Research On Seismic Safety Evaluation Of Subway Shield Tunnel Under Construction

With the acceleration of urbanization and the enhancement of population flow in China,the demand for efficient,convenient and other characteristics of the subway keeps increasing,thus promoting the subway construction in China to enter the high-speed development stage.Shield tunneling has become the preferred construction method in urban subway construction due to its features of safety,efficiency and little influence on the existing superstructure.China is located in the seismic belt around the Pacific Ocean,and 74% of the cities are located in the seismicity zone.Among the more than 300 cities in China,about 50%of the cities have seismic fortification intensity of 7 degrees or above.At present,the research on seismic safety of tunnel structures under construction needs to be further advanced.For the above reasons,this paper takes the shield tunnel under construction as the research object,mainly focuses on the deformation characteristics of shield tunnel construction ring under earthquake and the deformation law under different construction conditions,the deformation characteristics of the whole structure of shield tunnel and the deformation law under different construction conditions,and the safety evaluation method of shield tunnel under earthquake.The specific contents and results are as follows:(1)Based on dynamic time-history analysis method and finite element software,the deformation of shield tunnel construction ring under different construction conditions under seismic action has been analyzed.Under the transverse seismic action,the peak deformation time of the construction ring is consistent with the peak acceleration time of the acting seismic wave.The maximum value of relative displacement appears at the node near the top of the construction ring,the maximum value of diameter deformation rate appears at the node group near the inclined arch at 45° or 135°,and the maximum value of relative displacement between nodes appears at the node group near both sides.There are 6 construction stages of the construction ring from excavation to lining.The diameter deformation rate of the construction ring at the 4th construction stage after excavation and the relative displacement and relative displacement between nodes at the 6th construction stage after excavation are the maximum value of the construction ring without lining.The relative displacement,the diameter deformation rate and the relative displacement between the joints of the construction ring will increase with the advance of construction after the lining,and the trend conforms to the law of logarithmic growth.(2)Based on dynamic time-history analysis method and finite element software,the deformation of the whole structure of shield tunnel under different construction conditions under seismic action has been analyzed.Under the action of transverse earthquake,themaximum diameter deformation rate of the unlined section can be generated at 1/2 of the length of the structure of the unlined section in the shield tunnel under construction,and the maximum relative displacement and relative displacement between the maximum nodes of the unlined section can be generated at the connection between the unlined section and the end of the applied section.The maximum value of all kinds of deformation of the structure of the lining section occurred at 3/4 of the length of the lining section,and the maximum value was also the maximum value of the whole structure of the tunnel.With the progress of construction,the maximum value of each deformation of the tunnel structure under the action of earthquake increases continuously,and its trend also conforms to the law of logarithmic growth.According to the growth law,the deformation range of the whole structure of shield tunnel and the initial stage of structural deformation stabilization are predicted.(3)Based on the theory of Vague set and set pair analysis,the safety evaluation model of subway shield tunnel under earthquake was constructed.The evaluation results can reflect the seismic level of shield tunnel structures under different working conditions in detail.The seismic level of the tunnel structure decreases with the progress of construction,but it will gradually reach a stable state.Based on this,the seismic level of shield tunnel during the whole construction process is estimated.