The work and the technique: Ridracoli Dam, Italy
he Ridracoli Dam, is one of the largest and most crucial dams in Emilia-Romagna and northern Italy. The arch-gravity dam consists of a double-curvature structure with a section thickness of 36m at the base, tapering to just 6m at the crest, which is the peak of the structure.
Work began in October 1975 amidst numerous difficulties, due to both the relative inaccessibility of the construction area and the geological conditions of the foundation rock. Essentially formed of repeated layers of sandstone, siltstone and marl, it had a mediocre consistency and, on the right bank, these layers were arranged unfavourably. These conditions required incredibly detailed geological and geotechnical studies to be carried out, as well as exceptional caution during excavations and the use of numerous anchors. First of all, the waterways were diverted with special drainage tunnels at the bottom; the access routes and main link roads were then created, generators were installed to power the machinery, and the construction site services were arranged. When construction of the future crest neared, the required concrete mixing machines were installed. The two banks of the construction site were linked with six conveyor belts - some suspended, some in tunnels - spanning a total length of 1,200m, capable of bridging the approximately 80-metre height difference between them.
At the same time as the systems at the foot of the dam and the slopes of the adjacent hills were being constructed, work began on the excavation of the dam itself - removing more than a million cubic metres of material - and its consolidation, using special steel tie rods consisting of stranded wires inserted into the perforated rock, each strong enough to support a load of 15 tonnes.
In August of 1978, concrete pouring began for the construction of the segments of the dam, using custom-designed formwork moved by special cranes with a capacity of eight tonnes each, and the internal shafts were constructed, spanning a total of more than 2km.