Optimization Of Pile Spacing Based On Foundation Pit Monitoring At Xinfadi Subway Station In Beijing

The population base of China is relatively large and densely populated in cities,making cities increasingly demanding the use of three-dimensional space for measurements.The construction of high-rise buildings,underground shopping malls,subways and other projects,more and more deep foundation pits have emerged,and foundation pit support projects that can provide a safe construction environment have been also received unprecedented attention.Compared with the superstructure and foundation engineering,the development of the deep foundation pit support project was late in use,and it is still not mature enough.In the current construction,the main supports are the traditional geotechnical theory and regional experience,resulting in the results of the project itself is not insecure or conservative or even too conservative,resulting in waste.The optimization design of the deep foundation pit support project is to adjust the relationship between the safety and reliability of the support structure and the cost of the economy in the design process.This article relies on the foundation pit project of Xinfadi station of the second section of Beijing metro line No.19.In the daily construction monitoring data,it is found that the ground settlement around the foundation pit is large,and the deformation of the supporting pile is large.Therefore,based on this problem,combining with on-site monitoring data,modeling and importing FLAC3 D finite element numerical model were simulated by MIDAS to study the relationship between support pile spacing and deformation.Specific research contents include:Firstly,according to the site data,the characteristics and laws of the deformation of the site supporting piles are analyzed and summarized.Second,the actual engineering situation of the restoration site is calculated by the model,and the rationality of the foundation pit model is verified at the same time;Third,comparing the pile deformation in several different groups of supporting pile spacing design,find the most reasonable and economical pile spacing within the control value range.The specific findings are:The deep deformation curve of piles for supporting piles is characterized by “large middle deformation and small deformation at both ends”.The maximum deformation of the pile is 13 m-15 m depth in the foundation pit,and the maximum horizontal displacement of the pile is 18.6 mm.Deviation of the inner side of the pit,the vertical displacement of the supporting pile is 12 mm-13 mm,showing a bulging stateUnder the premise that other engineering conditions have not been changed,the horizontal displacement of piles in the area of foundation pits will gradually increase as the pile spacing of supporting piles increases,but it is still within the range of control values.When the shield pile spacing is 1.9m,and the standard segment spacing is 2.0m,the maximum horizontal displacement deformation is 24.88 mm,close to the control value of 25 mm.At this point,it can save 64 support piles and directly save costs 1.92 million yuan.Therefore,confirm this pile spacing as the best pile spacing.