Research On Long-term Settlement Of Tunnel-stratum System Under Subway Vibration Load

As a kind of metro tunnel disease,the long-term settlement of tunnel structure and surrounding strata induced by metro train load widely appears in the metro network of major cities.Especially when the metro tunnel is built in the soft soil stratum,the long-term settlement can even develop to an amazing value,which not only seriously threatens the structure and operation safety of the metro line,but also has a serious impact on the surrounding environment.Under this background,it is of great engineering significance to propose an effective method to predict the long-term displacement of tunnel-soil system induced by the cyclic metro train load and to find out its development law.In view of this,,taking Hanyou section of Nanjing Metro Line 2 as the research object,this thesis systematically studies the development characteristics and analysis methods of the long-term displacement of the tunnel-soil system induced by the cyclic metro train load through the methods of field test,theoretical analysis and numerical simulation.The main work and research results of this thesis are as follows:(1)Based on the long-term settlement observation results of Hanyou section of Nanjing Metro Line 2,the long-term settlement development law of tunnel structure in the section of Nanjing Metro Line 2 where has the characteristics of binary strata is analysed.It is found that the development of long-term settlement of tunnel structure is closely related to the properties of the underlying foundation soil and the buried depth of the tunnel,and a large part of its magnitude can be attributed to the long-term effect of train vibration load.(2)By using the 2.5-dimensional(2.5D)numerical method,the vibration characteristics of track-tunnel-soil system induced by the moving train are studied systematically,and the dynamic stress distribution laws of the strata around the tunnel are investigated when the tunnel is located in the muddy clay stratum and the silty sand stratum,respectively.Furthermore,combined with the cumulative plastic deformation characteristics of muddy silty clay and silty sand,the stratified summation method is used to analyse the development law and maganitude characteristics of the train-induced long-term settlements of the tunnel-soil systems both when the tunnel are located in muddy clay and silty sand,respectively,with the difference between the developments of long-term settlement of tunnel structure under different stratum conditions well revealed.(3)Based on the 2.5D method and the initial strain method,a new numerical model for analysing the train-induced long-term displacement of the tunnel-soil system is proposed,which effectively overcomes the limitations of the traditional analysis model on the problem concerned and can realize a comprehensive analysis of the long-term displacement distribution of the whole tunnel-soil system.(4)Using the newly proposed numerical model,the effects of stratum drainage condition,soil long-term deformation characteristic,train speed,train formation type,track fastener stiffness,tunnel segment outer diameter and stratum reinforcement on the development of the train-induced long-term settlement of tunnel-soil system are detailed studied.It is found that the stratum drainage condition,the soil long-term deformation characteristic,the tunnel segment outer diameter and the stratum reinforcement have important influences on the train-induced long-term settlement of the tunnel-soil system.