Simultaneous Identification of Rock Strength and Fracture Properties Via Scratch Test

Excerpt

Material properties are essential inputs for successful engineering applications in different industries and areas, and thus, a number of methods have been proposed to measure different properties for different materials. Some common measured mechanical properties include the yield strength, compressive strength and fracture toughness. In rock engineering, for instance, the uniaxial compressive strength (UCS) and the opening mode (mode I) fracture toughness, K _IC, are the two frequently employed parameters in geo-structural design and construction. Accordingly, the procedures to measure UCS and K _IC have been standardised by the International Society for Rock Mechanics (ISRM) (Ulusay and Hudson 2007). Although these standardised methods are relatively simple, they are expensive, time-consuming and challenging, especially for in situ measurement, due to the stringent requirements for the specimen shape and/or size (Chang and Wang 2013). As a result, the community has made great efforts to explore indirect methods to characterise the UCS from the Schmidt rebound number, point load index, sound velocity and impact strength (Kahraman 2001) and the K _IC based on its correlation with other properties such as density (Brown and Reddish 1997) and strength (Kahraman and Altindag 2004; Zhang 2002). However, the majority of these empirical methods were developed from regression analyses of data available for limited types of rocks, which are not necessarily applicable to other rocks. The results derived from these empirical prediction models are also accompanied by undesirably high variations, which in turn challenges the credibility of these models (Kahraman 2001). Moreover, the predicted results differ significantly and even sometimes are contradictory each other because of the different testing methods and conditions involved (Li and Itakura 2012). …