BEHAVIOUR OF DEEP TUNNELS UNDER SQUEEZING GROUND CONDITIONS

Abstract

Many of the hydroelectric projects in India are encountering the problems of squeezing and swelling rock conditions. The main problems under squeezing ground conditions are low excavation rate and high cost due to support failure, requiring rectifications arising out of poor anticipation of tunnel closures and support pressures. In this study, analysis of the highly squeezing sections of the Giri and Loktak tunnel has been carried out using the elasto-plastic properties of the medium for the different methods of excavation. The multiple drift and heading and benching method have been considered in analysis. In present study, a software package for FEM program ABAQUS 6.7 has been used by invoking the Drucker Prager yield criterion for 2D and 3D simulation of excavation of the tunnels. Based on numerical modelling, attempt has been made to predict tunnel closure and thickness of the rock mass broken zone developed around the tunnel and these results have been compared with results obtained in field by instrumentation. The study shows that software ABAQUS 6.7 is capable of simulating the effect of in-situ stresses and squeezing phenomenon.