# Experimental and Numerical Investigations on the Slate Shearing Mechanical Behavior
###### Abstract  
Multi-scale assessment of shear behavior in the tunnel carbonaceous slate is critical for evaluating the stability of the surrounding rock. In this study, direct shear tests were conducted on carbonaceous slates from the Muzhailing Tunnel, considering five bedding dip angles (\(\beta\)) and four normal stresses (\(\sigma_{\mathrm{n}}\)). The micro-mechanism was also examined by combining acoustic emission (AE) and energy rate with PFC2D Version 5.0 (particle flow code 2D Version 5.0 software) numerical simulations. The results showed a linear relationship between peak shear stress and normal stress, with the rate of increase inversely related to \(\beta\). Cohesion increased linearly with \(\beta\), while internal friction angle and AE activity decreased; the energy release rate is 3.92 \(\times\) 10\({}^{8}\) aJ/s at 0\({}^{\circ}\) and 1.93 \(\times\) 10\({}^{8}\) aJ/s at 90\({}^{\circ}\). Shearing along the preset fracture plane was the main failure mode. Increased normal stress led to lateral cracks perpendicular to or intersecting the shear plane. Cracks along the bedding plane formed a broad shear band with concentrated compressive force, and inclined bedding was accompanied by a dense tension chain along the bedding plane. carbonaceous slate; direct shear; bedding effect; acoustic emission; micro-mechanism Article Experimental and Numerical Investigations on the Slate Shearing Mechanical Behavior  
[PERSON], [PERSON], [PERSON], [PERSON], [PERSON], Z.  
acoustic emission (AE) parameter characteristics and strain field evolution during crack formation and propagation. It is pertinent to note that investigating the microscopic mechanisms of layered rocks should not be underestimated. In addition to laboratory tests, numerical simulations based on rock mechanical test results can enhance the comprehension of test conclusions [13]. Recently, AE has become prevalent for monitoring the microcracking process and understanding the failure mechanism of rocks [14; 15; 16]. Several researchers have explored its applicability in monitoring the degradation process of joint asperities under shear loading [17; 18; 19; 20]. Therefore, studying layered rock shear failure behavior from the perspective of AE characteristics and numerical simulation is imperative for a better and more thorough understanding [21]. Similarly, [PERSON] et al. [22] studied the anisotropic shear mechanism of slate by experimental and numerical analyses, revealing that the shear strength and failure mechanism of layered rocks is significantly influenced by \(\beta\). [PERSON] et al. [23] experimentally investigated the fracture behavior and micro-fracture process of anisotropic sandstone and analyzed it using particle flow code. The influence of bedding plane inclination angle on strength was found to be more significant than that of bedding plane spacing. Although extensive studies have been conducted earlier to reveal the mechanical anisotropies of layered rocks [24; 25; 26; 27; 28; 29], including their strength, deformation, and failure modes, the findings on the influence of different normal stresses (\(\sigma_{\mathrm{n}}\)) and bedding dip angles on the failure behavior of layered rocks, especially under shear, are sparse. Since under different engineering loads or natural conditions, rocks are subjected to varying stresses in various environments, such as the static or pseudo-static loadings in rainfall-induced rockslides and the dynamic loadings in earthquake-triggered rockslides, systematically studying the shear failure behavior of layered slate under different normal stresses and bedding dip angles is critical. Therefore, this research work is carried out in which the direct shear tests were conducted on rock specimens with varying \(\beta\) values (0\({}^{\circ}\), 30\({}^{\circ}\), 45\({}^{\circ}\), 60\({}^{\circ}\), 90\({}^{\circ}\)) under different \(\sigma_{\mathrm{n}}\) levels (5 MPa, 10 MPa, 15 MPa, 20 MPa). AE was used to monitor microcrack evolution during shear failure in real time.