A feasible design concept for the deep water breakwater of the proposed new Durban Dig-Out Port

[摘要] ENGLISH ABSTRACT: The Port of Durban is forecasted to reach its capacity in terms of container handling soon,which necessitates the investigation of an alternative port in the vicinity. The old DurbanAirport site has been identified as a potential location to develop a new deep watercontainer harbour. This is driven by a demand for deep water berth capacity as a result ofshipping liners preferring the benefits of scale in their operations, leading to the use oflarger ships with deeper drafts. To protect the new port from wave energy penetratinginside the basin as well as from sedimentation from the adjacent beaches, the design andconstruction of breakwaters are required.The proposed main breakwater for this dig-out port is expected to extend 1 200m intothe sea, up to depths of 30m at the seaward roundhead. The deeper parts of thebreakwater face wave onslaught in a different manner than a conventional breakwater inshallower waters. At these larger depths, the breakwater has to dissipate the energy ofnon-breaking waves.In this thesis, the wave climate nearshore, adjacent to the proposed breakwater is studiedand extreme wave events are simulated with a SWAN numerical model. The results for arange of wave conditions, corresponding to selected events up to a return period of one in100 years, are presented.A study of deep water breakwaters was undertaken to investigate other examples ofsimilar structures. This indicated a clear distinction between vertical wall typebreakwaters and the more traditional rubble-mound type breakwaters. For this thesis, arubble-mound breakwater was chosen as the breakwater type for testing underconditions of the Durban Dig-Out Port (DDOP). Focussing on a deep water trunk sectionof the proposed main breakwater, a concept cross-section was designed usingdeterministic design methods. The formulae incorporated in this method did however nottake into account the packing density of the armour layer and only assumed therecommended values.The hypothesis is thus put forward that the breakwater will still be hydraulically stablefor packing densities below the recommended values. This would decrease materialconsumption and save on cost over the entire breakwater. A physical model was designedto experiment with different armour layer configurations of single- and double layerCubipod arrangements. The unit was chosen for its massive shape and structural integrityeven during impact.A physical model study was performed at the facilities of the CSIR in Stellenbosch. Itentailed setting up a fixed-bed two-dimensional physical model in a glass wave flume.Measuring wave heights, wave reflection, overtopping, wave transmission and armourdamage, the hydraulic stability and operational performance were analysed for severaltests. Based on the results of the first few test series, alterations were made to thebreakwater geometry and armouring.The results confirmed the hypothesis that lower packing densities were still hydraulicallystable under 1 in 100 year return period wave conditions without inhibiting operationalperformance. A final cross-section is presented as concept design for the deep section ofthe proposed DDOP main breakwater.

[发布机构] Stellenbosch University