Steel Construction Vol 40 No 3 - Mining, Industrial, Import/ Export | Page 22

SAISC PROJECTS

Venetia Underground
“The headgears were designed to be assembled
in modules that could be pre-erected and then
lifted into place, thereby reducing the need for
the 100m boom 750 tonne super crane for the
full construction duration.”
The De Beers Venetia Underground Project will replace the existing
Venetia open pit diamond mine in the Limpopo Province. By 2021,
the diamond bearing ore will not be economical to mine through
the open pit method as the amount of waste stripping required will
be excessive, hence the requirement for the underground access. In
order to extend the life of the mine, De Beers and Anglo American
took the decision in 2007 to construct a new underground mine.
WorleyParsons RSA has been involved in the project since feasibility
stage and was commissioned to execute the detailed engineering
design for both the surface and underground infrastructure for
the new underground mine, which will comprise a twin shaft and
decline mining complex.
Both the production and services headgears are propped towers.
They consist of a 12m x 12m x 72m high (production headgear)
and a 12m x 12m x 52m (service headgear) braced tower each with
a 60° raking leg. A trade off comparison was conducted between a
concrete and a structural steel headgear.
The decision was influenced by the time constraints to erect the
headgear and the mining method used i.e. having the headgear
in place to assist in the sinking condition and then used for the
permanent condition (reduced change over period).
Steel proved to be the most practical material as it is quick to erect
and the changeover from sinking to permanent will be considerably
easier as there are many more openings to remove the sinking
equipment and steelwork as well as to bring in the permanent
condition equipment and steelwork.
The headgears were designed to be assembled in modules that
could be pre-erected and then lifted into place, thereby reducing
the need for the 100m boom 750 tonne super crane for the full
construction duration. All sheave beams (up 2.2m deep plate
girders 11m long) were to be normalized to ensure no residual
stresses in the beams after fabrication.

Project Team
Client: DeBeers
Structural Engineer: WorleyParsons
Quantity Surveyors: DeBeers
Project Manager: WorleyParsons
Main Contractor: Genrec
Structural Steel Detailer/Detailing Company: Genrec
20 Steel Construction Vol. 40 No. 3 2016

Of the total 1 700 tonnes of steel, 940 tonnes were plate girders,
including 290m of 1m x 1m Cruciform columns. This required
upfront planning to ensure that all the plate girders could be
fabricated to alleviate any delays in the program.
The sheave levels and raking legs were trial assembled in the
workshop to ensure that these critical items fitted perfectly
together. This proved to be a mammoth task as there were a total
of 7 250 holes to be drilled in the sheave levels for the diaphragm
plates alone and this could only take place after the sheave levels
had been assembled thereby ensuring that the diaphragm plates
would fit on site.