Repair of the Grančarevo Dam in Bosnia and Herzegovina
The Grančarevo Dam is located on the Trebišnjica River in the southeast of Bosnia and Herzegovina near its border with Montenegro. With 123 m, this arch dam, near the town of Gornje Grančarevo in the municipality of Trebinije, is the country’s highest dam. The adjacent Bileča Reservoir is the largest reservoir in Bosnia and Herzegovina in terms of active storage.
The Grančarevo Dam went into operation in 1967, and the two hydroelectric power plants, Trebinije-1 and -2, with a total output of 188 MW were completed in 1968 and 1979. Recently, the monitoring systems for the safety of the dam were rehabilitated and modernized. In order to ensure the long-term stability of the dam, permanent double corrosion protected strand anchors were installed in the right flank of the slope directly underneath the arch dam.
Electrically testable strand anchors
The anchors used were electrically testable strand anchors in lengths of up to 61.5 m. These anchors have been approved for permanent use (applications with a 100+ year design life). By electrically uncoupling the anchor head and the tendon from the anchor plate, a resistance test between the anchor and the soil can be carried out – the integrity of the corrosion protection sheathing can be tested at any point of time in the future by the use of standardized resistance tests. Furthermore, the anchors comply with SIA requirements.
In order to allow the owner to continuously monitor the prestressing forces in the strand anchors, 46 sensors were installed in the bond length of 23 anchors. The sensors also provided an additional mechanism for monitoring the forces during tensioning. Additionally, DSI supplied four multiplexers with a stainless steel casing for permanent outdoor use that were connected to the sensors in the anchors. Furthermore, DSI engineers installed a readout unit and a controller to automatically read the data.
The data measured by the sensors are continuously read and saved by a controller that is connected to the readout unit. The data is transferred via a glass fibre connection with the controller to a computer located in the control room and analysed once a month. The control room serves for the centralized monitoring of the complete dam.
The strand anchors supplied by DSI were tensioned using two coupled Hollow-Piston CFRP Cylinders. For additional protection, greased stainless steel caps were installed over the anchor heads. Thanks to the strand anchors, the slope underneath the Grančarevo Dam will be permanently monitored to help ensure the safety and reliability of the acting forces.