Stereological analysis of fractures in the Roselend tunnel and permeability determination

Abstract

Fracture traces and water fluxes have been determined along the 128 m long Roselend tunnel (French Alps). Fractures can be classified into two families: large fractures which intersect the tunnel and small fractures which partially intersect it. Three different zones in the tunnel are distinguished with mild, low, and high water fluxes, starting from the entrance. A stereological analysis of the trace length probability densities of small fractures provides the fracture diameter probability density distribution which is best approximated by a power law. Large fractures are assumed monodisperse, with a 5 m estimated radius. The generated fracture networks obtained by combining large and small fractures do percolate, while networks consisting of only small fractures do not percolate. Computed macroscopic permeabilities of the fracture networks are in agreement with the observed water fluxes when the fracture permeability is a power law of its lateral extent with an exponent equal to 3.