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

Abstract

Flysch materials are one of the most challenging geological materials and often give rise to slope 15 instability problems. Due to its natural heterogeneity, geomechanical characterization of Flysch 16 materials is somewhat difficult. The Spanish Basque Arc Alpine region is a very well-known 17 location for flysch materials. In this paper, an area of approximately 100 km 2 in the region is 18 intensively studied and their flysch materials geomechanically characterized. A total of 33 locations 19 are investigated by a broad geological-geotechnical investigation, involving petrographic analyses, 20 geomechanical stations, boreholes and mechanical laboratory tests. In addition, a slope inventory 21 was carried out to assess the situation in the existing slopes in the area. Characterization of 22 materials is carried out in terms of RQD, RMR and GSI as well as using the Hoek-Brown failure 23 criterion. Different correlations are assessed, establishing their appropriateness for estimating the 24 mechanical parameters of a flysch material rock mass.

Discontinuities Characterization and Estimation of the Geological Strength Index by AI Tools on Flysch Materials

“…This tectonic arc is affected by NW-and NE-directed thrust faults, sub-vertical strike-slip faults and NW-SE oriented major folds, which are represented by the Bilbao anticlinorium, the Biscay synclinorium and North-Biscay anticlinorium from south to north [35]. Modified from [6,35].…”

“…The Meso-Cenozoic basin is overlain by Quaternary fluvial and colluvial deposits (Figure 2). Modified from [6,47].…”

“…A total of 124 undisturbed rock samples were collected for various laboratory tests, including uniaxial compressive strength, point load, Brazilian and triaxial tests [6]. Direct shear tests were conducted to determine the angle of friction for rock joints.…”

“…In Spain, flysch formations can be found in the Basque Arc, an area geologically belonging to the Basque-Cantabrian Basin, an inverted Mesozoic extensional basin, connecting the Pyrenees in the East and the Cantabrian Mountains in the West. In previous research [6], the authors studied such flysch materials, in particular the ones found in an area of approximately 100 km2 around the town of Astigarraga (Basque Country, Spain). That work aimed at characterizing the rock mass following the classification proposed by Morales et al [7].…”

Proposal of a new method for calculating GSI

“…These systems are based on tests and field obser-_________ vations (Rodríguez et al 2018;Hassanpour et al 2022;Sachpazis 1986). This classification is essential for mining engineering and to contributes to the development of geotechnical applications, for which the classification systems RMR, MRMR, Q, GSI, among others, have been proposed, and whose purpose has been to contribute to the improvement of the stabilities of natural and anthropic constructions (Garzón-Roca et al 2021).…”