Effect of Porosity on Rock Brittleness

Excerpt

Most rocks show brittle behavior when they pass slightly beyond yield stress. Various researchers (e.g., Hucka and Das 1974; Singh 1986; Göktan 1991; Aubertin et al. 1994; Kahraman 2002; Hajiabdolmajid and Kaiser 2003; Gunaydin et al. 2004; Kahraman and Atindag 2004; Yagiz 2004, 2006b, 2009; Göktan and Yilmaz 2005; Tiryaki 2006; Gong and Zhao 2007; Yarali 2007; Yilmaz et al. 2009; Altindag and Guney 2010) have indirectly defined rock brittleness by using different approaches. The brittleness index is often determined using the tensile strength (TS) and uniaxial compressive strength (UCS) of rock in engineering practice. The presence of pores and micro-cracks (porosity) has a considerable effect on the mechanical properties of rock such as UCS and TS. It has been recognized that UCS and TS of rocks decrease with increasing porosity (Al-Harthi et al. 1999; Palchik and Hatzor 2004; Moh’d 2009; Gharahbagh et al. 2011; Rajabzadeh et al. 2012). As a result, the brittleness index changes as function of rock porosity. Despite the importance of relationship between porosity and brittleness of rock, the number of studies is limited (e.g., Tiryaki 2006). In this paper, with respect to significant effect of porosity on mechanical properties of rocks, the influence of porosity on the brittleness of eight types of rocks (gypsum, sandstone, travertine, marble, monzogranite, tuff, hornfels, and hololeucogranite) was investigated. Also, the ability of point load index (I _s50) for prediction of brittleness values was studied. …