DESIGN OF SUPPORT SYSTEM IN TUNNELING IN NJPC PROJECT

Abstract

Since underground excavations are associated with high overburden, high stress and different discontinuities and shear zones, the strength of the rock mass will be less at these regions which in turn results into broken or plastic zones. For the stability of the structure, these factors have to be considered during design of supports. In the present analysis proposed by Ladanyi the elasto-plastic behaviour of rock mass was considered which represent the actual field situation. The total area has been classified into five different classes depending upon the composition of minerals present. These classes will represent the entire length of the Head Race Tunnel (HRT) stretched between Nathpa and Jhakri. The various rock mass properties will be calculated based on the geological data available [such as RMR, Modulus of Elasticity, Uniaxial compressive strength, Poisson's ratio etc.). These properties will be utilised in calculating the various steps involved in the analysis. The Ground Response Curve (GRC) for different classes and Support Reaction Curves {SRC) for various support systems will be plotted. Suitability of the support systems will be checked and these will be compared with the actual support systems provided in the field. The stand-up time, active span and post saturation pressures will also be discussed.