MICROSTRUCTURE OF SHEAR ZONES IN FONTAINEBLEAU SANDSTONE

Amine El Bied (1) , Jean Sulem (1) , François Martineau (1)

1 CERMES - Centre d'enseignement et de recherche en mécanique des sols

On the basis of image analysis, porosity and grain-size changes have been studied inside the shear bands formed in triaxial testing on a Fontainebleau sandstone. For this rock the shear band is characterized by a white coloration visible to the naked eye. It is obtained that for specimens tested under relatively low confining pressure (7 MPa), the porosity reaches a maximal value of about 30% inside the band and decreases rapidly towards the initial value of 21% outside the band. This is interpreted as dilating shear banding at low confining pressure. For specimens tested under relatively high confining pressure (28 MPa), a different patterning is observed. A compacting zone with high grain crushing and low porosity (values between 2 and 19 %) is observed in the center of the band. This zone is surrounded by a dilating one with grain cracking and high porosity (up to 36 %). These two zones correspond to the thickness of the white coloration as observed on the sample (i.e. the shear band). This shear band is surrounded by third zone with initial porosity and healthy grains.

Mots clés: Sandstone; shear-band; porosity; image analysis

Domaines: Mécanique des solides [physics.class-ph]; Mécanique des solides [physics.class-ph]; Géophysique [physics.geo-ph]; Géophysique [physics.geo-ph]; Milieux et Changements globaux

Amine El Bied, Jean Sulem, François Martineau. MICROSTRUCTURE OF SHEAR ZONES IN FONTAINEBLEAU SANDSTONE. International Journal of Rock Mechanics and Mining Sciences, 2002, 39 (7), pp.917-932. ⟨hal-00311338⟩