A REVIEW OF METHODS OF. ANALYSING STRESSES IN LARGE TUNNELS

Abstract

An attempt has been made to review the methods of analysis of large tunnels. In practice, different types of tunnel design problems are met With, some o-f which are rather complex. There are three distinct methods of approach to the problem. k'i rs t method is based on past experience of design and behaviour of tunnels after construc-tion. Measuring devices were installed in the lining during construction of tunnels and the earth pressure distribution observed for a long period of time. The compilation and analysis of observations, supplemented by the measured soil properties at the location of tunnel can be correlated and given a form of mathematical equation. Second method is based on the theory of elasticity for analysing stresses within the soil nags surrounding the tunnel and this is obviously a more rational approach. In the third method, dimensions of tunnel ring are assumed and the stresses in the tunnel lining are analysed due to the forces acting on it. A critical review of various methods of analyses is made. The assumptions and limitations of I each method are discussed. Phe above methods of analysis of tunnels have been discussed with respect to four conditions of soil namely; 1. Tunnel in rocks. 2, Tunnel in granular soil, 3. Tunnel in cohesive soil. 4. Subaqueous tunnel. Finally with a view of rationalizing the methods of analyses, suitability of the methods is discussed in the light of new methods of finding stresses in the soil mathematically a experimentally. 2