December 2013
CONSTRUCTION WORLD
58
Specialist Contractors or Suppliers
B
Portside Basement Slab
T
he Portside building is a fast track Greenstar building project
currently under construction on the Foreshore in CapeTown. It will
be the tallest building in Cape Town when completed.
During the planning stages of the project Bobcrete were
approached by Murray & Roberts to see if it would be possible
to provide a suspended slab together with beams all in precast,
as an alternate to backfilling the basement with approximately
60 000 m
3
of selected crushed rock backfill which when compacted
would provide a hardcore support for a cast in situ surface bed.
Since Murray & Roberts wanted to build the building up as well as
it was going down, the logistics of moving in this quantity of crushed
rock were a headache.
Consultants on the project had designed a system of beams and
together with Bobcrete’s award winning Bobflor Hollowcore slab
system, this was put forward to Murray & Roberts as an alternate.
On costing the precast beamsystemandBobcrete’s Bobflor panels,
the initial costings proved too expensive.
Bobcrete were then tasked with redesigning the beams to sup-
port the Bobflor. It was necessary to have the flexibility tomake these
beams able to be carried in manually, due to the slabs above the
basement being constructed concurrently with the basement slab.
For this reason, Bobcrete devised a system of Precast Beam Sof-
fits 150 mm thick and approximately 300 mm wide which Murray &
Roberts could manually place, prop then cast the upper portion and
once this was done Bobcrete would place the panels.
Bobcrete proposed pioneering a new method of working which
would be a first for Cape Town namely, having the forklift run on top
of the completed panels, advancing and installing in thismanner.This
had never been attempted before.
A further complication was the requirement to be able to work
not only down the length of the ‘bays’ between the columns but to
be able to change ‘bays’ and still install the panels. This required the
forklift to bemodified both in height, because it was too tall, and then
with a stinger and a swivel attachment attached to the front so that
panels could be extended across to a new bay running parallel with
the already installed bay and then swiveled into the correct position.
The extra prestress required in the panels to accommodated this
load, had been factored in by Bobcrete during the initial costing and
this cost was thereforewas allowed for. As the Hollowcore panels were
placed they needed to be strong enough to carry the weight of the
forklift, approximately 5 tons, and theweight of the Hollowcore panel
being carried by the forklift plus the additional ballast in the added
ballast box. Moreover an impact load had to be also factored in as
the forklift was tramming over the existing panels. This revolutionary
method of installation proved to be an absolute winner and the work
was completed on time without any problem.
Project information
• Project name: Slope stabilisation and rockfall protection measures for
Chapman’s Peak Drive
• Company entering: Maccaferri SA
• Project start date: September 2012
• Project end date: April 2013
• Client: Western Cape Government: Department of Transport and Public
Works
• Main contractor: Penny Farthing Engineering
• Project manager: Western Cape Department of Transport and Public
Works
• Consulting engineer: Melis & Du Plessis Consulting Engineers
• Landscaping: Cape Contours
• Project value: R12-million
Slope stabilisation and rockfall protection measures
for Chapman’s Peak Drive
T
he stabilisation of the slopes on the stretch of road
along Chapman’s Drive came under consideration
after a rockfall incident that had occurred back
in 2004. The slopes along this section of the road had
become increasingly dangerous after the depletion
of the vegetation on the slopes due to the fires that
had occurred during 2000. It was concluded that the
slopes needed to be stabilised so as to prevent further
occurrences of such a nature, thus ensuring the safety of
pedestrians and vehicular traffic using this scenic route.
The contract was for the Slope Stabilisation and Rockfall
Protection Measures of Route M6 from SV 23 500 to
SV 24 100 on Chapman’s Peak Drive.
Themain contractor on this project was Penny Farthing
SA. The drape mesh, the gabions and the components for
the catch fences and including all wire rope cables were
supplied by Maccaferri South Africa, while the anchors
were supplied by Duraset. It was a requirement that all
products complied with Class A galvanizing. The design
for all the rockfall mitigation measures, as well as the full-
time on site supervision, was done by Melis & du Plessis
Consulting Engineers.
The project was successfully completed, and was also
completed well below the tendered price. On completion
of the project, the road ismuch safer to all road users as well
as pedestrian traffic, as the mitigation measures installed
serve as a preventative measure to arrest rocks that may
become dislodged over time thus possibly causing a haz-
ardous or dangerous situation.Thematerials used also have
a minimum impact on the environment and blend in very
well with the surrounding vegetation. Since completion
of the project, the vegetation has re-established very well
and appearing very lush in places.
