Geotechnical study in Doneztebe/Santesteban

In Doneztebe/Santesteban, substrates of slate and schist predominate, representing more than 85% of the local geology. These rocks, essentially impermeable, provide a bearing capacity generally adequate for construction, although occasionally they may present weakness surfaces associated with schistosity. The occasional presence of limestones, dolomites and marbles implies the possibility of encountering areas with variable mechanical conditions, where it is important to assess the ground homogeneity in order to correctly define the foundation type. Sandstones and conglomerates, although marginal, can offer points of higher permeability, but their impact on the works is usually limited owing to their scarce presence.

Seismic activity in the municipality is very low, with only 4 documented events over 30 years and a low maximum magnitude (Mmax 2.3), so seismicity does not represent a relevant constraint in structural design. However, the possible presence of karst phenomena associated with limestones and dolomites makes it necessary to verify the existence of cavities or dissolution before defining the foundation, as these can compromise the stability of the building. The non-clayey substratum rules out the problem of expansivity, so the main factor to control during the geotechnical study will be the characterisation and verification of the karst risk in areas with carbonate materials.