Analysis Of The Impact Of Excavation Of A Deep Foundation Pit On The Adjacent Subway Tunnel In Changchun

With the acceleration of China's urbanization process,road transport has been overloaded.In order to ease the traffic congestion in urban area,increasingly more rail transit are under construction.However,due to the high population density and complexity of existing buildings,excavation engineering is facing challenges especially those near subways.Load removal would affect subway operation and lead to safety issues by applying subsidiary stress and deformation on surrounding soils.Therefore,studying the impact of foundation pit excavation on existing subways is of great significance for protecting the safe operation of subway tunnels.Based on extensive literature review,related theory,modelling and data on variation of soil stress and deformation,ground rebound,deformation of retaining structure and ground settlement were studied.Based on the Mindlin solution,the subsidiary stress generated during the excavation of the tunnel is calculated and lateral deformation of tunnel was calculated by Winkler elastic foundation beam theory therefore,lateral and longitudinal deformation theory of the shield tunnel is verified Based on the theoretical research as stated above,3D numerical simulation was conducted for a deep foundation excavation project near a subway in Changchun,Jilin Province,and the main research results are:(1)The pit bottom uplift,the lateral displacement of the retaining structure,and the ground settlement outside the pit are significantly affected by the depth of the excavation.From the excavation of one layer to the very bottom,the maximum uplift increased by 104%;the maximum displacement value increased by 163%;The maximum settlement value increased by 108%.(2)The horizontal displacement of the tunnel caused by the excavation is generally shifted to the inner side of the pit,and the maximum displacement occurred on the south side of the foundation pit.The vertical displacement along the length of the tunnel showed concave shape where the peak value occurred in the middle.(3)The tunnel deformation is significantly affected by the excavation depth of the foundation pit,the thickness of the retaining structure,the excavation method,and the depth of its own embedment.The maximum horizontal displacement of the tunnel during the excavation of one layer to the bottom increased by 106%,The maximum vertical displacement generated in the tunnel was increased by 19%.During the change in the thickness of the selected envelope structure from 0.6m to 1.2m,the maximum horizontal displacement generated in the tunnel was reduced by 44%,and the maximum vertical displacement was reduced 72%.Excavation of the foundation pit and digging the farther side firstly will effectively reduce the tunnel displacement.Compared with layered overall excavation,the maximum horizontal displacement generated in the tunnel was reduced by 32%,and the maximum vertical displacement was reduced by 11%.In the process of increasing the embedded depth from 15 m to 21 m,the maximum horizontal displacement can be reduced by 44.7%,and the maximum vertical displacement can be reduced by 34.7%.