Key Technologies for Design and Construction of Horseshoe-Shaped Shield Used in Baicheng Tunnel on Menghua Railway
The Baicheng Tunnel on the Menghua Railway,as the world's first large-section mountain loess tunnel constructed with a horseshoe-shaped earth pressure balance shield machine,faces key engineering challenges in launching and receiving,excavation,posture control,and muck removal,etc.In view of this,specific solutions are proposed:(1)For the launching section,the C40 opencut structure is used instead of the conventional shield launching reaction frame used in subways to provide reaction force,the large pipe shed is used for end reinforcement instead of conventional end reinforcement,and steel arch casing and sealing is used instead of end wall and curtain rubber sealing to shorten the launching time and save masonry works.(2)For the receiving section,a splayed retaining wall is constructed at the portal to replace the conventional enclosure structure and reinforcement works in subway engi-neering,and a steel ring is set up and sealed at the portal to ensure the safe receiving of the shield.(3)The com-bined rotary cutter head + the high-pressure water jet device for blind area treatment + shield cutters solve the exca-vation problem in the old loess stratum.(4)The cutter head overturn correction combined with the mortar pumping and counterweight block can solve the problem of posture control.(5)The muck conditioning technology using foam and water with 3%original solution concentration and 15%injection rate as the main improvement medium and the uninterrupted muck removal technology with optimized continuous belt conveyor improve the muck removal problem.
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