ST 003-10 Lohr, 2010-03-17

MOSE Parts the Sea in Venice

Rexroth hydraulics transports components weighing 23,000 tons for a mobile tide barrier

The construction of one of the largest tide barriers in Europe, which is being built to protect the historically unique trade city from flooding, is entering the critical phase. Since in summer 2009 Rexroth has put the hydraulics for a caisson transfer system into operation, it moves concrete blocks, each weighing up to 23,000 tons, to the loading station. They form the foundation of the "mobile" tide barrier, MOSE, that protects the Venetian lagoon from the spring tides of the Mediterranean.

The gondolas on Canale Grande, St. Mark's Square and the magnificent Doge's Palace: Venice is one of the world's largest tourist attractions and, for nearly a thousand years, controlled East-West trade in the Mediterranean. But the city on the lagoon, declared a World Heritage Site in 1987 by UNESCO, is threatening to sink. Spring tides—more than 50 since 1993 alone—are gradually destroying the building fabric and threaten the future of this historically unique city. A mobile tide barrier, the Modulo Sperimentale Elettromeccanico, or MOSE, is therefore being constructed to protect Venice from the inward flowing Mediterranean. The project is scheduled for completion in 2012.

MOSE is based on the principle of air buoyancy. In a concrete construction situated on the seabed at the lagoon openings between the islands off the coast of Venice are 79, tightly spaced, hollow flood gates made of steel. They are connected to the foundation by means of a joint. While at rest, they lie flat on the bottom. If high water threatens, compressed air pushes the water out of the 20 meter-wide and five meter-thick steel bodies and pushes them upright within 30 minutes. The mobile tide barrier seals off the lagoon from spring tides as great as three meters high; the highest spring tide to date measured 1.94 meters.

Following the preparations on the seabed the placement of the approximately 1,600 meter concrete foundation, which holds the flood gates, have begun in the summer of 2009. It consists of precast concrete parts, each weighing up to 23,000 tons, with the dimensions of a soccer field. For this XXL foundation, TTS Handling Systems of Norway, a global leader in transfer systems and panel lines for shipbuilding has constructed a heavy-load transport system. It connects the pouring station on land with the loading equipment for sea transport. Rexroth is the system partner responsible for the project planning, delivery and commissioning of the hydraulic lifting and transport equipment.

The hydraulic system uniformly lifts the precast concrete parts at 84 points. Two axial piston variable displacement pump combinations generate a flow of 2 x 400 l/min that supplies four hydraulic circuits. The hydraulic synchronization keeps the foundations absolutely horizontal and prevents uncontrollable inclined positions: lifting occurs so uniformly that no tensions occur in the material. A turbodiesel engine with 290 horsepower supplies the hydraulic power unit with energy. The pressure control of the pump combination ensures high energy efficiency: the power unit only generates as much pressure as the consumers need at the moment. A special advantage of hydraulics: no energy is required to hold the 23,000 ton load in place, since the valves simply close once the transport height is reached.

Two other hydraulic power units, driven by a 62 horsepower turbodiesel engine, handle the forward motion of the concrete parts on a rail system that moves to a lowering platform. From there, the caissons are transported to their intended position and lowered to the seabed at the exact location. The transfer system is designed for a maximum load of 28,000 tons. Thus, if necessary, it can also transport components larger than previously planned.

Rexroth has worked together closely with TTS Handling Systems since the start of the design phase. As system partner, the manufacturer of all drive and control technologies has the system responsibility for the hydraulics and calculated the dimensioning of the power units. Both companies have in a common a long history of success in harbour and marine related applications on all of the world's oceans. As a global player, Rexroth supports TTS Handling Systems with its international organization.

Bosch Rexroth AG is one of the world’s leading specialists in the field of drive and control technologies. Under the brand name of Rexroth the company supplies more than 500,000 customers with tailored solutions for driving, controlling and moving. Bosch Rexroth is a partner for industrial applications and factory automation, mobile applications and using renewable energies. As The Drive & Control Company, Bosch Rexroth develops, produces and sells components and systems in more than 80 countries. In 2008 Bosch Rexroth AG, part of the Bosch Group, achieved sales of around 5.9 billion Euro with 35,300 employees.

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Susanne Herzlieb
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