## 3 Results Analysis
### Effect of Reinforced Oleander Root System on Slope Displacement  
The displacement contour maps considering vegetation root reinforcement for each rainfall condition are shown in Figure 6. The maximum displacements are presented in Table 4. It can be observed from Table 4 that regardless of whether vegetation root reinforcement is considered or not, the maximum slope displacement increases with increasing rainfall intensity. Rainfall intensity is one of the important factors to be considered in slope safety design. The surface layer of the slope is weathered and prone to hygroscopic expansion and desiccation cracking, resulting in numerous cracks on the surface. The permeability coefficient of the surface layer is relatively high. Rainwater erosion can easily lead to shallow instability of expansive soil slopes [29]. The saturation degree of the surface layer increases gradually with the increasing rainfall intensity, leading to a decrease in effective shear strength in the surface layer. As a result, the maximum slope displacement gradually increases. The root systems of vegetation form a chain reaction with soil particles [30], which enhances the shear resistance of the surface soil, restraining the upward movement of the zone where shear strength decreases. From a stress perspective, the maximum stress in a vegetation-reinforced slope is concentrated at the nodes where the vegetation roots are located. The vegetation roots enhance the shear strength of the soil by approximately three orders of magnitude, as shown in Table 5. The roots restrict the displacement of the surface soil layer, which is equivalent to increasing the cohesion of that layer and improved soil erosion resistance [31]. This forms a network reinforcement within the soil, improving the overall stiffness of the soil layer and reducing the displacement of the surface layer of the slope. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Without**} & \multicolumn{1}{c}{**Consider**} \\  & & & **Expansion** & **Expansion** \\ \hline
**Rainfall** & **Rainfall Intensity** & **Rainfall** & **Maximum** & **Maximum** \\
**Conditions** & **(mm/d)** & **Duration (h)** & **Displacement (m)** & **Displacement (m)** \\ \hline Condition 1 & 10 & 120 & \(1.947\times 10^{-4}\) & \(3.245\times 10^{-3}\) \\ Condition 2 & 30 & 120 & \(5.670\times 10^{-4}\) & \(1.151\times 10^{-2}\) \\ Condition 3 & 60 & 120 & \(1.223\times 10^{-3}\) & \(2.134\times 10^{-2}\) \\ Condition 4 & 120 & 120 & \(4.169\times 10^{-3}\) & \(3.907\times 10^{-2}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Maximum displacement calculation results with and without considering expansion. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Without**} & \multicolumn{2}{c}{**Consider**} \\  & \multicolumn{2}{c}{**Considering**} & \multicolumn{2}{c}{**Expansion**} \\ \hline
**Rainfall** & **Rainfall Intensity** & **Rainfall Duration (h)** & **Maximum** & **Maximum** \\
**Conditions** & **(mm/d)** & **Duration (h)** & **Displacement (m)** & **Displacement (m)** \\ \hline Condition 1 & 10 & 120 & \(3.245\times 10^{-3}\) & \(3.216\times 10^{-3}\) \\ Condition 2 & 30 & 120 & \(1.151\times 10^{-2}\) & \(1.139\times 10^{-2}\) \\ Condition 3 & 60 & 120 & \(2.134\times 10^{-2}\) & \(2.124\times 10^{-2}\) \\ Condition 4 & 120 & 120 & \(3.907\times 10^{-2}\) & \(3.941\times 10^{-2}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Maximum displacement with/without reinforcement considered. Figure 6: Displacement calculation contour plot with reinforcement considered (unit: m): (**a**) Condition 1, (**b**) Condition 2, (**c**) Condition 3, (**d**) Condition 4.