ACOUSTIC EMISSION CHARACTERISTICS AND FAILURE OF UNIAXIALLY STRESSED GRANITIC ROCKS: THE EFFECT OF ROCK FABRIC

Abstract

Laboratory experiments on rock samples were carried out to understand the relationship between the acoustic emission (AE) parameters and rock fabric. AE activity was recorded during the uniaxial compression with constant stress rate of several granitic rocks showing variable microfabric (e.g. grain size, shape and crystallographic preferred orientation) and macrofabric (e.g. magmatic isorientation, metamorphic banding). A broad band multichannel recording system with a high dynamic recording range enabled individual acoustic emission events to be analysed in a wide frequency and energy range. The microfabric of the rocks was studied by quantitative petrographic analysis of thin sections allowing precise description of mode, grain size and shape. It has been proved that the energy-frequency distribution of AE events strongly reflects the fabric of the samples. The characteristic energy value of AE events reflects the most frequently occurring grain dimensions. The AE parameters like acoustic rate or cumulative energy are highly sensitive to fabric arrangement in rocks with pronounced fabric (e.g. foliation, lineation etc.).