Consideration of fracture growth from an inclined slit and inclined initial fracture at the surface of rock and mortar in compression

There have been a number of studies on fracture growth inside rock under compression, and some studies examined near-surface fracture growth [1], [2]. However, fracture growth from an inclined initial fracture at the rock surface would occur much more easily than from a fracture located inside or close to the surface of the rock and such fracture growth would play important roles in spalling of mine pillars, borehole breakout, etc. Therefore, the present study was performed to clarify the direction of fracture growth from an inclined slit and an inclined initial fracture at the surfaces of rock and mortar. A number of theories, such as Sih's maximum tensile stress theory and the maximum energy release rate theory, have been proposed to predict the direction of fracture growth [3]. In Sih's theory, a fracture is assumed to grow at an angle 0 given by Eq. (3) when Eq. (1) is satisfied (see Fig. 1 for r and ). r K 2 IC (1)