Geotechnical study in Istán

In Istán, the geotechnical substratum is predominantly made up of sandstones, conglomerates and flysch, which reach approximately 41% of the area, followed by shales and schists at 31%. In general, these lithologies are compact and exhibit low deformability, which supports the ground’s bearing capacity. Igneous formations, such as granite and gneiss, as well as outcrops of limestones, occur occasionally and, in isolated spots, may provide very favourable conditions for shallow or deep foundations, although the general impermeability of the ground will be a factor to take into account in hydrogeotechnical performance.

Seismicity in Istán is classified as moderate, with 13 recorded events over the last 30 years and a maximum magnitude of 3.8; therefore, seismic constraints are usually manageable and do not pose a severe restriction when drafting the geotechnical study. Nevertheless, the presence of carbonate materials suggests a possible karst morphology, so a specific investigation of karst is essential before carrying out any type of foundation, as this may involve the risk of voids or localised subsidence. The absence of clayey soils eliminates the risk of expansivity in the area; accordingly, the main geotechnical design factor is verifying the possible presence of karstic cavities in areas where limestones and dolomites occur.