Measurements of effective elastic modulus and microcrack density

Abstract

The presence of microcracks in rocks have a significant impact on elastic properties, whereby the characterization and determination of material behavior involves effective properties. Several theories have been developed in an attempt to determine the effective properties of an elastic solid as a function of crack parameters. However, very little experimental work has been performed to support these theories. Two-dimensional experiments were conducted on artificially cracked aluminum plates and the results obtained were compared with some of the existing theories. In the case of a random distribution of cracks, the results show a very good agreement with the non-interacting approximation, even when interactions may be significant. These results were then applied to the characterization of microcracks in Charcoal granite matrix, assuming a random distribution of penny-shaped cracks of radius l. The properties of the matrix material were obtained upon closure of microcracks from the measurement of linear strain and hydrostatic pressure. The matrix modulus of about 84 GPa is reduced to about 50 GPa due to a crack density, defined as the sum of l3 divided by the total volume of the rock, of 39%.