Geotechnical study in Baztan

In the municipality of Baztan, ground conditions are predominantly composed of slates and schists, which make up the greater part of the subsoil, occasionally accompanied by sandstones, conglomerates, flysch and, to a lesser extent, limestones and dolomites. These materials usually confer a medium bearing capacity on the ground, although the local presence of fine sands and silts can reduce the load-bearing capacity and require specific characterisation in those areas. The dominant formations, which are impermeable or have low permeability, require a detailed analysis to determine the suitability of the foundation type; it is common to use shallow foundations on the firm substratum when it outcrops at little depth.

The seismicity in Baztan is classified as notable, with 141 events recorded in the last 30 years, although the maximum magnitude observed (Mmax 3.7) does not imply demanding structural design criteria. However, given the significant proportion of limestones and dolomites, the potential presence of karstic phenomena is an essential constraint that must be verified precisely through a geotechnical study before any installation of foundations. The subsoil is not clayey, so the risk of expansivity is ruled out. In short, the possibility of karst cavities is the main factor to consider in the geotechnical analysis of this locality.