Study On Optimization Of Construction Scheme Of Three Hole Super Large Diameter Pipe Jacking

In order to save surface space and alleviate urban traffic congestion and drainage difficulties,urban construction is gradually inclined to underground space construction.Open cut method,shield method,pipe jacking method and other construction methods are mostly used in underground space construction.As a non excavation construction process,pipe jacking method has the characteristics of small quantities and high construction efficiency.With the improvement of construction technology,pipe jacking is gradually developing in the direction of large diameter,multiple pipes and small spacing.Based on the existing research foundation,combined with the engineering practice,using ABAQUS software,when there are no existing buildings on the surface,this paper studies and analyzes the influence of different spatial layout of three hole pipe jacking on the surface deformation and segment stress,and determines the optimal construction scheme on this basis;When there are existing buildings on the upper layer of the ground,the effects of different construction schemes of three hole pipe jacking on ground settlement,segment stress,frame foundation settlement,frame displacement and frame stress are studied and analyzed,and the development law of stress and strain is summarized according to the calculation results of numerical simulation The most dangerous position,corresponding protection measures,optimal spatial layout and construction sequence are determined.The main research results are as follows:(1)When there are no existing buildings on the surface and there is plenty of underground space,the three hole pipe jacking shall adopt the space type of single-layer layout as far as possible.If the pipe jacking construction equipment meets the requirements of three hole pipe jacking at the same time,the construction scheme of three hole pipe jacking at the same time should be adopted.At this time,the ground subsidence is 18.77 mm,which meets the specification requirements,and the construction period is only 1 / 3 of the three hole jacking in turn,The construction period is greatly shortened;When the underground space is limited,the three hole pipe jacking can adopt the space type of double-layer layout.At this time,the optimal scheme for the sequential jacking of the three hole pipe jacking is "△" layout,and the construction sequence of "up first and down" is selected.In this case,the maximum surface settlement is 27.74 mm,which is slightly larger,which can be controlled by adjusting the soil bin pressure and controlling the grouting amount.(2)When the three hole pipe jacking is arranged in two layers and the optimal construction scheme is adopted,in order to improve the construction efficiency and shorten the construction period,the lower parallel pipe jacking can shorten the construction time through the construction scheme of asynchronous and simultaneous Jacking under the condition of meeting the requirements of surface settlement and preventing the tensile damage of pipe jacking.At this time,the k value of the lower pipe jacking interval should be k≥6L and should not be too large.(3)When there are existing buildings on the surface,considering the ground settlement at the lower part of the frame,segment stress,displacement change of frame beams and columns and internal stress of the frame,the "△" type layout should be adopted for the layered layout of three hole pipe jacking,and the construction sequence of "up first and down later" should be selected.At this time,the tensile stress distribution of each segment is relatively uniform for reinforcement,and the column base and surface settlement are within the allowable range of the specification,The frame has good stability in both vertical and horizontal directions.It is only seriously tensioned at the connection between the longitudinal beam and each column,which should be paid attention to.