Influence of internal structure of crinoidal limestone on fracture paths

In this paper, it is shown that the mode I fracture path in a crinoidal limestone is not only determined by the orientation of the principal stresses, but that is also influenced by the granular nature of the material, the internal structure of the grains, and the presence of defects present in the rock. The decrease in tensile strength as measured in a Brazilian test provides a first indication that an increase in the grain content facilitates fracture nucleation and fracture growth. The study of thin slices, SEM micrographs and reflection microscopy images on both intact samples and samples subjected to a Brazilian test reveal that cleavage planes and grain boundaries form preferential fracture paths for the fractures. The global direction of the primary fracture in a Brazilian test is perpendicular to the global minor (tensile) principal stress direction. However, locally, the orientation of the grains, the internal structure of the mineral grains and the presence of defects often affect the direction of the fracture. different microscopy techniques yield valuable information about the influence of the internal structure of the rock on the actual fracture surface, these techniques are often time consuming and difficult to automate, requiring a fair amount of operator input. Therefore, the possibilities are explored of a surface-scanning technique that makes use of a profilometer. It is shown how a few simple data processing techniques, applied to the profilometer records can provide information on the crinoid content of crinoidal limestone.