Brittleness is an important mechanical property of rock. There are several brittleness criteria exist to characterize rock failure based on rock mechanical properties. However, there is not a unique criterion available able to describe quantitative rock brittleness. In this study different rocks with uniaxial compressive strength values ranging between 7–215 MPa were tested to measure pre-peak and post-peak stress-strain relations. A stiff servo-controlled machine was used to undertake lateral displacement controlled tests. Postpeak stress-strain relations were obtained accurately using three-dimensional digital image correlation technique. Several brittleness indices were proposed based on pre-peak energy, elastic energy and post-peak energy. Analysing of the results demonstrated that a pre-peak stress-strain brittleness index proposed solely based on pre-peak stress-strain behaviour doesn't show any correlation with rock peak strength. On the other hand, the proposed brittleness indices based on pre-peak and post-peak stress-strain relations were found to competently describe an unambiguous brittleness scale against rock strength.
The ability to predict rock failure behaviour is very important for civil engineering and mining development projects. With the ability to predict rock failure, engineers could investigate the effect of rock behaviour on drilling and excavation performance and rock burst occurrence in deep mining. Brittleness refers to deformation that involves hard, strong material that fractures and splits rather than staying whole while pliably deforming. It is important to quantify the brittleness of a rock, so engineers can numerically assess and predict the deformational characteristics of rock masses. The study of brittleness in rock mechanics is relatively popular, and spans back to the 1950's. Many researchers since then have developed different numerical models to assess rock behaviour. Most mathematical models attempting to quantify rock brittleness (brittleness indices) are based on different intrinsic rock properties or on measured deformation of an intact rock specimen. The stress-strain curve is used to measure the deformation process of a rock specimen under compression. The stress-strain curve can be related the ductility-brittleness scale as well (Tarasov & Potvin 2012).
