Method to Address Brittle Rock Strength Scatter Through Fracture Density

Excerpt

Rock strength is an important criterion for the classification of rocks to optimize construction usage and surface or subsurface structure designs (Yilmaz 2009). Strength criteria include peak strength criteria, residual strength criteria, and yield strength criteria. The criteria are usually mathematical relations between various stress or strain components that belong to one point in the stress or strain field. However, the relation could be confused by many factors, which often make it inconceivable. These factors can be divided into three groups: (1) composition of the specimen, such as mineral composition, and arrangement of the mineral grains and cracks (Hattiangadi and Bandyopadhyay 2000) and formation conditions (Rajabzadeh et al. 2012); (2) geometrical conditions, such as size (Darlington et al. 2011) and shape (Malaikah 2005; del Viso et al. 2008); (3) external damage conditions, such as load path (Yang et al. 2011; Erarslan and Williams 2012), load rate (Mokhnachev and Gromova 1970; Li et al. 2013), temperature (Liang et al. 2006), and confining pressure (Maizel and Sokolov 1994). Therefore, it is meaningful to present a new strength index that can reduce the effect of these factors. According to the experimental experience, it seems that, for the same type of specimens, the larger the newly created fracture surface area is, the higher the strength is. The study by Dang et al. (2014) has the same point with the experience, but its fracture surface area is obtained by roughly artificial estimation, which makes the conclusion less likely. Several other researchers determined that the total three-dimensional area of the fracture surface is relatively large, as the tensile strength value is relatively low based on the strength test of cement paste with different supplementary cementitious materials (Li and Li 2015). The strength is influenced not only by the degree of fragmentation but also by the supplementary cementitious materials. Therefore, the previous research has several drawbacks in revealing the true relationship between strength and fracture surface area. …