ANISOTROPY OF GRANITES - A REFLECTION OF MICROSCOPIC FABRIC

The Paper contains the results of an inquiry into the mechanical anisotropy of granites from three North American localities. An assumption of an ellipsoidal distribution of elastic moduli was found to be justified ; the data suggest that the orthotropic elastic idealization may be suitable provided that non-linearity is accounted for. Engineering predictions for these rocks, if based on the idealization of linear isotropic behaviour, could lead to serious error. It was of interest to discover through microscopic fabric analysis that the interpreted cause of both non-linear and anisotropic behaviour was mechanistically the same, i.e. an effect produced by small preferentially orientated cracks. For all cases tested, directions of high compliance and low cleavage resistance could be related to microfractures in quartz grains. Observations of this fabric element can provide a rapid and inexpensive method for evaluating the anisotropy of the granitic rock mass. © 1969, Thomas Telford Ltd. All rights reserved.