The work and the technique: Kariba Hydroelectric Plant, Zimbabwe
In July 1956, a contract was awarded for the construction of the dam on the Zambezi River, the pipelines for water adduction to the power plant, the hydroelectric power plant, and the tunnels for unloading and returning water to the river. Among the top five international bidding groups, the operations were commissioned to a consortium of four Italian companies - Impresa Umberto Girola and Impresa Ing. Lodigiani (both merged into the Webuild Group), Imprese italiane all’estero, Impresa Ing. Giuseppe Torno.
Operation commenced a month later. 5,000 local workers were hired and trained who added themselves to the same number of Europeans.
Roads to reach the site and an airstrip for air connections to the capital were immediately built. Soon, the airstrip became an actual airport. Not very far from the construction site area, a small village was built with all the required services.
The Kariba construction site reached a mechanised level that for that period was extremely high.
The concrete production plants were also installed. Crushed stone was taken from a large rock quarry. It was transported to the grinding plant with dump trucks. It was then selected in various dimensions that were conveyed to the depots with conveyor belt systems. The cement arrived from a place that was 200 km away with special trucks. It was accumulated in the 80 silos that were available. The total capacity reached 240,000 quintals.
The main construction difficulty was jetting the foundations in the river's whirling waters. The river in fact has a flow rate that, even when waters are low, is the same as the Po River's (1.540 m³/s), the longest river (652 km) entirely within Italian territory. Still, it could quickly increase up to fifty times more.
To build the foundations in the riverbed, operations were divided into two stages.
The first included excavating rocks on the southern bank, creating an underground discharging canal that was 390 metres long, 12 metres high and 10 metres in width; then, on the northern bank, which during the dry seasons was not covered by water, the first cofferdam was built, a temporary concrete basin embankment to allow workers to carry out their activities protected from the river, so that they could erect the dam's first 5 elements.
The tunnel centerings were built during this stage, later becoming the discharging conduits of the water coming out of the turbines of the powerhouse.
When the first stage was completed, the first cofferdam was removed, and the river's water began to flow as per usual.
The second stage was more complex. It started on July 6, 1957, with the operations to build the second cofferdam on the northern bank and the third, in a central position.
During Spring 1958, the greatest flood of the river took place. Due to the extraordinary quantity of water that fell with the abundant rain, 17,000 m3 of water per second demolished everything. When the water subsided, people had to rebuild, reclaim, check, and repair the damages made by the water.
Afterwards, works started to be carried out much faster, and the other elements of the dam were built until it was compact, and it could be completed in height too.
The underground powerhouse was built, powered by the water's strength and movement that through the forced conduit falls onto the turbines from a height of 100 metres; it is made of hypogeal rooms, tunnels, and shafts and by a huge machinery room that is 40 metres high, 26 metres wide and 140 metres long.
Once operations were complete, the overhead lines for transmitting the generated electricity were built, the river was cleared of debris from the cofferdam demolition, and the commissioning tests were carried out. The dam was then handed over in 1960, six months ahead of the scheduled timeline.