# Anisotropy and Directivity Effects on Uniaxial Compression of Carbonaceous Slate Form Jinman Mine
## 3 Results and Discussion
### Acoustic Emission Response Characteristics  
Acoustic emission (AE) is the phenomenon of generating transient elastic waves during compression of rock, accompanied by external energy input and rapid release of strain energy [25; 28]. The AE cumulative ring number can directly reflect the structural  
Figure 6: Variation coefficients of slate samples. reorganization and redistribution of stress within a rock sample, thereby revealing the failure mechanism of slate. Figures 7 and 8 show the corresponding relationships between the AE cumulative ring number and axial stress of slate samples. The AE cumulative ring number is consistent with axial stress and is roughly similar to the evolutionary process of a quiet stage (stage I), a rapid increase stage (stage II), and a sudden increase stage (stage III). The slate sample is in the compaction stage and the primary cracks are compacted and closed, with almost no new fractures generated during the initial stage of axial stress loading. The AE activity is relatively weak, and the AE cumulative ring number has no significant increase, that is, the AE activity is in a quiet stage [25]. The existence of a weak surface in a slate sample causes local micro-fracture during the initial loading process, in turn, causes the AE activity to increase, and the AE cumulative ring number-time curve increases briefly. The vertical loading causes the principal stress to be in series with slate bedding plane (Figure 7), the compression process of slate sample is longer, and the increase in the AE cumulative ring number is small. The loading stress induces early tensile fracture of the weak surfaces and early initiation and expansion of internal fissures under parallel loading (Figure 8). A local microscopic fracture surface is formed, and the AE frequency and intensity are greater than that for vertical loading. The slate sample gradually enters the elastic deformation stage due to the internal fissures being compressed. The layered weak surfaces inside the slate sample induce new  
Figure 8: Evolution of AE cumulative ring number under parallel loading: (**a**) Gray samples; (**b**) Carbonaceous samples. Figure 7: Evolution of AE cumulative ring number under vertical loading: (**a**) Gray samples; (**b**) Carbonaceous samples. clefts to appear rapidly, the AE activity is slightly enhanced, and the AE cumulative ring number develops slowly, which is different from the AE characteristics of intact rock. The differences in loading directions lead to differences in AE characteristics at the elastic deformation stage. Fracture and slip of local weak layers cause the initiation of new cracks, and the drop in stress induces a stepwise increase in the AE cumulative ring number. In particular, when vertical loading is applied, the rock formation undergoes phased oblique shear rupture, leading to phased AE activities. The AE cumulative ring number shows a sudden, local increase around 600 s, 750 s, and 800 s as shown in Figure 7a. The AE cumulative ring number has a local sudden increase of around 650 s, as shown in Figure 7b. When the slate sample undergoes plastic deformation, the uncoordinated deformation between the slate rock layers is relatively active, leading to the initiation, expansion, and convergence of new internal fractures and brittle bursts appear during the formation of macro-cracks or micro-cracks. The AE activity at this stage is significantly enhanced; the AE cumulative ring number appears to increase suddenly, then it reaches a maximum value immediately thereafter. The cumulative values of the AE ring number for the slate sample are 23,048.75, 18,085, 14845, and 12,395. This shows that internal cracks penetrate rapidly; the microscopic cracks rapidly expand into macroscopic cracks, and the rock stability decreases sharply, until it ruptures. After the slate rock is loaded to the peak stress, the strain gauges break rapidly, thus failing to acquire the post-peak stress and strain data.