INDIAN EXPERIENCES WITH Q-SYSTEM AND RMR-SYSTEM

The and-systems of Barton et. al. (1974, 1975) and the RMR-system of B ieniawski (1973) have been evaluated on the basis of measured tunnel s upport pressures from 25 tunnel sections, 2 to 14 n wide, covering bot h squeezing and non-squeezing ground conditions. The comparison shows that the and-system is unsafe for large tunnels under squeezing ground conditions. A new correlation has been developed considering tunnel d epth, tunnel radius, tunnel closure, and Rock Mass Number- i.e., ''str ess-free Q''-to obtain reliable estimates of tunnel support pressures. Changes suggested by Sheorey (1991) for satisfactory application of t he Q-system to coal-mine roadways on the basis of 44 case histories ar e presented. Unal's (1983) correlation for coal-nine roadways is shown as overly safe for large tunnels under non-squeezing ground condition s, and unsafe for all sizes of tunnels under squeezing ground conditio ns. Correlations between tunnel support pressure, tunnel depth, tunnel closure, and Bieniawski's RMR have been developed to provide reliable tunnel support pressures for all sizes of rock tunnels under varying ground conditions. The correlations between RMR and and proposed by Bi eniawski (1976) and by Rutledge and Preston (1978) are not reliable, b ecause RMR and and are not truly equivalent. Therefore, an acceptable correlation between rock. mass number N and RMR(mod) i.e., RMR without joint orientation and intact rock strength, has been presented for a better interrelation.