ANALYSIS OF TUNNELS IN JOINTED ROCKS

Abstract

Assessment of stresses and closure of openings are complex engineering problems and form the most important aspects in designing the underground structures. Distinct Element Method is one of the popular methods used in assessing the stresses and closure behaviour of underground openings. In the present work, an attempt has been made to predict closure behaviour of some of the laboratory tests conducted on D-shaped tunnel models subjected to far field in-situ stresses. The laboratory test data available from literature (Choudhari, 2007) has been used for this purpose. The closed form solutions proposed by Bray (1987) along with standard expressions for the closure of an opening subjected to far field stresses (Singh and Goel, 2006) were used to predict the side wall and roof displacements of the tunnel model. The relationship between the closure and the internal support pressure were presented in the form of ground response curves. It was concluded that the stress dependency of the rock mass modulus plays very important role in predicting the closure of the opening at a given internal support pressure. Further, distinct element modelling of the tunnel models has been performed by using the commercial software UDEC to get insight of stress-strain behaviour of the jointed rock mass around the periphery of the tunnel. The numerical simulation has been conducted incorporating the steps followed in the laboratory. The resulting ground response curves have been compared with those obtained from laboratory tests. A good correspondence has been observed between laboratory and UDEC results. Parametric analysis has also been done for one joint configuration, by varying some of the parameters in the model, which otherwise could not be varied during laboratory testing programme.