Deformation in settlement and grouting remediation of thickened larger-diameter metro shield tunnel in soft soil: A case study

Shield tunnels built in soft soil are prone to settlement, which is often accompanied by convergence deformation, further resulting in a series of damages to the tunnel structure and compromise its safety in service. This paper presents an engineering case on the settlement development and internal drilling grouting remediation of a tunnel section in Shaoxing Metro Line 1, where the inner diameter and thickness of the tunnel linings are increased to be 5.9 m and 400 mm simultaneously. The tunnel settlement arises from a comprehensive analysis of several contributing factors, encompassing ground disturbances such as pile driving, pile extraction, backfilling of pile holes, road structure construction, and road traffic. A grouting remediation plan is thoughtfully designed, including a careful assessment on the necessity for a temporary steel support system which is based on a full-scale three-ring test of the tunnel structure. The deformation of the tunnel during settlement and grouting processes is thoroughly analyzed to investigate the deformation resistance capacity exhibited by the thickened larger-diameter tunnel. The case study and experimental results demonstrate that tunnel structures with an increased diameter and thickness have better deformation resistance than conventional metro tunnels in soft soil layers. The analysis of this study can provide a reference for tunnel structures optimization and similar grouting remediation projects in shield tunnels.