Design, excavation and performance of the Laúca underground powerhouse in Angola

The 2000 MW Laúca hydro project is being built on the Kwanza river in Angola and comprises a large underground powerhouse with approximate dimensions of 26 m wide x 60 m high x 300 m long, excavated by drill and blast in a metamorphic rockmass. To meet the demands of the project schedule, the design concept of the hydraulic circuit meant that the cavern had to be placed quite close to the valley slope, to eliminate the need for a surge chamber downstream of the powerhouse. This condition required a careful study of the in-situ stress state in the rockmass to allow its implementation. This paper describes the studies developed for the geotechnical design of an underground powerhouse, including numerical stress-strain analyses and hydrojacking tests for the investigation of in-situ stresses, numerical analyses and kinematic studies of excavation for dimensioning of the rock support. The paper also includes the sequence of the excavation, monitoring data and an analysis of the performance of the structure.