯通。压裂纹是在侧压下产生的次生裂纹,其贯通受制于两非共线的重叠裂纹间的岩距。当1<b/c<1.8(岩距与裂纹长度的比值为b/c)时,则压裂纹最为活跃,否则压裂纹较难生长。双轴作用下,三裂纹在峰值附近有两组贯通裂纹,在单轴情况则通常只发生一组贯通裂纹。此外,随着压力增加,预置裂纹间更加闭合,导致预置裂纹的内摩擦力增加,使裂纹的扩展方向改变并趋向于最大主剪应力方向。

The mechanism of the fracture coalescence between three flaws is studied using rock-like modelling material under confining pressure condition. The specimens contain three pre-existing flaws with different geometry distribution and different confining condition. Experimental and numerical results show that the mechanisms of crack coalescence is controlled by the geometric setting of the flaws and the confining pressure. Under the confining condition,there are four modes of coalescence between the rock bridge:tensile mode,shear mode,compression mode and mix mode(shear and tensile). The growth of tensile crack slows down with the increasing of confining pressure. Compressive crack is active when the flaws are overlapping and with a distance between two flaws 1<b/c<2. Under the confining pressure,the opening of flaws becomes more close,and leads to increase the friction between flaws. It also causes the growth of crack more close to the axial direction.