Brantut, Nicolas;
Petit, Leo;
(2022)
Micromechanics of rock damage and its recovery in cyclic loading conditions.
Geophysical Journal International
, 233
(1)
pp. 145-161.
10.1093/gji/ggac447.
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Abstract
Under compressive stress, rock ‘damage’ in the form of tensile microcracks is coupled to internal slip on microscopic interfaces, such as pre-existing cracks and grain boundaries. In order to characterize the contribution of slip to the overall damage process, we conduct triaxial cyclic loading experiments on Westerly granite, and monitor volumetric strain and elastic wave velocity and anisotropy. Cyclic loading tests show large hysteresis in axial stress–strain behaviour that can be explained entirely by slip. Elastic wave velocity variations are observed only past a yield point, and show hysteresis with incomplete reversibility upon unloading. Irrecoverable volumetric strain and elastic wave velocity drop and anisotropy increase with increasing maximum stress, are amplified during hydrostatic decompression, and decrease logarithmically with time during hydrostatic hold periods after deformation cycles. The mechanical data and change in elastic properties are used to determine the proportion of mechanical work required to generate tensile cracks, which increases as the rock approaches failure but remains small, up to around 10 per cent of the net dissipated work per cycle. The pre-rupture deformation behaviour of rocks is qualitatively compatible with the mechanics of wing cracks. While tensile cracks are the source of large changes in rock physical properties, they are not systematically associated with significant energy dissipation and their aperture and growth is primarily controlled by friction, which exerts a dominant control on rock rheology in the brittle regime. Time-dependent friction along pre-existing shear interfaces explains how tensile cracks can close under static conditions and produce recovery of elastic wave velocities over time.
| Type: | Article |
|---|---|
| Title: | Micromechanics of rock damage and its recovery in cyclic loading conditions |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1093/gji/ggac447 |
| Publisher version: | https://doi.org/10.1093/gji/ggac447 |
| Language: | English |
| Additional information: | © The Author(s) 2022. Published by Oxford University Press on behalf of The Royal Astronomical Society This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. |
| Keywords: | Science & Technology, Physical Sciences, Geochemistry & Geophysics, Elasticity and anelasticity, Friction, Geomechanics, Rheology: crust and lithosphere, SLIDING CRACK MODEL, MICROCRACK MODEL, BRITTLE SOLIDS, FAULT ZONE, SEISMIC VELOCITY, KM DEPTH, STRESS, DILATANCY, DEFORMATION, FRACTURE |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10162454 |
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