## 2 Materials and Methods
### Development of a Quantitative Method for Disturbance Factor on the Excavated Slope Face
Large-scale open-pit mine slopes, however, experience significant disturbance due to intensive production blasting and stress relief from overburden removal (\(D_{f}\) = 1.0). The first description of rock mass refers to small-scale excavation in civil engineering slopes, while the second pertains to large, multi-benched excavation slopes exposed to stress relief from overburden removal, such as those found in open-pit mines. The disturbance in the rock mass due to the excavation method is most pronounced at the initial stage of excavation, when the excavation surface is still close to the original topographic surface. As excavation depth increases, the effects of stress relief on the slope face become more dominant. It can be more clearly understood that the disturbance in the rock mass, resulting from stress relief, is directly related to the vertical overburden load from the original topography on the excavation surface. Considering the first description of the rock mass with disturbance factors on the slope face, the lowest disturbance factor on the slope face (\(D_{f}\)) of 0.5 for small-scale slope excavations corresponds to an \(EPI_{o}\) value of 80, which defines the lower boundary of blasting. A disturbance factor of \(D_{f}\) = 1 was used for the highest \(EPI_{o}\) value of 100. To connect these two data points between \(EPI_{o}\) and \(\mathrm{D}_{t}\), a linear relationship was used, as shown in Figure 3. For the excavation operation, which is expected to cause minimal damage to the rock mass, \(D_{f}\) = 0.5 is accepted when \(EPI_{o}\) is less than 80. The relation between \(EPI_{o}\) and the disturbance factor, especially for small-scale civil engineering slopes or for benches close to the top elevation of very large multi-benched excavation slopes where stress relief is negligible, was named the base disturbance factor relation and denoted by \(D_{b}\). The thickness of the overburden removal (\(h_{r}\)) was assumed to be 10 m or less for small-scale excavated rock mass slopes exposed to negligible stress relief. A similar procedure was followed for deriving the power-type relationship between \(EPI_{o}\) and \(D_{f}\) for slopes exposed to stress relief, depending on the thickness of the overburden removal, particularly in the excavation of very large slopes. This relation was denoted by \(\mathrm{D}_{u}\). For this purpose, the lowest \(D_{f}\) value of 0.7 was taken instead of 0.5, corresponding to an \(EPI_{o}\) of 40, which defines the boundary between weak and hard ripper. To reflect stress  
Figure 3: Developed procedure for determining \(D_{f}\) related to excavation damage and stress relief from overburden removal using \(EPI_{o}\). relief with depth for large-scale excavated rock mass slopes on disturbance, the disturbance factor of the rock mass was increased proportionally above \(D_{b}\) until the overburden removal thickness reaches 100 m or more. In other words, \(h_{r}\) varies between 10 m and 100 m, with proportional interpolation between the \(D_{b}\) and \(D_{u}\) relations. The graphical representation of the developed procedure, including Equations (18)-(21), is shown in Figure 3.  
\[D_{b}=0.025 EPI_{o}-1.5 \tag{18}\]  
\[D_{u}=0.005 EPI_{o}+0.5 \tag{19}\]  
\[D_{f}=D_{b}+\Delta D \tag{20}\]  
\[EPI_{o}=EPI_{opt}+\Delta EPI \tag{16}\]0  
Two slope excavation cases presented in Figure 4 were compared to each other, considering the overburden thickness on multi-step deep excavation slopes with identical geometry, in order to better understand the disturbance of the rock mass due to stress relief from the overburden removal. Let us assume the same excavation method is used for both cases. As shown in Figure 4, the disturbance of the rock mass due to stress relief is expected to be nearly identical for the bench face at the highest elevation of the overall slope profile, as the thicknesses of the overburden removal in both cases are almost the same. However, the overburden removal thickness in case 1 is greater than in case 2, with an increase in excavation depth.