| China is one of the countries which with the most karst distribution in the world.With the development of underground rail transit,the construction of shield tunnels in karst areas is inevitable.At present,the researches of shield tunnels in karst areas mainly focuses on the tunnel construction stage.However,as more and more shield tunnels are built in karst areas,the focus of researches should not be limited to the tunnel construction stage.We should also gradually pay attention to the impact of karst caves which are untreated or undiscovered during tunnel construction on the dynamic responses of operating shield tunnels.In this dissertation,taking the Guangzhou Metro Line 9 as an example,MIDAS GTS software is used to establish a finite element model to study the train vibration responses and lateral seismic responses of shield tunnel segments in underlying karst strata.The main research contents and achievements are as follows:(1)By consulting relevant data,the numerical modeling method of underground structure dynamic calculation are understood,and the karst caves that have important implications on the research are selected and basic karst conditions are determined to lay the groundwork of subsequent researches.(2)The corresponding influence rule is obtained by establishing a three-dimensional finite element model and studying the influence of the horizontal position,roof thickness,height,span and filling factor of the karst caves in underlying karst stratum on the vibration responses of the shield tunnel segment under a single metro train load.The train vibration responses of the shield tunnel segment under the karst condition and the non-karst condition are compared.By comparing with the non-karst condition,the results show that the occurrence of the karst caves in the bottom rock layer of the tunnel has no obvious influence on the response laws and amplitude of vertical displacement and vertical acceleration about the tunnel segment under a single metro train load.And it also has no significant effect on the response laws of principal stress about the tunnel segment.However,it has a great influence on the max tension stress and the max compression stress of the tunnel segment.(3)The corresponding influence rule is obtained by establishing a two-dimensional finite element model and studying the influence of the horizontal position,the roof thickness,height,span and filling factor of the karst caves in underlying karst stratum on the vibration responses of the shield tunnel segment internal force under the lateral seismic.The vibration responses of the shield tunnel segment internal force due to lateral seismic under the karst condition and the non-karst condition are compared.By comparing with the non-karst condition,the results show that the occurrence of the karst caves in the bottom rock layer of the tunnel has no obvious influence on the distribution rule of the tunnel segment internal force along the circumference direction under the lateral seismic.Remarkably,the karst caves near directly below the tunnel will increase the response amplitude of the tunnel segment internal force under lateral seismic. |
PDF Full Text Request