Study On Optimization Of Construction Plan Of Pilot Tunnel In Metro Station Constructed By Pile-Beam-Arch Method

ABSTRACT:In this paper, two PBA stations at two typical strata are analyzed. The first one is the Pingguoyuan Nanlu Station along the west extension of subway Line6, locating at the coarse grain formation represented by sandy gravel, and the second one is Nanbalizhuang Station along subway Line14, situated at the fine coarse formation represented by sand and clay. On the basis of above analysis, FLAC3D software is applied to simulate17pilot tunnel construction plans for PBA station, and surface settlement law and law of pipeline gradient change with varying excavation alternatives are analyzed, to conclude the optimal pilot tunnel construction plan for PBA station at specific stratum.(1) The pilot tunnel construction for PBA station at the above two strata follow the general conclusions below:an increase in quit excavation distance will lead to reduce surface settlement; if pilot tunnel for a different layer is conducted upon completion of pilot tunnel cut-through at the same horizontal plane, surface settlement can be effectively reduced without increasing the quit excavation distance.(2) Pilot tunnel construction for PBA station at the coarse grain formation represented by sandy gravel:in horizontal plane, the method with inside pilot tunnel construction followed by outside one is more effective than the other way round in controlling surface settlement; in vertical plane, the method with lower pilot tunnel excavation followed by upper one is more effective than the other way round in controlling surface settlement; the method with lower pilot tunnel excavation followed by upper one, and inside pilot tunnel construction followed by outside one has better effects in preventing sharp gradient change of local pipelines in the settler, so as to reduce the possibility of damage to pipeline due to stress concentration.(3) Pilot tunnel construction for PBA station at the fine coarse formation represented by sand and clay:in vertical plane, the method with upper pilot tunnel construction followed by lower one is more effective than the other way round in controlling surface settlement; in horizontal plane, the method with inside pilot tunnel construction followed by outside one is more effective than the other way round in controlling surface settlement; the method with upper pilot tunnel excavation followed by lower one, and outside pilot tunnel construction followed by inside one has better effects in preventing sharp gradient change of local pipelines in the settler, so as to reduce the possibility of damage to pipeline due to stress concentration.