TECHNICAL | TBM TUNNELING
Above: McNally slats were used at Yin Han Ji Wei water tunnel, in China, where the works also experienced numerous rock bursts
In 2015, based on then recent experience of TBM
success among many prior tunneling projects in the Qinling Mountains of the region, a TBM once again began to bore in the region, this time for the Yin Han Ji Wei water diversion tunnel. The Robbins machine was chosen after the manufacturer had prior success in the mountains with two larger diameter Main Beams, for the West Qinling Rail Tunnels project. Suitability of TBM tunneling also had reference
Below:
Robbins Main Beam for Yin Han Ji Wei project, China
to a project on the other side of the world, in Peru, on the Olmos water tunnel project in the Andes mountains where a 5.3m-diameter (17.4ft) Main Beam handled high overburden and rock burst conditions, as anticipated would be the case in China. At Olmos, the McNally support system was used as part of the solution. The McNally system was also used for in part of the Liaoning NOW water transfer project, in China,
where an 8.53m-diameter (28ft) Main Beam was used on Lot T5. It would also be specified from the outset for the Yin Han Ji Wei water diversion tunnel. The diversion tunnel is one of three in a larger
program of tunneling for a water transfer and hydropower scheme in the Hanjiang and Weihe catchments. While most of the tunneling will be by drill and blast, the method was expected to face more challenges with multiple headings and adits under high overburden. The decision was taken to use a TBM for the most challenging sections of the diversion tunnel. Project owner is Hanjiang-to-Weihe River Valley
Water Diversion Project Construction Co, and the contractor was China Railway Tunnel Group (CRTG). In addition to the high overburden and stresses in hard granite rock along the alignment, they also saw risk of groundwater inflows to the tunnel works. The cutterhead of the Robbins Main Beam had 8 x
17” centre cutters and 43 x 20” single cutters, and the machine has maximum thrust and torque of 21,087kN and 14,614kNm, respectively. It had main drive power of 3300kW. The machine was supported by a continuous conveyor. TBM boring for the tunnels was executed in two drives – 9.9km (6.2 miles) and 7.6km (4.7 miles) lengths. From early on the challenges expected did present
themselves – hard and abrasive rock, high cutter wear and consumption, and inflows. Rock bursts were numerous and support needed to be installed. UCS rock strength ranged from 107MPa – 309MPa, averaging close to 200MPa, and the quartz content was high. The difficulties were more than expected per geological indications from the bid documents, although site investigation in mountains is limited, as is typical – although the other TBM local projects, and their successes despite challenges – gave some information and context.
32 | Spring 2023
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