Crack initiation and damage thresholds in some brittle metamorphic rock types

Giacomo Pepe (a), Andrea Cevasco (b) & Riccardo Berardi (c)
(a) Department of Earth Science, University of Firenze, via La Pira 4, Firenze 50121, Italy. E-mail: giacomo.pepe85@gmail.com (b) Department of Earth, Environmental and Life Sciences, University of Genoa, Corso Europa 26, 16132 Genova, Italy. (c) Department of Civil, Chemical and Environmental Engineering, University of Genoa, Via Montallegro 1, 16145 Genova, Italy.

In this study 60 unconfined compression laboratory tests performed on three brittle metamorphic rock types were analysed in order to evaluate the stress thresholds associated with the onset of stable and unstable microcracking which are known in literature as the "crack initiation stress" and the "crack damage stress", respectively. The crack initiation stress was identified applying the lateral strain response (LSR) methodology while the crack damage stress was detected where total volumetric strain reversal occurs. Although the mineralogical and textural features were quite similar among the investigated rock types, the results of this study showed that the crack initiation and damage stress values were affected by variability. However, when the normalized stress values ci/UCS and cd/UCS were considered, the scatter in results decrease consistently suggesting that the stable and unstable crack growth begin at similar stress levels in the investigated rock types

brittle rock, crack initiation threshold, crack damage threshold, lateral strain difference, lateral strain response method, metamorphic rock