Granite is well known as an anisotropic rock. It usually has three planes normal to each other being called the rift, grain and hardway, and these planes have different physical properties and strengths. In this study, Pocheon granite in Korean was selected to investigate its elastic anisotropy and strength anisotropy. According to scanning electron microscope observations, Pocheon granite has a higher density of microcracks in the rift plane compared to the other two planes. Elastic characteristics and indirect tensile strength of Pocheon granite were measured through free-free resonant column testing and Brazilian tensile strength (BTS) tests. It is found that the ROD wave is the smallest for the rift plane (3180 m/s) whereas it is the highest for the hardway plane (3761 m/s). S wave has no obvious difference among the three planes. BTS test results show that the average values for the rift, grain and hardway planes are around 6.1 MPa, 8.3 MPa and 8.8 MPa, respectively. Moreover, the failure plane of Pocheon granite in BTS tests were scanned by X-ray CT and roughness of the failure planes were evaluated. Analysis results show that roughness of failure plane is lower for the rift, and higher for the grain plane. Minerals ratio, and their distribution along failure planes influence roughness. No clear relation between BTS and roughness was found at this scale.
Granitic rocks are characterized by three orthogonal planes of weakness that present different mechanical and physical properties (Dai & Xia 2013). Since a long time ago, quarryman have identified and named them as rift, grain, and hardway planes (Dale 1923). They have taken advantage of these planes of weakness because the rock mass can easily split along the rift plane than along the other two (Takemura et al. 2003).
Various researches have studied the mechanical properties along these planes and have found on them distinctive characteristics (Lee et al. 2001). Porosity, density, permeability, wave velocities, and unconfined compressive strength of granites have been reported to exhibit significant anisotropy (Zhang & Takeda 2003). Moreover, changes in ultrasonic wave propagation speed have been used to study different properties of granites. A recent study of Pocheon granite, in South Korea, reported anisotropic characteristics with different values of primary wave velocity for each plane (Kang et al. 2014).
Additionally, roughness assessment of natural and manmade surfaces has been conducted for more than four decades (Rengers 1970), and although roughness is a not well defined property, it is generally accepted as any superficial deviation from an ideal plane, and it is scale dependent (McCarroll 1996).