Canadian consulting engineer SNC-Lavalin has prepared a feasibility project report for The National Power Corporation in the Philippines for the construction of the 225 MW Agus III hydroelectric power project.

The project, situated on the Mindanao Islands, southern Philippines, includes a 3km long intake tunnel and a 400m long diversion tunnel.

The tunnels will be driven by drill and blast through volcanic basalts of varying thickness interspersed by discontinuous weathered layers of soft material including tuffs. The area is intersected by numerous faults.

The 3km long power tunnel will be excavated as a modified horseshoe section with a final id of 6.6m and will transfer water from the intake to the surge tank. The 400m long diversion tunnel will be a 5.4m diameter structure designed to handle a 1 in 10 year flood discharge of 350 m&#179:/s.

Both tunnels will utilise a full-face heading using a truck mounted, four-boom jumbo capable of drilling a cross-section of 30 square meters. The nature of the poor to moderate rock quality requires extensive rock support provided by rock bolts and shotcrete, plus substantial drilling and grouting to rectify rock permeability. Water ingress is not seen as a particular problem as 85% of the tunnel is aligned above the known water table.

The hydropower project is included in the 1999 Power Development Program of the National Power Corporation and is intended to be built via a build-operate transfer scheme. The project is slated for commissioning by 2007. At present, information on the start of construction, contract cost and financing is still to be determined.

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Agus III