# Slope Stability Analysis of Open-Pit Mine Considering Weathering Effects
## 2 Laboratory Tests of Weathering Effects
### Mechanical Properties Test Results  
The weathering effects exerted a profound influence on the experimental outcomes of the Brazilian splitting test. The failed specimens in the Brazilian splitting tests, uniaxial compression tests, and direct shear tests are displayed in Figure 3. As detailed in Table 2, the average tensile strengths of black shale decreased gradually with the increase in weathering time. The integrity of the rocks was compromised by weathering, leading to an increase in microcracks and porosity within the rock matrix. This, in turn, diminished the overall strength of the rock. In the case of unweathered rocks, the Brazilian splitting test typically produced relatively smooth and flat fracture surfaces. However, weathered rocks exhibited irregular fracture surfaces due to the presence of internal microcracks and pores, resulting in multiple fracture planes. This phenomenon contributed to the increased dispersion of test results. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**ID**} & \multirow{2}{*}{
\begin{tabular}{c} **Weathering** \\ **(Days)** \\ \end{tabular} } & \multicolumn{3}{c}{**Number of Specimens**} \\ \cline{3-5}  & & **Brazilian Split** & **Uniaxial** & **Direct Shear** \\  & & **Tests** & **Compression Tests** & **Tests** \\ \hline
1 & 0 & 3 & 3 & 3 \\
2 & 7 & 3 & 3 & 3 \\
3 & 14 & 3 & 3 & 3 \\
4 & 21 & 3 & 3 & 3 \\
5 & 28 & 3 & 3 & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The design of the experimental programs. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Weathering (Days)**} & \multicolumn{3}{c}{**Specimen**} \\ \cline{2-3}  & **Diameter (mm)** & **Height (mm)** & **Tensile Strength** \\ \hline
0 & 47.08 & 23.6 & 9.82 \\
7 & 46.94 & 24.42 & 6.91 \\
14 & 47.36 & 24.12 & 5.09 \\
21 & 47.20 & 24.02 & 4.02 \\
28 & 47.26 & 23.96 & 2.98 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The average tensile strengths of black shale at different weathering times. Figure 2: Testing equipment: (**a**) uniaxial compressive strength test, (**b**) direct shear test, and (**c**) Brazilian splitting test. The uniaxial compression tests revealed that weathering significantly affected the compression properties of the rocks (Table 3). As weathering progressed, the uniaxial compressive strength and elastic modulus of black shale gradually decreased, while the Poisson's ratio gradually increased. The decrease in elastic modulus indicated that the rock became more susceptible to deformation under external forces. This is attributed to the gradual development of transverse and longitudinal cracks within the rock during the weathering process. These cracks weaken the structural integrity of the rock, leading to a reduction in its compressive strength and stiffness. The longitudinal cracks directly contribute to the decrease in uniaxial compressive strength of the specimen, while the development of transverse cracks accelerates radial deformation during the loading process. Consequently, the Poisson's ratio gradually increases with the increase in weathering time. This decline in strength can be attributed to the breakdown of mineral grains and the formation of microcracks and pores within the rock matrix. Furthermore, weathering enhances the deformability of rocks. Rock specimens with higher degrees of weathering exhibit greater strain under compressive loads compared with their less weathered counterparts. This enhanced deformability is primarily due to the softening of the rock matrix and the development of microcracks and pores. The mechanical properties of black shale obtained from direct shear tests at various weathering times are displayed in Figure 4. The test results demonstrate significant decreases in shear strength for the weathered rocks. During the direct shear tests, a linear correlation was observed between the deformation and the applied load, as summarized in Table 4. This linearity suggests that the rocks exhibited elastic behavior until they reached the point of failure.