“EVERyBODy THINKS ABOUT THE HIGH-
TECH SIDE OF TUNNELLING, BUT THERE
ARE LOTS OF junctions and inteRfaces
WHERE tRaditional skills ARE NEEDED”
Martin Knights, International Tunnelling Association
retreated,” explains Skates. “We have every- seconds – it is now safer and faster. This
thing from rock to boulder clays, sand, gravel – is thanks in part to sophisticated tunnel
and overlying the whole lot is a material boring machines, as well as the much
known as ‘Sleech’, a soft, estuarine clay.” improved and highly developed approach
This kind of mixed ground can be a to risk management within the industry.
problem, because the machines work best “A huge amount of nursing goes on
when cutting through uniform material. with the machines, coaxing them through
When this changes from relatively soft clay Belfast’s different strata,” explains Skates.
to much harder sandstone, for example, “But if everything is going well, they can
work has to stop so that the picks and romp along quite happily at 40 metres
tunnel cutters can be changed. a day. That’s above the average
“We kept the depth of the that the contractors had
tunnel to 30 metres,” says originally anticipated.”
Skates. “The aim was to
22 end up in reasonable Art and science
tunnelling strata as Schemes like the
much as possible. Belfast Sewers Project
Mostly, we’re in either deliver significant
boulder clay or sand- social, economic and
stone, but occasionally environmental benefits.
we intercept areas that are But because the work is
mixed – these present the rarely seen by the public,
biggest challenges.” it doesn’t attract the attention
No stone is left unturned in the quest to it deserves. Railway schemes, on the
avert problems. In the case of Belfast’s storm- other hand, tend to enjoy a rather higher
water system, that meant spending a year public profile.
planning the project carrying out site investiga- The Gautrain Rapid Rail Link project in
tions, drilling boreholes, selecting sites for South Africa is one such scheme. Currently
access shafts and choosing the best route. under construction, it will provide a high- ground stations. Atkins’ locally-based design conditions are essentially soil-like,”
It’s a painstaking process. But even with speed link between the capital, Pretoria, team draws on expertise from the UK, South explains Dr David French, Chair of Atkins’
modern ground investigation techniques, and Johannesburg. It will be a totally new Africa, Hong Kong, India and Scandinavia. Geotechnical Network, another source of
there’s always scope for the unexpected. transport option for people moving between The landscape of the Veldt, through which technical expertise to which clients have
“A lot of investigative work will have been these two major commercial hubs. The 80km the project passes, includes hard-rock granite access. “There, we can use a construction
carried out, so you’ll have a pretty good idea railway also promises to cut congestion and and volcanic lava, but weathering – the technique called diaphragm walling.”
of what you’re facing, but there are still offer an environmentally friendly alternative chemical and mechanical erosion of the rock This involves marking out the station box
challenges because of the inherent variability to road transport in time for the 2010 World – can still reduce it to a soft soil over time, – in this case, about 200 metres in length and
of the ground conditions,” adds Skates. Cup football tournament. with various stages in between. The ground up to 20 metres wide – then using specialised
Tunnelling remains one of the toughest Atkins is playing a key role in delivery of at Park station, Gautrain’s city-centre terminus equipment to cut deep, narrow slots down to
jobs in construction. But, despite the heat the project, undertaking detailed design for in Johannesburg, lies somewhere in between. solid rock. The slots are filled with concrete to
and the noise of the machinery – which the contractor, Bombela Civil Joint Venture, “At Park, where the excavation depth is create a wall in situ. The soil between the
carries away a tonne of material every seven including the construction of three under- in the order of 25 metres, the ground walls is then removed to create a huge void in
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