The Civil Engineering Contractor August 2018 | Page 26

TECHNOLOGY
"Tunnel boring machines (TBMs)
are typically too expensive
under South African conditions
of abundant labour and scarce
capital, and so a hybrid practice
of part-mechanisation part-labour
has emerged."
That we are at an early stage is due
primarily to economics and available
land rather than skills or technology.
It is not commonly known that the
veritable maze that is the London
Underground owes its existence, at
least in part, to a brilliant South
African-born railway engineer
named James Henry Greathead. His
‘Greathead shield’, designed by him
in 1869, was used in the completion
of the Tower Subway, which ran under
the River Thames, close to the Tower
of London. It was circular in design
and was advanced by screw jacks; the
tunnel subsequently lined with cast-
iron rings for support.
24 - CEC August 2018
If South Africans were integral to
the emergent steps of underground
infrastructure, they are just as integral
today in the form of South African-
born billionaire entrepreneur, Elon
Musk.
Safety, efficiency, versatility
Underground construction in South
Africa, for example in the pipe
jacking industry, often involves human
resources with handheld breakers
for softer material, or rock drills
where hard rock is encountered, and
drilling and blasting is required. This
is primarily because conventional
excavation machinery will not fit
in confined underground working
areas. The problem with that is a
person can only hold a hammer for
so long. “A more specialised machine
such as a Brokk demolition robot
can do the work of 20 workers and
doesn’t tire. The challenge is that
so much more waste material gets
dislodged at a quicker rate and then
becomes a bottleneck unless the entire
process of removal is simultaneously
mechanised,”
explains
Robin
Jackson, director of Demolition &
Drilling Equipment.
In circumstances where roof
collapse is a possibility where it is not
supported, a Brokk demolition robot
becomes a necessary safety factor.
In the event of a cave-in, only the
machine is buried, with the operator
holding a remote several metres
behind and being safely surrounded
by a concrete pipe with a steel shield
in front.
Such equipment is more expensive
initially, but is usually cost effective
for road tunnels, metros, and mining
over the term of a specific project,
says Jackson.
Tunnel boring machines (TBMs)
are typically too expensive under
South African conditions of abundant
labour and scarce capital, and so a
hybrid practice of part-mechanisation
part-labour has emerged: lesser
mechanisation is employed, such as a
drum cutter, rock splitter or hydraulic
hammer, requiring a lot less upskilling,
but which is less efficient than a TBM.
Labour does the rest. “This is a lot
cheaper because it requires one quick-
but in urban design, to keep the earth’s
surface relatively free. However,
there are important funding issues
which mitigate against underground
construction. Van der Merwe points
out: “The rule of thumb in engineering
is that the ratio of constructing on
ground is R1 compared to R10 for
elevation above the ground and R100
for below ground.” From a cost point
of view, building underground should
always then be the last option in
infrastructure.
Lifestyle solutions must increasingly
consider climate change and enable
a form of urban development that
supports the health and the
well-being of urban dwellers in the
face of increasing population pressure.
In South Africa, this trend is in
its embryonic stages. Buildings
increasingly have multiple floors of
underground parking, and it is close
to a decade since we had the first
underground ‘metro’ system in the
form of the Gautrain.
Jack van der Merwe, CEO of Gautrain
Management Agency, is planning phase
two of Gautrain.
hitch machine such as a demolition
robot with different heads. Unlike
most machines, the Brokk comes
with the quick-hitch standard,” adds
Jackson.
The softer the material the cheaper its
removal by off-the-shelf tools without
the need for drilling or blasting and
can even often be removed by hand.
“One prepares accordingly based on
the geotechnical report,” Jackson says.
At the extreme end of technological
solutions is Herrenknecht AG, which
has TBMs capable of boring 2.5–3m
tunnels, but which is expensive and
requires considerable time to set up
the project. Apart from Gautrain and
other transport tunnels such as Cape
Town’s Huguenot Tunnel, Jackson
describes tunnels in South Africa as
being in the region of one to two-
and-a-half metre in diameter and
being constructed for water or utility
services.
One of the biggest recent and
current tunnelling projects in South
Africa involves the transfer tunnel
being constructed as part of the
Lesotho Highlands Water Project. This
year sees the start of phase two of the
water project; the first phase of which
was completed in 2002. Phase two