ABSTRACT

In recent years many new tunnels have been planned and designed or constructed near to existing tunnels in order to develop and extend underground transportation systems. In the design of new tunnels, it is important to ensure that any existing underground transportation systems in close proximity to the proposed tunnelling activities can continue to operate safely both during and after construction. Therefore, it is necessary to understand the interaction mechanisms between new and existing tunnels, to ensure that no damage occurs to the existing tunnel. In general, this interaction may be strongly dependent on the spacing between the tunnels. If the new tunnel is constructed at a large distance from the existing tunnel, the individual tunnels can be considered separately as single tunnels and analysed as such. However, if the influence zones of the two tunnels overlap, some degree of interaction between tunnels will take place. This interaction will affect the state of stress and the displacements in the ground around the tunnels, the ground surface displacements and the support loads.