Behavior Of The Joint Between Shield Tunnel And Underground Station Impacted By The Deep Excavation

The excavation of deep foundation pits will have a negative influence on the nearby subway station,which may affect the force-deformation of metro lines and station,even the safe operation of the subway.The influence on the safety of metro structure caused by deep excavation and other geotechnical activity has been an important topic of underground engineering.Because of the different on load transfer mode and structure stiffness between station and tunnel,major differential deformation may occur on the joints between stations and shield tunnels,which may be the sensitive weak link.The stress and deformation behavior of the joint,which may affect the safe operation of the subway,attract few attention at home and abroad.By using the 3-D numerical analysis method combined with case history,the stress and deformation behavior of the joint caused by the new excavation of foundation pit next to the metro station is investigated.The effect of excavation scale,the distance between station and excavation,excavation depth and relative location between the excavation and the joint are analyzed.Meanwhile,a new index have been proposed to evaluate the safe state of the joint.The main studies of the paper contain the following parts:1.Based on the numerical analysis method,the distribution and development of deformation of station and tunnels caused by the excavation that shares a same diaphragm wall with metro station was studied,and the stress and deformation behavior of the joint was investigated.The curvature radius and relative bending,which came from the deformation,will be used to evaluate the safe state of the joint.Some results can be concluded.Because the metro station heaves and the shield tunnels settle due to soil unloading in the excavation,the stress and deformation behavior of the joint,which is worse than the largest settlement of tunnels,is complex because of the differential settlement between station and shield tunnel.With the increase of excavation depth and area,the curvature radius of joint decreases and the relative bending increases.If the foundation pit shares a same diaphragm wall with metro station or far away from the tunnels,the curvature radius of joint is relatively larger.2.The mechanical characteristics of the joints during the construction of deep foundation pits which have the different diaphragm wall with metro station are investigated.The results show that the station and shield tunnels have different settlements because of the difference on stiffness.Thus the stress and deformation behavior of the joints,which is worse than the largest settlement of tunnels,is complex because of the differential settlement between station and shield tunnel.With the increase of excavation depth and the decrease of distance between station and excavation,the curvature radius of joint decreases and the relative bending increases.3.Based on the results of three-dimensional numerical analysis,a new index,relative angle change rate,have been proposed to evaluate the safe state of the joint.The numerical simulation and field data show that the new index has a negative correlation to curvature radius,which can be used to evaluate the rotation of the joint and the tension of the bolt.Based on the field data,the relative angle change rate is 0.0038°/m under a curvature radius of 15000 m.4.Based on the field data of Shanghai Century metropolis and Shanghai west station,the mechanical characteristics of the joints during the construction of deep foundation pits next to the metro station are investigated.Combined with the results of numerical simulation and relative protective measure,it is obtained that the simulation results are accordance with the field data,and some measures,like division of foundation pit,from far to near and soil reinforcement,can be used to control the settlement of tunnels and deformation of stations,which can finally improve the stress state of the joint.