STRESS AND DEFORMATION BEHAVIOUR OF CIRCULAR TUNNELS SITUATED IN ROCK MASS

Abstract

Increasing use of Tunnels for underground roadways, metro rail or railways makes it an important area for study. Construction of tunnels through the rock or soil mass would require the determination of induced stresses and deformation resulting from in situ stress conditions. This thesis involves study of the theoretical solutions provided by various researchers related to stress and deformation around a circular tunnel and a comparison among them simultaneously for stresses and strains keeping certain parameters constant around the tunnel. This has been carried out in two steps. First step involves casting and model testing in the laboratory to evaluate stress and strain induced in the model under uniaxial loading. This has already been carried out by Kumar, P. and the final readings of that model test have been adopted directly for further analysis. The salient features of this experiment are, experimental model of circular tunnel casted using Perspex box specially designed to act as a mould. Plaster of Paris was used as the casting material to simulate weathered rock mass. Strain gauges were attached at the tunnel periphery at specific intervals. Second step involves comparing the various solutions given by researchers using ultimate load as the input from the model testing and computing stresses and corresponding strain values analytically considering the plane stress and plane strain condition for stresses and strains respectively. Deformation profiles, stress vs strain curves for different solutions were obtained for further study and conclusions were drawn.