New Wuchieh Diversion Tunnel

Project Overview

The New Wuchieh Diversion Tunnel is part of a water transfer system that feeds into the Sun-Moon Lake Hydraulic Power Plant, one of the largest single power sources in Taiwan. Project owners Taipower commissioned the new 6.3 km (3.9 mi) long tunnel after the original Wuchieh Diversion Tunnel was found cracked and degraded after 70 years of service.

The tunnel stretches from its source at Sun-Moon Lake to the intake structure at the hydraulic power station. The new tunnel, along with another water transfer tunnel feeding into Sun-Moon Lake, will increase the output of the power plant to 7,600,000 KWh annually.

Taipower awarded the construction contract for the new diversion tunnel to Kumagai Gumi Co. Ltd. The contractor chose a 6.2 m (20.3 ft) diameter Robbins Main Beam TBM for the project.

Geology

The tunnel passes through quartzite, sandstone, and slate. There are also some areas containing broken rock.

TBM

Robbins rebuilt a used 6.2 m (20.3 ft) diameter Main Beam TBM for the New Wuchieh Tunnel. The refurbished TBM featured 17 inch (432mm) wedge-lock cutters and 1,890 kW (2,534 hp) of cutterhead power. The 380 tonne (420 ton) machine also generated a maximum torque of 1,774,415 N-m (1,307,550 lb-ft) at the cutterhead.

Tunnel Excavation

The TBM began boring in July 2000 and finished in 24 months on June 7, 2002. The TBM’s average monthly advance was over 400 m (1,312 ft) and it acheived a best month of 650 m (2,133 ft). After half of the tunnel had been excavated some broken ground was encountered and tunnel linings such as ring beams, mesh, and shotcrete were applied. Some portions of the tunnel were also lined with cast iron segments for additional support.

In September 2001, Typhoon Toraji hit the area and flooded the site with mud, water, and rocks. Some of the shipping containers containing spare parts, cutters, and workshops were completely submerged. Fortunately, the flood level stayed below the working tunnel level and operations were merely delayed. The remainder of the excavation went smoothly and the finished tunnel was celebrated as the first tunnel ever completed solely by TBM in Taiwan.