Design aspects of the underground structures of the Serra da Mesa Hydroelectric Power Plant

The Serra da Mesa Hydroelectric Power Plant, located in the Tocantins river, 210 km north of Brasilia, Brazil, is under construction and power generation will start in 1998. The installed power capacity is 1,200 MW. This project includes one of the largest underground power plants in Brazil, totaling 550,000 m 3 of underground excavations for the hydraulic circuit. The underground hydraulic circuit, composed by 3 intake tunnels, 3 pressure tunnels, a powerhouse cavern, 3 suction tunnels, a surge chamber, an tailrace tunnel and 8 shafts, was excavated in a very high quality granite. Laboratory and in-situ tests, including hydraulic fracturing, small flat jack and triaxial tests, were carried out to determine the in-situ stress tensor and the geomechanical properties of the rock. Test results were summarized to yield parameters for a 3D numerical simulation of the structures, using the Boundary Element Method. Results in terms of strength factors, using the Mohr-Coulomb and Drucker-Prager criteria, are presented and discussed. Copyright © 1997 Elsevier Science Ltd