Study On Longitudinal Stress In Concrete Segments In Small Diameter Shield Tunnel Construction

With the rapid development of Chinese economy,the application of small diameter shield is more and more wide.Taking Beijing Huaifang Recycled Water Factory as engineering background,this paper studied longitudinal stress of small diameter shield concrete segment in construction through three methods which include theoretical analysis,field monitoring analysis and FLAC3 D numerical simulation.The Research contents and study results are that:(1)In theory analysis,this paper introduced and analyzed five kinds of constitutive model of soil and structure interfaces and selected the coulomb sliding constitutive model as a foundation to study the change rules and influence factors of small diameter shield segment longitudinal stress while single loading and unloading and circulation of loading and unloading.(2)Through the analysis of field monitoring results of small diameter shield concrete segment in construction,we get the following conclusions:(1)With shield tunneling,the longitudinal stress of segment goes through four variation phases,i.e.periodical sharp fluctuation phase,dynamic stability phase,gradually decay phase and stable phase.The longitudinal stress of segment goes stable around 0.2~0.3MPa after the distance between shield tail and the segment is 108 rings.(2)The longitudinal stress of segment decreases with the distance between segment and shield tail increase during shield tunneling.The longitudinal stress of segment increases firstly and then decreases with the distance between segment and shield tail increase during segment assembling.(3)The longitudinal stress(the initial value is 1.6MPa)of segment after 50 rings behind shield tail is 5% less than that when segment assembling.(3)Through the FLAC3 D numerical simulation study of segment longitudinal stress change rule and influence factors while single loading and unloading and circulatory loading and unloading,we get the following conclusions:(1)With the increase of the tunnel buried depth,the longitudinal stress of segment show a decreasing trend in dynamic stability phase and stable phase.At the same time,the influence of shield jacks also showed a trend of decreasing.(2)With the increase of friction Angle of tunnel section grouting solidification body,the longitudinal stress of segment show a decreasing trend in dynamic stability phase and stable phase.At the same time,the influence of shield jacks also showed a trend of decreasing.(3)With the increase of elastic modulus of grouting in tunnel solidification section,the longitudinal stress of segment show a increasing trend in dynamic stability phase and stable phase.But,the influence of shield jacks also showed a trend of decreasing.(4)With the increase of the solidification length of grouting,the longitudinal stress of segment show a increasing trend in dynamic stability phase and stable phase.At the same time,the influence of shield jacks also showed a trend of increasing.(5)With the increase of shield jacks unloading pressure,the longitudinal stress of segment show a increasing trend in dynamic stability phase and stable phase.But,the influence of shield jacks also showed a trend of decreasing.