# Stabilization Methodology in Foundation Soils by ERT-3D Application in Estepona, South Spain
## 2 The Model Development
### Application  
Some results reported in the literature and obtained in the last eleven years regard the application of the ERT-3D method to study geotechnical anomalies in the subsoils on slopes after landslides located in different geographical contexts.Such reports make us consider the ERT method as a tool and methodology very suitable to investigate these geotechnical anomalies of the subsoil during the pre-event and post-event phases of a disaster cycle [30; 31; 59; 60; 61] or simply a poor foundation support subsoil (anthropic fill). In fact, during the pre-event phase, the resistivity contrasts that characterize ERT-3D allow defining the geological environment of the subsoil. They allow identifying areas of high-water content that could be responsible for reactivation events. In the post-event phase, ERT-3 Denablesus to reconstruct the damaged or altered subsoil body by also providing information on the volume of the removed or altered material. This information can help to better plan future mitigation activities. Our original application not only detects these subsoil alterations in real time, but we also propose an original tool for subsequent mitigation, in case of affecting existing buildings or infrastructure in a non-invasive way and thus preventing their collapse. One of the biggest drawbacks of 3D tomography for the investigation of shallow and disturbances in the subsurface was the fact that it did not provide continuous acquisitions over time, which made it unsuitable for the study of the dynamic nature of shallow and disturbances. Fortunately, the development of systems for the continuous acquisition of electrical resistivity time and software for data inversion [61] are paving the way to test this method during the emergency phase, such as the application and methodology developed in the present work, where in real time we are applying the geoelectric investment data and carrying out the consolidation of the subsurface area, increasing its resistivity in the emergency case, and thus being able to recover existing constructions in the altered subsoil. The possibility of using ERT-3D to monitor geotechnical changes and alterations in the first layers of a ground clearance-settlement area will add important information during the emergency phase. At this time, the preliminary results obtained in our methodology when applying the ERT-3D for this purpose are very encouraging. The proof of this is that we were able to recover the building that was based on the geotechnically altered substrate, where the grout cement, filler material proposed in our methodology for consolidating the subsoil, satisfactorily filled the gaps that water and air occupied in the altered substrate. Cement grout has advantages over other fillers, such as its economy, easy means of performing on site, ease of dosing, and versatility, among others. In applying our methodology in these cases of emergencies where there is a removal of surface soil after a shallow of the subsurface that affects buildings and infrastructures [62; 63], we have observed that a low resistivity zone lies in the upper area from the surface to a depth up to 4.00 m, and the zone shows a higher resistivity of greater than 400 \(\Omega\) m. According to the data obtained in this work, the upper area of the soil unit consists of mostly silt soil with granule from the erosion of the bedrock. Therefore, we thought that the anomaly in the upper area is attributed to the silt soil and granule with low resistivity. This zone of low resistivity coincides with the zone of removal and presence of water, which we consolidated with our grout cement filling methodology and in real time the monitoring was carried out to verify the satisfactory level of the landfill. The procedure followed by the authors clearly defines the altered surface material with cavities and gaps of the rocky matrix (phyllite) by lower resistivities in the bedrock (50-150 \(\Omega\) m).