DavyMarkham - News
320T Cutterhead For China's Biggest TBM Tunnelling Project

Sheffield heavy engineering company DavyMarkham has fabricated and shipped a 320 tonne cutterhead for a 12.4m diameter tunnel boring machine (TBM), being built by The Robbins Company of Ohio, the world's foremost manufacturer of underground construction machinery. It has been despatched to the mountains of Sichuan Province, China, where it will be instrumental in one of the biggest TBM-driven tunnelling projects in Chinese history, for the new 4,800MW Jinping II hydropower station on the Yalong River. Once completed in 2010, this will be the largest power station in an ambitious project for owners Ertan Hydropower Development Company, which will transmit electricity to many eastern provinces and such cities as Shanghai and Beijing.

Fabricated in six sections and test assembled at DavyMarkham's Sheffield works prior to despatch, the cutterhead and associated Main Beam TBM are being finally built by Robbins in a massive underground launch chamber, pre-excavated by drill and blast methods. The same on-site assembly technique was also employed on the earlier Niagara Falls TBM contract, for which DavyMarkham again supplied the cutterhead.

In a contract valued at £1.15 million, the Sheffield firm applied precision engineering standards to the heavy machining and fabrication. In order to improve competitiveness when dealing with such large steel pieces, DavyMarkham employed a newly-developed cutting tool for rough machining, which resulted in a metal removal rate 5 times faster than normal, and deployed the latest carbide U-drill technology, which cut holes 8 times faster.

Tunnel boring machines are amongst the largest, most complex pieces of equipment made and, with 50 years of innovation and experience, Robbins is regarded as the leading exponent, holding 94% of all world records for TBM production. Its Main Beam TBMs bore more than 200km of tunnel every year, establishing them as the workhorses of hard rock excavation. The cutterhead is the rotating head at the front of the TBM, which actually cuts through the rock, and DavyMarkham has supplied Robbins with these and many other TBM elements over the years, including the literally groundbreaking Channel Tunnel machine.

For the Jinping II project, the 12.4m (40.1ft) TBM will bore a headrace tunnel almost 17km long and one of the longest in the world, which will deliver water under pressure to the turbines of the hydropower plant currently under construction. DavyMarkham fabricated the machine's main cutterhead in six separate sections, for ease of shipping and lowering below ground: one inner head weighing 60 tonnes, another at 52T and four outer segments each weighing 38T, all incorporating free-issue 19' (4825mm) cutters supplied by Robbins.

After test assembly, the cutterhead was disassembled and shipped in manageable sections from Southampton to Shanghai, for onward freighting to Sichuan Province. Tunnelling is scheduled to start in Spring 2008 after on-site assembly, with the TBM boring the first of four headrace tunnels through a complex geography of marble, shale and limestone, as well as coping with large inflows of water.