Challenges and countermeasures for using pile-beam-arch approach to enlarge large-diameter shield tunnel to subway station

The Jiangtai station (on Line 14 of the Beijing Subway) is the first station in China constructed by using the pilebeam-arch (PBA) method to enlarge a large-diameter shield tunnel. This study illustrates the construction method, layout, geological and hydrological conditions, and construction processes of the station. The challenges in station construction are analysed, and targeted countermeasures are presented. The field test results showed that in the test section, the asymmetrical removal of B-segments caused the middle wall to bear large eccentric loads. In the standard section, and after construction optimisation, the eccentric loads acting on the middle wall were effectively controlled. In addition, the ground surface settlements of the station were systematically monitored during construction. The monitoring results showed that the maximum ground surface settlement values of different monitoring sections were between 46.1 and 56.8 mm. The ground surface settlements were mainly caused by the shield tunnelling, side pilot tunnel construction, and middle pilot tunnel construction, accounting for approximately 11.2-14.1%, 45.4-48.1%, 30.1-32.5% of the total settlement, respectively. This investigation is intended to serve as a reference for similar projects.