## 2 Experimental Methodology
### Testing Tank Dimensions  
The dimensions of the testing tank and its material were chosen to fulfil the following criteria.  
* The scale factor of 10 for simulation and dimensional analysis and to handle the material easily.
* The plane strain condition and minimum friction effect between the backfill soil and the sides of the testing tank.
* The pressure isobars of the strip footing extend laterally to almost two times the footing width, from the center line of the footing, and extend deeply to five times the footing width.
* The extent of the potential failure surface of slope stability analysis, using the slices method with no influence of tank boundaries on the tested elements: sand, nails, facing wall and the footing.
* The coefficient of the material friction is controlled by using the Perspex plates.
* A large ratio of width to height of the tank to minimize the effect of side wall shear stresses and consequently, reduce the active earth pressure.  
Considering the above criteria for the material and dimensions of the tank, an open frontal Perspex box measuring 1760 \(\times\) 850 \(\times\) 1000 mm was chosen as the experimental model. The loading system used in this research work is specially designed to prevent any disturbance to the experimental model and is shown in Figure 1. The loading system consisted of the loading frame, loading frame base and hydraulic loading system. The box contained the nailed slope of 2250 kg of dry sand and steel bar nails. The sand used in the slope model experiments was air-dried, clean, siliceous yellow sand. The physical and mechanical properties of the sand used are given in Table 1. The sand bed in the model was formed, using an automatic sand raining system to control the soil density.  
The thickness of the Perspex plate as a wall facing in the model was 5 mm to simulate the shotcrete facing with a thickness of 140 mm. A steel rigid plate of dimensions \(840\times 150\times 22\) mm thick was used as a footing to give distributed load on the soil. The properties of the facing and footing are given in Table 2. The diameter of the model nails was 5 mm to simulate the actual nail of diameter of 50 mm. The properties of the adopted nails were as follows.  
\begin{table}
\begin{tabular}{c c} \hline
**Property** & **Value** \\ \hline \% of clay & 0.00 \\ \% of silt & 1.33 \\ \% of fine sand & 39.17 \\ \% of medium sand & 58.63 \\ \% of coarse sand & 0.87 \\ \% of fine gravel & 0.00 \\ Effective diameter (D\({}_{10}\)) mm & 0.126 \\ Coefficient of uniformity (C\({}_{\text{u}}\)) & 1.99 \\ Coefficient of gradation (C\({}_{\text{u}}\)) & 1.00 \\ Specific gravity (G\({}_{\text{s}}\)) & 2.62 \\ Minimum unit weight (\(\gamma_{\text{min}}\)) (kN/m\({}^{3}\)) & 15.30 \\ Maximum unit weight (\(\gamma_{\text{max}}\)) (kN/m\({}^{3}\)) & 17.80 \\ Minimum void ratio (\(\epsilon_{\text{min}}\)) & 0.472 \\ Maximum void ratio (\(\epsilon_{\text{max}}\)) & 0.712 \\ Relative Density (D\({}_{\text{r}}\)) (\%) & 48 \\ Angel of internal friction (\(\phi^{\circ}\)) & 34 \\ Unit weight (\(\gamma_{\text{b}}\)) (kN/m\({}^{3}\)) & 16.41 \\ Void ratio (e) & 0.597 \\ \hline \end{tabular}
\end{table}
Table 1: Soil model properties.  
Figure 1: Sand filled tank and testing loading frame with base.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Plate Element** & **Material** & **Width (mm)** & **Thickness** & **Young’s Modulus** & **Bending Stiffness** & **Axial Stiffness** \\  & & **(mm)** & **(kN.mm\({}^{2}\))** & **(kN)** \\ \hline Footing & Steel & 150 & 22.0 & 21.2 \(\times\) 10\({}^{7}\) & 188,186.6 & 4665.78 \\ Facing & Perspex plate & 140 & 5.0 & 4200 & 0.04375 & 0.021 \\ \hline \end{tabular}
\end{table}
Table 2: Facing and footing plate properties.  
Young's modulus (E) = 21.2 \(\times\) 107 kPa; flexural rigidity (EI) = 6.51 \(\times\) 10\({}^{-3}\) kPa/m. Normal stiffness (EA) = 4165.9 kN/m; maximum tensile strength = 8.8 \(\times\) 10\({}^{5}\) kPa. Strains at ultimate stress = 7625; maximum tensile force = 17.36 kN.