Geomechanical characterization and analysis of the Upper Cretaceous flysch materials found in the Basque Arc Alpine region

Flysch materials are one of the most challenging geological materials and often give rise to slope instability problems. Due to its natural heterogeneity, geomechanical characterization of flysch materials is somewhat difficult. The Spanish Basque Arc Alpine region is a very well-known location for flysch materials. In this paper, an area of approximately 100 km2 in the region is intensively studied and their flysch materials geomechanically characterized. A total of 33 locations are investigated by a broad geological-geotechnical investigation, involving petrographic analyses, geomechanical stations, boreholes, and mechanical laboratory tests. In addition, a slope inventory was carried out to assess the situation in the existing slopes in the area. Characterization of materials is carried out in terms of RQD, RMR, and GSI as well as using the Hoek–Brown failure criterion. Different correlations are assessed, establishing their appropriateness for estimating the mechanical parameters of a flysch material rock mass