Research On Micro-deformation Control Technology Of Closely Undercrossing Existing Station In PBA Construction Method Of New Station

Under the situation of increasingly scarce urban land resources,urban rail construction is developing more and more toward the three-dimensional and cross-over type.Among them,the construction of the new station is more difficult due to the strict settlement control standard of the existing station for the closely undercrossing project.Based on the background of the undercrossing project of Pingguoyuan Station of Beijing Metro Line 6,this paper analyzes the important and difficult points of the project.The deformation law of overlying strata and existing subway stations under the disturbance of PBA construction method,as well as the force characteristics of existing stations and newly built stations are investigated.Four micro-deformation control technologies including advanced grouting,grouting lifting,lead screw support and side span CD method for excavation and set up the middle door are put forward,and the effect and rule of settlement control are proved.By comparing and analyzing the construction scheme of PBA construction method combined with micro-deformation control technology and PBA construction method,the mechanical response rule of stratum and station in the construction of micro-deformation control PBA construction method is obtained,as well as the optimization effect of micro-deformation control technology on the construction of PBA construction method.Finally,the measured data are analyzed,and the numerical simulation results are compared with the measured data to verify the accuracy of the numerical simulation.The main research contents of this paper are as follows:(1)This paper analyzes the important and difficult points of the undercrossing project of Beijing Metro Line 6 from three aspects: the proximity between the new subway station and the existing subway station,the spatial position relationship and the construction risk.This project is a close stick oblique undercrossing project,is a special risk project.The settlement control requirements of the existing station are strict,but it is difficult to control the settlement under the condition of sand and gravel stratum.Therefore,the major difficulty of the project lies in controlling the settlement of the existing station,ensuring the normal operation of the existing station and the safe construction of the new station.(2)Midas GTS NX three-dimensional finite element numerical analysis software is used to establish the construction model of the new station undercrossing existing station with PBA construction method,and the whole construction process of PBA construction method is simulated.The deformation law and mechanical response law of stratum,existing station and new station caused by PBA construction method are revealed.The simulation results show that the settlement of the existing station track structure exceeds the control value by nearly one time,which does not meet the requirements of settlement control,and the station structure maximum settlement is close to the control value.This indicates that although the settlement control effect of PBA construction method is good,the project still needs to take measures to further control the settlement of the existing station,so that it is within 2mm micro-deformation.(3)In order to achieve the purpose of micro-deformation control,four micro-deformation control technology schemes are proposed,including advanced grouting,grouting lifting,lead screw support and side span CD method for excavation and set up the middle door,which are combined with the PBA method of this project.The numerical simulation method is used to obtain that the most suitable thickness of advance grouting reinforcement for this project is1.5m.The effect of grouting lifting can be achieved only when the grouting pressure reaches a certain level.The lead screw support can provide some support for the existing station,which is conducive to the overall establishment of the new station structure.The force of the newly built station can be changed by the method of side span CD method for excavation and set up the middle door,which is conducive to the construction safety.(4)The finite element software is used to establish the construction model combining micro-deformation control technology schemes and PBA construction method,and the actual construction process is simulated.The results show that the micro-deformation control technology can effectively control the deformation of existing stations,and the station structure settlement and track structure settlement can meet the settlement control requirements.Through the analysis of monitoring data,the settlement law of actual construction station structure and track structure is obtained.The accuracy of the numerical simulation results is verified by comparing with the numerical simulation results.