Geotechnical study in Híjar

In the municipality of Híjar, soils of gypsum, anhydrite and salts predominate, accounting for almost 30% of the area, which implies a significant risk of dissolution processes that can affect both ground stability and the bearing capacity for shallow foundations. The complementary presence of sandstones, conglomerates and flysch favours areas with greater strength, suitable for supporting structures, whereas compact gravels and sands, although less frequent, can provide good local bearing capacity. It is essential to identify the distribution of these materials before defining any foundation system, as there is a potential risk of differential settlement, particularly over sulphate-bearing sedimentary soils.

Seismicity in Híjar is appreciable, with 65 recorded events over the last three decades, although the maximum documented magnitude (Mmax 3.5) is moderate and does not constitute a first-order structural constraint. The non-clayey substrate rules out the presence of clays with expansive behaviour, thereby minimising the risks associated with differential heave. It is important to highlight the possible existence of karstic phenomena, especially over gypsum and limestones; therefore, the verification of voids and ground stability must be incorporated without exception in the geotechnical study prior to any foundation. The most significant constraint is the incidence of soluble materials and associated karstic processes.