# Slope Stability Analysis of Open-Pit Mine Considering Weathering Effects
## 3 Numerical Simulation of Slope Stability Analysis
### Weathering Assessment Results  
The computational model established for slope stability analysis was tailored to reflect the specific geological conditions. The model dimensions were approximately 900 m \(\times\) 360 m, and it was discretized into 170 \(\times\) 66 grids. In the real mining operations, the open-pit slope is excavated down to the current level of 2080 m, resulting in a slope height of 50 m. Subsequently, the slope is further excavated to the next stage, increasing its height to 90 m. This process continues, with the slope advancing to subsequent stages and ultimately reaching a height of 120 m. Therefore, to assess the slope stability under varying conditions, simulations and calculations were conducted using slope heights of 50 m, 90 m, and 120 m. These calculations were performed for slope angles of both 45\({}^{\circ}\) and 47\({}^{\circ}\), taking into account the mechanical properties of the rock mass at different weathering degrees. For each step height, a detailed analysis was conducted to evaluate the slope stability at both slope angles, incorporating the varying mechanical parameters associated with different weathering degrees. As an illustrative example, the calculated results for a slope height of 50 m, slope angles of 45\({}^{\circ}\) and 47\({}^{\circ}\), and a weathering time of 28 days are presented in Figures 6 and 7.  
Figure 5: Constitutive model and material division in the mining areas.  
Figure 6: Calculated results for slope height of 50 m at angle of 45\({}^{\circ}\).  
Regarding the horizontal displacement of the slope surface, a gradual decrease was observed. At the slope's apex, the horizontal displacement was directed positively along the  
Figure 7: Calculated results for slope height of 50 m at angle of 47\({}^{\circ}\).  
\(x\)-axis. However, as the slope extended downwards, the influence of excavation activities was equal to the displacement, resulting in negative values. This indicated a higher degree of deformation and damage at the slope's base. When comparing slopes with angles of 45\({}^{\circ}\) and 47\({}^{\circ}\), an increase in the final slope angle led to an elevation in horizontal stress on the slope surface. To assess the slope's stability, the distribution of plastic zones was analyzed to identify failure-prone areas. It was evident that in the initial excavation stages, prior to weathering of the black shale, there was no discernible presence of plastic zones on the slope surface or within its interior. However, as the weathering process advanced, the extent of plastic zones both on the slope surface and within its depths began to gradually expand. Consequently, the areas susceptible to shear and tensile failures within the slope also increased in scope.  
Regarding the impact of weathering effects, it was observed that in the initial stages of weathering, a distinct range of shear and tensile failure areas had already emerged within the slope. At slope angle of 45\({}^{\circ}\), during the early weathering, there was no evidence of plastic failure either on the slope surface or within its interior. However, at the weathering duration of 28 days, extensive plastic zones had developed within the slope, and the slope also exhibited widespread plastic deformation. This underscores that in the later stages of black-shale weathering, the material in its weathered state is susceptible to plastic failure. Comparing the plastic-zone distributions of slopes with angles of 45 and 47, it was evident that as the slope angle increased, the extent of the plastic zone on the slope surface gradually enlarged. The areas of stress, strain, shear failure, and tensile failure within the slope progressively expanded, potentially forming a contiguous zone across the slope surface and interior. Given that the strength of the black shale was significantly reduced after 28 days of weathering, it is advisable to implement appropriate support measures for the exposed slope.