Continuous dredging works in ports and harbours are the prerequisite for keeping the access lanes open and hence to secure maritime operations, economic development and long-term employment. Yet, in all dredging projects the challenge is what to do and where to go with the dredging sediments. Disposal at sea is at least criticized and in many countries prohibited on the ground of environmental concerns. This is especially the case in the sensitive marine environment of the Mediterranean Sea which is all but enclosed by land masses.
In several countries various schemes for disposal of dredged material have been developed, both on land and offshore. The Livorno Port Authority awarded the construction contract for a confined disposal facility (CDF) to SIDRA, one of the subsidiaries of DEME Goup. The engineering solution constitutes a waterproof basin, subdivided in six sub-basins and encased between two breakwater piers for a total volume of 360.000 m³.
The two external piers which delimitate the new disposal facility consist of rock material, a core of coarse quarry material, stone filter layers, a cover layer of rock blocks, and a horizontal berm on top at the quote of 4 m. The construction method, executed both from the land side and from sea by way of pontoons, allowed a shortening of the execution time.
Within the reclamation, internal embankments were constructed to create six sub-basins by recycled inert material. These sub-basins work as weir boxes, allowing a gradual reduction of fine particles in the dredged material which are then directed to a collector for further settlement and clarification. The internal embankments as well as the bottom of the sub-basins have been waterproofed by means of a geomembrane. By double hot welding of HDPE a continuous area is obtained which is protected by a 100 percent propylene geotextile both at the top and at the bottom of the basins.