Geotechnical study in Santiago de Compostela

In Santiago de Compostela, the predominant subsoils mainly comprise slates and schists, metamorphic materials that cover more than 60% of the ground and that generally exhibit favourable bearing capacity, although it varies depending on local fracturing. Sandstones, conglomerates and flysch-type materials are also common, with mechanical characteristics likewise suitable for direct foundations under conventional loads, except where there are signs of alteration. Fine sands and silts are not very representative and only occasionally may have a negative influence if they are found at the surface. Widespread low permeability limits the circulation of groundwater, thereby favouring stability against differential settlement.

Seismic activity in the municipality is moderate, with 50 events in the last 30 years and a maximum recorded magnitude of 3.4, which implies low seismic influence in the structural design of buildings. There is no evidence of risks associated with karst processes, nor are any problems with expansivity detected, given that the subsoil is not clayey. Therefore, the main geotechnical consideration in Santiago de Compostela lies in the careful assessment of the near-surface alteration and fracturing of the rock during the investigation campaign.