## 4 Numerical Modeling: Validation  
The finite element numerical model of earth slopes is analyzed to judge the accuracy and validity of the experimental slope model results. The two-dimensional model of the nailed-soil slope is developed, using the finite element method-based PLAXIS software  
Figure 28: Influence of nail inclination on vertical stresses behind the nailed soil mass at mid height of slope.  
Figure 27: Influence of nail inclination on horizontal stresses behind the nailed soil mass at mid height of slope.  
because of the plane strain condition of soil slope. Four types of elements are used to model the sand, steel, and Perspex glass material. A nonlinear elastic (hyperbolic) model is used to simulate the sand material. The soil parameters used in the material model are given in Table 3. The discretized model of the soil slope with boundary conditions is shown in Figure 29.  
To verify the accuracy of the laboratory results, a numerical model of the nailed soil slope of height (H) of 700 mm is developed with the length of the horizontal nails as H and the vertical spacing of the nails as 0.4 H. The lateral or horizontal slope displacements are computed at the top, middle and bottom nail locations, i.e., at distances of Z = 70, 350, and 630 mm from the top surface. These distances are expressed as 0.1 H, 0.5 H, and 0.9 H. The results are taken at footing pressures of 0.0, 10.0, and 30.0 kPa. The plots of the computational and experimental results at different surcharge pressures, i.e., at the excavation stage and loading stage, are depicted in Figure 30.  
It is clear from the figures of horizontal slope displacements (D/H, %) that the maximum horizontal slope displacement occurs at a surcharge loading of 30.0 kN/m\({}^{2}\) in both the laboratory and numerical models. The maximum horizontal displacement occurs at the lower point of the slope in the numerical model, whereas it occurs at the middle point in the laboratory model during the excavation stage. In the loading stages, the maximum displacement is at the mid-point in both models. Moreover, the percentage of difference at maximum displacement ranges between 14.68% at surcharge loading of 30.0 kN/m\({}^{2}\) and 29.01% at 10.0 kN/m\({}^{2}\). It is inferred from the results that the trend of the behavior of the slope is almost the same in the experimental model and the numerical model.  
The settlement of the footing in the experimental model is also compared with numerical results of footing settlement at surcharge pressure of 0, 5, 10, 20, 30 kPa and Figure 31 shows the comparison of the footing settlement obtained in the experimental and finite element models. It can be seen from the figure that the maximum footing settlement occurs at a surcharge load exerting a foundation pressure of 30.0 kN/m\({}^{2}\) in both models. The  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Density** **(kN/m\({}^{3}\))**} & \multicolumn{3}{c}{**Mohr-Coulomb Model**} & \multicolumn{3}{c}{**Plastic Straining**} & \multicolumn{3}{c}{**Plastic Straining**} & \multicolumn{3}{c}{**Elastic Unload-**} \\  & & & & **Due to Deviator** & **Due to Primary** & **ing/Reloading** & **Dependent** \\ \cline{2-10}  & \(\varphi\) & C (kPa) & \(\psi\) & \(\upsilon\) & **Loading (E\({}_{\text{so}}\)) ref** & **Comp.-(E\({}_{\text{so}}\)) ref** & **(E\({}_{\text{so}}\)) ref** & **(E\({}_{\text{so}}\)) ref** & **Stiffness (m)** \\ \hline
16.41 & 34 & 0.2 & 4 & 0.31 & 1959 & 1959 & 5877 & 0.2 & 0.5 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Soil parameters of sand used in material model.  
Figure 29: Discretized model of slope.  
percentage of difference in settlement between the laboratory and numerical model ranges from 13.37% to 40.59%.  
Figure 30: Horizontal slope displacement.