Study On Vibration Response Of Shield Tunnel-Stratum-Ground Building System Due To Subway Train Loads In Ground Fissure Site

With the continuous expansion of the urban scale in china,the construction of rail transit has been widely launched in many major cities.The metro has become an important form of rail transit because of its advantages of rapidness,punctuality and large transport volume,etc.However,with the rapidly increasing density of urban subway network,the problems of environmental vibration and noise caused by subway operation are becoming increasingly prominent.The dynamic response of tunnels,strata and ground buildings caused by subway train loads has become a topic of great practical significance.Because the metro lines in Xi'an are generally across the ground fissures,which leads the problems of dynamic interaction among tunnel,stratum and ground building,and the vibration response of the interaction system caused by subway train loads in the ground fissure site to become particularly complex and mysterious.This subject is an urgent issue to be solved in the study of environmental vibration problem induced by subway train operation in special sites,and has great significance to the construction of subway engineering and theoretical research.This article relies on the National Natural Science Foundation Project of China,that is “Research on the interaction among stratum,ground fissure and tunnel under subway dynamic loads(Approval No.: 41172257)”.The shield subway tunnel engineering orthogonal crossing the ground fissure belt in Xi'an is selected as the research background in this article.The large physical model test for the interaction among tunnel,ground fissure,stratum and ground building system under subway train loads is designed and carried out.The dynamic response characteristics of the model system are studied systematically,and the results of the physical model test are supplemented and verified by means of numerical simulation.Based on the analysis results of the vibration response of the research system,some suggestions on the tunnel structure design and ground building structure design are proposed.The major research works and achievements in this paper are as follows:(1)The general analysis theories of environmental vibration caused by subway train operation are summarized.The data acquisition and processing methods of subway vibration,the evaluation indexes and their calculation methods,the relevant specifications and limit value standards and so on are described in detail.The general propagation and attention laws of subway vibration in soil and ground buildings are summarized.(2)The transmission and distribution laws of dynamic stresses caused by subway train loads in the ground fissure site between the lining and soil,and in the soil are revealed through the model test and numerical simulation study.The influence range of ground fissure on the dynamic stresses in soil along the vertical direction,and the transverse and longitudinal directions along the tunnel is obtained.The results show that the dynamic stresses caused by subway train loads in the soil under the lining in ground fissure site are far less than that the static stresses caused by gravity load,but the inhomogeneous distribution characteristic of dynamic stresses exists in the soil near the ground fissure,so it is easy to cause uneven settlement of soil,thus affecting the safety service of the tunnel and track structure.Based on this conclusion,some suggestions on the tunnel structure design and foundation soil treatment in the field where crossing the ground fissure zone are proposed.(3)According to the present situation that a large number of unidentified hidden ground fissures exist in the urban area of Xi'an,the similarities and differences of subway vibration response of the site under the condition of exposed and concealed ground fissures are revealed by means of numerical simulation.Meanwhile,the influence laws of subway train loads on ground fissures are analyzed,and the conclusion that the subway train loads may aggravate the dislocation between the hanging wall and footwall of the ground fissure.The study deepens the understanding of the vibration response under the subway train loads in the ground fissure site.(4)The propagation and attenuation laws of vibration acceleration in soil and ground surface under subway train loads in ground fissure site are analyzed by means of model test and numerical simulation.The results indicate that the ground fissure has the amplification and reduction effect on the vibration acceleration response of the site.In the meantime,the influence range of ground fissure on the ground surface vibration acceleration is obtained.According to the above research results,same suggestions on the analysis and evaluation of metro environmental vibration in the loess ground fissure site,and the vibration damping design of subway track are summarized.(5)By using the methods of model test and numerical simulation,the vibration response of ground buildings on the ground fissure site caused by subway train loads is analyzed and evaluated from the aspects of vibration level,vibration acceleration level and effective value of vibration acceleration,and the distribution laws of the vibration acceleration in the buildings are obtained.The results show that the ground fissure has the amplification and reduction effect on the vibration level and the vibration acceleration response of the ground buildings,and the z vibration levels in the buildings generally exceed the prescribed limit values in the relevant specifications.(6)Based on the results analysis of model tests,the influence laws of subway train operation speed on the vibration responses of the ground fissure site and ground buildings are obtained.The results indicate that reducing the vehicle speed properly can effectively attenuate the vibration responses of the site and buildings.(7)Based on the numerical simulation of the vibration response of the upper building structures,and taking z vibration level as the evaluation parameter,then the influence laws of the structural parameters on the vibration response of the buildings induced by subway train operation in ground fissure area are analyzed,thus the structural design suggestions for the newly-built buildings in the ground fissure area along the subway line are put forward.(8)By means of model tests,the vibration acceleration transfer functions of the tunnel to the ground surface and ground buildings in ground fissure area are obtained.In view of the particularity of the ground fissure site,the prediction method of metro environmental vibration which based on the prediction method of vibration response transfer function,and combining the methods of numerical simulation,model test and field test is summarized.