Permanent support recommendations based on Q-values and span/ESRThe first Version of the system was published in 1974, and through the years the system has been updated many times to include new and improved tunnel support technology. NGI has developed a Q-system app and a users guide that can be downloaded free of charge.
Financial support for the preparation of the handbook was provided by the Norwegian Road Authority.
Permanent support recommendations based on Q-values and span/ESR
The Q-system is developed to classify rock masses around an underground opening, as well as for field mapping. Based on estimation of six rock mass parameters, a Q-value for a rock mass can be calculated. This value gives a description of the rock mass quality. The Q-value depends on the underground opening and its geometry, and is therefore not an independent characterisation of the rock mass. The Q-value in an undisturbed rock mass may be different.
The different Q-values are related to different types of permanent support by means of a schematic support chart. This means that by calculating the Q-value it is possible to find the type and quantity of support that has been applied previously in rock masses of the similar qualities. The Q-system can therefore be used as a guideline in rock support design decisions and for documentation of rock mass quality.
The Q-system was developed at NGI between 1971 and `74 (Barton et al. 1974). Since the introduction of the Q-system in 1974 there has been a considerable development within support philosophy and technology in underground excavations. Several new types of rock bolts have been introduced, and the continuous development of fibre reinforced technology has in many ways changed the support procedure. Application of sprayed concrete has gained acceptance even for good quality rocks masses due to demands for a higher level of safety during the recent years. Reinforced ribs of sprayed concrete have replaced cast concrete structures to a large extent.
Since the introduction of the system in 1974, two revisions of the support chart have been carried out and published in conference proceedings. An extensive updating in 1993 was based on 1050 examples mainly from Norwegian underground excavations (Grimstad and Barton, 1993). In 2002, an updating was made based on more than 900 new examples from underground excavations in Norway, Switzerland and India. This update also included analytical research with respect to the thickness, spacing and reinforcement of reinforced ribs of sprayed concrete (RRS) as a function of the load and the rock mass quality (Grimstad et al. 2002).