Theoretical and Experimental Investigation on Underwater Ground Anchors

摘要

Abstract Deepening of harbours has become a priority, necessary to the ongoing operationof the wharves in the face of deeper draft merchant vessels and cruise ships. It is now standard practice in many areas to provide for harbours to be dredgedto significant depths below mean sea level, in the order of 12.00 m (39 ft) forexisting berths and 15.00 m (49 ft) for new wharf construction. The RavennaPort Authority initiated a project to deepen the harbour bottom at selectedwharves to a depth of 12.00 m (39 ft). In preference to reconstruction of thewharves with longer and heavier sheet piling or other equally disruptivereconstruction, they identified the structural reinforcement of the existingwharves by means of deep underwater tie rods as a possible alternativecost-effective solution. Having defined the design concept, effort was concentrated on developing therequired technology. A technique, already in use for the installation of tierods by means of robotics, was identified as potentially suitable forunderwater use. It was decided to carry out the fine tuning and the evolutionof the technology for a marine environment of the robot unit and of the relatedremote control software that controls the installation of the tie rods. Anexperimental test site was set up to refine the drilling, installation, grouting, monitoring and testing of underwater tie rods. The purpose was toconfirm the feasibility of the proposed solution and the reliability of thesetie rods for use in the reinforcement and construction of wharves. The paper also discusses the theoretical and experimental study of underwatertie rods dealing with the theoretical analysis of the interaction between tierod and soil, aimed at identifying the correlation between the forces ofapplied traction and the corresponding measured elongations. A series of testswere carried out with positive results, both at the operating load of 300 kN(67 kips) and at the nominal maximum load of 630 kN (142 kips). The tests werecarried out on seven tie rods, of which three were installed at a depth of 5.00m (16 ft), principally to test the reliability of the operating and remotecontrol systems in the presence of a significant hydrostatic pressure, and fourwere placed at a depth of 8.00 m (26 ft) to check the load bearing capabilityof the tie rods positioned at the depth called for by the currentproject. Introduction In a port environment, deepening of the harbour is increasingly becoming apriority requirement, necessary for guaranteeing the ongoing operability of thewharves in the face of a continual increase in traffic and in the tonnages ofmerchant and cruise ships. Hence it is now standard practice that ports'regulatory plans provide for harbours to be dredged to significant depthscompared to mean sea level, in the order of 12.00 m for existing berths and15.00 m for new wharf construction.