Abstract: The traditional temporary invert constructed by Isteel + shotcrete is complex in the construction process. Moreover, its construction quality is greatly affected by human factors and cannot be reused. Therefore, a novel detachable concretefilled steel tube temporary invert and its supporting structure, designed for easy and rapid disassembly, are proposed. The structures are tested and applied to the highspeed Zongka #2 tunnel of the TongrenSai′erlong railway. The steel pipe has an outer diameter of 108 mm and a wall thickness of 8 mm, and is filled with C30 fine stone concrete. The detachable components comprise a sleeve and a builtin wedgeshaped unloading block, and the concretefilled steel tubes are inserted from both sides to achieve segment connection. Field application results reveal the following: (1) The proposed temporary invert structure is safe, reliable, and feasible and can realize factory prefabrication and quick disassembly on site. The proposed temporary invert can improve construction efficiency by 643% and reduce the settlement deformation rate of the arch and peripheral convergence rate by 657%~661% and 746%~795%, respectively, compared to the traditional temporary invert constructed by I-steel + shotcrete. (2) The axial force value measured during the operation of the structure is less than the calculated and designed ones, indicating that the structure is in a safe state. The reutilization rates of the segment and detachable structure are up to 94.5% and 100%, respectively.

Key words: tunnel, detachable components, temporary invert, concretefilled steel tube, quick disassembly and assembly, recycling