Failure of three sedimentary rocks in triaxial and hollow cylinder compression tests

Results are presented of a laboratory study designed to examine the possibility of predicting the behaviour of rocks around model underground excavations from the results of triaxial compression tests. Series of triaxial and hollow cylinder compression tests were performed on three British sedimentary rocks with the emphasis being placed on macroscopic failure development. Measurements of strain localization were made to determine the point of failure surface initiation during triaxial tests. Studies of the failed specimens showed that failure can manifest itself in different ways depending on the microstructure of the rock. A qualitative model based on the concept of microcrack development in heterogeneous media is shown to be able to describe the failure patterns of all three rocks in both uniaxial and hollow cylinder compression tests. It is shown that, qualitatively, a parallel can be drawn between uniaxial and hollow cylinder tests in terms of both pre- and post-failure behaviour. However, the results cast doubt on the quantitative prediction of failure development around circular underground excavations using conventional approaches