Study On Structural Safety Of Shield Tunnel And Vehicle Dynamic Behavior Under Disease Condition In Beijing Subway

Shield tunneling is widely used in subway construction because of its small environmental impact and high degree of construction automation.The proportion of shield tunnels in the mileage of existing tunnels is increasing year by year.The characteristics of "multi-joint" of shield tunnels determine that their integrity is poor,so that the diseases such as segment deformation and leakage are unavoidable.Since the operation of the first shield tunnel in Beijing Subway in 2007,the problem of diseases has become increasingly prominent.There are great potential safety hazards in the service of tunnel structure and train operation.Taking Beijing Subway as the research object,the disease detection of shield tunnels in the whole network of subway operation is carried out.The lining structure,the safety of track structure and the dynamic characteristics of train running under the condition of the disease are studied by numerical simulation and dynamic simulation.(1)The disease status of shield tunnel in Beijing Subway was investigated and summarized in an all-round way.The shield tunnels of Beijing Subway have been extensively inspected.41 typical sections of 12 subway lines with shield tunnels in Beijing have been counted.Based on 20 evaluation indexes,the status quo of 7 common diseases of subway shield tunnels has been summarized.The main results are as follows:1)Leakage water is the most common disease of shield tunnel in Beijing Subway,more than 70%of the tunnel diseases are leakage water,bolt holes and segment joints are the main channel for groundwater infiltration into the tunnel;2)Cracks are the main form of overall tunnel bed of shield tunnel.The cracks in the tunnel bed are mainly inclined cracks at 45 degrees at the position of the support block and transverse cracks in the crack bed slab.Generally,the depth runs through the bed slab.3)Tunnel deformation has a direct impact on structural durability,safety and driving safety.(2)Based on the numerical simulation method,a refined finite element dynamic model is established.Based on the field test data,a three-dimensional refined dynamic model of shield tunnel-integral ballast-track is established by using Midas-GTS finite element software.The mechanical deformation characteristics of lining and track structure of shield tunnel under different deformation conditions are analyzed,and the dynamic response of track structure under vehicle load is studied.The main conclusions are as follows:1)When the maximum transverse or vertical deformation of tunnel is less than 15mm,the tensile and compressive stresses of segments do not exceed the limit value,but when the transverse deformation is more than 25mm or the vertical deformation is more than 35mm,there is a risk of cracking of segments;2)With the increase of the transverse or vertical deformation of tunnel,the transverse or vertical deformation of rail increases linearly;3)The acceleration of vertical vibration of rail increases the transverse deformation of tunnel;The deformation is not sensitive,but will increase sharply with the increase of the vertical deformation of the tunnel.(3)Based on the results of finite element analysis,a multi-body dynamic simulation model is established to analyze the relationship between the deformation of shield tunnel and the dynamic characteristics of train.Simpack multi-body dynamics software is used to establish the train-track coupling calculation model.The rail additional deformation caused by shield tunnel deformation and random track irregularity are superimposed as the input model of track excitation.The relationship between tunnel deformation and driving safety and stability is analyzed.The main conclusions are as follows:1)The influence of tunnel deformation on driving is positively correlated with train speed.When the deformation is the same,the influence of transverse deformation on driving is greater than that of vertical deformation;2)When the transverse deformation of tunnel is less than 25mm or the vertical deformation is less than 35mm,the safety and stability evaluation indexes of train running are within the limits.