On May 19, 2021, the world witnessed the delivery of the first and largest cross-section rectangular hard rock pipe jacking machine, Tianfei 1, marking a significant milestone in the railway industry. This technological breakthrough will be utilized in the railway-related embedded project of Putian railway station, which is the first difficult project in China where multiple large cross-section rectangular pipe jacking passes through the operating railway simultaneously.
Improved Excavation Capabilities
The excavation section of Tianfei 1 is 12.6m wide and 7.65m high, with a combined layout of two layers, three front, four rear cutter heads. The adjacent cutter head’s cutting areas cross each other, with a section excavation coverage rate of 95%, making it more efficient than traditional methods. Its rock breaking capacity and tunneling efficiency are impressive, capable of digging in high-strength hard rock strata and rock strata meeting 100MPa, while ensuring minimal disturbance to the stratum. The pipe jacking machine also guarantees the safety of undercrossing the existing Hangzhou-Shenzhen railway.
Benefits of Rectangular Tunnel with Pipe Jacking Construction
Compared to shield construction, the rectangular tunnel with pipe jacking construction has several advantages. The pipe jacking construction method makes effective use of space than the circular tunnel under the same cross-sectional area. Additionally, when utilized for underpasses, such as pedestrian and vehicle crossings, the need for ground paving is eliminated, saving time and reducing the project’s cost.
Overcoming Design Challenges
At the project’s initial design phase, the pipe jacking machine with a multi-cutter head structure had a problem with a milling blind area in the structural design. Failure to mill the rock mass in these areas synchronously would affect the entire tunneling process of the pipe jacking machine and incur additional costs due to secondary milling and excavation.
To address this issue, China Railway sought assistance from Yichen Company, which designed and manufactured two milling modules using its R&D expertise and practical experience. The first module is a shell rotary milling head, developed based on Yichen’s vertical drum cutter. Its shell and milling head are an integrated structure, rotating simultaneously when working. The spiral blade efficiently transports excavated waste to the rear and effectively solves the milling blind area of the upper and lower edges of the Tianfei 1 pipe jacking machine.
The second milling module, installed on both sides of the Tianfei 1 pipe jacking machine, is called the milling drum. It is used for milling and excavating the rock mass in the blind area on both sides of the pipe jacking machine.
Equipped with a shell rotary milling head and a milling drum, Tianfei 1 pipe jacking machine can complete the milling and excavation of the whole square surface at the same time. The design and manufacture of these milling modules have successfully solved the problem of cross-section rectangular pipe jacking machine construction blind area, reduced construction costs, and laid a solid foundation for the completion of the Putian railway station project on schedule.
Tianfei 1 represents a significant milestone in the pipe jacking machine industry, with its impressive excavation capabilities and improved construction efficiency. The successful solution to the milling blind area problem is an impressive feat of engineering and design, showcasing the innovative spirit of the Chinese railway industry. The use of rectangular tunnel with pipe jacking construction will continue to revolutionize the construction industry, providing more efficient and cost-effective methods to tackle complex construction projects.