Abstract: To clarify the adverse effects induced by lateral unloading of an adjacent foundation pit excavation, a shield tunnel structure model is established based on the joint force-displacement equation and the interaction relationship between a metro shield tunnel and a foundation pit in Hangzhou, China. Then, an elaborate stratum-shield tunnel finite numerical simulation method is used to explore the force and deformation mechanisms of the segments and joints of the existing shield tunnel caused by lateral unloading. The effectiveness of the proposed method is validated by comparison with field monitoring data. The results reveal the following: (1) The deformation of the shield tunnel can be divided into a convergence deformation zone and a ring dislocation zone. (2) A 7.5 mm vertical settlement and an 8.5 mm horizontal displacement towards inner foundation pit are induced, and the displacement along longitudinal direction shows a stepped shape due to dislocation between segmental rings. (3) The segmental ring exhibits an elliptical convergence deformation, and the longitudinal joints at the tunnel crown and the arch waist open towards inside and outside of the tunnel, respectively. The maximum in-ring compression stress reaches 7.66 MPa, leading to leakage of the longitudinal joints at the tunnel crown and compression crack at the arch waist. (4) Dislocations between adjacent rings occur at circumferential joints, leading to leakage. (5) Foundation pit dewatering is a primary factor affecting tunnel displacement, which contributes 82% of settlement and 46% of horizontal displacement, respectively.

Key words: foundation pit excavation; foundation pit dewatering, shield tunnel, segment joint, settlement, segment force, numerical simulation