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On May 15, as the cutterhead of the hard-rock rectangular shield pipe-jacking machine slowly emerged, the pipe-jacking section of the Auxiliary Ramp A project at the C traffic node of the N-district road interchange in Chongqing Liangjiang New Area was successfully completed. This marks the first time that 100% full-face excavation coverage has been achieved on a large-section rectangular pipe-jacking machine, solving the difficulty of treating blind spots, especially hard rock, on special-shaped shield machines. Wang Kai, Deputy General Manager of China Railway Engineering Equipment Group (CREG), attended the breakthrough ceremony.

The "Tunneling No." (China Railway No. 1112) rectangular hard-rock shield pipe-jacking machine has an excavation cross-section 10.42 meters wide and 7.57 meters high. It is the first to adopt a six-cutterhead plus six-drum composite rock-breaking technology. Through a two-layer six-cutterhead combined arrangement, supplemented by cutting by the cutting drums, the cutting areas overlap with each other, achieving a cross-section excavation coverage rate of 100%. The project R&D team also carried out targeted designs in the settlement control system and the rock-stratum attitude control system. The equipment has stronger rock-breaking capability and tunneling efficiency, and can meet the excavation and tunneling requirements of rectangular tunnels in composite strata or hard-rock strata, while causing minimal disturbance to the strata, ensuring controllable safety risks for underpassing the expressway.

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It is reported that the project where "China Railway No. 1112" is applied connects Lushan Avenue at the North Square of North Station and the Inner Ring Expressway toward Renhe, and needs to underpass two major urban dual-carriageway arteries, the Inner Ring Expressway and the Airport Road. It does not have open-cut conditions. The overburden above the tunnel is about 4 to 5 meters thick, belonging to an ultra-shallow-buried tunnel, making construction extremely difficult! At the same time, among domestic rectangular shield pipe-jacking constructions, this project is the longest pipe-jacking tunnel crossing an existing expressway, and road settlement control imposes stringent requirements on equipment stability!

To address the above construction difficulties, the design team equipped it with an intelligent system capable of remote control of the equipment. The system includes three major systems: intelligent advancement, muck conditioning, and friction and drag reduction. It can efficiently and precisely control the cutterhead and shield body cylinders, adjust the tunneling direction in real time, and dynamically observe the coefficients of muck and drag-reducing materials, effectively improving production efficiency through adequate conditioning. The maximum monthly advance is about 30 meters, and the construction period is halved compared with manual excavation, saving 60% of auxiliary labor, greatly reducing project cost and workers' labor intensity, and improving construction safety.

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The successful breakthrough of this project has accumulated precious experience for CREG's subsequent hard-rock shield pipe-jacking projects, filled the gap in the domestic field of large-section hard-rock rectangular shield pipe-jacking construction, and contributed valuable experience to hard-rock rectangular shield pipe-jacking construction. In the future, with the continuous improvement of the transportation network in Liangjiang New Area, this tunnel will play an increasingly important role and inject new vitality into regional economic and social development.