Ground deformation due to construction of closely spaced overlapping shield tunnels in reclaimed silt: case study

Abstract

The construction of closely spaced overlapping tunnels in soft reclaimed strata poses significant challenges to the tunnels’ structural integrity. This paper presents a case study of the Shenzhen Metro Line 5 obliquely overcrossing the existing Line 11 in a silt reclamation stratum. A three-dimensional finite element model was developed using Plaxis 3D to evaluate the influence of shield construction parameters on surface settlement and existing tunnel deformation. Key parameters considered include face pressure, tail void grouting pressure, and grout hardened strength. The numerical results, validated by field monitoring data, indicate a "heave-ahead, settle-behind" morphology. Surface settlement in reclamation silt strata exhibits a clear inverse relationship with face support pressure, tail void grouting pressure, and the elastic modulus of the hardened grout. Meanwhile, the deformation of the underlying existing tunnel demonstrates negligible sensitivity to variations in these parameters, as its structural response is primarily governed by global ground unloading rather than local stability parameters. These findings offer a critical reference for construction parameter optimization and vibration control in similar complex reclaimed geological conditions.