Breakthrough on the Pinglu Tunnel in China has been achieved, Robbins announced on 27 December.

The contractor, a Sino-Austria Hydraulic Engineering Company JV led by Alpine Bau holed through on the 25.4km, single-drive TBM tunnel on 14 November 2010.

A 4.8m diameter Robbins double shield TBM was used for the bore that forms part of China’s Yellow River Water Diversion Project. The advance rate reached around 70m per day, encountering difficult geology including coal seams and abrasive sandstone with up to 70 per cent quartzite content.

Described by Robbins as a ‘veteran’ machine, it was also in use a decade ago for a 12km section of the same project. During this run, it set two world records for its size class: best month – a 1,855m drive and highest monthly average at 1352m. The records have yet to be beaten.

Despite being originally designed for similar geological conditions, some changes were needed for the TBM to operate efficiently on this drive. “The back-up frame was extended from one stroke to two strokes. This was a key change, especially for such a long tunnel,” said Meik Mueller, Technical Director for Alpine’s Asia Division. “The modification allowed the machine to maintain good advance rates despite transit times of up to 70 minutes for muck trains travelling from the machine to tunnel entrance.”

Lining for the Pinglu Tunnel, consisted of unique hexagonal segments and was produced near the jobsite by Alpine. A crew of nearly 400 people worked at the remote site and segment factory to cast the specialised structures. During tunnelling the segments were placed in rings of four elements in a honeycomb configuration staggered longitudinally.

The Pinglu tunnel will be up and running by October 2011 and will connect the North Main Line of the Yellow River Project to allow water transfer to Pinglu, Shuozhou and Datong.