The crack propagation and fracture around the excavation

Many studies have been done for the fracture of excavation in geological engineering and rock mechanics. For a small crack in a rock, fracture mechanics can be applied. Microscopic study has been made(Yokobori, 1954) in mechanical engineering.But the direction of a crack growth is not always made clear yet in the case of rock. Griffith(1921) and, Erdogan. F. and Sih G. C.(1971) postulated that the a crack would open up in the plane normal to the direction of maximum tangential stress, and the direction of Maximum decreasing rate of total potential energy (Anderson, CP. ••• 1971).Recently, Sih(1973 ) has proposed strain energy density theory. By the way, rock masses has complicated mechanical properties, that is, the strength is different for tension, compresion and these combined stress.Fracture behavior in such a materials have not been studied perfectly in the past.