ABSTRACT
Tunnel construction entails complex three dimensional operations. Consequently, any numerical modelling methods should, in principle, attempt to closely represent such characteristics. It has been a common practice, however, that two dimensional modelling methods have been used for convenience to perform parametric studies for the optimization of tunnel design and construction. The main limitation of such two dimensional modelling methods is that they do not provide any information on the behaviour of tunnel headings. A recent investigation on NATM tunnel collapses revealed that most failures occurred during or soon after excavation of tunnels before completing linings, which suggests that intermediate stages of construction are becoming more critical. A conclusion can be drawn that three dimensional analyses are required for the cases of tunnel headings.
