Geotechnical study in Foios

In Foios, the dominant geological substrate is mainly composed of fine sands and silts, accompanied by gravels and compact sands. These materials usually provide good bearing capacity, although their local compactness and stability must be verified through in situ tests to underpin an appropriate foundation type selection. Limestone, dolomite and marble formations, although infrequent, may indicate the presence of more competent ground locally, especially if deep foundations are considered. The high permeability associated with prominent aquifers in the area may also affect drainage and the possible regulation of groundwater levels—aspects that should be analysed for the safety and durability of the structure.

Seismicity in Foios is very low, with only 2 recorded events in the last 30 years and a maximum magnitude of 3.2, meaning the seismic risk is practically negligible in terms of structural design. However, due to the presence of limestone and dolomitic formations, it is essential to verify the existence of karst processes before carrying out any foundation, as voids or unexpected instabilities could occur. On the other hand, the non-clayey substrate rules out the risk of expansivity in the soils, so the main geotechnical constraint for the municipality is the need to rule out karst phenomena in the supporting ground.