# Impact of Rock Mass Strength Anisotropy with Depth on Slope Stability Under Excavation Disturbance
## 4 Slope Stability Evaluations of a Hypothetical Slope Model
The factors of safety determined for criteria points 1 and 2 on the slope profile with the potential failure circles passing upwards along the slope profiles were given in Figures 6-11 for the six approaches considered in this study. The factors of safety determined for the drained condition and the static case by using the four approaches to the potential instability passing through the critical point 1 varies between 2.791 and 3.403 depending on the considered approach (Figure 12a. The factors of safety obtained from AP1 and AP3 were close, at 2.791 and 2.91, respectively, while higher factors of safety, above 3, were determined for AP2, AP4, AP5, and AP6. When the determined FOS values for critical point 2, which is important in terms of evaluating the stability of the mudstone, are evaluated, it is seen that the results are similar to the results belonging to critical point number 1. However, it is notable that the lowest safety coefficient was obtained with AP3 (Figure 12a). In addition to the drained condition, stability evaluations were also conducted when the pore water pressure ratio (r\({}_{\text{u}}\)) was set to r\({}_{\text{u}}\) = 0.2 (Figure 12b). Although the factors of safety decreased due to the pore water pressure, the distribution of the factors of safety based on the considered approaches remained similar to those in the drained condition. However, the factors of safety decreased to lower than the limit equilibrium conditions for AP1 and AP3 when critical point 2 was considered. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{2}{c}{**Limestone Rock Mass**} & \multicolumn{2}{c}{**Mudstone Rock Mass**} \\ \cline{2-5}  & **Description** & **Rating** & **Description** & **Rating** \\ \hline RMR (or GSI) & GSI = 45 & 5 & GSI = 30 & 10 \\ UCS (MPa) & 75 & 3 & 5 & 12.5 \\ Fore dipping structure & Not available & 0 & Not available & 0 \\ Back dipping (toppling) structure & Not available & 0 & Not available & 0 \\ Perpendicular (release) structure & Not available & 0 & Not available & 0 \\ Groundwater pressure & None & 0 & None & 0 \\ Controlled blasting & Not free & 7.5 & Mechanical excavation & \(-\)15 \\ \hline Confinement & Straight & 0 & Straight & 0 \\ \hline Total rating & & 15.5 & & 7.5 \\ \hline In situ stress ratio factor (k\({}_{0}\)) & Not determined & 1 & 1 \\ \hline Rock mass disturbance rating, DR & 15.5 & & 7.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Rock mass disturbance rating evaluation for limestone and mudstone masses (ratings with their descriptions of rock mass in DR classification proposed by [PERSON] et al. [10] are available on the website of [[https://www.researchgate.net](https://www.researchgate.net)]([https://www.researchgate.net](https://www.researchgate.net)) (accessed on 1 October 2024). Figure 6: The overall slope stability evaluations by considering the first approach (AP1). Figure 7: The overall slope stability evaluations by considering the second approach (AP2). Figure 8: The overall slope stability evaluations by considering the third approach (AP3). Figure 9: The overall slope stability evaluations by considering the fourth approach (AP4). Figure 11: The overall slope stability evaluations by considering the fourth approach (AP6). Figure 10: The overall slope stability evaluations by considering the fourth approach (AP5). In addition to the factor of safety against overall slope failure, another important consideration in hazard assessments of a possible slope failure is the volume of sliding material above the potential failure surface. When the results of the stability analysis of the four approaches considered in this study are evaluated from this perspective, it is seen that the highest amount of mass above the potential failure surface was obtained from the stability evaluations based on AP1 (Figure 13).