# Slope Stability Analysis of Open-Pit Mine Considering Weathering Effects
## 2 Laboratory Tests of Weathering Effects
### Mechanical Properties Test Results
Based on this linear relationship, the cohesion and internal friction angle of black shale were calculated. Generally, as the weathering time increased, the cohesion and internal friction angle of the black shale tended to decrease gradually. This decrease in shear strength can be attributed to the weakening of the rock matrix due to weathering processes. Weathering leads to the breakdown of mineral grains, resulting in the formation of cracks and pores within the rock structure. The cracks and pores reduce  
Figure 3: The failed specimens: (**a**) Brazilian splitting test, (**b**) uniaxial compression test, and (**c**) direct shear test. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Weathering** **(Days)**} & \multicolumn{2}{c}{**Specimen**} & \multicolumn{2}{c}{**Uniaxial Compression**} & \multirow{2}{*}{**Elastic Modulus**} & \multirow{2}{*}{**Poisson’s Ratio**} \\ \cline{2-2} \cline{5-6}  & **Diameter (mm)** & & & & \\ \hline
0 & 47.22 & 95.44 & 66.48 & 13.29 & 0.160 \\
7 & 47.18 & 95.80 & 39.51 & 4.70 & 0.295 \\
14 & 47.26 & 96.26 & 24.25 & 4.34 & 0.339 \\
21 & 47.04 & 94.46 & 15.29 & 3.92 & 0.379 \\
28 & 47.12 & 95.08 & 10.09 & 3.55 & 0.408 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The uniaxial compression mechanical parameters of black shale at different weathering times. the effective contact area between the grains, thereby decreasing the shear strength of the rock. A comprehensive set of physical and mechanical parameters was obtained through laboratory tests, which included uniaxial compressive strength, elastic modulus, Poisson's ratio, uniaxial tensile strength, cohesion, and internal friction angles, as detailed in Tables 5 and 6. Additionally, the determination coefficients for each correlation function are also provided. The uniaxial tensile strength, uniaxial compression strength, and cohesion of the rock specimens exhibited a negative exponential relationship with weathering time. This indicates that as the weathering time increased, these mechanical properties decreased The modulus of elasticity demonstrated a negative quadratic relationship with weathering time, suggesting a decrease in stiffness over time. Conversely, the Poisson's ratio exhibited a positive quadratic relationship with weathering time, indicating an increase in lateral deformation relative to axial deformation. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Weathering (Days)** & **Fitting Results** & **Correlation Coefficient (R2)** & **Cohesion** & **Internal Friction Angle** \\ \hline
0 & y = 0.9086x + 3.2702 & 0.9999 & 3.28 & 42.22 \\
7 & y = 0.9298x + 1.6042 & 0.9611 & 1.60 & 42.92 \\
14 & y = 0.8398x + 1.0663 & 0.9941 & 1.07 & 40.02 \\
21 & y = 0.7849x + 0.6717 & 0.9946 & 0.67 & 38.10 \\
28 & y = 0.7368x + 0.3809 & 0.9977 & 0.38 & 36.41 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Cohesion and internal friction angle at different weathering times. Figure 4: The direct shear testing parameters at different weathering times. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Weathering (Days)** & **Uniaxial Tensile Strength (MPa)** & **Uniaxial Compression Strength (MPa)** & **Elastic Modulus (GPa)** & **Poisson's Ratio** & **Internal Friction Angle** & **Cohesion (MPa)** \\ \hline
0 & 9.82 & 66.48 & 13.29 & 0.160 & 42.22 & 3.28 \\
7 & 6.91 & 39.51 & 4.70 & 0.295 & 42.92 & 1.60 \\
14 & 5.09 & 24.25 & 4.34 & 0.339 & 40.02 & 1.07 \\
21 & 4.02 & 15.29 & 3.92 & 0.379 & 38.10 & 0.67 \\
28 & 2.98 & 10.09 & 3.55 & 0.408 & 36.41 & 0.38 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Mechanical properties of black shale obtained from laboratory tests. The correlation functions derived between weathering time and mechanical properties offer profound insights into deleterious effects of weathering on rocks. As the degree of weathering intensified, the elastic modulus of the rock diminished, indicating a heightened susceptibility to deformation under external forces.