Geotechnical study in Horta de Sant Joan

In Horta de Sant Joan, soils are mainly composed of sandstones, conglomerates and flysch, accompanied by infrequent formations of gypsum, anhydrite and salts, with a limited deposit of compact gravels and sands. These lithologies provide a generally favourable bearing capacity for buildings, thanks to their rocky and stratified nature, although the occasional presence of gypsum and salts can locally compromise stability due to dissolution processes, and the low occurrence of silts or peats reduces the likelihood of severe differential settlement in the foundations.

Seismic activity in the area is very low, with only 3 recorded events over 30 years and a maximum magnitude of 1.9, which minimises the design requirements regarding seismic ground movements. However, given the potential for karstification in the substrate, it is essential to carry out a specific check for cavities or instabilities before designing foundations. In addition, the absence of clayey soils rules out the risk of expansivity; therefore, the main factor to consider is the prior assessment of karst phenomena and the local analysis of gypsum and salts with respect to dissolution processes.