Model Test Study On The Change Of Subway Tunnel Induced By Excavation

In-depth and systematic research on the mechanism and control measures of the impact of foundation pit excavation on neighboring existing tunnels has become a major issue that needs to be solved urgently.1.This article focuses on the reduced size model to simulate the different excavation depths of the foundation pits,no groundwater,groundwater,and different water level heights.In the model test,the earth pressure change on the top of the underground pipeline and the change of the tunnel convergent deformation value and the excavation range of the foundation pit are analyzed.The law of distribution in space and above,and explore the mechanism that causes these changes.Through the analysis of the actual measurement results of the existing engineering cases,the influence of the excavation of the foundation pit,and a useful reference for actual engineering is obtained.2.The results show that,during the excavation of the foundation pit,there is an earth pressure influence line on the existing tunnel below.When it reaches a certain depth,the excavation of the foundation pit only affects the area below the earth pressure influence line above the tunnel,which can be called influence Zone,through the calculation of the test size parameters,the angle between the line of influence of the earth pressure and the top plane of the tunnel is approximately 60°.When the foundation pit is excavated,due to the unloading in the middle of the foundation pit and the unloading outside the scope of the foundation pit,the relative rigidity of the underlying tunnel outside the excavation scope will gradually decrease,which will continue to be compressed and converged.Produce a "straw hat" deformation.Under the influence of groundwater,the displacement of the measuring point increases with the increase of the excavation depth of the foundation pit,and the convergent deformation curve of the tunnel is a "parabola" with an opening upward.3.Compare the three working conditions of foundation pit excavation depth,no groundwater,groundwater and different depths of groundwater for analysis.When there is no groundwater in the foundation pit,the cumulative earth pressure change ratio of each measurement point during the excavation of the foundation pit When there is groundwater,the cumulative earth pressure change at each measuring point is smaller,and the higher the groundwater level,the greater the cumulative earth pressure change at each measuring point.When the ratio of the excavation depth of the foundation pit to the bottom of the pit to the top of the tunnel is less than 1,the excavation of the foundation pit has little effect on the earth pressure of the tunnel outside the pit.When the ratio of the depth of the excavation of the foundation pit to the bottom of the tunnel to the top of the tunnel is greater than 1,The influence of excavation of foundation pit on the change of earth pressure above the tunnel outside the pit will increase sharply.The cumulative displacement change of each measurement point is larger,and the higher the groundwater level,the greater the displacement change of each measurement point.The measurement point with the groundwater level 110cm Cumulative displacemen>Cumulative displacement of the measuring point of 100cm groundwater level>Cumulative displacement of the measuring point of 90cm groundwater level>Cumulative displacement of the measuring point without groundwater.4.The actual measurement results show that for the tunnel upward line,the vertical displacement of the tunnel measuring point 0.67 times the width of the foundation pit excavation center has little change,and the distance from the excavation center of the foundation pit reaches 1.33-2 times the excavation width of the foundation pit.The amount of settlement is the largest when left and right;the cumulative vertical deformation curve of each measuring point in the area affected by the excavation of the foundation pit is roughly a middle-high "W" shape;the tunnel bulges in the foundation pit and sinks outside the foundation pit,which affects the entire construction "Poll-shaped" deformation occurs in the area;for the downline of the tunnel:the closer the distance to the excavation center of the foundation pit,the greater the settlement,and the area where the excavation has a more obvious impact on the tunnel is 0.67 times the distance from the excavation center of the foundation pit.Within the excavation range,when it reaches 1.33-2 times the width of the excavation of the foundation pit,the pipeline settlement will be the largest,and the cumulative vertical deformation curve of each measuring point on the downline is roughly a small"M"-shaped distribution in the middle.Figure[58]table[7]reference[39]...