Geotechnical aspects of the design of the containment area of the port of Gaeta

The completion of filling works on the containment area of the port of Gaeta represented a great challenge. The Port Authority required immediate seabed dredging up to a depth of -12.5 m asl, to render the new Cicconardi pier fully operational. To achieve this goal, high productivity dredges were required although apparently irreconcilable with the poor capacity of the pre-existent containment area. More specifically, the nominal volume of said containment area was inferior to the dredged volume, even ignoring the initial expansion of the fine grain sediments caused by the process of excavation and disposal in the containment site. The result was accomplished by increasing the capacity of the containment area accelerating the consolidation process in the sediment already inside it and significantly reducing the mud volume thanks to an original drainage system integrated with a circuit of vacuum pumps. Consequently, consolidation is faster and, therefore, a greater reduction in the mud volume occurs during the disposal operations. This phenomenon is also magnified by the effects of the vacuum pumps that induce greater stress states than those due solely to their own weight. In addition to the installation of classic, prefabricated, vertical drains, three horizontal drainage systems (dividing the dredging operations in three phases) were also constructed, two of which were connected to the vacuum system and kept below the atmospheric pressure. The combination of laboratory and in-situ test results yielded the information needed to calibrate constitutive relations (extended to very low stresses and high void ratios), essential to model a large-strain consolidation process. Predictions of trends in settlements and the final geometrical configuration in drained conditions were obtained by carrying out simplified analyses of the subsystems the problem was divided into and superimposing the results.