Optimization Analysis On Middle Pile Supporting System Of Single-layer Guide Hole Large Diameter Middle Pile Method

With the acceleration of the process of urbanization in the world,China's rail transit construction has also entered a period of rapid development,the construction technology of subway stations continuous improvement and innovate.Pile-beam-arch tunneling method,which based on the traditional shallow excavation method,which has absorbed the technical achievements of the cover excavation method.,is a new construction method formed by a combination of mature construction techniques,such as small guide pilot,buckle arch,pile and so on.However,due to environmental and resource considerations,the existing pile-beam-arch tunneling method has room for further optimization and research.In the past five years,the underground excavation station of Beijing Metro is taken as the research background.Through the means of data statistics,theoretical analysis,numerical simulation and field monitoring,the influence of different methods of pile-beam-arch tunneling method on the stratum is analyzed and studied on the optimization and improvement of the large diameter pile in the single layer guide hole,the main work and achievements are as follows:(1)Through the study of the field monitoring data,the influence of the three different methods of pile-beam-arch tunneling method on the surface subsidence is statistically analyzed,and then the Flac3D software is used to model the "pile and strip foundation method","pile and long pile method" and "the single-pilot large-diameter pile method",combined with field data,educing "the single-pilot large-diameter pile method" is the best control effect on the formation of deformation.(2)Comprehensive consideration of station size and disturbance caused by construction,using finite element software and field data,the span and buckle arch radii of the station are optimized and analyzed.(3)In actual projects,the pile diameter and pile length of the "single-pilot large-diameter pile method" are often too thick and too long,resulting in wasted engineering.In order to optimize this method,numerical simulation of large diameter middle piles by continuous-discrete coupling method,combined with the data of the static test of middle pile,conduct comparative analysis.The research shows that the ultimate bearing capacity of the middle pile can be much larger than that of the actual load in "the single-pilot large-diameter pile method".Thus,the pile diameter and pile length can be reduced and optimized in different degrees.(4)Combined with the actual engineering needs of Suzhou Bridge Station on Line16,to study the technical feasibility and related technical measures for the "zero embedding" pile foundation in the large-diameter middle-pile excavation station with single-layer guide tunnels.The research shows that the construction method of the "zero embedding" pile foundation of the steel tubular column of Suzhou Bridge Station,meeting the force requirements.At the same time,the numerical simulation results of the measured data of Suzhou Bridge station can meet the requirements of the evaluation system from 4 aspects:the criterion of the concrete strength,the strength discrimination index of the steel tube column,the discrimination index of the strength of the fixed steel plate and the strength of the anchor bar and the stability criterion of the steel tube column.Therefore,the "zero-embedding" structural measures for steel columns are safe and feasible,has guiding significance for the subsequent project.