# Stabilization Methodology in Foundation Soils by ERT-3D Application in Estepona, South Spain
## 3 Case Study
### Approach Methodology: Application

Table 3: UTM coordinates of the tomography profiles; location of the profiles according to the distribution of Figure 6.  
compactness; and resistivity \(>\) 1000 \(\Omega\) m, in red, indicated anomalies due to the presence of interstitial gaps. Figure 7 shows resistivity anomalies presented in slices of subsoil supporting the foundation of the damaged building. The red color shows a higher resistivity value, up to 3000 \(\Omega\)m, which suggests that there are cavities causing the resistivity to rise. From the obtained resistivities, combined with the geotechnical data (SPT standards) [85; 86], the physicochemical properties of geological materials can be determined. The survey depth was established as 5.80 m, considering the previous geotechnical results of Table 1. From that depth, level III began to appear, determined by a rocky matrix of phyllite. The main anomalies were located on the main load-bearing walls, specifically A and B. The structure of the building had been seriously damaged by the seat of its foundation and the turning of the building, specifically in the main facade between pilasters and the main bearing wall (wall B). There were also apparent interstitial anomalies in the subsoil up to 3.90 m deep in the dielectric profile E2 (wall B), and 2.00 m in the dielectric profile E1 (wall A). The anomalies and settlement in the foundation of wall B (S2) were of greater importance than the settlement at the base of wall A (S1), with a characteristic angular distortion of \(\beta\) = 0.0086, hence the forward inclination of the building. In summary, according to the algorithm developed in Figure 6, the first phase of the tomographical campaign was carried out, by analyzing the resistivities of the subsoil supporting the building and considering previous data, including the initial geotechnical data. Anomalies and areas with low compaction and/or gaps were identified and isolated in ERT-3D for the building's main load-bearing walls (Figure 8), so this knowledge might be acted on in the future. Given the powerful information about the subsoil under the building's main load-bearing walls, the second phase of this methodology was proposed: consolidation injections into the subsoil for those detected anomalies (flow diagram, Figure 5). Figure 9 isolates the areas to be treated with injections via the RES3 DINV investment program. The damages observed in the analyzed building and the initial geotechnical tests confirmed the diagnosis from the ERT-3D tomography methodology. The initial ERT-3D results--that is, the application of the first phase of the flow chart (Figure 5)--showed high coincidence in the geological composition of the supporting subsoil beneath the damaged building: altered clay edges and coluuvial sand from the meterisation of the rock matrix (phyllite). This innovative intervention technique allowed the researchers to evaluate the induced effects in the field and, in light of them, carry out possible modifications in the distribution  
Figure 7: Advanced inversion algorithm of 3D synthetic data (RES3 DINV software). Electric Ground Section ERT-3D: cross-section diagram of the ground, with the probable behavior of the soil and foundation. Cross-section scheme, with the likely behavior of the soil and foundation. of injection points to consolidate the subsoil. In the procedure's second phase, after the injections in the anomalies were made, the ERT-3D contrast was repeated to check the consolidation results.