| The metro system has been rapidly developed as an important means to relieve the heavy load of ground traffic when population keeps boosting as result of urbanization.The phenomenon of newly-bulit metro lines being constructed crossing over old ones which are under operation is gradually increased.However,the existing metro tunnel can be greatly affected by the construction-induced disturbed strata,especially when the newly-built tunnel is going below an old one.In this term,deformation control and prediction of existing metro tunnel becomes the key point when it comes to subway operation,which makes it pivotal to study the specific influence of shielding tunnel construction-induced disturbance on upper metro tunnels.Based on the project of a new loop line shield tunnel,with the existing Railway Tunnel crossing over,this paper is aimed to investigate specific influence on of shield tunneling on the upper existing tunnel as well as giving solutions on tunnel deformation control management by the method of field measurement and numerical simulation.The main contents and conclusions are as follows:(1)The calculation method of ground loss is deeply analyzed,taking both applicable conditions and accuracy into consideration.This paper summarizes a set of calculation methods for the loss rate of formations applicable to different stages of underpass construction,and verifies the reliability of the method by appling it in the project of research.(2).Based on the underpass project in research,a three-dimensional shield tunnel construction model is established to analyse the effect of tunneling underpass construction on strata and existing tunnels.The results show that the deformation of the existing tunnel is induced by the reduction of soil pressure,and the existence of the existing tunnel limits the propagation of the deformation.The Impact of undercrossing construction on existing tunnels mainly occurs within the interval of one diameter before and after the crossing point of the excavation face.(3)By analyzing the monitoring data such as surface deformation and deep soil displacement caused by underpass tunnel construction,the strata deformation law of the whole process of shield construction is obtained.The monitoring results show that the influence of shield construction on the surface mainly occurs within the range of two diameters from the excavated surface to the excavated surface.The longitudinal horizontal displacement of the overlying soil layer of the existing tunnel is mainly the reverse deformation of excavation,and the shallower the buried depth,the greater the longitudinal horizontal displacement.(4)Based on the three-dimensional numerical model of shield tunneling,the influence of key factors on the settlement and deformation of existing tunnels,such as stratum elastic modulus,covering soil thickness,distance between new and old tunnels,underpass angle,tunnel diameter,ground loss and so on,is discussed and evaluated through parameter sensitivity analysis and calculation of multiple schemes.(5)Numerical simulation method is used to evaluate the deformation control effect of grouting reinforcement measures and to optimize the reinforcement extent.It is found that the closer the reinforcement measures are to the newly-built tunnel,the better the deformation control effect will be,and it is more reasonable to reinforce the tunnel longituinally with a length of about four diameters in advance grouting reinforcement scope. |
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