MODERN APPROACH TO TUNNEL SUPPORT DESIGN WITH REFERENCE TO -NATHPA-JHAKRI TUNNEL (H.P.)

Abstract

The design of tunnels in rock is mainly based on three approaches; analytical, observational and empirical. Two approaches currently popular for estimating support pressures are: i) classi-fication Systems and ii) Elasto-plastic theory. The empirical approach using classification systems is based on case records of existing practice and attempts to provide a simple solution by correlating information about the rock mass conditions with the supports that were used. If an empirical design is backed by a systematic approach to ground classification, it can effectively utilise the valuable practical experience gained at many projects, which is so helpful for exercising one's engineering judgement. Rock mass classifications which thus form the backbone of the empirical design approach are widely employed abroad in rock tunnelling. But this approach does not distinguish conservative supports and it does not consider rock-support interaction