Uncertainties and tunnelling risks
The rockmasses surrounding an underground opening form a complex structure. Interpretations and extrapolations made to work out the geological setting, as well as extrapolation from the known conditions in the surface to the unknown along the tunnel, may introduce considerable uncertainties. Although extensive field investigation and good quality descriptions will enable the engineering geologist to predict the behaviour of a tunnel more accurately, it cannot remove the risk of encountering unexpected features.
Characterization and RockMass index (RMi)
In contrast to most other materials used for construction purposes, the quality of the rockmass is based on observations and evaluations rather than test results. This causes great challenges in the characterization of the parameters of the complex construction material called rockmass. Contrary to civil engineering and mining, the construction materials (rockmasses) in underground excavations are not characterized by their strength properties. As a consequence of this, the RockMass index (RMi) has been developed, with input of the geological parameters that have the greatest influence on rockmass strength.
Rock engineering and classification systems
An important requirement for all rock engineering is that the method or tool used, adequately covers the behaviour of the ground surrounding the tunnel or cavern. Frequently, rock engineering is based on observations, experience and personal judgement, where rockmass classification systems play an important role. How can such systems be applied correctly? What are the limitations?