Luzzone dam - repair of slide gate tunnel

The Luzzone dam and the sliding tunnel

The water resources of the canton of Ticino were pooled in the middle of the 20th century for the general energy supply of the consumer areas north of the Alps and put into operation with the Blenio power plants in 1963. The waterworks consist of 3 dams and 3 power stations.

The Carassina, Malvaglia and Campra dams were designed as gravity dams. The Luzzone dam, however, is a V-shaped dam cut deep into the rocky valley and designed as a sharply curved gravity dam. To increase the storage capacity from the original 87 to 107 million m³, the Lago di Luzzone dam was raised by 17 m in the 1990s. After the 225 m high Luzzone dam, the Brenno di Luzzone flows downstream from the reservoir.

The technical structures, such as pressure pipes, slide chambers, control centers and underwater channels are located inside the mountain and are thus protected against rockfall, avalanches and flooding during high water. All systems are remotely controlled and monitored from the joint control center in Locarno.

At the Luzzone dam, the water is discharged via an overflow or via the bottom outlet. The bottom of the bottom outlet is exposed to extremely high forces and must be specially protected against wear and tear. The floor and side walls are lined with concrete, the vault is usually unlined or covered with shotcrete. In order to protect the floor of the tunnel from further wear and tear and to strengthen the floor for further use, a special concrete was to be installed that is extremely durable and resistant to the enormous water forces.

The concrete was produced at the Holcim Beton plant using a CEM I 52.5R cement, silica fume, a particularly resistant aggregate including quartz sand, and our shrinkage reducing agent D-SOLO, and transported to the dam. There, the concrete was pumped to the outlet structure and outlet tunnel, approx. 100 m deep into the valley, using a concrete pump. At the tunnel entrance, the concrete was reloaded into a 1 m³ dumper truck and driven approx. 300 m into the tunnel. At the end of the tunnel, just before the slide gate, the concrete was reloaded again and an approx. 0.3 m3 small motorized mini-dumper drove the concrete to the installation site and unloaded it there.

The installation of our shrinkage-reduced special concrete ensures that the floor could be formed without cracks and joints, thus minimizing the wear and tear of the newly concreted tunnel floor caused by the water power and remaining extremely robust against the water forces.