ABSTRACT
This paper provides a well-illustrated guide to the workings of the Q-system, with many examples demonstrating its use. Not only rock exposure logging, but also core-logging, and tunnel-logging are illustrated with quantified examples. The Q-system was developed 40 years ago for describing rock mass quality in a quantitative way, using six important parameters and ratings of quality. These were first related to structural geology, in particular the number of joint sets, their roughness, whether there was clay-filling, followed by the effects of water and the stress/strength ratio. A logarithmic-like scale from about 0.001 to 1000 was the result. All the ratings of the key parameters are given in this guide, and include footnotes and a field-logging sheet and examples of its use. Linked to the Q-value and the span or height of the excavation in rock, and also reflecting the final purpose of the excavation, is an updated chart of recommended support and reinforcement for the arch and walls of underground excavations. Both tunnels and caverns are catered for, from roughly 3 m to 60 m span. In 1993, the S(mr) support was updated by the same authors, replacing mesh reinforced shotcrete with fiber reinforced sprayed concrete or S(fr). The recommended PVC-sleeved (CT) bolts were more resistant to corrosion. The Q-system has always reflected single-shell B+S(fr) concepts of permanent support, as encompassed in the Norwegian Method of Tunneling (NMT). During the 40 years of its use the Q-value has been shown to have empirical relationships to seismic velocity, deformation modulus, and tunnel or cavern deformation. It can also be used for helping to quantify the benefits of high-pressure pre-injection, and to estimate permeability. In addition, the Q-value has been extended for use in TBM prognosis. This is the subject of a separate chapter in this five-volume set.
