Abstract: In order to clearly understand the self-organized critical phenomenon of shale in the process of tension and compression fracture, uniaxial compression and Brazilian splitting tests were carried out for shale with brittle characteristics at different rates. The number of acoustic emission (AE) events in the whole process was collected synchronously. The information entropy H of AE event number was defined by combining information entropy theory with AE event number, and the evolution law of AE event number in the process of loading was obtained. The research results show that under the tension and pressure conditions, the information entropy of AE events increases with time, and the law is similar. When the information entropy of AE events keeps stable (r≈0.95), the rock enters the critical state. According to the acoustic emission localization map, the entropy value is maximum when the critical point is reached, and the penetrating crack begins to form. After entering the critical state, the entropy value is in steady a state, and the location signals gather towards the fracture area until the failure. Through the acoustic emission localization changes of four states, the evolution process of defects in shale from the disordered state of slow random development to the orderly state of instantaneous development according to certain laws is revealed, which is well corresponding to the entropy change. The energy probability density function satisfies the power law distribution (P≈X-r) in the process of tension and compression, which has a similar critical index.

Key words: geotechnical engineering, shale, acoustic emission, the number of acoustic emission events, information entropy, critical state

摘要： 为了清晰了解页岩在拉、压破裂过程中的自组织临界现象，对具有脆性特征的页岩进行不同速率下的单轴压缩和巴西劈裂试验，同步采集全过程声发射事件数。将信息熵理论与声发射事件数结合，定义了声发射事件数信息熵H，得到了加载过程中熵的演化规律。研究结果表明：在拉、压状态下，随着时间推进声发射事件数信息熵呈增长变化且规律相似，当声发射事件数信息熵值保持稳定时(εr接近0.95)，岩石进入临界态；通过声发射定位图发现，到达临界点时对应的熵值最大，贯通性裂纹开始形成；进入临界态后，熵值处于稳态，定位信号向着破裂面积聚，直至破坏；通过4个状态的声发射定位变化，揭示了页岩内部的缺陷从开始的缓慢随机发展的无序状态到瞬速按照一定规律发展的有序状态的演化过程，与熵变化形成良好对应；拉、压过程中能量概率密度函数满足幂律分布PX-r，并存在相近的临界指数。

关键词: 岩土工程, 页岩, 声发射, 声发射事件数, 信息熵, 临界态