# Anisotropy and Directivity Effects on Uniaxial Compression of Carbonaceous Slate Form Jinman Mine
## 3 Results and Discussion
### Effect of Rock Structure on Stress-Strain Curves
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & \(\sigma_{e}\)**/MPa** & \(\sigma_{cd}\)**/MPa** & \(E\)**/MPa** & \(\epsilon_{zz}\times\mathbf{10^{-3}}\) & \(\epsilon_{yy}\times\mathbf{10^{-3}}\) & \(\epsilon_{p}\times\mathbf{10^{-3}}\) \\ \hline No. 1 Gray sample & 63.27 & 50.26 & 35.11 & 1.802 & \(-\)0.290 & 1.222 \\ No. 2 Gray sample & 61.63 & 49.63 & 43.01 & 1.433 & \(-\)0.561 & 3.110 \\ No. 3 Gray sample & 45.02 & 39.02 & 36.39 & 1.237 & \(-\)0.254 & 0.727 \\ No. 4 Gray sample & 63.45 & 51.45 & 41.35 & 2.972 & \(-\)0.517 & 1.938 \\ Average & 58.34 & 47.59 & 38.97 & 1.861 & \(-\)0.406 & 1.749 \\ \hline No. 1 Cinerous sample & 22.41 & 19.41 & 32.02 & 1.365 & \(-\)0.114 & 1.137 \\ No. 2 Cinerous sample & 53.93 & 30.77 & 32.49 & 2.047 & \(-\)0.169 & 0.609 \\ No. 3 Cinerous sample & 70.19 & 68.19 & 64.34 & 1.091 & \(-\)0.204 & 0.683 \\ No. 4 Cinerous sample & 69.17 & 57.55 & 38.06 & 1.373 & \(-\)0.930 & 0.487 \\ Average & 53.93 & 43.98 & 41.72 & 1.469 & \(-\)0.354 & 0.927 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mechanical parameters for vertical loading. Figure 5: Stress\(-\)strain curves under parallel loading: (**a**) Gray samples; (**b**) Cinerous samples. The stress-strain curves in the damage accumulation stage (stage III) demonstrate an increase in yield after elastic deformation due to the expansion of partial pores caused by compression. The stress concentration between weak surfaces leads to an accumulation of damage to the rock samples, which intensifies the propagation of new fragments [15,16]. The overall stiffness is gradually reduced due to an increase in the deterioration degree of rock samples. There is a significant difference in the yield shape of stress-strain curves between vertical loading and parallel loading, which is related to the difference in the structural expansion mechanism of slate samples. The low bedding cohesion causes the fragments and original defects to quickly penetrate when the load is parallel to weak surface structures, which is manifested as the rapid development of damage deformation. The superimposed slate is segregated into thin slices and the slate samples with lower strength show buckling failure [23]. Significant lateral deformation causes the volumetric stress-strain curve to deviate from the original development trajectory, resulting in multiple inflection points. The hoop deformation due to parallel loading is greater than the axial deformation due to further increases in axial stress. A weak surface structure gradually plays a leading role in the overall deformation, and the rock body shows a significant expansion [24]. However, the yield deformation curve due to vertical loading has a trend opposite that of parallel loading. In this study the slate samples entered a failure stage as the axial stress was increased significantly. The internal cracks gradually penetrated and began to rupture. Cracks developed rapidly to form macroscopic fracture surfaces, the rock samples showed structural dislocation, and the bearing capacity of the samples decreased rapidly. The strain gauges underwent sudden failure and were therefore unable to obtain post-peak stress-strain data. Therefore, only the pre-peak stress-strain curves could be obtained from the stress-strain data coupling system.