Location: Chioggia, Italy
Client: Venezia Nuova Consortium - Ministry of Public Works
Services: Surveys and investigations, preliminary, detailed and final design
The mobile gates at the ends of Vena Channel are sector type hideaway doors, automatically operated by hydraulic motors. A remote control system is implemented. Either the opening or the closing operation is about 8 minutes long.
The doors are 18 m long, 3.3 m wide and 80 cm maximum thick. This solution was chosen among other alternatives (miter gates, flap gates) because of the combination of the following factors: great functionality and maneuverability, smaller dimensions, better architectural setting, easier maintenance, easier management relating to boat traffic.
The doors are made of steel, with suitable protection against corrosion due to sea environment. Cathodic protection is provided by galvanic anodes.
The gates were completed in workshop, transported by truck to the site and installed using a mobile crane. Each gate is a cast in situ r.c. foundation structure and is 20 m long and 10 m wide.
The main issue in construction was that excavating and draining at such a small distance from the surrounding existing buildings would have been hazardous for the stability of their foundations. Filtration would have reduced the water pore pressure in the soil and hence the overall bearing capacity. A special solution was investigated on purpose: a watertight steel box was assembled, submerged and anchored to the sea bottom by means of a series of micropiles. The box was then dried up and the r.c. foundation structure was cast inside the box, by using it as a formwork. Therefore the water pressure in the surroundings remained unchanged. Afterwards, the upper portions of the box were removed.
A specific pumping station with sea discharge, which is located near the southern gate, permits to control the level in the Vena channel depending on the various weather conditions and the water quantities discharged in the town drainage system. The pumping system consists in three immersed pumps and provides great flexibility to the management of the system. The pumps usually work two at a time. The third one works when further flow rate is needed. The total capacity of the pumping station is 3 m3/s.
The gate is operated by PLC and raises the closing position (83°) when the system is started either automatically or manually. A maintenance position (180°) will be reachable by manual operation when necessary.