Desiree Willis, Technical Writer, The Robbins Company

After Onsite First Time Assembly (OFTA), this 12.43m (40ft) diameter Robbins TBM is into a 16.7km (10.4 mile) drive to complete No 1 of four headrace tunnels for the Jinping-II hydropower station in Sichuan Province, China. The machine's tunnel will draw water from Yangtze River tributary Yalong and joins a 7.2m (23.7ft) diameter Robbins machine launched earlier in 2008 to bore a drainage tunnel on the same project.

Assembled and ready for launch

Assembly of the big main beam TBM and its backup began in mid-April 2008 and finished on August 11. Crews then walked the TBM and the first three back-up gantries forward by 200m (650ft) to a launch chamber where the conveyor system and six other gantries were assembled.

"Everything has gone remarkably well in retrospect," said Steve Smading, Project Manager for Robbins. "Of course we had problems, but our on-site assembly team has managed them as they occurred and without adversely affecting the assembly process.

Launch chamber for the giant TBM

Assembly was completed on schedule and no-load testing of all critical systems has gone smoothly. We are now into a 1,000m long test-boring program to fully commission the tunnelling system."

Bypassing test assembly in a manufacturing facility eliminated many shipping risks for the big TBM to its remote job site. The accelerated manufacture schedule meant that most of the heavy TBM structures were shipped from the Robbins manufacturing facility in Dalian, China ahead of the low water season on the Yangtze River when such shipments are impossible.

The TBM's OFTA team

Due to go online in 2010, the Jinping-II hydropower station will develop a natural 180-degree bend on the Yalong River and a 60m (200ft) drop in elevation to generate 4,800MW of electricity annually. The project, for the Ertan Hydropower Development Company, is located 17km (10.5 miles) downstream of the Jinping-I power station which, when completed in 2014, will have an annual generating capacity of 3,600MW.

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