ELASTO PLASTIC ANALYSIS OF DEEP TUNNELS

Abstract

There are three mein epproschos namely analytical, observation!' and empirical, available for the design of support system of tunnels. The empirical approach*, are based on rock mess classification systems, the observational approach basically represents a "design as you go' philosophy, and the analytical solutions are mostly based on some simplifying assumptions about the ground behaviour. In the absence of any batter technique being available, the designers mostly depend upon one empirical method or the tunnel instrumentation. Improvements in the design methods of tunnel supports and lining are obviously needed. It is necessary to understand the mechanism of behaviour of the system comprising support system end the surrounding medium, which, it is believed, may be achieved by a combination of theoretical consideratians end monitoring tunnel behaviour in the field. The excavation of a damp tunnel in a rock mass usually causes the formation of _yield zone in the surrounding rock. Ground support interaction curve may be desired by accounting for the peek and the residual strength of the rock mass. Within the thus defined domain the ground behaviour is determined by the rate of strength lees with increasing strains. The ground reaction curve may have fundamentally different shapes depending upon the Post failure rock behaviour. Corresponding to failing or yielding zones of the groundL the desirability of the supporting system will be decided. The convergence confinement method of 19b,, Characteristic curves for the stability of the tunnel when stabilization pressure is applied for the case of a non dilatant rock with some - value of residual cohesion and reduced elastic modulus, 87