Research On The Deformation Law Of Half Cover Deep Foundation Pit Of A Subway Station In Hefei

With the rapid development of the city and the increasing development of the underground space,the subway construction is in full swing.Subway station is an important part of subway construction.The construction of subway station is accompanied by a large number of deep foundation pit projects.However,in the process of deep foundation pit construction of general metro station,due to the limited urban space and the large traffic flow of the upper trunk road,higher requirements are put forward for the construction method of deep foundation pit.The half cover excavation method can not only ensure the traffic above the foundation pit,but also reduce the impact of space constraints on the construction progress.Therefore,the half cover excavation method is more and more used in the subway station engineering.In the construction process of half cover excavation method,the traffic pressure can be relieved by passing vehicles on the half cover plate,but at the same time,large vehicle load acts on the cover plate and its supporting structure,which also causes partial load on the retaining structure.Therefore,it is of great theoretical and practical value to study the deformation characteristics of the construction process of half cover excavation of deep foundation pit in metro station.In this paper,the half cover deep excavation of a subway station in Hefei is taken as the research object.Through the numerical modeling of the retaining structure of the foundation pit,the surrounding soil conditions and load conditions,the deformation and internal force changes of the retaining structure,the surrounding ground surface and the differences between the two sides of the foundation pit are analyzed.The deformation characteristics of the half cover deep excavation of the subway station are discussed by comparing with the field monitoring data.At the same time,the analysis is made The deformation of half width cover plate under vehicle load and the main factors affecting the deformation.The main achievements are as follows:(1)The deformation of the retaining pile is in the shape of "bow",and the deformation of the surface settlement is in the shape of "groove".Due to the partial load of half cover excavation and the asymmetry of top soil excavation,the deformation laws of both sides of the foundation pit are different: the horizontal displacement value at the top of the retaining pile is larger at the cover excavation side than at the open excavation side;the groove bottom of the surface settlement curve at the open excavation side is closer to the foundation pit,and the settlement value at the edge of the foundation pit at the cover excavation side is larger.(2)In the early stage of foundation pit excavation,the middle column will produce downward settlement deformation under the action of larger vertical load.After the excavation depth of foundation pit becomes larger,it will produce upward displacement under the uplift action of foundation soil.The differential settlement between the retaining piles on both sides and the middle column will produce greater additional bending moment and shear force on the transverse structure of half cover plate,so the differential settlement value should be strictly controlled.(3)In the half cover plate support system,there is a large negative bending moment at the concrete support and support at the open excavation side,so the upper longitudinal reinforcement at this position should be paid attention to in the structural design;when the cast-in-place cover plate is used,a reasonable proportion should be adopted between the thickness of the cover plate and the height of the tie beam to ensure the uniform distribution of the internal force of the cover plate and reduce the waste of materials.