Stability Analysis Of Large Span And Small Spacing Tunnel

As the continuous expansion of urban traffic pressure.our country has adjusted the strategy of urban transport development and built a modern comprehensive transport system whose main part are subway and other mass rapid transportion in recent years.There are lots of successful cases of Proximity Tunnel in construction of the subway.However, the strcutural shapes are circle in many cases, there are a few cases whose upeer structure is large span pit and the lower one is double shield tunnel. Choosing a reasonable proximity schemes of construction to ensure the structural stabilities are focal points in constrcting and operating. So,it is necessary for in-depth research..This thesis takes the interval tunnel from Nanshan to Qian Hai-wan in Shenzhen Metro Line NO.11as study subject and usees FLAC3D numerical software with the embedded FISH language to analyse the sequence of construction, the surface subside in different conditions,the Principal Stress of Lining segments, the yield approach index in whether considering Fluid-Strucure Interaction or not. then has obtained the following basic conclusions:(1)The surface subsidence is caused mainly by the upper excavation.and useing the construction sequence of upper then under is more favorable for it.(2) Excavating double-holes one by one is more favorable for the. principal stress of lining segments when constructs the lower double shield tunnel.(3)The lower double-shield tunnels have different stress state,and the right one is in the more dangerous condition, when the tunnels staggered up and down.(4)The proximity is not obvious when the spacing is2D of the tunnels.(5)The yield approach index of the rock between the tunnels has a larger value,when considering Fluid-Mechanical Interaction.As the rapid deveploment of underground rail transportation in our country,the cases of proximity tunnels is growing day by day.The above views about proximity shield tunnels and Fluid-Strucure Interaction have important significance to ensure the safety when contructs.and provide a refernce value for the construction of similar cases in the future.