Abstract: Constructing metro stations that closely undercross operating metro stations in soft stratum is challenging. In this study, a case study is conducted on an underground bundled integrate tunnel (UBIT) with a cross-sectional width of 40 m and a cover-to-span ratio of 0.01. The underpass section, with dimensions of 42.0 m (length) × 41.6 m (width) × 9.6 m (height), is located 0.2 m away from the existing station slab. A two-stage underpinning scheme using steel-concrete columns is adopted, and a corresponding rigid beam-column joint is designed. A series of environmental impact control measures are established in three aspects: pipe jacking, prestress tensioning, and equipment selection. Furthermore, equivalent-stiffness solid elements are used to simulate steel-concrete pipes, and coupled elements are defined to simulate the joint between the pipes. Spatial mechanical performance analysis is conducted through numerical simulations. The results reveal the following: (1) The adopted technical scheme meets safety requirements and has minimal impact on the existing station. (2) Owing to the comparable longitudinal and transverse dimensions of the underpass section, the UBIT structure deviates from an ideal transverse force state, resulting in significant internal forces and deformations in the longitudinal midsection and beam pipes. (3) Owing to the excavation of the working shaft, the bottom slab of the existing station shows obvious uplift deformation. The shallow pipe-jacking construction at a depth of 0.2 m increases the uplift deformation on both sides of the underpass section, whereas the central area experiences a decrease in uplift owing to the deflection caused by the upper soil cover and self-weight of the existing station.

Key words: underground bundled integrate tunnel, metro station, underpass, underpinning, coupling element