Dyskin, AV & Pasternak, E 2008, 'Rotational Mechanism of In-Plane Shear Crack Growth in Rocks Under Compression', in Y Potvin, J Carter, A Dyskin & R Jeffrey (eds), Proceedings of the First Southern Hemisphere International Rock Mechanics Symposium
, Australian Centre for Geomechanics, Perth, pp. 99-110, https://doi.org/10.36487/ACG_repo/808_46
In-plane growth of shear fractures in rocks in the presence of high magnitude compression routinely observed in both laboratory testing and in the field so far eludes explanation. Indeed, in-plane growth of shear crack is difficult to explain based on the Linear Elastic Fracture Mechanics. We propose here a mechanism that reconciles the observations and the theory. We assume that what presents itself as a Mode II crack is in fact a crack driven by relative rotations of grains at the crack tip. The relative rotations are created by the conventional shearing of the crack faces, which leads to a concentration of moment stresses at the crack tip. The moment stress – the bending moment per unit area created in the intergranular bonding due to the relative rotation of the grains – ruptures the bonds in front of the crack creating en-echelon formation. This affects the in-plane growth when the conventional out-of-plane growth (kinking) caused by the concentration of tensile stress is suppressed by the high ambient compression.
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