ABSTRACT
Given the construction constrains at ground surface in the major urban environments the use of underground to install infrastructure and transport networks has increased considerably in the last decades. However, this solution is also approaching its limit, with a substantial part of the underground already being occupied. In this scenario it has become more frequent to excavate new tunnels in close proximity to existing ones, leading to interaction problems that are necessary to take into account in the design stage. Evidences of such interaction have been reported in the literature and are strongly dependent on the distance between tunnels. However, most of these studies focus on the displacements measured at ground surface and scarce results are available in the literature about the stress redistribution and mobilised stresses that occur in the central pillar of soil. In this paper a numerical study of the construction of side-by-side twin tunnels excavated sequentially is performed with the purpose of further investigate this aspect. The results show that depending on the distance between tunnels the mobilised stress levels in the pillar rise with the excavation of the 2nd Tunnel, leading to an increase of the yielded area. A parametric study conducted also showed that the area affected by the excavation is dependent of the initial stress conditions considered in the analyses.
