Research On The Influence Of The Deep Foundation Pit Excavation Of Subway Structures

With the rapid development of Chinese city construction,subway construction has become a symbol of the city,The first and second tier city in China,Metro shuttle back and forth in the central city,it is a label from on the other side,the subway is also a city’s economic development level.The utility model has the advantages of safety,time and efficiency,no ground space,safety and environmental protection,and is convenient for people to travel.After the subway line was built,along the subway line,And other large civil engineering projects such as the subway station built later came into being,the deep foundation pit is emerge in an endless stream.The excavation of the foundation pit is unloading,which breaks the original internal equilibrium state of the subway tunnel,which leads to the problem of the safety of subway operation.In the construction of foundation pit excavation along the subway,the slightest mistake is seem to impact on the subway or even destroy the structure,so the research work of deep foundation pit excavation of subway operation safety structure is very important.This paper is based on the Xi’an Metro Line 4 TJSG-11 train station construction project,to meet the operation of Metro Line 4,the first to complete the implementation of advanced line tunnel,National Railway Station changed late stage,A sort of station and ancillary facilities are all synchronous implementation,to realize subway station operation function.The width of the excavation pit is about 20 m,the depth is about 20.9m,the bottom of the foundation pit is close to the bottom of the tunnel,the distance between the station and the excavation interval is about 8.5m,and the tunnel is located in the excavation area.Based on the two methods of numerical simulation and geotechnical centrifuge test,the influence of the structural displacement and mechanical properties of deep foundation pit excavation of Xi’an metro line four station is studied.Through the study the following conclusions are drawn :1.Foundation excavation is a process of unloading for the tunnel overall stress,but the effect of each part of the tunnel is different,the whole vertical force is greater thanhorizontal directionthe,impact to influence the level of stress for the tunnel top and bottom effect.Special attention is paid to other parts of the excavation stress is reduced,but with the excavation of the right abutment,the stress is not increased,but the added stress value is in the controllable range.2.By the centrifugal experimental data and numerical simulation of the extracted data analysis,and comparing the value of moment changes of tunnel,tunnel inflection point is along the tunnel axis counterclockwise trend,at the same time the whole tunnel also has trend along the tunnel axis counterclockwise rotation.3.For tunnel displacement,the whole tunnel is "floating",in particular,the tunnel soil stress around,the pit direction "pushed" to the pit direction,but the top of the tunnel has a reverse pit moving trend.In accordance with the technical requirements of the engineering design of Xi’an metro line four,the vertical and horizontal displacement values of the subway tunnel structures are within the allowable range.4.The soil pressure of tunnel is analyzed,the effect of pit excavation for tunnel soil pressure of each part is different,in general the earth pressure decreases,but the decreasing degree is also different.The soil pressure to the tunnel bottom and right tunnel arch waist the soil pressure is greatest impact.