Robbins hybrid TBM launched on Pearl River project

1 April 2021

A 9.16m-diameter Robbins Crossover TBM – the largest such machine in China – has begun boring Lot PZH-1 of the 2.5km (1.6mi) Pazhou Line of the Pearl River Delta Intercity Railway Project in Guangzhou.

Onsite First Time Assembly (OFTA) was used to build the TBM – Robbins’ system which first assembles the machine at the job site rather than in the factory. The company claims this can result in ‘greatly reduced’ shipping and manpower requirements. In this case, the time from the start of assembly to machine launch was just five months.

Contractors Sichuan Jinshi Heavy Equipment Leasing Co and CREC Bureau 2 will drive the machine below rivers, weathered ground and other challenging conditions. This is expected to include moderately-to strongly-weathered argillaceous shales and sandstone, to mixed face conditions. Much of the rock is fractured, while the quartz content may be as high as 50%. Beneath rivers and other water bodies, the machine will work under 20-31m of overburden in highly permeable ground and anticipated water pressures of more than 7bar.

Yongsheng Qi, Project Manager for Robbins China said: “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. It will be a test of performance and tunnelling efficiency for the machine.”

The Crossover TBM features both hard rock and EPB modes and is optimised for the alignment’s rapidly-changing ground conditions: it began excavating in EPB mode but, after 1.5km, it will shift to hard-rock mode to continue excavation. An adaptable cutterhead design and two-speed gear reducers – known as the Robbins Torque-Shift system – are designed to enable efficient tunnelling in hard, mixed and soft ground. Further flexibility is provided by the adaptable screw conveyor which can be mounted in the centre or bottom of the mixing chamber, depending on the mode. High-pressure seals allow the machine to operate in water pressures up to 30bar.

The Pearl River Delta tunnel is scheduled to be completed by the end of 2021 and, as part of the Pazhou line, will facilitate better commutes for Guangzhou residents travelling to and from University City. Opening is scheduled for 2023.