WorleyParsons was engaged to provide basic and detail design of all structures and installations of the hydro power plant on an EPC turnkey contract.
The main geotechnical features of the project are the underground works excavated on granite and metasedimentary rocks. The tunnels, shafts and caverns can be summarized as follows:
-
A 6,637 m-long low head tunnel excavated in rock with an arch-rectangular section (width-height = 7.7-7.85 m). Special care was required when crossing a stream valley with a length of 300 m. In this region, the predicted rock overburden was less than 8 m and boreholes had indicated poor conditions in the rock mass.
-
A downstream service access tunnel has been excavated with an arch-rectangular section (9 - 7m) for construction purposes. The lower stretch of this tunnel is to be used as a surge tank. This solution eliminated the need to excavate an upstream shaft which was planned in the feasibility studies for use as a surge tank.
-
A shaft (with a cross sectional area of 100 m2) was excavated for the operation of the main control gates.
-
Two pressure tunnels. These conduits, excavated by raise boring machine, have a diameter of 3.55m.• An underground power cavern, 17 m wide, 64.2 m long and with a maximum height of 40 m. The type and extent of rock support were determined based on extensive structural and geological
studies, as well as three-dimensional numerical modeling to simulate excavation of the caverns and adjacent tunnels.
-
A 377 m long access tunnel for equipment (with dimensions of 7 - 6.5 m) was excavated on the right side of the power cavern to transport equipment.
-
A tunnel (7 - 7.6 m) on the left side of the power cavern with length of 300 m was excavated for two purposes: for ventilation and to link the power cavern to the switchyard located on ground surface.
-
Two discharge tunnels with an arch-rectangular section.
-
A downstream surge tank excavated in a shaft with an almost elliptical section and a cross sectional area of 183 m2.
-
One low-head outlet tunnel with an overall length of 333 m, which finishes in a short outlet channel, at the right bank of the Itajai-Acu river, 12 km from the intake.
The geotechnical studies also include seepage and slope stability analysis for earth works related to downstream scheme (switchyard; control building, etc).
