Geotechnical study in Getxo

In Getxo, the dominant geological substrate consists of limestones, dolomites and marbles, representing more than 70% of the soils. These lithologies offer a high bearing capacity and stability for the direct foundation of buildings, owing to their compact, strong nature. Secondary formations, such as sandstones, conglomerates and flysch, occur occasionally and provide good mechanical conditions, while the occasional presence of made ground or loose materials requires caution in supporting studies to avoid differential settlements. In general, the low permeability of the rock materials limits underground flow, although local shallow aquifers associated with discontinuities or porous zones may exist.

The seismicity in Getxo, with 94 events over 30 years and a maximum recorded magnitude of 3.7, is considered notable; this implies the recommendation to assess seismic actions in the structural analysis, particularly for significant constructions. Since the substrate is not clayey, it effectively rules out the risk of expansivity for practical purposes. In the absence of karst development and given the predominance of hard rocks, the main factor to be assessed in local geotechnical studies is the identification of areas of loose materials or made ground and the possible presence of shallow groundwater levels that may influence foundation behaviour.