Veteran Double Shield completes one of the World’s Longest Single-Drive Tunnels
|Machine Type||Double Shield TBM|
|Diameter||4.8 m (15.7 ft)|
|Tunnel Type||Water Transfer|
|Tunnel Lengths||25.4 km (15.8 mi)|
|Owner||Shanxi Province Water Bureau|
|Contractor||Sino-Austria Hydraulic Engineering Co. Ltd (SAHEC) JV, led by Alpine Bau GmbH|
|Location||Shanxi Province, China|
The Pinglu Tunnel, part of the Yellow River Water Diversion Project, was undertaken in 2006 by Joint Venture Sino-Austria Hydraulic Engineering Co. Ltd (SAHEC), led by Alpine Bau GmbH. At 24.5 km (15.8 mi), the Pinglu Tunnel marks one of the world’s longest single-drive TBM tunnels ever excavated. The entire scheme will transfer water from the Yellow River to dry regions of Shanxi Province, an area that receives just 400 mm (16 in) of rainfall per year on average.
The completed Pinglu Tunnel will go into operation in October 2011, connecting the North Main Line of the Yellow River Project to transfer water to Pinglu, Shuozhou, and Datong areas. The South Main Line of the Yellow River Water Diversion Project was completed between 1999 and 2001, which encompassed over 100 km (62 mi) of tunnel excavated using five TBMs, four of which were Robbins Double Shield TBMs.
The Robbins Double Shield TBM excavating the Pinglu Tunnel was previously used on the record-breaking 12 km (7 mi) long segment of the Yellow River Diversion in 2000. During that project, the Double Shield set two world records in its size class of 4 to 5 m (13 to 16 ft): best month (1,855 m/6,085 ft) and monthly average (1,352 m/4,435 ft). Both records still stand.
Since the TBM was used on a prior tunnel for this project and designed for similar geology, only the back-up system was modified. Due to the length of the tunnel, the back-up frame was extended from one stroke to two strokes. This key change allowed the machine to maintain good advance rates despite 70 minute transit times for muck trains from the machine to the tunnel entrance.
The machine began boring at the remote jobsite on September 30, 2006. Tunneling was a challenging process, as the geology consisted of 12 m (40 ft) thick coal seams and abrasive sandstone that required intensive monitoring of tunnel air for particulates. Up to 70% quartzite content made the rock very abrasive. This combination of 70% quartzite and 6% corundum made the rock seven times more abrasive than quartzite—equal to the material that grinding wheels are made of. This required rigorous maintenance of the cutterhead with a daily 4-hour shift, and replacement of the bucket lips.
Muck removal was by trains of rota-dump muck cars in two tracks using California switches. The back-up system was equipped with floor chain movers to shunt the muck cars as they filled. Ventilation in the long tunnel was generated at a minimum rate of 5.4 m3/sec (190 ft3/sec) by high-powered fans. The fans, situated at the portal, deliver fresh air to the tunnel face via 1.4 m (4.6 ft) diameter flexible ducting.
Lining for the Pinglu Tunnel, which consisted of unique hexagonal segments, was produced near the jobsite by Alpine. A crew of nearly 400 people worked at the remote site and segment factory to cast the specialized structures. During excavation, the segments were placed longitudinally in a honeycomb configuration in rings of four elements which allowed high-speed, continuous boring with no downtime while erecting segments. Advance rates topped out at 50 ring sets, or about 70 m (230 ft), per day.
On November 13, 2010, Alpine celebrated the Robbins machine break through with a crowd of more than 500 including Austrian and Chinese guests of honor and the entire tunneling crew.