Abstract:  Shield is the preferred method for tunnel construction in metro sections. However, due to the contradictions of construction speed and organization between shield sections and metro stations, the advantage of the shield method in longdistance tunneling could not be fully used. Based on summarizing the technology of "shield first and then station" in China and abroad, an expanding construction method for metro stations based on doubleline shield tunnel using inserttube freezing method is proposed. First, the construction process, key techniques, applicable conditions, technical advantages, and defects of the construction techniques are discussed in detail. Second, based on a finite element model, the frozen pipes are simulated using shell elements, frozen soil is simulated using reinforcement circles, and the segment joint mode is simulated using the stiffness reduction method; and the characteristics, such as the structural deformation, loadcarrying capability, and surface settlements during the expanding construction of a doubleline shield tunnel are analyzed. The results are obtained as follows. (1) The law and maximum value of surface settlement caused by the expanding construction are obtained. (2) The deformation stage of the existing shield structure with the construction process is clarified. (3) The forcesensitive areas of the existing shield, supporting beams, and columns during the expanding construction are determined. (4) The reinforcement scheme and waterproofing measures of the existing shield tunnel segments are proposed. This study aims to clarify the inserttube freezing method for expanding the construction of metro station based on doubleline shield tunnel and its mechanical characteristics, and provide an effective approach for the construction contradiction between shield sections and metro stations, and scheme of "shield first and then the station".

Key words: metro station, inserttube freezing method, shield tunnel, expanding construction, mechanical[JP] characteristics