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The upper dam is a rock fill type dam with earth center core. The dam is 136m high, with a crest length of 444m and dam volume of 7.3 million m3(Fig.4.12).
This type of dam was selected based on the topographic conditions of the dam site, the properties of the foundation rock, and availability ofembankment materials near the dam site.
Most of embankment materials for the upper dam were collected from the quarry and borrow area near the dam site.Those areas were submerged in the reservoir. Only the embankment material for the earth center core, its volume of 0.8 million m3, were collected from thedownstream area near the dam site.
The upper dam is a very compact dam in the mountainous area (Fig.4.13).
Fig.4.12 Profile of Upper Dam
Fig.4.13Bird’s-eye View of Upper Dam
4.4.2 Headrace and tailrace tunnels
The headrace and tailrace, 2,445m and 2,270m long respectively, are circular pressure tunnelswhich inner diameter is 8.2m. And the maximum flow rate is 340m3/s and the maximum flow velocity is 6.3m/s.
These tunnels were excavated by benchconstruction method using the New Austrian Tunneling Method for supporting system. High pressure consolidation grouting was applied around the concrete lining.Sound rocks from tunnels were used for aggregates of concrete and materials of road foundations.
4.4.3 Penstock
Fig.4.14 shows underground structuresimage around the power station.
The penstock, inner diameter of 8.2m to 2.3m and length of 1,398m, is all-welded steel pipe embedded in concrete.