Investigations on Mechanical Properties and Crack Propagation Characteristics of Coal and Sandy Mudstone Using Three Experimental Methods

Excerpt

Anisotropy, which controls the mechanical behavior of rock mass, presents considerable challenges in rock engineering applications. Anisotropic properties can be found in many layered sedimentary rocks, such as slate, sandstone and shale, and depend mainly on the presence of stratification and original macro-or micro-fissures (McLamore and Gray 1967; Al-Harthi 1998; Heng et al. 2015; Gao et al. 2015). Chenevert and Gatlin (1965) tested three laminated rocks (sandstone, shale and limestone) and showed that bedded formations exhibit sizable directional variations in their elastic constants and yield strengths. In addition, igneous rocks also possess obvious anisotropic properties. Nasseri et al. (2005) and Nasseri and Mohanty (2008) investigated that fracture toughness of granite exhibits strong anisotropy in terms of micro-crack distribution and their orientations based on cracked chevron notch Brazilian disk (CCNBD) test. Furthermore, many researchers investigated anisotropic mechanical properties using various experimental methods, including the uniaxial compression test, triaxial compression test, Brazilian tensile test and notched semicircular bend (NSCB) test. Ajalloeian and Lashkaripour (2000) presented that anisotropy has a marked influence on the strength properties of mudrock. Moreover, both mudshale and siltshale exhibit maximum uniaxial compressive strength in the direction perpendicular to the planes of anisotropy. Additionally, Tavallali and Vervoort (2010) used the Brazilian tensile test to demonstrate that the failure stress and fracture pattern of layered sandstone are considerably affected by layer orientation. Dai and Xia (2010, 2013) and Dai et al. (2013) investigated the anisotropic properties of mode I fracture toughness, flexural strength and tensile strength of Barre granite using the NSCB fracture test and Brazilian test in three principal directions. Barre granite exhibits strong anisotropic properties of mode I fracture toughness and tensile strength under static loading and diminishing anisotropy in dynamic loading. …