In late March 2021, the world’s biggest Crossover (XRE) TBM was opened in Guangzhou for contractors Sichuan Jinshi Heavy Equipment Leasing Co., Ltd and CREC Bureau 2. The 9.16m (30ft) diameter Robbins TBM was designed using Onsite First Time Assembly (OFTA), which took just five months from the start of assembly to system launch. The hybrid machine is boring the Pearl River Delta Intercity Railway Project’s Pazhou Line Lot PZH-1, which will boost commutes for Guangzhou residents commuting to and from University City.
During the bore, the system can experience a range of ground types, including moderately to highly weathered argillaceous shales and sandstone, as well as mixed face environments. The rock is fragmented throughout, and the quartz content can exceed 50%. “Not only are the land conditions weak, with soft to hard rough ground, broken areas, and full-face hard rock, but these parts also tend to alternate frequently, which is the biggest challenge of the project.
The system will be put to the test in terms of accuracy and tunneling efficiency,” said Yongsheng Qi, Project Manager for Robbins China. With a shield of 20 to 31 meters, the tunnel is supposed to pass under rivers and other bodies of water (65 to 100ft). The river is related to the ground strata, which is extremely permeable, resulting in water pressures predicted to reach 7 bar. The project’s viability hinges on its ability to maintain stability.
The Crossover TBM is built for the project’s dynamically shifting ground and contains both hard rock and EPB modes. The Robbins Torque-Shift mechanism, which incorporates an adaptable cutterhead configuration with two-speed gear reducers, allows for effective tunneling in rough, mixed, and soft terrain. Depending on the mode, an adaptable screw conveyor may be installed in the middle or bottom of the mixing chamber. High-pressure seals are mounted on the system to combat high water pressures, and it can hold up to 30 bar statically. The XRE TBM started its excavation in EPB mode and will switch to hard rock mode after 1.5 kilometers (0.9 miles) have been bored.
The one-of-a-kind project is one of many mixed field operations in China that use Robbins Crossover TBMs. In ground conditions ranging from weathered mixed granite to weathered pegmatite and adamellite, two 6.91 m (22.6ft) diameter XRE machines are currently boring sections of the Chongqing Metro Phase 2 in ground conditions ranging from weathered mixed granite to weathered pegmatite and adamellite. The project is being carried out by the same contractors who worked on the Pearl River Delta bore.
“At the Chongqing Metro project, we won the trust of the contractor with the performance of the Crossover machines; to date the highest monthly advance rate in Chongqing is 365m (1,197ft). This is one of the main reasons the contractor again selected a Robbins Crossover TBM for the Pearl River Delta project,” observed Qi.
The Pearl River Delta tunnel is planned to be finished by the end of 2021 and placed into service in 2023, based on Chongqing Metro speeds.