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Immersion of caissons for Venice storm-surge barrier: first caisson immersion on 7 June

06 June 2014

In the coming months, Strukton Immersion Projects will immerse eight concrete caissons as part of the storm-surge barrier near Venice, Italy. The immersion of the first caisson will begin on Saturday, 7 June. The elements, which are 60 metres long and 40 metres wide, are being shipped to Chioggia, near the Venetian lagoon, where they will be immersed.

Caissons underwater 

The eight enormous caissons were built in 2012 and 2013 in a dry dock. After construction, the dock was flooded; the caissons now lie in the dock, ready to be floated to the surface, transported and then immersed. Tugboats will be used to transport each of the 21,000,000 kg concrete giants to the entrance of the lagoon. The last caisson will be immersed at the end of August this year.

Maximum 24 hours

Chioggia is home to a very large fleet of fishing boats, so the inlet blockage must be cleared as quickly as possible. The requirements state that the inlet must not be blocked for more than 24 hours. The immersion operation also needs to take into account the large flow rate caused by the tides on the lagoon; the water flows through the inlet twice a day. In addition, immersion must be possible even with a wave height of 75 cm.

Preparations

The surveyors at Geocon, a subsidiary of Strukton Civiel, completed their activities in the construction dock in January and February 2014. The elements were dimensioned there so that all of the measurements needed to properly determine the place on the seabed are known.

In order to transport the caissons, they will ultimately need to float. So in March 2014 water was pumped for the first time into the dry dock where the eight caissons are located. At the moment, people are working hard to put the final touches on the construction of the various pontoons. The pontoons are needed in order to let the caisson sink in a controlled fashion. In addition, there are two pontoons with winches on them to control the position of the caisson diagonally.

MOSE Project

The MOSE Project is the largest engineering project in Italy and it has been in the works for a decade already. The project involves the construction of a storm-surge barrier in Italy to be able to seal off the Venetian Lagoon from the Adriatic Sea. Strukton, as the lone foreign party, is also helping Venice to combat high-water at Chioggia.

The storm-surge barrier is being constructed at the three inlets to the lagoon, at Lido, Malamocco and Chioggia. The storm-surge barrier is made up of a system of caissons containing movable flood gates. The system will only be closed in cases of extremely high water, similar to the Maeslant Barrier in the Netherlands.

The storm-surge barrier is expected to officially be put into use in 2017.