Monitoring And Analysis Of Local Internal Support System Of Deep Foundation Pit Near The Subway Station

With the development of China's social economy,the construction and development of the central city is exceptionally rapid.The foundation pit of the old city is often close to or adjacent to the subway,and the construction of the foundation pit must ensure the safety and normal operation of the subway,which puts forward higher and more complex requirements for the support of the foundation pit.Based on the design and construction of a deep foundation pit supporting system of a construction project near Changsha Metro Line 2,this paper discusses the comprehensive application and comparison of various supporting schemes for foundation pit,uses finite element software to analyze the local internal supporting structure near the subway station in the foundation pit,and monitors the supporting system in the construction process.Through the above work,the main conclusions are as follows:(1)In the selection of supporting schemes for deep foundation pits adjacent to Metro stations,two-stage excavation support is adopted.According to conventional support,first part of the basement is constructed,and then part of the internal support system with the main structure of the basement as the fulcrum is adopted to carry out the second excavation.The construction time and exposure time of the whole foundation pit can be reduced,and the uncertainty affecting the safety of metro operation can be reduced.It is a safe and reasonable technical scheme.(2)The main structure of the basement is the fulcrum of the local internal support system.The strength and stiffness of the main structure and the supporting action point should be paid attention to.In the analysis of supporting action point,it is found that the maximum stress value appears in the supporting position of supporting action node and joint beam,and the stress value of floor slab is higher after that.In the design,attention should be paid to the local strength of joint.The stress diffusion effect of the floor is obvious,and it should be more advantageous for the joints to be located in the floor.(3)In addition to joint setting and design,the axial force of local internal support is similar to that of common internal support structure with the change of earthwork excavation and support installation sequence.(4)For the foundation pit support adjacent to the operating subway station,it is necessary to strengthen on-site monitoring,timely forecast construction risks,and ensure the safe operation of the subway.(5)Through the finite element analysis and field measurement,the lateral displacement of the supporting piles near the metro is very small,and the strength and stability of the internal support fully meet the requirements;the supporting joints on the main structure of thebasement have small deformation,strength meets the requirements,and there are no cracks and other phenomena.This shows that the technical scheme of local internal support is reasonable,and the design of detailed joints is safe and reliable.During the construction of the foundation pit near the subway station,the subway has not been affected,and still maintains normal operation.