Onset of pore collapse and dilatancy in porous sandstone under true triaxial compression: Experimental observation and micromechanical modeling

We present new true triaxial compression data obtained in the ductile regime on Bleurswiller sandstone. The deformed samples show a range of failure modes qualitatively similar to what was reported by earlier experimental studies performed in conventional conditions (axisymmetric compression). In particular, visual inspection and X-ray Computed Tomography imaging reveal compaction localization in all our deformed samples. The pore collapse model of Zhu et al.( 2010) 1 is extended to include the role of the intermediate principal stress and our new data for the onset of shear-enhanced compaction are in basic agreement with this extended model that includes three stress invariants. Published true triaxial data obtained in the brittle regime highlights the impact of the intermediate principal stress on the onset of dilatancy. The predictions of the conventional sliding wing crack model extended to true triaxial conditions are in poor agreement with these data. Another energetic approach pioneered by Wiebols & Cook shows a better agreement with the experimental results. Our new data and analysis will help the interpretation of inelastic deformation under polyaxial compression in various geotechnical and tectonic settings.