Stress Analysis of Lined Pressure Tunnels using Finite Element Method

Résumé ou Introduction

Under ground openings are integral part of any hydro-electric power generation projects in the form of power tunnels and power house cavities. In recent times there has been rapid growth in under ground hydro power projects in India. Under ground power house usually consists of large openings such as power house cavern, transformer cavern, surge chamber etc. which are joined by pressure tunnels, bus galleries, draft tube tunnels and access adits.

The majority of tunnels for hydro electric purpose are located in mountainous region and the rock medium in which these openings are made is usually heterogeneous and anisotropic. This discontinuous behavior of rock mass may lead to complex rock mechanics problems. The excavations in such a complicated rock medium needs a thorough understanding of the geological, structural features of the rock mass i.e. its response to the process of excavation.

In the present work, analytical and numerical solutions of stress distribution around underground openings located in an initially stressed medium are studied and compared. The analytical solutions are restricted to openings of simple geological features while the numerical modeling has emerged as a powerful tool in the case of complex geological structures. Several numerical techniques are available to model the rock mass as equivalent continuum or as discontinuum with explicit representation of the structural features. The present work is concerned with the stress analysis of Tehri head race tunnel with circular cross section. It deals with the stress analysis of concrete lined pressure tunnels for various problems, which will arise, in the construction of pressure tunnels. The numerical modeling provides the reasons for the observed behavior of the rock mass, development of cracks in the concrete lining and a base for support design. In the present work of stress analysis, finite element method has been used.