# Monitoring and Data Analysis in Small-Scale Landslide Physical Model
## 2 Physical Model
### Rainfall Simulator  
One of the most important issues in the physical models that simulate landslide initiation and motion caused by rainfall infiltration is a full control of the intensities of artificial rainfall applied to slope models. Rainfall simulators are a widespread tool for studying hydrologic processes such as the interaction of rainfall with soil, soil erosion, surface runoff, and infiltration [35]. Although it was possible to use already-developed rainfall simulators [35; 36; 37], due to the lack of standard designs and necessity to develop a rainfall simulator adjusted for rainfall intensities characteristic for the precipitation events in Croatia, the rainfall simulator was constructed inside the project. The idea was to develop a rainfall simulator that could be used on a wide spectrum of soil materials from sand to silt and clay. As each material has a very different hydraulic conductivity and ability to infiltrate different amounts of water in the same period, a simulator that can cover all soil types had to be designed in adequate scale ratio. The artificial rainfall also should have sufficient spatial uniformity. Rainfall simulator system was constructed of three sprinkler branches, each branch consisted of four different axial-flow full-cone nozzles with spray  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Physical Properties of Soil** & **Symbol** & **Values** \\ \hline Specific gravity & \(G_{S}\) & 2.7 \\ Dry density & \(\rho_{d}\) (g/cm\({}^{3}\)) & 1.52 \\ Total density & \(\rho_{t}\) (g/cm\({}^{3}\)) & 1.55 \\ Effective particle size & \(D_{10}\) (mm) & 0.19 \\ Effective particle size & \(D_{60}\) (mm) & 0.37 \\ Uniformity coefficient & \(c_{u}\) & 1.947 \\ Minimum void ratio & \(e_{min}\) & 0.641 \\ Maximum void ratio & \(e_{max}\) & 0.911 \\ Hydraulic conductivity & \(k_{s}\) (m/s) & \(1\times 10^{-5}\) \\ Friction angle & \(\varphi\) (\({}^{\circ}\)) & 34.9 \\ Cohesion & \(c\) (kPa) & 0 \\ Initial porosity & \(n_{i}\) & 0.44 \\ Initial void ratio & \(e_{i}\) & 0.78 \\ Initial relative density & \(Dr_{i}\) & 0.5 \\ Initial water content & \(w_{i}\) (\%) & 2 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Basic physical properties of the Drava River sand built-in in the model and initial conditions at the start of the tests.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Segments** & & **Layers** \\ \hline
**Symbol** & **Dimensions (cm)** & **mT (kg)** & **Symbol** & **Layer Tickness (mm)** \\ \hline L (low) & 81/100/30 & 377.3 & L1 & 63 \\ M (middle) & 142/100/30 & 658.21 & L2 & 122.25 \\ U (upper) & 31/100/30 & 145.96 & L3 & 181.50 \\  & Total & 1181.47 & L4 & 240.75 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Details of sandy material build-up in the slope model.  
angle of 60\({}^{\circ}\). Each branch was placed at such a height as to allow water to reach the edges of the plexiglass sides without creating too much water at the edges or water coming out of the model. This solution covers a wide range of rainfall intensities, from below than 30 L/h/m\({}^{2}\) to above than 140 L/h/m\({}^{2}\) at the reference pressure of 2 bar. Wide range of rainfall intensities and possibility of changing location of rainfall by switching branches on/off gives the ability to model different rainfall patterns and different rainfall intensities applied to the slope model.