The Fracture of Rock around Underground Openings

Abstract

The authors have carried out researchs on the mechanism of the failure of rocks which is found at underground openings by means of experiments with models and stress analysis by photoelasticity as well as by field observations and arrived at the following conclusion. The fracture of rock on the inner surface of underground openings takes place when the theoretical maximum stress, tensile or compressive, under the assumption that the ground is perfectly elastic, multiplied by a corresponding factor reaches the tensile or compressive strength of the rock. There is a great difference between the factors for tension and compression fracture, namely that the former is about 0.45, while the latter is 0.95. This theory explains many rock pressure phenomena in solid ground which have not been heretofore understood, such as the compression fracture frequently found on the side wall of a drift. It is pointed out that the state of rock pressure can be inferred to some extent by observing the state of fracture of rock around underground openings.