4. Cagliari: Porto Flavia Tour
See how a special crew of miners expert in explosives and rock climbing was assembled. They worked in shifts, day and night, to complete the excavations in record time. Despite safety measures being practically ignored to speed up work, no casualties were reported in the building phase. Because the tunnel was without angles or trenches, the usual technique for dynamite drilling was impossible (the crew used those angles and trenches as shelter while blowing up charges just a few meters away). Instead, small cavities were excavated at regular distances to allow the workers to gain cover after igniting explosives. They are still visible in the guided tour.
The workers began drilling the upper gallery, 37 metres (121 feet) above sea level with dynamite and mechanical drills (many mines at the time mostly used pickaxes) until they reached the sea. They then hung from ropes and began drilling the lower tunnel from the cliff face, 16 metres (52 feet) above sea level, going the opposite direction under the upper gallery. This way, they could dump the removed rocks directly into the sea. Finally, the reservoirs were excavated by creating holes in the basaltic rock starting from the bottom of the cavities and going up. This again eased the removal of rubble, although this procedure was dangerous. Each storage reservoir was 4 to 8 metres (13 to 26 feet) in diameter and 20 metres (66 feet) high. Venting holes were opened on the side of the galleries. Mechanical iron hatches were installed along with the electric railway into the upper tunnel. The train brought the ore to the loading hatches of the reservoirs, while in the lower tunnel the unloading hatches fed the ore to the conveyor belt leading to the ships. The belt was covered with a steel casing to prevent the wind blowing away zinc oxide powder. It was extensible, and retracted after a load was delivered to the ship's hold. The main conveyor belt featured an innovative movable alignment system, designed to reduce the risk of the belt escaping the driving wheels under the pressure of the falling ore. The main belt dumped the ore on the slightly lower extensible conveyor belt, which could be protruded for 15 metres (49 feet) and channeled the ore powder into a vertical shaft going to the hold of a moored ship.
Construction took only two years, ending in 1924, a remarkably short period of time for a work of that size. The ends of the tunnels facing the sea were adorned with concrete towers and decorative nameplates. They were not necessary to the operation, but were asked to be constructed by the owner of the company as a mark of prestige. Vecelli's daughter, Flavia, was born earlier in 1924 and the engineer obtained from the company to name the harbor after her.