基于核磁共振技术的花岗岩三轴压缩峰前裂隙发育及损伤规律研究

Development and Damage of Cracks in Front of Granite Triaxial Compression Peak Based on Nuclear Magnetic Resonance

基于核磁共振技术,对花岗岩三轴压缩作用下的裂隙发展规律进行分析,得到花岗岩在20 MPa围压条件下的应力-应变曲线、以及不同轴压状态下岩石孔隙度和T_2谱曲线。结果表明:T_2谱曲线直观、真实地反映岩石内部裂隙发育过程,孔隙度随轴向应力增加呈指数形式增长。花岗岩三轴压缩低轴压阶段,岩石损伤以裂隙数增加为主要诱因;高轴压条件下,岩石损伤主要由裂隙数增加及裂隙贯通引起。三轴压缩过程中,花岗岩存在轴向应力临界值,当超过该值,新生裂隙受到抑制,同时已有裂隙扩展至贯通,试验中花岗岩的轴向应力临界值为峰值强度的50%~70%。20 MPa围压状态下的花岗岩损伤度随岩石孔隙度、轴向应力的变化特征符合指数函数关系。

Based on nuclear magnetic resonance technology, crack development laws of granite were analyzed under triaxial compression condition, the stress-strain curves, T_2 spectrum curves and porosity under axial pressure of 20 MPa were obtained.The results showed that T_2 spectrum distribution reflected the process of crack development visually and factually, and the porosity increased exponentially with axial stress. When the granite was in the low axial compression stage, rock damage was mainly caused by the increase of fracture number; under the high axial pressure, rock damage caused by both fracture number and crack connection. In the triaxial compression process, the axial stress threshold of granite was present, the new fractures were inhibited and the existing cracks have been extended to the penetration when it exceeded that limit, the axial stress threshold of granite in this experiment was 50% to 70% of peak strength. The variation characteristics of granite damage degree with rock porosity and axial stress accord with exponential function relation under confining pressure of 20 MPa.