A study of interaction effects due to bored tunnels in clay

Abstract

As more and more tunnels are being bored in urban environments it is essential to understand the effects that this will have on adjacent structures, for example, the state of Singapore, which has been expanding its underground transit system extensively. The effects of tunneling twin tunnels in Singapore marine clay are outlined, analyzed and discussed. Three different configurations are taken into account, side-by-side tunnels, piggyback tunnels and angular-offset tunnels, located at a typical depth for Singapore. Empirical correlations, derived from extensive field data, are used to calculate ground movements caused by twin bored tunnel constructions using superposition. Non-linear finite element analysis is used for the same situations, as well as for analyzing the stresses in the tunnel lining. The use of superposition was tested using the non-linear analysis to check whether or not its use with empirical methods is appropriate. Although the numerical solutions suggest that superposition is a good approximation for twin tunnel bores, there is a clear discrepancy in the magnitude and distribution of ground movements calculated by empirical and numerical solutions.