RMR and SMR are two of the most applied classifications for tunnels and slopes, respectively, excavated in rock masses. Five parameters are used to compute the basic RMR classification for each discontinuity set. However, it is not clarified the whole Rock Mass RMR value. Here, the rock engineering community interprets the possibilities of calculating RMR in different ways. In addition, given that SMR is calculated from RMR by adding four correction factors, different interpretations arise. In this work, different cases of rock masses were analysed and both indexes, RMR and SMR, were assessed using different interpretations of RMR calculations. From this analysis, it can be concluded that, occasionally, there is a significant difference in the RMR and SMR values obtained depending on the followed procedure.
Assessing the stress-strain behaviour of a rock mass is a complex task which has not been conveniently solved to date. It is well known that the strength of the rock mass is a function of the strength of the intact rock, the shear strength of the discontinuities, the structure of the rock mass and the geo-environmental conditions to which the rock mass is subjected, mainly, in situ stress and hydrogeological conditions.
The establishment of the whole behaviour of discontinuities and intact rock is a complicated task. However, there is a vast experience acquired on successful and failed construction practices depending on the state of the rock masses. The needed information comprises the properties of the intact rock along with the discontinuities, and the structure. The application of this experience makes it possible to determine which properties are more important and which others are less important to predict whether a rock mass will behave properly during and after a geotechnical work. This led to the birth of rock mass classifications.
Rock mass classifications enable assigning a quality index to the rock mass, estimating its behaviour, and proposing support measures for proper functioning. Specifically, the Rock Mass Rating (RMR) system was introduced 50 years ago by Professor Bieniawski (Bieniawski 1973) and was later updated in 1989 (Bieniawski 1989). From then until today, its intensive use has allowed a relative homogenisation of criteria of a complex problem as the characterisation of rock masses, facilitating communication between geologists and engineers.
