Interaction of twin tunnels and shallow foundation at Zand underpass, Shiraz metro, Iran

Tunnel construction in urban areas may inevitably require crossing close to adjacent structures. In this paper, the driving of Shiraz metro twin tunnels beneath Zand underpass of a major municipal artery built 15 years ago has been analyzed. The earth pressure balance (EPB) operation parameters consisting of face pressure, grout pressure and thrust force, which are effective on the ground movement and tunnels–underpass interaction, were investigated. For precise analysis, the effects of twin tunnels construction on modification of normal forces and bending moments of the underpass structural members and first tunnel lining were also studied. The results showed that, face pressure as compared to grout pressure and thrust force had a more significant impact on the underpass settlement. The rate of displacement differences because of increasing those EPB operation parameters at tunnel crown was greater than the surface and piles toe of the underpass. The changes in normal forces of the underpass were greater than bending moments, which could be related to high bending moment of the underpass members. The normal forces showed remarkable variations in the upper concrete plate of the underpass. The effects of second tunnel construction on the first one, regarding to the changes in normal forces, bending moments and displacements showed less than 10% increment.

Research highlights
► We model a dual interaction problem between twin tunnels and an underpass.
► Simultaneous analysis of the tunnel construction parameters effects and the presence of adjacent structures were considered.
► Increasing face pressure and grout pressure lead to decrease induced surface settlement.
► Among TBM operation parameters, face pressure has more influence on the underpass displacements.