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基于岩石三轴压缩应力–应变全过程渗透特性试验,结合三维声发射监测信息,研究花岗岩在不同围压条件下力学损伤演化机制及其对岩石渗透特性影响规律。本研究对常规渗透试验方法进行改进,通过在试样两端加工渗透小孔,实现岩石不同破坏形式下渗透性变化规律的测量。试验结果表明,在压缩应力作用下,花岗岩的损伤演化始于微裂隙的产生和扩展,并在岩石破坏时和峰后阶段发展迅速。该损伤演化的阶段性特征与声发射监测数据一致,进一步说明了裂隙扩展是导致花岗岩力学特性劣化的根本原因。随着微裂隙的扩展,岩石渗透性不断增强,但在峰前加载阶段渗透性变化明显滞后于损伤演化过程。该结果表明,在裂隙贯通并产生宏观破坏面之前,裂隙扩展对花岗岩渗透性影响非常有限。在低围压条件下,岩石渗透性随围压增大迅速减小;当围压增大到一定程度后,该趋势逐渐减弱。结合声发射监测数据,对不同应力条件下损伤演化与渗透特性的相互关系进行分析,并提出花岗岩渗透率与损伤和围压的相关经验公式。
Based on the triaxial compression tests of stress-strain process and the 3D acoustic emission monitoring information, the mechanism of mechanical damage evolution of granite under different confining pressure and its influence on rock permeability are studied. In this study, the conventional method of penetration test was improved, and the penetration of small holes in the specimen was measured at both ends of the specimen to measure the variation of permeability under different failure modes. The experimental results show that under the compressive stress, the damage evolution of granite begins with the generation and expansion of micro-cracks and develops rapidly during and after the rock failure. The stage features of the damage evolution are consistent with the acoustic emission monitoring data, further illustrating that the fissure expansion is the fundamental reason leading to the deterioration of the mechanical properties of granite. With the extension of microcracks, the permeability of rock increases continuously, but the permeability change obviously lags behind the damage evolution during the loading phase. The results show that the crack propagation has a very limited effect on the granite permeability before the fracture penetrates and produces macroscopic failure surfaces. Under low confining pressure, the rock permeability decreases rapidly with the increase of confining pressure. When the confining pressure increases to a certain extent, the trend decreases gradually. Based on the acoustic emission monitoring data, the relationship between damage evolution and permeability under different stress conditions is analyzed. Relevant empirical formulas of granite permeability and damage and confining pressure are proposed.