Geotechnical study in Oliana

In Oliana, substrates formed by sandstones, conglomerates and flysch predominate; these materials usually offer an adequate bearing capacity and competent behaviour for shallow foundations, provided that intervention on low-strength strata is avoided. Expansive clays, present only occasionally, may pose a localised risk, which makes it essential to characterise their exact extent during the geotechnical survey. On the other hand, the marginal presence of limestones, dolomites, marbles and gypsum implies that particular care must be taken regarding possible dissolution in areas with gypsum, anhydrite and salts, and in addition foundations should not be built on fine sands, silts and soft soils.

The seismicity recorded in Oliana is very low, with just three events over thirty years and a maximum magnitude of 2.5, so its impact on structural design is limited. However, the location of limestones and dolomites means it is necessary to investigate the possible existence of karst cavities before carrying out foundations, due to the inherent risk in this kind of ground. Added to this, the non-clayey substrate eliminates concern about expansivity. The factor requiring a more detailed assessment is the potential presence of karst and gypsum, since both condition the long-term safety of structures.