Due to the increasing development of infrastructure systems in urban areas of China, many subway tunnels are being constructed near existing subway lines. Shield tunneling underneath will inevitably cause settlement of the existing tunnel and may even threaten the safety of running trains. In this study, based on an analysis of extensive monitoring data from massive undercrossing construction cases in the Shenzhen metro area, the deformation characteristics of existing tunnels and the ground caused by the construction of a new shield tunnel underneath were analyzed. The additional longitudinal stress of the existing tunnel, which is the main reason for water seepage and structural damage of the tunnel lining, was studied. The difference between the settlement of greenfield and the existing tunnel was analyzed. Several key influence factors of existing tunnel settlement, such as the spatial position, support pressure and tunnel stiffness, were discussed and an empirical equation for estimating the settlement of existing tunnels induced by the excavation of a new shield tunnel was proposed. The settlement profiles obtained using the new prediction equation were compared with the real monitoring records, and good agreement was observed. The new equation derived from the cases studied in this paper can provide a reference for predicting and controlling the deformation of existing tunnels induced by shield tunneling.
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