Responses of Cross-River Tunnel Due to Overlying Shield Tunnel Construction (I): Influence of Construction Procedure

Gradually increasing tunnels across the Huangpu River and the rapid development of subway tunnel network in Shanghai will inevitably induce the new subway tunnel construction close or above cross-river tunnels. Therefore, it is meaningful and essential to study the influence of subway shield tunnel construction on the existing underlying cross-river tunnel. By considering the longitudinal rigidity discount of shield tunnels, stress history in situ ground, and construction procedure of subway shied tunnel, the writers conducted a numerical analysis by three dimensional finite element program to investigate the responses of existing underlying cross-river tunnel due to the construction of subway tunnel above. The change law of displacements and internal forces in the lining of cross-river tunnel with the advance of tunnel boring machine was given special concern. Results shows that the maximum values of vertical displacement and lateral displacement of cross-river tunnel occur at the cross section rightly below the axis of subway tunnel, and the lateral value is comparatively smaller than the heave value. Meanwhile, the moments in cross section decrease and the axial forces in cross section tend to be even after the completion of subway tunnel excavation. The longitudinal stresses and moment increase gradually with the advance of TBM, and the leak at the crown of cross-river tunnel should be paid more attention since the tensile stress at this point increases during the construction of subway tunnel. As for the influence scope, beyond the horizontal distance of about 2D (D represents the external diameter of cross-river tunnel) to the axis of cross-river tunnel, the effect of excavation of overlying subway tunnel on the cross-river tunnel can be ignored.