Deformation and Control of Metro Structures during Asymmetric Bilateral Zero-Distance Excavations

With the continuous expansion of metro networks, zero-distance excavations on both sides of metro lines in urban underground spaces have become increasingly common. However, limited research has been conducted on the deformation response and corresponding control measures for such excavations. Based on extensive field measurements, this study analyzed the deformation of an existing metro station and tunnels caused by large-scale zero-distance asymmetric excavations on both sides. The results show that excavations caused massive heave of the metro station and tunnels, which exceeded the original control value by approximately 50% and 100%, respectively. The metro station transmitted the heave significantly, extending the influence range of the excavation to more than 10 times the excavation depth (H), which is much larger than the common 2H–4H excavation influence range; the tunnels exhibited lower transfer effects, and the influence range was 3H. The metro station had good structural integrity, exhibiting horizontal displacement toward the deeper excavation, while the twin tunnels moved in opposite horizontal directions and toward their respective adjacent excavation sides. The tracks inclined toward the excavation on the north side and away from the excavation on the south side, causing slight torsion along the longitudinal direction. Furthermore, measures to control metro station heave were examined, and the results indicated that surcharge loading was effective. The control effects of different loading schemes were further studied by numerical simulations. For the same total loading strength, compared to single-stage loading, multistage loading during excavation has better control effects when the heave is extremely large at greater excavation depth. The special influence characteristics of asymmetric bilateral excavations at zero distance on the metro structures and control methods discussed in this study can provide useful reference information and guidance in the future for more rapid development and utilization of underground space.