DavyMarkham built cutterheads for tunnel boring machines used on railroad tunnel project in China
(24/02/2010)

Tunnelling plays an increasingly important role in the development of transportation links and renewable energy schemes and China reportedly ranks first in the world, both for the number of tunnels and pace of construction. In bypassing areas of natural beauty, it often has significant ecological benefits; in the Qinling Mountains, when a national highway was rerouted by tunnel, it enabled the plantation of 500 acres of bamboo and the bridging of two giant panda populations.

DavyMarkham of Sheffield, is nearing completion of two 10.3m (40ft) diameter cutterheads, which will be fitted to the front ends of tunnel boring machines being built by the Robbins Company of Ohio, for the major railroad tunnel project in China. Each 226 tonne cutterhead is despatched in modular components to the company’s TBM assembly facility near Chendu, Sichuan Province, home of the giant panda. After the machines have been assembled and tested in the factory, they will be disassembled and sent to a remote location in Gansu Province, where the TBMs and cutterheads will be reassembled by local labour.

As part of the reduced lead time, DavyMarkham is fabricating the cutterheads in the fastest time ever, by recruiting additional contract welders, effectively doubling its skilled welding resource, and working 3 shifts, 6 days a week. The contract is valued at £2.7 million ex works.

This is the latest in a series of cutterhead contracts for Robbins, including a giant 320 tonne, 12.4m diameter unit for China’s biggest TBM tunnelling project, a 10m diameter cutterhead for burrowing beneath India’s largest tiger sanctuary, and a 12.5m diameter fabrication for the Niagara Falls hydroelectric project, all of which have enabled DavyMarkham to build a close working partnership with the world’s foremost manufacturer of underground construction machinery.

The rotating cutterhead, which matches the diameter of the tunnels, plays a critical role in the boring process. Fitted on a large slew ring bearing at the front of the TBM, it holds a series of tungsten steel cutting discs, each 483mm (19”) in diameter, and rotates continuously at speeds up to 8rpm. As the cutterhead turns, hydraulic thrust cylinders push the cutters into the rockface, causing fractures in the surface and chips to break away, which are deposited onto a belt conveyor within the TBM.

Each cutterhead is custom-built according to the geological conditions, to ensure smooth, efficient boring, and DavyMarkham fabricates them to a standard, modular Robbins design, modified according to required diameter and disc cutter configuration. This basically comprises two inner box sections with radiating cutter boxes, four outer quadrants with peripheral cutter housings, a central slew ring and integral bearings, plus motor/gearbox drive arrangements. In all, some 400 parts have been cut and formed from heavy carbon steel plate, for each cutterhead, then welded together to form these very large and complex fabrications, with all processes including finish machining and heat treatment carried out in-house.

“The Robbins Company is famous for its high quality, large-scale tunnel boring machines and we are pleased to have developed a strong working partnership with them, which dates back many decades,” says DavyMarkham MD, Kevin Parkin. “Our high quality fabrication and capacity to meet strict deadlines allows Robbins to place an order and know that we will progress it effectively, to the exacting standards they demand. The knowledge that Sheffield engineering is helping to execute key infrastructure projects deep underground in China is a definite bonus.”