Study on Key Technology of Rapid Construction of Underground Excavation Station with PBA Method in Loess Area
The Hejiaying Station of the Xi'an Metro is the first underground excavation station that applies the PBA excavation method of the"upper four lower two"six-pilot tunnel to the loess area.The excavation of group holes itself has a high risk,furthermore,the construction period of this project is tight.Therefore,it is necessary to speed up the construction progress.MIDAS GTS NX was used to optimize the excavation scheme of the original pilot tunnel,and the method of simultaneous excavation of the upper and lower pilot tunnels and alternate distance was adopted.Through comparative analysis,the results show that the surface settlement is small when the optimization scheme is used for excavation.The vertical deformation of the vault of the upper side pilot tunnel is obviously increased,and the vertical deformation of the other pilot tunnels is slightly smaller than that of the original scheme.The bending moment of the primary support structure of the upper side guide hole increases slightly,and the bending moment of the primary support structure of other guide holes decreases slightly.Through the comparative analysis of technical and economic indicators,the optimized excavation scheme can greatly improve construction efficiency and effectively shorten the construction period and cost while ensuring safety.After the excavation is completed according to the optimized scheme,the measured surface settlement does not exceed the construction control requirements,and it is in good agreement with the calculation results.
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