| There are many urban rail transit lines.More and more intensive commercial development projects are in the periphery of the subway,which has caused frequent construction of foundation pits projects around the operating subway.The location of foundation pits and subway tunnels is relatively complicated.For example,above,on both sides,on the same side,and so on.During the construction of foundation pits,the influence of the surrounding soil layers is more complex and sensitive,and the deformation of the subway tunnel structure is more significant.Therefore,the safety of subway operation will pose a great threat.First of all,according to the excavation foundation pit project,this paper studies the influence of factors,such as the pit size and relative position,on the safety of the adjacent subway tunnel.Second,this paper studies the effect of excavation foundation pits on the proximity of subway shield tunnels.This paper derives the theoretical formulas for the deformation and internal forces of metro shield tunnels under excavation foundation pit at equilibrium.In addition,the study used numerical analysis calculation experiments,discussed the impact of the foundation pit on the adjacent tunnel,simulated the construction excavation process of the foundation pit group,and compared the monitoring data of the nearby metro shield tunnel during the construction of the group foundation pit project.Based on the results of calculations and numerical simulations,the safety influencing laws of group foundation pit excavation on near shield tunnels are summarized.This paper collects 34 engineering cases about foundation pits adjacent to subway tunnels in Shanghai,and summarizes the settlement changes of adjacent tunnels.This paper analyzes 96 sets of numerical calculation tests for the spatial positions of foundation pits and tunnels.The following conclusions are obtained:The displacement of the shield increases with the excavation depth and the excavation width;decreases exponentially with the increase of the horizontal distance;and gradually decreases with the depth of the shield.Relying on the excavation of three foundation pits in Shanghai Beiwaitan.The monitoring plan and monitoring data during the construction of this group were studied.The monitoring plan and monitoring data during the construction of this group were studied.This paper uses large-scale 3-D numerical simulation group engineering construction.Using the methods of theoretical calculations,numerical simulations,and on-site monitoring data,the deformation and stress of adjacent tunnels under excavation of the group foundation pit were studied.By simulating the method of excavating different foundation pits,how to ensure the safety of group foundation excavation to the structure near the shield tunnel.It is concluded that the excavation of a group of foundation pits is 50%larger than that of a single pit.The excavation sequence and method of group foundation pits have a great influence on the proximity of shields.Excavation of foundation pits at the same time is more unfavorable to the safety of shield tunnels.The excavation method adopts the construction of large-area-area foundation excavation far away from the subway after the construction of a small cross-section area pit near the shield tunnel,which is more favorable to the operation safety of the tunnel.Finally,based on the research results and engineering applications,it proposes how to carry out the excavation construction and protect the safety engineering measures for the operation of the shield tunnel.The measures mainly include that large-scale foundation pit excavation adopting separate section,foundation pit reinforcement,optimize the excavation and the "micro disturbance grouting" of the tunnel deformation zone. |
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