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Shield Tunneling under Railway Station Throats in Soft Soil Areas: A Case Study

Railway station throats have the most stringent standards for permissible deformation caused by adjacent construction. This paper describes the case of a safely implemented shield tunneling project beneath the throat of a large railway station with more than 11 tracks in soft soil areas. By identifying major design constraints, the route scheme and line alignment were established to balance the engineering conditions, which have a potential impact on the railway switches. Finite element model simulations were performed to estimate the track displacements. These simulations demonstrated the need for ground improvement. The ground improvement strategy involved the use of compact machinery to operate in the small area between the tracks. Furthermore, the earth-pressure-balanced shield machine, tunnel segments, and synchronized slurry were optimized to the site conditions. A trial section of tunnel boring was used before reaching the railway to confirm appropriate shield machine parameters. An automatic monitoring system provided continuous feedback for precise control of the construction parameters. Ultimately, the construction project achieved its goals, causing a maximum track displacement of 8.4 mm. This report also describes our experience in organizing a joint workshop consisting of the railway administration and operation teams, the metro design team, and construction, survey, and consulting companies to enhance project planning. This study provides valuable insight and can serve as an important reference for similar future projects.