Research On Settlement Control Technology Of Station And Tunnel Tnterval Construction Of Wuzixueyuan Station Line6,Beijing Subway

In the metro construction, the shield construction method has been used in most of theinterval tunnels. The related researches and construction experience has been summarizedsufficiently. But during the interval tunnel constructions, irregular cross-section constructionoften arises. Large-variable cross-section tunnel has complex characteristics. The groundsurface settlement characteristics caused by construction of large-variable cross-section tunnelis different from common tunnels. The application of PBA occupies a more importantposition among various metro construction methods. This paper is on the bases of BeijingMetro Line6Wuzixueyuan Station Construction and the construction monitoring data. It isaimed at the construction of large-variable cross-section tunnel and a station construction withPBA technique. Numerical simulation is carried out with Midas/GTS software. Thesimulation of different construction sequence on the influence of surface subsidence has beencompared and analyzedAiming at the influence of large-variable cross-section tunnel construction application onthe ground surface and according to the actual monitoring data, reasons of different resultshave been analyzed. Considering the actual construction situation, this paper believes that inthe construction of variable cross section tunnel, the direction of the horizontal displacementof tunnel construction on ground surface settlement should not be ignored. It will reduce thesettlement at both ends of the tunnel, at the same time the position of varying cross sectionhas large settlement. The biggest settlement will arise at the variable section area. Thisposition will be the most unfavorable position of ground surface settlement, that’s whysettlement control in construction of this area should be paid more attention to. When usingnumerical simulation to analysis the construction sequence of variable cross section tunnel,considering the results of two conditions: excavating from big section to small section andfrom small section to big section, this paper draws the following conclusions: excavating frombig section will make a bigger maximum settlement value and a smaller sphere of influence.And excavating from small section has a bigger influence scope with differential settlement.Because of the cross-section always changes and the ground surface settlement is not thatwell-distributed, different designs should be carried out according to different ground surfacesituations.The PBA method is excavating heading at the first to compose a pile-beam-archstructure as the initial support construction.Then excavating the remains section. This paperbased on the monitoring data of PBA station construction, considers the upper middle pilottunnel and buckle arch position excavation as the largest influence on the ground settlementconstruction step. The settlement accounts for more than70%of the total settlement amount caused by this step. According to the numerical simulation results of different sequence ofsmall heading construction in the PBA method, this paper believes making the lower headingconstruction first has less effect on the ground surface settlement. The arch construction has asimilar amount of settlement. The settlement is almost completed after the arch is finished.The next steps of construction have little influence on the surface subsidence. To control thesettlement, the construction of a station should pay more attention to these steps.