基于裂纹体应变的深埋大理岩加、卸荷破坏机制研究

Failure mechanism of deep-buried marble under loading-unloading conditions based on crack volumetric strain

为了弄清深埋硬岩的加、卸荷破坏机制,系统开展了深埋大理岩的常规三轴试验、保持σ_1不变的卸围压试验和变σ_1的卸围压试验等。以裂纹体应变为主要分析变量,结合体应变、等效塑性应变等参量深入分析上述不同应力路径下硬岩的破坏过程。运用裂纹体应变-轴向应变曲线、等效塑性应变-轴向应变曲线和轴向应力-应变曲线来解释岩石破坏过程所产生的现象与规律。结果表明:在裂纹闭合阶段岩样裂纹闭合的变化程度(裂纹体应变改变的大小)可以反映岩石的初始损伤程度;裂纹闭合阶段对岩石弹性模量的计算有重要的影响,需要根据合适的阶段划分,消除裂纹闭合阶段对弹性模量计算的影响,进而得到较为准确的弹性模量;在卸围压点处岩石的可闭合程度突然增加,裂纹体应变-轴向应变曲线发生突变;岩石卸荷破坏过程中裂纹扩展存在滞后性。研究成果有助于进一步理解深埋硬岩的加、卸荷破坏过程和机制,为深埋隧洞的灾害防治提供理论依据。

To explore the failure mechanism of deep-buried hard rock, a series of experiments was performed, including conventional triaxial tests and the compression tests by decreasing the confining pressure under constant or variable axial stress. The crack volumetric strain is selected as the key analysis variable, and using volumetric strain, crack volume strain and equivalent plastic strain, the rock failure process is analyzed under different stress paths. The phenomena and characteristics of rock failure process are clarified by using the volume strain-axial strain curve of the cracks, the equivalent plastic strain-axial strain curve and the axial stress-strain curve. It is shown that the crack volumetric strain can be used to reflect the extent of rock initial damage, the crack closure has an important influence on the calculation of elastic modulus of rock, and to obtain accurate modulus, the crack closure needs to be divided into appropriate stages to eliminate the influence of the crack closure stage on the elastic modulus calculation. In addition, at the moment that the confining pressure decreases, the cracks of rock sample are closed suddenly, leading to a mutation of the volumetric strain-axial strain curves of the cracks. There exists hysteresis in the crack growth during the unloading failure of rock. The above results can help understand the process of rock failure, while providing a theoretical basis for preventing the failure of hard rock under high stress conditions.