压缩应力条件下花岗岩损伤演化特征及其对渗透性影响研究

 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。

INVESTIGATION ON DAMAGE EVOLUTION CHARACTERISTIC OF GRANITE UNDER COMPRESSIVE STRESS CONDITION AND ITS IMPACT ON PERMEABILITY

Based on a series of triaxial cyclic loading-unloading and permeability tests，the damage evolution of granite under compressive stress condition and its impact on rock′s permeability are investigated. In this study，the conventional permeability test method is optimized by drilling two small boreholes from the sample surfaces，which allows measuring the permeability variation of rock sample with different failure modes. The testing data reveal that the damage evolution is initiated simultaneously with the appearance of microcracks，and accelerated in the failure and post-peak phases. A consistent tendency between the damage evolution and the accumulation of recorded acoustic emission(AE) events is noticed，which verifies that the initiation and propagation of the microcracks are the essential mechanism related to the degradation of mechanical behaviour of granite. The permeability is also mainly increased during the failure and post-peak phases，and its variation is found to be hysteretic compared to the damage evolution before rock failure. It means that the impact of damage evolution on permeability is limited before the coalescence of microcracks. With the increase of confining pressure，the permeability is decreased abruptly at first；and then the decreasing tendency becomes less pronounced when the confining pressure reaches a certain level. Based on the AE data，an empirical equation describing the impact of damage evolution and confining pressure on rock?s permeability is established.