Features similar in size, appearance and orientation to previously reported compaction localization features were found in a suite of constant mean stress true triaxial tests. Tests were run at five different stress states ranging from axisymmetric compression to axisymmetric extension at five constant mean stresses ranging from 30 to 150 MPa. Most of the specimens that formed compaction localization-like features exhibited a plateau in the stress - strain curve without a stress drop, suggesting that these specimens represent a deformation mode that is transitional between true compaction localization and bulk compaction. Compaction localization features were observed in all of the stress states above 75 MPa mean stress. As the deviatoric stress state shifts from axisymmetric compression to axisymmetric extension, a higher mean stress is required to cause compaction localization. These results suggest that compaction localization may be more common than previously thought.
Compaction localization and porosity reduction are topics of great importance to the geologic community. Acting as barriers to fluid flow, compaction localization can affect resource extraction and carbon sequestration. These features could also be useful in inferring stress histories of rock masses. Recent papers on the topic range from field observations, to experimental data sets, to theories that predict compaction localization. This paper will examine similarities and differences between previously reported experimental compactant features (compaction bands, compaction localization and compactant shear bands) and similar features observed under the true triaxial states of stress used here. One of the first reports of pure compaction bands was by Mollema and Antonellini  who documented these bands in aeolian sandstone in Utah. The rock masses in these locations are similar: both have high porosity, on the order of 20%, and both have relatively large grain sizes of approximately 0.2-0.4 mm on average.
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