# Stabilization Methodology in Foundation Soils by ERT-3D Application in Estepona, South Spain
## 3 Case Study
### Approach Methodology: Application  
Had the proposed methodology not been applied in this case, the building could have been damaged to a critical point, making its repairs too expensive to pursue. Other, more invasive proceedings, such as underpinning through micropyles [5; 80; 81; 82], were not feasible due to the state of the building and the structural topology of the load-bearing walls. However, making consolidation injections into the subsoil allowed recovery, to a certain degree, of the differential settlement suffered and rendered the building useable again. The first necessary action involved using electrical tomography to analyze the subsoil beneath the affected foundations. In an initial campaign, this study accomplished various tests with spacings of 0.80, 1.00, and 1.50 m to identify the best resolution for checking the subsoil's state. A spacing of 0.80 m was chosen, based on another recent research [11]. The Syscal Switch 48 (V114 ++) from IRIS Instruments was used as electrical tomography equipment. It is a multi-electrode piece of equipment with an integrated computer capable of managing up to 900 electrodes, with resolution characteristics of resolution/accuracy:1 uV/0.2% [43]. The equipment power source is 250 W and 2.5 A, which generates 880 Vp-p pulses, and the manufacturer has incorporated a transmitter and receiver into the system. Among the equipment's features are a time injection adjustment, an apparent resistivity and chargeability automatic processor, a 3D real-time resistivity control, a voltage and current injection curve control, an integrated PC, and a commutation processor. The locations of the two topographies' parallel profiles (E1-E2) were shown via coordinates given by a GPS from Garmin Etrex Ventura [14], with a WG84 coordinate system. The results are listed in Table 3.  
In the developed methodology, two parallel profiles (E1 and E2) were selected, covering an area of approximately 240 m\({}^{2}\), which included the main affected building area in accordance with Figure 6 and Table 3. The electrodes were placed in parallel. building pathology. As discussed previously, an inter-electrode separation of 0.80 m was estimated as suitable for this methodology. The two profiles extended along 28 m, with 72 electrodes distributed according to the coordinates listed in Table 3 and Figure 6.  
Figure 7 shows a 3D electrical resistivity model from the studied terrain and the depths reached, in this case, up to 5.80 m depth. Both profiles show resistivity values represented in a range of colors for better and easier observation of the variations in subsoil vertical and horizontal resistivities. Zones with resistivity values between 0-55 \(\Omega\) m corresponded to levels of clay or colluvial material, represented in green; zones between 55-1000 \(\Omega\) m, shown in orange, corresponded to fillings or collu  
Figure 6: (**a**) Longitudinal scheme of the methodology and installation of the electrodes at 0.80 m in the building (house), as well as the subsoil analyzed with ERT -3D. The analyzed subsoil has a depth of 5.80 m, which corresponds to levels I and II of the geotechnical layers detected. (**b**) ERT -3D (TE1-3D) delimited tomography surface, covering the main building’s foundation structure, within the parallel profiles proposed: E1 and E2. Circles refer to the E1 profile, while squares refer to E2; orange refers to the initial UTM coordinates, while green refers to the final ones (Table 3). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Start UTM Coordinates of Tomography** & \multicolumn{2}{c}{**Final UTM Coordinates of Tomography**} \\  & **Profile E\({}_{1}\).** & & **Profile E\({}_{2}\).** \\ \hline
**X** & **Y** & **X** & **Y** \\ \hline
306,385 & 4,037,250 & 306,383 & 4,037,254 \\
306,403 & 4,037,262 & 306,388 & 4,037,281 \\ \hline \hline \end{tabular}
\end{table}