Study On Deformation Law Of Shallow Buried Tunnel In Zhengzhou Metro

With the high speed development of economy,lots of people are pouring into big cities,such as Beijing,Shanghai,Guangzhou and so on,which leads to the urban traffic congestion directly,so the construction of metro are starting in more and more cities to solve this problem.As a main method of metro construction,shallow tunnel construction method doesn't need to move surroundings,it has not only less interference to ground traffic,but also lower cost,therefore shallow tunnel construction method is widely applied during the construction process of metro.But the shallow tunnel construction will have disturbance to formation,produce deformation of surface and soil,and also lead to the cracking of underground pipeline?the inclination of buildings and the uneven settlement of ground,which threaten people's life and properties,so the study of deformation law of surface is necessary during the excavation of construction for shallow-burial Tunnel.Because the number of pipelines which are surrounding the construction yard are large,and they are close to channel,so the shallow tunnel construction of No.1 and No.2 passageway of New Zhengzhou University station can not use pipe shed for advance support before the excavation of channel,so the scheme of advanced support by using grouting technique of leading conduit to replace pipe shed was proposed,and then monitored and measured the whole process of channel excavation.This paper studied two main contents: one is that it used FLAC3 D to simulate the construction process of shallow tunnel construction pre and post the advanced small pipe grouting,then by combining with practical monitoring data,it verified the feasibility of using leading conduit grouting technique for advanced support,and analyzed the deformation features and change law of surface during construction process.The other is that after shallow tunnel channel construction,when traffic and automobile was running through the top of channel this paper measured it's acceleration,studied the surface deformation law of shallow tunnel channel construction under the effect of traffic load by using FLAC3 D,and compared with practical data and results of static load,then analyzed the effects of traffic load to shallow tunnel channel construction.The main conclusions of this paper are drawn as follows:(1)Through the analysis of practical monitoring date,this paper obtained that variation law of ground settlement caused during the construction process is basically according to the stage of minimal settlement to rapid settlement and then to slow settlement and then to stable settlement,as well as the accumulated settlement amount and settlement rate are not exceed the early warning value during the process of construction,which showed that shallow mining method of small duct grouting is feasible to the construction of access of station of Zhengzhou metro.(2)This paper simulated the shallow tunnel construction pre and post the advanced small pipe grouting by using FLAC3 D,and took survey line of one cross section as example.After strengthening surface by advanced small pipe grouting,the maximum settlement of surface is-3.81 mm,which decreased 1.86 mm compared to the maximum settlement before strengthening.Through the verification of engineering example,this showed that pre-grouting with small conducting tube can obviously decrease the ground settlement and is an effective auxiliary measure to CRD method of the shallow-burial tunnel.(3)This paper counted the upper traffic flow of No.1 passageway of shallow-burial tunnel firstly,through date acquisition instrument it measured the acceleration versus time date of surface and the top channel caused by loaded car(including bus,cement mixing truck,dregs transportation vehicle and so on),and then treated the vehicle dynamic load as forms similar to excitation which can reflect the feature of vehicle load cycle?the effect of running speed and geometric irregularity,then numerical simulation was conducted to get the acceleration of surface and top channel by FLAC3 D,which verified the rationality of dynamic load model.(4)During the construction stage of various operation conditions,it simulated the surface deformation caused by dynamic load of loaded car by using FLAC3 D,then compared it with simulation results of static load and practical monitoring date(without dynamic load of loaded car),the results shows that the maximum value of settlement increased 16.3%,which explains that dynamic load of loaded car has bigger influence on the surface settlement.So Zhengzhou metro had better take the influence of dynamic load of loaded car into consideration when it uses the method of shallow-covered excavation,which can be the theoretical support and technical reference for the similar projects in the future.