Geotechnical study in Santa Margalida

In Santa Margalida, soils of fine sands and silts predominate, accounting for almost two thirds of the near-surface materials. To a lesser extent, carbonate formations occur (limestones, dolomites and marbles), together with occasional occurrences of gypsum, anhydrite and salts. These materials, especially sands and silts, usually provide moderate bearing capacity, whereas the presence of gypsum implies attention to the risk of dissolution, which may affect the stability of foundations. Extensive aquifers with moderate permeability indicate the presence of groundwater, which may influence the choice of foundation depth and the protection against possible subsidence.

Seismicity in Santa Margalida is moderate, with 24 recorded events over 30 years and a maximum magnitude of 3,2, which does not represent a relevant structural constraint. The possibility of karst development in the limestone and dolomite strata should be verified by means of a specific geotechnical study prior to any foundation project, in order to rule out or identify underground cavities that could compromise safety. As the bedrock is formed essentially by non-clayey materials, the risk of expansivity is ruled out. As the main factor to analyse, the possible development of karstification stands out, along with the risks associated with the dissolution of gypsum and salts.