Confinement basin for polluted dredged sediments | San Giovanni Beach | Teduccio | IT

The remediation project of the sandy beach and the seabed of San Giovanni in Teduccio, Italy, consists in the construction of an impervious wall that will confine polluted soils that will be dredged in the area and that have higher concentration of pollutants than allowed in the Italian regulations (Decreto Ministeriale DM 471/99).

This new structure is located near the sheltered dock 'Darsena di Levante' and is split in two different projects: three sides of the impervious basin to be built with a conventional steel sheet pile wall is part of one project. The second phase is the construction of a double wall that will be used for the installation of the steel pipes for the water intake structure of the power plant 'Tirreno Power'. One of these walls constitutes the fourth impervious wall of the basin.

An impervious layer of 'tuf' is at a depth of 21 m below the normal seawater level. The sheet piles are driven down into this layer in order to prevent water flow below the toe of the sheet pile wall. The top of the wall is at +1.0 m above seawater level. In order to improve the horizontal watertightness of the whole sheet pile wall, the interlocks are sealed over the whole length with the Roxan™ system. The excellent performance of this sealant system was previously confirmed in 2008 by an in-situ test on the Lusore-Brentelle canal in Porto Marghera, in collaboration with the Polytechnical Institute of Milano.

The existing soil level varies along the walls and the design required different section properties for different cross-sections. Based on the several design criteria, AU 20 and AU 23 sheet pile sections were chosen. Being 750 mm wide is one significant advantage of the AU sections for this specific application: imperviousness is improved as there are less sealed interlocks per wall length. Besides, the design engineers estimated that in these soil conditions, no steel protection was required in order to achieve the 50 years of service life of the structure.

The installation of the sheet piles was performed partly from land and partly from a barge, using different types of cranes and free hanging vibratory hammers, like for instance one powerful PTC 60HD.

The works finished in 2009. The new basin is now fit to accept polluted materials from excavations and dredging in the surroundings of the San Giovanni Beach.

ArcelorMittal Commercial RPS collaborated with the design engineers and contractors throughout the project. In particular the technical department elaborated the layout drawings of the sheet pile walls (including special corner piles) which are required for a correct installation of the sealed steel sheet piles.

 
 

First publication: 2009

Last revision: 01/2019