Deepening of harbours has become a priority, necessary to the ongoing operation of the wharves in the face of deeper draftrnmerchant vessels and cruise ships. It is now standard practice in many areas to provide for harbours to be dredged tornsignificant depths below mean sea level, in the order of 12.00 m (39 ft) for existing berths and 15.00 m (49 ft) for new wharfrnconstruction. The Ravenna Port Authority initiated a project to deepen the harbour bottom at selected wharves to a depth ofrn12.00 m (39 ft). In preference to reconstruction of the wharves with longer and heavier sheet piling or other equallyrndisruptive reconstruction, they identified the structural reinforcement of the existing wharves by means of deep underwaterrntie rods as a possible alternative cost-effective solution.rnHaving defined the design concept, effort was concentrated on developing the required technology. A technique, already inrnuse for the installation of tie rods by means of robotics, was identified as potentially suitable for underwater use. It wasrndecided to carry out the fine tuning and the evolution of the technology for a marine environment of the robot unit and of thernrelated remote control software that controls the installation of the tie rods. An experimental test site was set up to refine therndrilling, installation, grouting, monitoring and testing of underwater tie rods. The purpose was to confirm the feasibility of thernproposed solution and the reliability of these tie rods for use in the reinforcement and construction of wharves.rnThe paper also discusses the theoretical and experimental study of underwater tie rods dealing with the theoretical analysis ofrnthe interaction between tie rod and soil, aimed at identifying the correlation between the forces of applied traction and therncorresponding measured elongations. A series of tests were carried out with positive results, both at the operating load of 300rnkN (67 kips) and at the nominal maximum load of 630 kN (142 kips). The tests were carried out on seven tie rods, of whichrnthree were installed at a depth of 5.00 m (16 ft), principally to test the reliability of the operating and remote control systemsrnin the presence of a significant hydrostatic pressure, and four were placed at a depth of 8.00 m (26 ft) to check the loadrnbearing capability of the tie rods positioned at the depth called for by the current project.
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