Abstract: A flexible and easy-to-construct steel cushion beam underpinning technology is proposed to dismantle and remedy tunnel subgrade structure issues while keeping railway tunnels operational. The principle, process, and structural form of the steel cushion beam are introduced. The load-bearing characteristics of the steel cushion beams under the live loads of trains C80 and CRH3 are analyzed using full-scale loading tests and numerical simulations of the steel cushion beam structure. In addition, the effects of span and beam spacing on the deformation characteristics of the steel cushion beams are investigated. It is found that the longitudinal beam stress and middle crossbeam deformation increase with the length of the longitudinal beam. Furthermore, the position of the middle crossbeam has a greater influence on lateral displacement compared to vertical displacement. Application cases in heavy-haul and high-speed railway tunnels reveal that the deformation and dynamic response of the steel cushion beam are controllable during train operations. After the underpinning remediation, the deformation of the tunnel subgrade structure remains stable. These results indicate that the steel cushion beam is suitable for underpinning and remediating railway tunnel subgrade structures.

Key words: railway tunnel, subgrade disease, structure underpinning, steel cushion beam, model test, numerical simulation