Crossover TBM operations in China 07 Apr 2021

Following a five-month Onsite First Time Assembly (OFTA), a 9.16m diameter Robbins Crossover TBM, the largest of its type to be used in China, is launched in Guangzhou for a 2.5km long drive for the Pearl River Delta intercity Pazhou Line railway project.

Largest Robbins Crossover TBM to be used in China

The hybrid machine will complete the drive through various ground types from moderately to strongly weathered argillaceous shales and sandstone to mixed face conditions for Chinese contractors Sichuan Jinshi Heavy Equipment Leasing Co and CREC Bureau 2. Much of the rock is fractured with a quartz content as high as up to 50%. "Not only are there poor ground conditions such as soft to hard uneven, fractured zones and full-face hard rock, but these sections appear to alternate frequently, which is the biggest challenge of the project," said Yongsheng Qi, Project Manager for Robbins China. “It will be a test of performance and tunnelling efficiency for the machine.”

The drive also passes under rivers and waterways with a cover of 20m to 30m. Water pressures in the highly permeable strata are anticipated at above 7 bar. The success of the project lies in stabilizing water pressure at the face, while ensuring acceptable advance rates and construction safety.

The Crossover TBM features both hard rock and EPB modes and is optimized for the rapidly changing ground conditions. An adaptable cutterhead design and the Robbins two-speed torque-shift gear reducers will enable efficient excavation in hard, mixed, and soft ground. An adaptable screw conveyor can be mounted in the center or bottom of the excavation chamber depending on the mode. To combat high water pressures the machine is fitted with high-pressure seals that will hold up to 30 bar in static state. The XRE machine is launched in EPB mode and will shift to hard rock after 1.5km of the 2.5km drive.

The new rail project is one of several mixed ground Robbins Crossover TBM operations in China. Two 6.91m diameter XRE machines are currently working on sections of the Chongqing Metro Phase 2 in ground conditions ranging from weathered mixed granite to weathered pegmatite and adamellite. The project is being progressed by the same contractors. "At Chongqing, we won the trust of the contractor with the performance of the Crossover machines where to date, the highest monthly advance rate is 365m (1,197ft),” said Qi. “This is one of the main reasons the contractor again selected a Robbins Crossover TBM for the Pearl River Delta project.” With the Chongqing Metro rates as a precedent, the Pearl River Delta tunnel is scheduled to be complete by the end of 2021 and opened for rail operations in 2023.