Knowledge of the rock mass strength is important for the design of all types of underground excavations. An improved rock mass strength prediction, as well as a better understanding of the failure process in a rock mass enables e.g., reduced stability problems in underground design and reduced waste rock extraction, improved working conditions underground, and, ultimately, reduced operating costs for underground and mining work. This report constitutes a portion of a PhD project, which was initiated due to the relatively limited knowledge of failure behaviour and the rock mass strength. The aim of the project is to develop a methodology to estimate the strength of hard rock masses. Case histories, where the determined/estimated rock mass strength from a criterion/system can be compared to a measured/determined rock mass strength, are presented in this report. Hence, this report is a summary of all collected field data of observed or documented rock mass failures within this PhD project. For each case presented in this report (except the Stripa case), the following requirements were fulfilled: 1. a rock mass failure has occurred in an underground excavation, with typical tunnel dimensions (approximately 2-10 m), for which the rock mass can be treated as a continuum, 2.the failure is stress induced, for instance spalling, shear failure, slabbing, buckling or compressive failure, 3.stress measurements has been performed (or good knowledge of the in- situ stresses exists), and 4.the uniaxial compressive strength of intact rock (laboratory scale) was above approximately 50 MPa. A total of 14 cases where failure has occurred are presented in this report. First, mining industry cases are presented, comprising three cases from Sweden and one case from Finland. Secondly, two cases of underground storage facilities from Sweden are described. Thirdly, a large scale test from Sweden is presented, and finally, three tunnel cases from Norway are described.
Luleå: Luleå tekniska universitet, 2006. , 82 p.