Abstract: In recent years, frequent surface collapse phenomena have been observed around underground engineering works in rail transit projects. To prevent such occurrences, a theoretical model for calculating the extent of cavities beneath the ground surface is established, and a corresponding theoretical formula is derived. The causes, processes, and mechanisms of ground collapse, along with countermeasures, are analyzed through both practical and theoretical approaches, revealing the internal relationships among underground rail transit construction, pipeline leakage, and surface collapse. The results show that: (1) Sudden surface collapses around underground engineering works in rail transit projects are primarily induced by pipeline leakage, dewatering operations, and ground loss settlement. (2) Ground settlement is positively correlated with leakage from surrounding pipelines, with erosion and settlement deformation mainly concentrated from the ground surface to 1－2 m beneath the pipe bottom. (3) The process and mechanism of surface collapse are clarified, and a theoretical model for the critical void zone of sudden collapse is proposed—a collapse may occur when the void length reaches 1.6 m. (4) Improving the strength of road structures is a relatively economical and effective preventive measure, based on sensitivity analysis of key parameters. Effective countermeasures are proposed from the perspectives of both active control and passive defense.

Key words: urban rail transit, underground engineering, surface collapse, road structure, formation cavity, theoretical model, countermeasures