The strengthening of West Quay was necessitated by the increase in the draft of car carrier ships, and in anticipation of the increased import and export activity through the terminal.

"The 14-metre high quay wall (from foundation to top of quay) required strengthening so that contractors could dredge the river deeper and closer to the quay footing. This was necessary to create more depth for deeper drafted ships to berth alongside the quay," says Owen Hensburg, engineering technician at the South African National Ports Authority (NPA).

The scope of work covered the strengthening of approximately 254 metres of the West Quay. This was done through a combination of rock anchors, and the construction of a reinforced concrete extension to the coping beam overhanging the water by 1,5 metres and 1,2 metres in depth. Fendering units were then cast integrally with the extended cope beam at 8,7 m centres, extending a further 2 m below the soffit of the cope beam and each 4,5 m in length.

NPA in-house contractor, Protekon, was appointed to do the work. They used a purpose made mobile scaffold on tracks to form the reinforced concrete cope beam. "Once our in-house contractor completed this task, we proceeded to drill 160 mm diameter holes at a 30° angle through the cope beam, quay wall, and finally, into the rock.

"We then inserted rock anchors ranging from 19 metres to 28 metres in length, into the drilled holes. The porosity of the rock had to be tested in each hole before the anchors were inserted, grouted up, tested and finally tensioned," explains Owen, adding that they installed 41 anchors in total.

The quayside extension has been completed, but the dredging activity using a rock grab, will continue until the berthing depth of 10,7 metres has been attained. The 254-metre quay wall extension took seven months of construction.

Hensburg explains that the dredging service is an ongoing activity with two existing campaigns, a summer campaign and a winter campaign. "Our dredger 'Piper' visits from Durban twice a year and we are allowed access to a designated disposal site once we have acquired the necessary disposal permits."

"Currently we use a sand trap of 20 metres deep, with a 14-metre deep entrance channel. This navigation area needs to be maintained as it usually results in approximately 550 000 tons of sand being dredged per year," says Owen.

The dredging activity is accompanied by hydrographic surveys - a survey that is conducted with the use of an Echo Sounder and GPS in order to determine the water's depth. Specialised equipment is then used to do the lead line soundings before the data is collected and input into an interactive engineering design package called Civil Designer, in particular, its Survey & Terrain module. Hensburg points out that once they have entered all the data into the program, they are able to get an accurate model of the area with exact dimensions and volumes to be dredged.

In addition to the NPA's dredging service, they also assist with the drafting of conceptual plans, and have recently designed the plans for a new car terminal. The area was previously an old quarry that had been used as a container parking area. The multi level car terminal can house approximately 2800 vehicles and has a dedicated road from the DaimlerChrysler factory.

The conceptual plans of the car terminal were completed with the help of design software, AllyCAD, in accordance with space availability, and the maximisation of traffic flow.

For more information contact Knowledge Base Software, 021 701 1850.