We report results from laboratory triaxial deformation experiments on sandstone specimens containing pore fluid in which the evolution of microcrack damage was continuously monitored by acoustic emission (AE) output. We use the AE output to calculate the evolution of mean strain energy release rate, mean crack length and crack density. We then calculate the evolution of a damage parameter and relate microcracks to the constitutive stress-strain behaviour describing the deformation history. For "drained" experiments there is good quantitative agreement with experimental results.

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