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2020-06-14 - Colloque/Article dans les actes avec comité de lecture - Anglais - 8 page(s)

Wattier Marie-Laure , Vandycke Sara , Gonon Maurice , Descamps Fanny , Mohammad Samir, Wertz Paul, Tshibangu Katshidikaya , "Roughness indices determination for fracture surfaces in Luxemburg Sandstone" in ISRM International Symposium Eurock 2020, 8, Trondheim, Norvège, 2020

  • Codes CREF : Géologie (DI1411), Mécanique des roches (DI1418), Essais non destructifs (DI2832), Déformation, rupture matériaux (DI2113)
  • Unités de recherche UMONS : Génie Minier (F408)
  • Instituts UMONS : Institut de Recherche en Science et Ingénierie des Matériaux (Matériaux)
  • Centres UMONS : Ingénierie des matériaux (CRIM)
Texte intégral :

Abstract(s) :

(Anglais) This study is a computation of fracture roughness indices for a series of subvertical joints and faults in ‘Luxemburg Sandstone’ rock mass within a well-identified geological context complemented by general description of the sandstone, combining on-site work and rock mechanics lab testing. The selected fractures in this Lower Lias, Hettangian-aged rock were all representative of the general tectonic system affecting the rock mass as observed in central Luxemburg. For comparison, identical roughness computation methods were conducted on lab-generated fractures in cylindrical samples of the sandstone. Fracture roughness was computed from laser surface topography acquisition every 172μm. Large sets of natural and lab-generated surfaces cover both shear and tensile modes. The roughness indices computed are: average asperities height (Ra and associated σa), Z2 root-mean-square (RMS) value, fractal dimensions Dvar (semi-variogram) and Dyard (yardstick rule). This was complemented by comprehensive background information issued from field work - taking into consideration the main structural directions and including key petrophysical properties. The Luxemburg Sandstone presents fair porosity (18%), matrix permeability of 17mD with intense fracture networks, combined to a moderate to strong mechanical behaviour (56MPa unconfined compressive strength). Due to a coastal-type depositional environment, the sandstone reveals compositional differences between calcarenite and sandstone sensus stricto. Studied natural samples present computed roughness indices as follow: Ra= 0.020mm (σa= 1.222), Z2= 0.46, Dvar= 1.36, Dyard= 1.0080. Lab-generated fractures give the following indices: Ra= -0.039mm (σa= 0.818), Z2= 0.34, Dvar= 1.37, Dyard= 1.0047. Natural surfaces present higher computed values than lab-generated fractures, whether sheared or produced in tensile mode.