## 4 Results and Discussion
### Simulation of the Effects of Rainfall Intensity on Slope Stability
#### 4.5.1 Simulation Case of a Clay Soil
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**FEM (SLIDE 2D)** & \multicolumn{2}{c}{**FoS in Sunny Conditions**} & \multicolumn{2}{c}{**FoS in Rainy Condition**} & \multicolumn{2}{c}{**FDM**} & \multicolumn{2}{c}{**FoS**} \\ \hline
**Slope Composition** & **Clay Slope** & **Silt Clay** & **Loam Clay** & **Clay Slope** & **Silt Clay** & **Loam Clay** & **Water Level** & **Clay Slope** & **Silt Clay** & **Loam Clay** \\ \hline Bishop’s simplified & 0.659 & 1.536 & 1.469 & 0.229 & 0.284 & 0.257 & & & \\ Janub’s Simplified & 0.612 & 1.424 & 1.364 & 0.203 & 0.264 & 0.228 & 1000 m\({}^{3}\) & 1.42 & 1.94 & 1.99 \\ Janub’s corrected & 0.643 & 1.497 & 1.434 & 0.221 & 0.284 & 0.247 & & & \\ Spencer & 0.760 & 1.675 & 1.610 & 0.231 & 0.306 & 0.257 & 1500 m\({}^{3}\) & 1.37 & 1.76 & 1.72 \\ Corp of Engineers’Number & 0.833 & 1.708 & 1.640 & 0.256 & 0.350 & 0.303 & & & \\ Corp of Engineers’Number & 0.894 & 1.717 & 1.654 & 0.263 & 0.340 & 0.327 & & & \\ Two & 0.731 & 1.636 & 1.572 & 0.246 & 0.297 & 0.327 & & & \\ Clo/Morgastern Price & 0.721 & 1.636 & 1.540 & 0.231 & 0.296 & 0.257 & 2500 m\({}^{3}\) & 0.79 & 1.20 & 1.25 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Simulated FoS of the slope using different methods. Simulations of the FoS Using SLIDE Model under Rainy Conditions in Clay Soil Slope  
Simulation scenarios similar in conditions to those in the previous section were set up. The difference is that this time, the clay soil typical to the Thulamela area was tested. The outcome of the simulation work is summarised in Figures 11-14. For all computational methods used, it can be seen that FoS values are all below 0.3 and range between 0.203 and 0.263. This means that the soil type is also prone to failure even under moderate raining conditions. In-situ observations support the simulation outcomes with evidence of multiple tension cracks around the area. In simple terms, clay soil slopes in the area do not require a lot of water pressure in order to collapse. Simulations of the FoS Using FLACSlope (FDM) Model under Sunny to Rainy Conditions in Clay Soil Slope  
Further simulations of FoS have been conducted using the Finite Difference Method (FLACslope), with reference to Figures 15-18. The simulation was performed in both sunny and rainy conditions, nevertheless, sunny conditions were simulated then followed by rainy conditions in which an increase in water table was implemented to identify the behavior of the slope with change in rainfall or extreme rainfall. The results of the simulations have revealed that during sunny conditions the simulated slope could be considered unstable with the FoS of about 1.42 (see Figure 15 and Table 5). It is crucial to indicate that this FoS gives the impression that the slope is not stable however the slope cannot be categorized as a collapsed slope yet. Nevertheless, the slope is actually closer to the border of stability. Therefore, it could be assumed that the slope is less stable in this condition. This brings us to discuss the results of the simulation in rainy conditions with the increase in the water table. With the reference to Figures 16-18, it was discovered that as the water table increases with time the FoS rapidly decreases (FoS range from 1.37 to 0.79) leading the slope to collapse. The results of the simulation correlate very well with the results simulated by finite element methods in rainy conditions (see Figures 16-18). Nevertheless, it has been revealed that the slope does not immediately collapse, but this failure of the slope seem to occur with time when the material is changing in phases (solid-like to liquid-like then solid-like) due to accumulation of water or increase in the water table. Arguably, the situation was addressed by several numerical techniques, meanwhile, the technique seems to fully agree to each other, therefore this gives an impression that the slope failure within Area A could have been highly influencing by the extreme rainfall.