基于声发射的盐岩变形破坏过程的分形与损伤特征研究

为研究盐岩变形破坏过程中损伤变量和分形维数之间的关系，对取自某地的纯盐岩开展了单轴压缩和三轴压缩试验。在基于声发射振铃计数的损伤模型和基于声发射定位点空间演化的分形维数计算的基础上，对盐岩变化破坏过程中的损伤变量和分形维数进行了研究。研究表明：在盐岩变形破坏过程中，盐岩分形维数逐渐降低，损伤变量逐渐增加，且分形维数下降的各个阶段与损伤变量增加的各个阶段相对应；盐岩变形破坏前分形维数不再明显下降，且不同应力状态下，盐岩变形破坏前分形维数不同；随着围压增大，盐岩变形破坏前分形维数逐渐降低，其中单轴压缩和三轴压缩应力状态时，分形维数分别低于2.42和2.31、2.20时，预示着试件内部损伤开始汇集，逐渐形成宏观破裂面，导致试件变形破坏；围压对盐岩声发射活动有明显的抑制作用，随着围压的增大，盐岩变形破坏过程中声发射活动逐渐减少，且在此过程中可以发现：在应力加载初期，盐岩分形维数快速下降时所对应的应力百分比逐渐增大，在应力加载后期，当盐岩分形维数不再明显减小时对应的应力百分比逐渐增大；在盐岩变形破坏的加载初期，损伤变量较小，能量释放较少；盐岩变形破坏前损伤变量增加较快，能量快速释放。

Study of fractal and damage characteristic in the deformation and failure process of salt rack based on acoustic emission

Uniaxial and triaxial compression tests have been carried out on pure salt rock to study the relationship between damage variable and fractal dimension of salt rock in the deformation and failure process. The damage variable and fractal dimension in the deformation and failure process of salt rock have been studied by using the damage model based on acoustic emission ringing count and fractal dimension calculation based on the spatial distribution of acoustic emission event. The results showed that the fractal dimension of salt rock gradually reduced and the damage variable slowly increased in the deformation and failure process of salt rock. Moreover, each stage of the declined fractal dimension were corresponding to each stage of the increased damage variable. Before the failure of salt rock, the fractal dimension of salt rock was not significantly reduced and was different under different stress states. With the increase of confining pressure, the fractal dimension of salt rock gradually reduced. Under stress states of uniaxial compression and triaxial compression, the fractal dimension of specimen below to 2.42, 2.31 and 2.20 respectively indicated that the internal damage of specimen gathered together to form a macroscopic fracture surface, leading to the specimen deformation and failure. The confining pressure had obvious inhibitory effect on acoustic emission activities. With the increase of confining pressure, there were less acoustic emission activities in the deformation and failure process of salt rock. When the stress state of rock changed from the uniaxial compression process to triaxial compression process, it was found that in the initial loading period, the percentage of stress gradually increased when the fractal dimension of salt rock decreased rapidly. However, in the late loading period, the percentage of stress gradually increased when the fractal dimension of salt rock reduced slightly. In addition, the damage variable was small and energy releasing was less at the early loading time of the deformation and failure process of salt rock. While the damage variable fast increased and energy quickly released before the failure of salt rock.