Mechanical Response And Deformation Control Of Shield Undercrossing The Existing Railway Bridge By Long Distance

With the acceleration of urbanization in China,the urban rail transit network has been continuously densified.There are more and more phenomena that the new metro shield tunnel crosses the existing railway overpass bridge.The construction of the shield tunnel inevitably disturbs the surrounding strata,resulting in additional deformation of the overpass bridge foundation,which poses a great potential safety hazard to the safe operation of the existing line.Therefore,it is of great significance to study the impact of shield tunneling through railway overpass bridges.Based on the engineering background of Changsha Metro Line 6 shield tunneling under the frame bridge of Beijing-Guangzhou railway and the rigid frame bridge of Changsha-Zhuzhou-Xiangtan intercity railway for a long distance,the mechanical response law and deformation control method of long-distance undercrossing the existing railway overpass were studied by using the methods of theoretical analysis,numerical simulation and field measurement,so as to provide a basis for the safe construction of the shield and the normal operation of the railway.The main research work and results are as follows:(1)Based on Mindlin’s basic solution,the formulas for calculating the longitudinal and transverse settlement of the ground surface under the frame bridge caused by shield underpass and the horizontal displacement of the pile foundation caused by shield side crossing construction were derived.The effects of shield additional thrust,shield shell friction,shield tail grouting pressure and ground loss rate on the deformation of the ground surface and pile foundation were analyzed.(2)ABAQUS software was used to conduct three-dimensional numerical modeling for shield tunneling under the existing railway overpass bridge for a long distance.The deformation laws of overpass bridge and track structure caused by shield tunneling under different grouting pressure,soil warehouse pressure and stratum reinforcement conditions were analyzed to provide basis for proposing corresponding control measures.(3)Based on the static excavation model of shield tunneling through railway frame bridge,the dynamic coupling model of train track foundation shield system was established.Through joint simulation with numerical software,the dynamic response law of train track system and railway frame bridge interaction under different train speeds,shield tunneling positions and construction conditions was studied.(4)According to the above theory and numerical calculation results,the active control technologies such as shield tunneling parameter control and passive control technologies such as stratum grouting reinforcement were proposed;Automatic monitoring technology was used to monitor the structure of railway overpass bridge.By analyzing their change rules,shield tunneling parameters can be adjusted in time to ensure the smooth construction of shield and the safe operation of railway overpass bridge.