The Chimay hydro power project is located on the Tulumayo river, on the eastern side of the Andes mountain range in central Peru, at some 1200m asl. The scheme was executed as an engineering, procurement and construction project with José Cartellone C C of Argentina as the civil contractor, a consortium of three European equipment suppliers, with electrowatt Engineering of Switzerland responsible for the detailed design. The owner of the project is the private Peruvian electric power company Edegel SA. Chimay was implemented over a period of only 25 months and commissioning was finished in September 2000.

The major project structures comprise, in the headwork area, a barrage consisting of a 100m wide concrete weir and intake structure; a 160m wide earthfill dam which forms a regulation reservoir with a storage volume of 1.5M m3 for peaking power generation during the dry season; a headrace canal and desanding structure; and a headpond and power intake to the tunnel. The waterways comprise an unlined pressure tunnel, concrete-lined surge and pressure shafts, and a steel-lined high pressure tunnel. Two Francis turbines (2MW each) are installed in the surface power house.

Power tunnel

The pressure tunnel which was designed for a discharge of 82m3/sec has a total length of 9262m. Due to the short construction programme the tunnel was excavated both conventionally and by TBM. The table below shows the main characteristics of the different stretches.

Considering the general geological conditions the tunnel was designed without a concrete lining. Where necessary, rockbolts and shotcrete with mesh or fibre-reinforcements have been applied, and in a few smaller stretches steel ribs were indicated. Two rocktraps have been constructed to prevent loose stones entering the pressure shaft, one between the conventional and TBM section, the other one immediately upstream of the pressure shaft.

The conventional section has been excavated with three faces, two from a construction adit at 2095km and one from the upstream end of the tunnel. Performance rates in the order of 180m per month and face have been achieved. The TBM stretch was excavated from the downstream end, starting inside a construction adit. The works were carried out with a Robbins hard rock machine, reaching a monthly average performance rate of 409m and a maximum of 755m.

The first inspection of the underground structures — after three weeks of trial operation — showed a satisfactory behaviour with very little material in the rock traps.

Details of excavation methods