Refuge harbour and navigation lock at the entrance of Lido Treporti (Italy)

To improve the safety of the Lido port, a refuge basin has been planned in the north side of the port entrance, including a navigation lock to allow hydrofoil and passenger vessels to enter the lagoon during the closure of the barrier. The basin, before satisfying the final objective, is planned to be the dry construction area of 7 concrete cellular caissons 60x35x9 metres. All structures of the basin are therefore designed to satisfy both objectives.  

The detailed design includes:

• The reinforcement of the shore between the landward end of the north breakwater and the seaward side of the refuge harbour, modifying the profile of the breakwater to limit overtopping
• The reclamation (about 7 ha.) at the end of the refuge harbour bound by the link dyke between the main breakwater and the lock area. The backfill has been achieved using sediment from the undersea excavations, whilst the material unsuited to this purpose has been used for morphological works inside the lagoon.
• The prefabrication yard for the dry construction of the concrete caissons, delimited by a temporary sheet pile cofferdam and by a plastic diaphragm wall 28m high, executed with the Cutter Soil Mixing (CSM) method. The dimensions of the refuge harbour on its south side are compatible with the possibility of obtaining an area some 100 m wide and about 500 m long, with a depth of –8.70 m, to allow the prefabrication of the caissons for the Lido Treporti barrier.
• The first phase of the works for the refuge harbour on the north side of the inlet, destined to harbour small craft wishing to exit the lagoon during the period of closure of the barriers.
• The area of the navigation lock, involving the driving of sheet-piling to delimit the lock area and the realization of the lateral embankments to act as construction sites.

The contract included the provision of the following services:

• Detailed design of the structures described
• Bill of quantities and cost estimate
• Tender documents
• 2-D and 3-D mathematical model study of system for emptying the cofferdam of water
• in-situ well permeability tests to verify the assumptions made for the filtration analysis