On May 15, 2024, the world’s first hard rock rectangular pipe jacking machine “CREC 1112”, developed and manufactured by China Railway Engineering Equipment Group, Co. Ltd. (CREG), successfully broke through on the pipe jacking section of the N-Standard-Partition Street Interchange C-Traffic-Node A-Ramp project in China’s Chongqing Liangjiang New Area.
It is the first time, say CREG, that a large cross-section rectangular pipe jacking machine has undertaken a full-face excavation – solving the problem of a blind excavation area – especially in hard rock, using a non-circular TBM.
With 10.42m in width and 7.57m in height, the pipe jacking machine facilitates the ‘six circular cutter heads + six drum cutters’ combined rock breaking technique. Through the two-layer arrangement of the six circular cutter heads and the six drum cutters, the tunnel face is 100% covered. The CREG team also customized the machine regarding the settlement control system to allow it a stronger rock breaking capability required through the composite or hard rock strata, whilst minimalizing ground disturbance whilst passing under the expressways that pass over the alignment.
The project links the Lushan Avenue near the North Square of the Chongqing North Railway Station and the Chongqing Inner Ring Expressway (to Renhe direction). The alignment had to pass under the two bi-directional main roads, namely the Chongqing Inner Ring Expressway and the Airport Road. Cut and cover was deemed unusable, and with a super-shallow overburden of only 4-5m, construction was considered extremely challenging. Moreover, the project is the longest pipe jacked tunnel under an existing expressway, bringing strict requirements for road settlement control.
To deal with these challenges, CREG equipped the machine with three intelligent systems to allow remote control; the intelligent thrust system; the soil conditioning system; and the friction reduction system. These can efficiently and precisely control the cutter head and shield articulation cylinders and allow the real-time adjustment of the advance direction, and the dynamic monitoring of the muck and friction reduction material coefficient to improve construction efficiency.
With a maximum monthly advance rate of some 30m, it cuts the construction period in half and saves 60% in labor costs compared with the hand excavation method, and improves the construction safety factor.
According to CREG, “the successful breakthrough of “CREC 1112” fills the gap in construction by a large cross-section hard rock rectangular pipe jacking machine in the world, and furthers the experience for hard rock pipe jacking machine projects.”
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