Study On The Multi-tunnel Effect Due To Urumqi Ba Low Subway Station Construction With Cave-pile Method

With the rapid development of social economy,more and more cities commence to the construction of subway.Conventional subway construction methods,such as Open-cut method,Covering method Etc,have no longer meet the needs of developing city,which makes the Cavepile method,a new rising method,applied in the construction of urban subway in more and more cities.By combining the conventional construction technologies of Undercutting method and integrating the mature technologies of small pilot hole,digging pile and buckled arch,Cavepile method makes it a common support system and guarantees construction safety.The method was first used in the construction of the Beijing subway and achieved good social and economic benefits.It turns out that the method possesses good prospects for development and promotion,however,the study of the cave-pile method is not very profound,especially in the application of practical engineering.In order to further analyze the influence to subway station structure and surface subsidence resulted from the different stages of the Cave-pile construction,the actual engineering of eighth floor station of the Urumqi Metro Line 1 is provided to analyze from the following aspects:(1)A three-dimensional numerical model,built by The Midas-GTS-NX,was used to simulate the excavation of pilot hole,then we analyzed the influence on The multi-tunnel effect caused by some factors including excavation phase of the pilot hole,excavation method and excavation face distance between the pilot holes.Some indicators from various construction schemes like maximum surface subsidence,dome subsidence,uplift of inversion arch and surface subsidence tank curve were also analyzed.By comprehensive comparison,the optimal construction scheme for pilot hole is as follows: step method for the left and right small pilot hole,CD method for the middle large pilot hole,the excavation sequence is 2-1-3-4,and the excavation distance is 15 m.(2)The Midas-GTS-NX software was used to simulate the construction process of the eighth floor station,and the impact of the main construction stages on the buckled arch,mainly in buckled arch settlement and the arch stress,was analyzed.And it was found that in the construction,the buckled arch has significant changes in settlement and stress,especially in the demolition phase of initial support.(3)We also used The Midas-GTS-NX to simulate and analyze the deformation and stress of buckled arch,concentrating on various construction stages,including the excavation pilot hole,the construction of buckled arch,the excavation of upper and lower layer.And we analyzed the surface subsidence and axial force of retaining piles.We found that surface residences is obvious during the excavation of pilot hole and buckled arch.(4)Field measured data that was used to analyze the trend of axial force of retaining piles and surface subsidence during construction was compared to the date from numerical simulation,and it turned out that they were closed to each other,with similar tendency.