ROCK MASS - TUNNEL SUPPORT INTERACTION ANALYSIS

Abstract

Tunneling in weak rocks presents some special challenges to the geotechnical engineer since misjudgments in the design of support systems can lead to very costly failures. In order to understand the issues involved in the process of designing supports for this type of tunnel, it is necessary to examine some simple basic concepts of how rock mass surrounding a tunnel deforms and how the support systems acts to control this deformation. This Rock-Support interaction can be analyzed by 3D numerical modeling or Convergence-Confinement Method. During the excavation stage, the TBM shield will acts as the support system. So at this stage, the TBM shield replaces the support system in the above mentioned interaction phenomenon. In mechanized tunneling process, problems such as squeezing behavior, heavy load on TBM shield may adversely affect the TBM advance. So, prediction of squeezing potential and ground pressure imposed on TBM shield before encountering such conditions will prevent the TBM jamming and subsequent consequences. In this thesis a HRT tunnel of 23.5km long and 5.4m diameter, coming under the influence both Kashmir Nappe and Indus techno- stratigraphic zone is analysed. The ground condition along the tunnel length as well as the pressure over the TBM shield is determined. The squeezing potential is assessed by Empirical as well as semi empirical methods. The CCM is used to predict the critical sections where, TBM shield has subjected to high ground pressure. The suitable support system is suggested for the tunnel determining the equilibrium pressure and deformation. Mainly closed form solutions suggested by Ladany (1974), Carranza-Torres and Fairhurst, 2000) are used for the analysis and the comparison has been done. iii