In the Wanta-Sunglin hydropower project of Taiwan Power Company, a 5,947m-long tunnel passing through metamorphic slate formations was constructed by NATM method. Before the breakthrough of this tunnel in 2011, due to the variation of geological conditions, the excavation was blocked by shear zones with squeezing and creeping effects, until remedial measures and supporting adjustment were applied. Beside the difficult geological conditions, part of the alignment of this tunnel underpasses the Chuoshui River, which makes the support design even more challenging. This paper summaries the support designs, the tunnel deformation instrumentation, and the feedback analysis. In addition, the treatment and reinforced adjustment for the sections of river underpassing and shear zones were also illustrated and discussed. The experiences learned from this project can contribute to the other newly-built or rehabilitation hydropower projects in a similar situation.
In order to more efficiently obtain the hydropower from the Wushe Reservoir, which is situated at the upstream of Chuo-Shuei River, Taiwan Power Company planned and constructed the Wanta-Sunglin hydropower project. It comprises the extension of Wanta hydropower plant and the newly built Sunglin hydropower plant. In the former Wanta extension project, a new intake shaft was built with a new tunnel passage to the power plant. And a long tunnel from the new Sunglin Weir to a new underground plant were built in the latter Sunglin project. The total length of tunnels built in the Wanta- Sunglin project is 5947m, see Figure 1. For the objectives, this hydropower project can generate green electrical power 0.125 billion KWH per year. In contrast with hydrocarbon generated power, this project can reduce the emission of CO2 by 67000 tons per year. In addition, as part of the hydropower system, it can improve the operation of the water reservoirs, in which the water for irrigation and utility usages can be more flexibly supplied.