Geometric analysis of damaged microcracking in granites

Practically identical samples are tested at the same confining pressure and temperature but at different deviatoric stress levels. Thin sections are o bserved using an optical microscope and recorded as images in order to stud y the crack network evolution. The compound cracks are decomposed into elem entary cracks (right segments) with constant orientation and then reassembl ed in order to determine crack length and cumulated crack length. The resul ts of crack observations are discussed in the light of the mechanisms of cr ack evolution at microscopic level compared to the stress-strain curves. It results from our observations that mean crack length increases only modera tely in comparison with maximal crack length and the number of cracks. Zhao reports similar results (cf. Zhao, Y., 1998. Crack pattern evolution and a fractal damage constitutive model for rock. Int. J. Rock. Mech. Min. Sci. 35 (3), 349-366). The evolution of microcracking can be attributed more to new crack nucleation rather than to growth of the pre-existing cracks. (C) 2000 Elsevier Science Ltd. All rights reserved.