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“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 1,5metres, and
1,2metres in depth. Fendering units were then cast
integrally with the extended cope beam at 8,7m centres,
extending a further 2m below the soffit of the cope
beam and each 4,5m 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 160mm diameter holes at a 30-degree
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. |
