On October 15, the Φ16.16 m air-cushion slurry balance shield machine "Guanyue", designated for the Nanhu Section of Wuhan Lianghu Tunnel, successfully completed offline acceptance. Independently researched and manufactured in China, this super-large-diameter shield equipment will undertake tunneling works for the sub-lake tunnel of the Nanhu Section, delivering core tunneling equipment support for this world-class double-deck urban sub-lake tunnel project.

Wuhan Lianghu Tunnel ranks as China’s largest urban double-deck highway tunnel constructed beneath lakes. Upon completion, the project will open up a north-south express corridor in the Wuchang area, connecting the Donghu and Nanhu subdistricts. It will effectively relieve traffic pressure on Luoshi Road and the Second Ring Road, cut travel time between northern and southern Wuchang, improve the backbone road network in the southern Yangtze River area, and facilitate the upgrading of the comprehensive transportation network of Wuhan, a national central city.

The Nanhu Section features complex construction conditions and stringent boundary constraints, with overall construction difficulty comparable to river-crossing and sea-crossing tunnels. The tunnel alignment runs beneath Nanhu Lake, traversing strata consisting of high-plastic silty clay, heavily karstified bedrock, and alternating soft-hard composite formations. Dense karst caves are developed in partial sections, where the uniaxial compressive strength of rock layers reaches more than 50 MPa. Construction carries risks such as cutterhead muck cake, rapid cutter wear and chipping. The tunnel has a minimum curve radius of merely 700 m. The tunneling route repeatedly passes beneath existing rail transit lines, with the minimum clear distance between the tunnel structure and nearby high-rise buildings and municipal pipelines less than 7.8 m. The overburden above the tunnel under the lake is thin; pore water pressure fluctuates seasonally, requiring millimetre-level control of ground settlement. Under high sub-lake water pressure, conventional hyperbaric intervention for cutter replacement poses prominent safety hazards, making this a high-risk, highly complex super-large-diameter shield project.

To address the extreme working conditions of karst development, alternating soft-hard strata, highly cohesive lake-bed soil and high water pressure in the Nanhu Section, our company established a special R&D team to tackle two core technical bottlenecks: formation adaptability of cutting tools and safe atmospheric cutter replacement. The team successfully developed a full cutting tool scheme and supporting technological system for atmospheric cutter replacement tailored to this project. Targeting engineering pain points including hob chipping and eccentric wear induced by rock fragment impact in karst caves and alternating cutting of soft and hard rock, as well as scraper wear and cutterhead muck cake caused by highly cohesive clay, the R&D team carried out multiple rounds of formation simulation tests. Material of cutter substrate, cutting edge geometry and cutter zoning layout on the cutterhead were optimized. Zoned high-wear-resistant hobs and scrapers were custom-developed to enhance impact resistance and wear resistance, meeting the composite tunneling requirements of both soft soil excavation and hard rock breaking. Meanwhile, in accordance with the structural characteristics of the large-opening atmospheric cutterhead of the shield, the installation, positioning and disassembly structures of cutters were optimized, and construction procedures for atmospheric cutter replacement were refined. With the optimized cutter layout and cutterhead openings, cutter inspection, disassembly and replacement can be performed under atmospheric pressure on the premise of maintaining face stability. This technical solution greatly reduces the need for personnel to conduct maintenance inspections inside the high-pressure sealed chamber under hyperbaric conditions, effectively avoiding major safety risks brought by entry into high-pressure sub-lake chambers and lowering hazards in cutter replacement. At present, our company has supplied the complete set of cutting tools for the "Guanyue" shield machine, providing robust core "teeth" guarantee for long-distance safe tunneling beneath the lake.

Major national heavy equipment bores through mountains and lakes; precision cutting tools safeguard tunneling operations. We wish steady progress for the Wuhan Lianghu Tunnel Project. May the "Guanyue" shield launch smoothly, advance stably, and achieve tunnel breakthrough at an early date. Empowered by domestically produced core cutting tool equipment, this world-class sub-lake tunnel project will be constructed to boost the high-quality development of transportation infrastructure in Wuhan.