Study On The Stress And Deformation Characteristics Of The Mixed Enclosure Structure Of Deep Foundation Pit

In recent years,with the development of urban construction and urban rail transit,more and more deep foundation pit projects appear in the cities.In many enclosure structures of deep foundation pits,the pile-anchor composite enclosure structure is widely used cause of good stability and little space occupation.In this paper,on the background of the construction of deep foundation pits engineering of Shijiazhuang Subway Line 3 Dongli Station Passage,analyze the force and deformation characteristics of the enclosure structure in the region during foundation pit excavation,furtherly analyze the stress and deformation of prestressed anchor cable under the geological conditions of fine sand layer.The paper mainly include the following sections:(1)The advantages and disadvantages of different enclosure structures of deep foundation pit and their application are summarized in the paper.Combined with the geological conditions and environmental factors of this project,it came conclusion that the envelope structure of bored piles with multi-pivots is suitable in Shijiazhuang.Namely,we usually can use the structure type of bored piles and steel pipe support.As the research project in this paper needs to arrange the track well,according to the engineering characteristics of the track well,the deep foundation pit enclosure structure in this section should adopt the bored piles and prestressed anchor cable type.(2)Use FLAC3 D software to establish a numerical model,analyze the force and deformation characteristics of pile-anchor enclosure structure of deep foundation pit under different excavation depths in fine sand layer,and obtained corresponding laws.Through analysis and comparison with on-site monitoring and measuring data,provide a reference for engineering practice.(3)In FLAC3 D software,the numerical simulation is carried out to study the influence of the incident angle of anchor cable,pre-tensioning force and free length of anchor cable on the loss of prestressing force during the construction of anchor cable.Besides,both compensate tension and super tension of compensation measures were analyzed to determine the best anchor stress compensation measures.