Abstract: To address the need for dismantling and remediation of tunnel substructure damage without interrupting operation, a flexible, easy-to-construct, railway-operationally-adapted steel pad beam replacement technology for tunnel substructures has been proposed. The principle, process and structural form of steel pad beam are introduced. The load bearing characteristics of steel pad beams under live load of C80 and CRH3 trains are analysed by means of full-scale loading test and numerical simulation of steel pad beam structure. The influence of span and beam spacing on the deformation characteristics of steel pad beams is investigated. The longitudinal girder stress and vertical deformation in the tunnel longitudinal girder length increase, and the position of the middle crossbeam of the steel pad beam has more influence on the lateral deformation than the vertical displacement. The deformation and dynamic response of the steel pad beam during the passage of a train can be controlled by combining the application cases of the buttress remediation technology in heavy railway and high-speed railway tunnelling projects. The deformation of the tunnel substructure is stable after the buttress remediation. The results show that the pad beams are suitable for railway tunnel substructure replacement remediation, and can provide technical support for similar railway tunnel substrate disease remediation.

Key words: railway tunnel, subgrade diseases, structure underpinning, steel pad beam; model testing, numerical simulation