A study of the crack network in thermally and mechanically cracked granite samples using confocal scanning laser microscopy

Confocal Scanning Laser Microscopy (CSLM) was used to characterise 3D crack networks in La Peyratte granite samples in which cracking was artificially induced either by heating samples at selected temperatures in order to induce thermal cracking, or by performing mechanical tests in order to develop stress-induced cracking at room temperature. Our goal was to recognise typical crack patterns associated with the different cracking mechanisms. We have taken advantage of the ability of CSLM to image thin slices within the rock sample in two different ways: first there are no overprojection problems for stereological studies, and second, one can obtain series of images at different depths from which the 3-D crack network can be reconstructed. Stereological analysis and 3D reconstructions revealed that thermally cracked and mechanically cracked samples differ in anisotropy of crack orientation distribution, with mechanically cracked samples characterised by strongly anisotropic crack networks. (C) 1999 Elsevier Science Ltd. All rights reserved.