Browning, J;
Meredith, PG;
Stuart, CE;
Healy, D;
Harland, S;
Mitchell, TM;
(2017)
Acoustic characterization of crack damage evolution in sandstone deformed under conventional and true triaxial loading.
Journal of Geophysical Research. Solid Earth
, 122
(6)
pp. 4395-4412.
10.1002/2016JB013646.
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Abstract
We present a comparative study of crack damage evolution in dry sandstone under both conventional (σ1 > σ2 = σ3), and true triaxial (σ1 > σ2 > σ3) stress conditions using results from measurements made on cubic samples deformed in three orthogonal directions with independently controlled stress paths. To characterize crack damage, we measured the changes in ultrasonic compressional and shear wave velocities in the three principal directions, together with the bulk acoustic emission (AE) output contemporaneously with stress and strain. We use acoustic wave velocities to model comparative crack densities and orientations. In essence, we create two end-member crack distributions; one displaying cylindrical transverse isotropy (conventional triaxial) and the other planar transverse isotropy (true triaxial). Under the stress conditions in our experiments we observed an approximately fivefold decrease in the number of AE events between the conventional and true triaxial cases. When taken together, the AE data, the velocities, and the crack density data indicate that the intermediate principal stress suppresses the total number of cracks and restricts their growth to orientations subnormal to the minimum principal stress. However, the size of individual cracks remains essentially constant, controlled by the material grain size. Crack damage is only generated when the differential stress exceeds some threshold value. Cyclic loading experiments show that further damage commences only when that previous maximum differential stress is exceeded, regardless of the mean stress, whether this is achieved by increasing the maximum principal stress or by decreasing the minimum principal stress.
| Type: | Article |
|---|---|
| Title: | Acoustic characterization of crack damage evolution in sandstone deformed under conventional and true triaxial loading |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1002/2016JB013646 |
| Publisher version: | http://doi.org/10.1002/2016JB013646 |
| Language: | English |
| Additional information: | © 2017. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. |
| Keywords: | Science & Technology, Physical Sciences, Geochemistry & Geophysics, crack, acoustic, triaxial, damage, velocity, elastic, WESTERLY GRANITE, VELOCITY ANISOTROPY, SEISMIC VELOCITIES, SPATIAL EVOLUTION, POROUS SANDSTONES, ELASTIC-MODULI, ROCK STRENGTH, FAILURE, DEFORMATION, TIME |
| 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.ucl.ac.uk/id/eprint/1561118 |
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