Geotechnical study in Allande

In the municipality of Allande, the dominant geological substrate is mainly composed of slates and schists, which represent more than 80% of the ground. These lithologies are characterised by their low permeability, which considerably limits infiltration and the bearing capacity usually depends on fracturing and the degree of alteration of the rock. The foundation design in this type of ground must take account of the variability in strength and any associated shallow aquifers in altered zones, ensuring that adequate prior characterisation is carried out in order to select the most suitable foundation solution.

Seismicity in Allande is moderate, with 28 events over the last 30 years and a maximum magnitude value of 4,2, so it should be considered in the geotechnical risk assessment, although without severe requirements. Since the presence of karst has been indicated, it is essential to verify possible cavities or dissolution before defining foundation levels, as these may seriously compromise stability. The absence of expansive clays reduces concern regarding swelling-related problems. The main constraint in Allande lies in the detailed verification of karst processes and the heterogeneity of the metamorphic rocks.