December 2013
CONSTRUCTION WORLD
56
Specialist Contractors or Suppliers
B
Culverts for Tweefontein Optimisation Project
E
ight hundred giant precast concrete culverts, three-and-half
metres high and just over five metres wide, are being used for
the construction of two buffer (stockpile) tunnels at Glencore’s
Tweefontein Optimisation Project near Witbank.
International consulting engineering concern, DRA Mineral Proj-
ects, is responsible for the engineering, project management and
construction work. DRA is also handling the design of the system
in collaboration with the civil and structural consulting engineer-
ing company, Holley and Associates. The main civil and earthworks
subcontractor is WBHO.
This is the first time that DRA has used concrete culverts for coal
stockpile tunnels. The other construction material options consid-
ered for the tunnels were steel and in-situ concrete. According to
the project engineer, Arthur Oosthuizen, of DRA, recent durability
and maintenance concerns with steel tunnels and time constraints
with in-situ concrete construction prompted the decision to opt for
precast concrete.
Weighing 12,8 tons each, these are some of the largest culverts
ever made in South Africa and could well be the largest single culvert
order ever. Manufactured by Concrete Manufacturers Association
(CMA), member, Aveng Manufacturing Infraset, and designed by
technical marketing manager, Coenraad Groenewald, they were
produced at its Brakpan manufacturing facility.
“The units are comprised of solid steel-reinforced concrete and
are designed to handle well in excess of the maximum 20 ton load-
ing they are likely to encounter at the Tweefontein buffer zones,”says
Groenewald.“Each contains 600 kg of reinforced steel and measures
3,5 m (height) x 5,3 m (width) x 1 m (depth). The walls are tapered,
measuring 350 mm at the top and 300 mm at the bottom.”
The initial requirement was for a height of 4,7 m but this proved
too large for transportation by road. To make up the shortfall, the
foundations on which the culverts are installed include elevated
uprights measuring 500 mm. Once in place the joints between the
culverts are sealed with bitumastic sealant on the outside and grout
on the inner joints.
Given the culverts’ non-standard dimensions, six custom-made
steel moulds are being used for casting.
Casting is done horizontally and once cured, the culverts are
loaded in the horizontal position onto low-bed trucks, each truck
carrying two culverts.
“The simple and safe handling of the culverts, both at the Brakpan
plant and at the colliery also required some additional engineering.
Steel lifting beams were designed by Groenewald. Rather than using
additional machinery to shift the culverts into a vertical position on
site, Groenewald adopted an innovative approach by using the force
of gravity.This is done by attaching a steel beam to the top end of the
culvert and then by simply lifting this end with a crane, the culvert
swings into a vertical position. It is then easily raised and placed into
position on the in-situ foundation.
“We are under a severe time constraint and are currently working
a double shift, which means at maximum output we can produce
12 units a day. We are also working on Saturdays to ensure that the
culverts are delivered on time,”concludes Groenewald.
Project information
• Name of project: Culverts for Tweefontein Optimisation
Project
• Company entering: Aveng Manufacturing – Infraset
• Client: DRA Mineral Projects
• Main contractor: WBHO
• Project manager: DRA
• Supplier: Infraset
