## 3 Application to Resistive Driven-Rod Method: Testing with Some Examples
### Real Examples with Internal Resistance  
So far, only synthetic resistivity profiles have been considered in order to test the feasibility of the RDR method for recovering the soil structure when real electrodes and practical procedures are used. Next, some real cases corresponding to coarse sampling grounding resistance test will be analyzed. The data has been kindly provided by the INGESCO Lighting Solutions firm, located in Terrassa, Barcelona (Spain), for academic purposes. A real case that comes from the measurement of a soil located in Girona, Catalonia (Spain) is considered first. Five galvanized steel rods 1.5 m long and 9 mm radius are assembled as described previously and driven into the ground piece by piece, measuring each time the grounding resistance of the buried part. Measurement data are shown in Table 6.  
The parameters of the model obtained from the minimization procedure are \(\rho_{1}=105.78\)\(\Omega\)m, \(\rho_{2}=943.53\)\(\Omega\)m, \(\rho_{3}=36.71\)\(\Omega\)m, h\({}_{1}=2.01\) m, and h\({}_{2}=3.25\) m. Figure 8 shows by using diamonds markers the values on the Table 6. The red continuous line stands for the calculated grounding resistance from the solution. In the subfigure, the percentage error just defined as \(\epsilon_{R}=(R_{\mathit{meas}}-R_{\mathit{estim}})/R_{\mathit{meas}}\), where \(R_{\mathit{meas}}\) is the measured grounding resistance, whilst \(R_{\mathit{estim}}\) is the grounding resistance from the estimated soil model. Next, consider another real case from measurements of a soil located in Castelldefels, a region of Barcelona, Catalonia (Spain). As in the previous example, seven rods 1.5 m long and 8 mm radius are assembled and driven into the ground piece by piece, measuring each time the grounding resistance of the buried part. Measurement data are shown in Table 7.  
The parameters of the model obtained from the minimization procedure are \(\rho_{1}=80.28\)\(\Omega\)m, \(\rho_{2}=13.28\)\(\Omega\)m, \(\rho_{3}=14.54\)\(\Omega\)m, h\({}_{1}=2.39\) m, and h\({}_{2}=4.78\) m. Figure 9 shows by using dia \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**L (m)** & 1.5 & 3.0 & 4.5 & 6.0 & 7.5 \\ \hline
**R (\(\Omega\))** & 68.01 & 53.99 & 50.02 & 22.00 & 12.10 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Buried rod length L (m) and the corresponding measured grounding resistance R (\(\Omega\)) of the rod located in Girona. Figure 8: Measured and calculated grounding resistance in Girona. monds markers the values on the Table 7. The red continuous line stands for the calculated grounding resistance from the solution. In the subfigure, the percentage error defined as \(\epsilon_{R}=\left(R_{meas}-R_{estim}\right)/R_{meas}\), where \(R_{meas}\) is the measured grounding resistance, whilst \(R_{estim}\) is the grounding resistance from the estimated soil model. In this soil, a Wenner sounding has been carried out with the purpose of comparing the models resulting from the application of the two methods, namely the driven-rod method addressed in this paper and the method based on the apparent resistivity profile obtained from the Wenner sounding. The apparent resistivity profile is shown in Table 8.  
From data of Table 8, a three-layer resistivity model with parameters \(\rho_{1}=80.18\)\(\Omega\)m, \(\rho_{2}=104.12\)\(\Omega\)m, \(\rho_{3}=13.96\)\(\Omega\)m, h\({}_{1}=1.77\) m, and h\({}_{2}=0.44\) m has been obtained. Although this model is essentially different from the one obtained from Table 7, a simulation of RDR logging carried out with the obtained parameters gives a resistance profile very close to that shown in Table 7. This is a situation similar to that found in the synthetic model test of Figure 5. Again, the coarse sampling of resistance is at the origin of the differences. The most reliable model in this case is the one that comes from the Wenner sounding since there is a greater number of data involved preventing fine structures in the resistivity profile from being underestimated.