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.