DESIGN CRITERIA FOR SUPPORTS AND LININGS OF UNDERGROUND STRUCTURES FOR WATER RESOURCES PROJECTS - SOME CASE STUDIES

Abstract

Inspite of extensive research performed in the field of rock engineering, innovation in design has not proceeded as rapidly as in other engineering fields. It is interesting to note that rock bolts and shotcrete represented the last major innovations in underground excavation support technologies. While rock bolts were enormously successful since their introduction in 1940's, even today rock bolt parameters and layout are specified primarily on the basis of empirical procedures and practical experience. In this dissertation twenty case studies of power houses and water tunnels related to water resources projects , have been taken up. The support requirements have been worked out by using Terzaghi's method, Wickham's RSR method, Bieniawski's RMR method and Barton's Q system. The minimum support pressure has been compared with the support pressure accommodated by the actual supports and observed pressures provided at site. It can be inferred that in case of massive to moderately jointed rocks, Q system gives the minimum support pressure. For very seamy and closely jointed rocks, RMR method gives the lowest support pressures. In the case of squeezing and swelling rocks also, the RMR method give the minimum support pressures. Terzaghi's method gives the maximum support pressures for 100 percent cases of large excavations and for more than 95 percent cases of water tunnels. The observed rock pressures are either nearer or these are enveloped by calculated rock pressures by Q system. Hence based on this study it can be inferred that Q system of rock classification and rock support design, can be safely used.