Numerical Analysis Of The Technology Of Pit Excavation And Its Influence On Pit In A Metro Station In Hefei

With the continuous development of economy and the demand of transportation,urban subway projects are rising constantly.The structure of subway station is usually deep and large foundation pit engineering.Due to the structural characteristics or functional requirements,it is necessary to conduct two or more excavation in the local foundation pit during the construction,forming the pit within the pit.Pit-in-pit construction in subway station is a big problem in foundation pit engineering.Pit-in-pit excavation will complicate the stress and deformation of the surrounding foundation pit or the surrounding construction section,which increases the risk of construction.At present,the case of pit within pit in subway foundation pit is common,but there is no mature theoretical research,there are few literatures on pit within subway foundation pit,and there is no complete specification for relevant construction technology to refer to.Geotechnical engineering problems have strong non-linearity,and the existing theoretical research is mostly focused on the type of foundation pit with regular shape,and there is little research on pit within subway foundation pit.It is difficult to obtain the influence of pit within pit excavation on the stress and deformation of the whole foundation pit by using the general foundation pit calculation method,and it is difficult to provide safe and reliable guidance.In view of the above problems,this paper takes a pit in a subway station in Hefei as the engineering background,combined with theoretical analysis,numerical simulation and construction monitoring methods to carry out a numerical analysis and research on the excavation technology of a pit in a subway station and its influence on the external pit.The ANSYS APDL software was specifically used to build a numerical model of local pit in pit structure,and the rules of lateral movement of the surrounding structure and surface settlement caused by different pit in pit excavation schemes were calculated and analyzed.The main research contents are as follows:(1)The earth pressure calculation of the retaining structure and the deformation of the foundation pit engineering are summarized,including the description of the MohrCoulomb and Druker-Prager constitutive characteristics of the earth pressure calculation and the four forms and main deformation factors that usually appear in the excavation process of the foundation pit engineering are summarized.(2)A new circular excavation technology at four corners of a pit is proposed.Compared with the conventional step backward excavation,the supporting structure erection sequence is more symmetrical and reasonable in space by using this excavation technology.Through numerical simulation combined with actual monitoring data,the deformation rules of the retaining structure under the new excavation technology and the conventional step-back excavation technology were analyzed and compared respectively.(3)In view of the proposed new pit in pit excavation technology,the influence of pit in pit excavation on the basement settlement deformation of adjacent outer pit is analyzed through numerical simulation,and the safe construction range of the bottom plate of the main structure of outer pit during the construction of pit in pit excavation is obtained.