Comparison and Selection Research on the Excavation Methods for Large-Section Underground Subway Stations

As the construction conditions of metro stations in cities become more and more complex, a new station construction technology “tunnel before station” method emerged and became more mature, and the appropriate excavation method is a key part of the “tunnel before station” method. Based on an underground subway station project of Line 4 in Chongqing City, this paper uses finite element software FLAC3D to conduct numerical simulation of three excavation methods (double-sidewall diversion method, CD method and three-step seven-step excavation method). The settlement law of the stratum under three excavation methods and the stress-strain response law between station supporting structure, shield temporary segment lining and excavation are studied. The results show that: The formation settlement increases with the increase of buried depth, in which the two-sidewall diversion method produces the smallest settlement, and the three-step seven-step method produces the largest settlement. Under the three excavation methods, the stress distribution of the bolt and the secondary lining is almost the same, in which the axial force of the double-wall driving method is about 30% higher than that of the other two excavation methods, while the stress characteristics of the secondary lining with the three-step and seven-step method are superior to the other excavation methods. Compared with the stress and strain distribution of shield temporary segment lining, the double-sidewall heading method is obviously superior to CD method and three-step seven-step method.