Abstract

En-echelon fractures have been often identified in faults in rocks at different length scales. To enhance our understanding of the role of en-echelon cracks in the formation of a shear rupture, blocky Carrara Marble specimens, containing multiple artificial en-echelon flaws (about 13 mm long), are uniaxially tested in this study. Based on the experimental observation, the fracturing process can be divided into four stages. These stages indicate that instead of tensile wing cracks commonly observed as linking cracks in moulded gypsum specimens, Carrara Marble only produces white patches along similar trajectories to bound an elliptical rock bridge, while the linking coalescence cracks directly connect a flaw tip to the neighboring flaw tip to divide the elliptical rock bridge into two parts. A large relative sliding across the shear rupture is observable only after the initiation of the cracks along the path of either quasi-coplanar or oblique white patches at the two outer flaw tips. A short discussion over the influence of flaw configuration, loading condition and material property will be provided towards the end of the paper, suggesting that different combinations of these factors can possibly lead to the same coalescence pattern.

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