Evolution of en-echelon flaws to a shear rupture in moulded gypsum under uniaxial compression

Abstract

Cracking processes in rock specimens containing one, two or multiple artificial flaws under compression have been studied systematically and extensively in the laboratory for the past decades. To enhance our understanding of the role of en-echelon cracks in the formation of a shear rupture, specimens containing artificial en-echelon flaws are studied in this paper. Rock-like material Hydrocal-B11 gypsum is used to mould block specimens, which contain en-echelon flaws cut by the Waterjet. The fracturing processes of the specimens under uniaxial loading are observed and recorded by a camcorder and a high speed video system. For the studied en-echelon flaws arrangement, three stages of fracture development are observed. The results show that tensile wing cracks (TWCs) are involved in coalescing the pre-existing flaws and fragmenting the bridge zones. The TWC development is strongly influenced by the stress field around adjacent flaw tips as indicated by the curvature of their crack paths. The development of a shear rupture across the entire specimen is attributed to the development of two short shear cracks emanating from the two outer flaw tips, which coalesce with two previously initiated steeply inclined tensile cracks. Copyright 2013 ARMA, American Rock Mechanics Association.