Okutadami and Otori hydro power stations are located in Fukushima Prefecture, Japan. The Electric Power Development Corporation (EPDC) has the responsibility of constructing additional facilities to the two existing hydro power stations in order to expand total output from 455MW to 742MW.

Okutadami hydro station consists of an existing 157m high dam and an underground power house. The expansion work includes:

•Digging the dam itself and constructing one more intake.

•Extending the underground power house and setting an additional turbine generator unit.

•Excavating a waterway tunnel parallel to the existing one.

The tailrace tunnel of Okutadami is 3.5km long and is characterised by its cross-sectional shape. Shotcrete and fibre reinforced concrete will be used to line the tunnel. Fibres mixed in the concrete will improve strength, durability and stability and tests are currently being carried out to find those which meet such requirements.

Otori is located 8km downstream of Okutadami. Here, EPDC will construct a new waterway and an underground powerhouse.

Construction at both sites started in July 1999, with initial operation of the additional capacity (200MW and 87MW) set for June 2003. Construction will last for about four years as activities are restricted to only six months a year due to preservation of valuable birds like the golden eagle.

Respective project dimensions
Summary of Lahmeyer International’s tunnelling work