4D synchrotron X-ray imaging of multiscale failure and compaction localization in triaxially compressed porous limestone
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AbstractAn understanding of the failure and strain localization in a porous rock is of fundamental importance in poromechanics and rock physics. Confined compaction experiments on porous limestones and sandstones have revealed a broad spectrum of failure mode. Techniques such as acoustic emission (AE) location and velocity tomography provide kinematic information on the partitioning of damage and localization of strain. Complementary observations on deformed samples using microscopy and microcomputed tomography (CT) can also be used to image microscale damage and its distribution. Only by synthesizing such measurements on multiple scales could one infer the multiscale dynamics of compaction localization and similar rock failure phenomena.
Located at the European Synchrotron Radiation Facility (ESRF beamline ID19), the HADES rig is a miniature triaxial rig that is transparent to the high flux of X-rays produced by a synchrotron, which allows direct in situ 3D imaging of the whole rock sample as it is subjected to increasing differential stress, at confinement up to 100 MPa and pore pressure up to 100 MPa. With a spatial resolution of 6.5 m, the microCT data provide an integrated perspective of the spatiotemporal evolution of damage and strain localization on scales ranging from grain to continuum.
We conducted an experiment on Leitha limestone (with an initial porosity of ~22%) at a confining pressure of 20 MPa. With increasing differential stress, the sample strain hardened and two distinct yield points can be identified in the stress-strain curve. Given the relatively simple mineralogy (basically all calcite) the CT images can readily be segmented into solid grains and pore space. The spatiotemporal evolution of local porosity and damage were analyzed at multiple scales. At an intermediate scale of 10 voxels (65 m), the time-lapse microCT images reveal the strain partitioning associated with the first yield point and development of strain localization with the second. The latter development of three discrete compaction bands is the first unambiguous observation of such a bifurcation phenomenon in a porous carbonate rock, with geometric attributes comparable to compactions bands observed in porous sandstones. The CT data on the voxel scale elucidate in refined details the nucleation and propagation of a discrete compaction band under quasi-static loading, as well as the micromechanical processes, which in the past can only be inferred from a synthesis of kinematic observations of AE activity and post-mortem observations of microstructure and damage.
Acceptance Date20/12/2018
All Author(s) ListLingcao Huang, Patrick Baud, Benoit Cordonnier, François Renard, Lin Liu, Teng-fong Wong
Name of Conference5th International Workshop on Rock Physics
Start Date of Conference23/04/2019
End Date of Conference26/04/2019
Place of ConferenceHong Kong
Country/Region of ConferenceHong Kong
LanguagesEnglish-United States

Last updated on 2019-22-05 at 09:56