Geotechnical study in Berastegi

In Berastegi, slate and schist soils predominate, characterised by their high abundance and competent behaviour, although they may show a certain foliation that is unfavourable for deep foundations. To a lesser extent, calcareous formations, dolomites, marbles, and small proportions of sandstones and gypsum are found. Slate and schist usually provide adequate bearing capacity for conventional use, but their low permeability can promote the development of areas with surface water or perched groundwater accumulations. The occasional presence of gypsum, anhydrite and salts entails a potential risk of dissolution, which must be carefully investigated when selecting the foundation level in order to avoid unexpected differential settlements.

Seismicity in the municipality is classified as moderate, with 19 events recorded over 30 years and a low maximum magnitude (Mmax 2.9), implying limited seismic risks in structural design. However, since karst is present, it is essential to verify the possible existence of cavities and karst-related phenomena before defining the foundation solution, especially in calcareous and dolomitic areas. In addition, the absence of clayey substrates eliminates the risk of expansiveness, simplifying the selection of foundations. The main geotechnical constraint in Berastegi is related to the risks of dissolution and potential voids associated with the presence of soluble and karstified materials.