# Experimental and Numerical Investigations on the Slate Shearing Mechanical Behavior
## 3 Test Results
### AE Characteristics  
AE activity and energy release can be used to assess the microcrack development and propagation during direct shear tests. AE count is a commonly used metric to characterize AE activity. AE energy represents the energy released during the rock failure process. When \(\beta=0^{\circ}\) and \(\sigma_{\rm n}=20\) MPa, the curve showing the variation in AE count rate and cumulative AE counts with shear stress and time is presented in Figure 9a. The entire loading process can be divided into four stages. In the initial loading stage (Stage I), relatively strong intermittent AE signals are generated, and the cumulative AE count increases slowly. These signals in Stage I are because of the internal pores of the slate and the closure of the gap between the shear box and the specimen. During the continuous stable deformation stage (Stage II), AE signals become noticeably denser, yet the overall count rate remains relatively small. Also, the cumulative count curve approximately parallels the loading curve, signifying a stable rate of microcrack evolution with the fastest growth rate throughout the loading process. Toward the end of Stage II, a slight stress decline in shear stress corresponding to a larger count rate is observed. Moving into the unstable deformation stage (Stage III), the AE signals decrease, and the cumulative count increases at a lower rate. Stage III reflects the influence of the stress release of the preceding stage, entering a relatively quiet period. In addition, energy accumulates gradually and is suddenly released during peak stress, generating more AE signals and a sudden increase in cumulative counts. Stage IV represents the post-peak deformation stage, in which AE signals intermittently intensify until the end of the test while the cumulative AE count also increases.  
The variation in AE energy release rate and cumulative released energy with the shear stress-time curve is depicted in Figure 9b for \(\beta=0^{\circ}\) and \(\sigma_{\rm n}=20\) MPa. This curve can be divided into four stages. During Stage I and Stage II, the AE signals primarily consist of low-energy signals, resulting in a slow increase in the cumulative released energy curve. However, a small stress drop in Stage II significantly increases the cumulative energy release, signifying more energy release. Only a small amount of energy is released in Stage III, and the cumulative released energy curve remains almost horizontal, while a sudden increase in AE energy is observed at the peak stress point, with the largest increment. The post-peak energy release characteristic aligns with AE activity, indicating intermittent energy release with a smaller contribution to cumulative energy. The AE activity and energy release characteristics of the remaining samples are similar to those of the aforementioned slate samples, though the specific values differ. Mean values of the maximum AE count rate and maximum energy release rate for slate with different \(\beta\) values are presented in Figures 9c and 9d. Overall, as \(\beta\) increases, the AE count and energy release rates decrease linearly. The energy released with vertical bedding is the least, indicating tensile microcrack generation along the bedding plane, weakening the energy release to some extent.