With the use of an MTBM (Micro Tunnel Boring Machine) drill head with a hydraulic soil removal system and the smooth surface of jacking pressure pipes, a water treatment project in Venice has managed to keep costs to a minimum.

Situated between the drainage basin of the mainland and the sea, the lagoon of Venice is the largest in Italy. Subjected to growing pollution as a result of increasing industrial and agricultural developments in the region, the Regional Government of Veneto set up a plan in 2000 to prevent further pollution and treat the water running from the basin into the lagoon.

The Fusina project, consisting of a 20 km long outlet to the sea, conveys the treated water 10 km from the plant in Fusina to Lido di Venezia and another 10 km to the sea where large tanker ships dock. In order to cross the Lido sandbar, 351 m DN 1400, PN 6 pipes were installed by microtunnelling.

“It took a long time for us to find a pipe that suits our requirements”, explains engineer Meneghini, site manager at Mantovani SpA. “We needed a jacking pipe that would also withstand the operating pressure of the line.”

Article continues below…

Normally, two different pipe systems would have been utilised to match all the requirements necessary. After a long research period, however, they chose HOBAS CC-GRP Jacking Pipes for their mechanical strength as well as their hydraulic properties.

The pipes were chosen in 3 m long sections, with an external diameter of 1720 mm and a wall thickness of 85 mm, allowing a maximal jacking force of 6926 kN. The leak-tight pipe system is produced to withstand an operating pressure of 6 – 10 bar. The smooth outer surface of the pipes enabled comparably low jacking forces and allowed a single jack over the complete section of 351 m. Only the starting and receiving pit were used, saving on three originally planned intermediate stations.