Coupling Response Of The High Speed Train Track-subgrade-tunnel System Under The Loadings By The Tunnel Construction And The Subway Operation

The transportation pressure of the city has been becoming one of the main issues of the transportation jam on the city roads.The widely-used shield tunneling is the good alternative tool to release the severe stress of the city transportation.The shallow tunnel is inevitably cut across the existing buildings,such as the railway track.How to maintain the stability of the surrounding soils around the shallow tunnel is the controlling aim during the shield tunneling.Moreover,to ensure the safety of the track-subgrade-tunnel system by the moving loadings along the railway tracks at the ground and the tunnel is also important in engineering practice.However,current solutions are not effective for the mechanism of the ground loss by the tunneling excavation.In addition,the dynamic response of the track-subgrade-tunnel system by the moving loadings can’t be revealed by the available methods.Therefore,it is significant to focus on the coupling response of the track-subgrade-tunnel system by the tunneling excavation and the moving loadings along the railway tracks at the ground and the tunnel both in theory and in engineering application.The essential issue of the response of the track-subgrade-tunnel system is the soil-structure interaction.That is to say,the stresses are applied to the track and the tunnel from the subgrade by the external loadings.At the same time,the structures react to the surrounding soil.This kind of interaction should be basically taken into consideration.However,the interaction can’t be easily tackled because of the difficulties of the problem.In particular,there are few solutions for the dynamic response of shallow tunnel by the moving train loading at the ground surface due to the orthogonality of boundary conditions along the ground and the tunnel surfaces.On the basis of the thorough investigations on the available researches and engineering background of Line 2#of Fuzhou metro system,the settlement mechanism and dynamic response of the track-subgrade-tunnel system have been studied in this paper.The main contents and originalities of this study are outlined as follows:(1)In terms of the simplified stochastic medium theory and the upper bound theorem in the limit analysis,the failure mechanism of the tunnel roof has been investigated.The surface settlement is estimated for the collapse of the tunnel roof in the light of the stochastic medium theory.The failure criterion is adopted by the yield function of the series power.Based on the failure curve expressions of collapse blocks,the effects of the geometry and material parameters on the potential range of the failure mechanism are discussed.(2)Analytical solution is proposed for the collapse mechanism of the tunnel roof in the layered soil by means of the stochastic medium theory.The shape curve of the collapse is assumed to be smooth.The displacement curve of the ground surface is determined by the stochastic medium theory.The collapse mechanism of the tunnel roof in the layered soil is obtained by considering the coupling effect of the layers of the soil.The effect of layer properties of the foundation on the collapse mechanism is examined.(3)An analytical solution has been proposed for the stress and deformation of the railway track at the ground surface by the tunneling.The coupling of the deformations along the longitudinal and transverse directions can be considered in the present method.The longitudinal and transverse deformations are derived for the undrained clay in the light of the zero volumetric strain,respectively.The railway track is assumed to the beam on elastic foundations.The loadings on the beam are calculated in terms of the deformations by tunneling.The analytical solutions to the respective governing equations of the beam at the longitudinal and transverse directions are obtained.Parametric study has been performed to investigate the effects of the materials properties of the subgrade and the railway track.(4)Numerical model has been established to study the dynamic response of the subgrade-railway track-shallow tunnel system due to the railway moving loading in the tunnel.The influences of the properties of the structures and the subgrade are investigated thoroughly.(5)Model test has been performed for the settlement mechanism of the subgrade by the shield tunneling.The test indicates that the closer to the tunnel roof,the greater of the soil disturbance.At the tunnel portal,the pressure at the shield machine is small and the ground surface has subsided.With the increasing of the tunneling to the centre of the model,the pressure at the tunnel face increases greatly.(6)The model test and numerical study have been performed for the dynamic response of the subgrade-railway track-shallow tunnel system by the high-speed moving loadings along the overlying railway track.Parametric study shows that the soil pressure at the prescribed location increases with the decreasing of the speed of the moving speed.Moreover,the stress transfer path decreases with the decreasing of the embedded depth of the tunnel.