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CONSTRUCTION WORLD
APRIL
2017
36
GEOTECHNICAL ENGINEERING
While there has been some local adoption
of horizontal directional drilling (HDD) in
small bore applications, with holes measure
less than 500 mm in diameter, South Africa
has not realised the potential of large bore
HDD, according to LR Civil operations
manager, Daniele Carnicelli.
Partnering with geotechnical engineers,
Geopractica and HDD experts TRG Inter-
national, LR Civil recently completed
an HDPE pipeline a kilometre long under
a Port Alfred beach and out to sea. “This
contract demonstrated a number of benefits
that this technology has to offer in South
Africa, including little or no environmental
impact, much less time spent on permits
and approvals, and no disruption or danger
to the public,” says Carnicelli.
The project
Drilling horizontally at depths of between
20 and 30 metres, the 150 tonne Maxi-
Rig drilled the outfall pipeline for the new
reverse osmosis desalination plant at Port
Alfred, without any threat to the pristine
beach environment.
“With the capacity to install pipelines of
up to 900 mm in diameter, this powerful rig
has a maximum torque of some 70 tonnes
and 150 tonnes of pull-back force,” he says.
“This makes it capable of working through
rock with a hardness exceeding 250 MPa,
and to achieve daily horizontal distances
well in excess of conventional trenching.”
He estimates that, on the desalination
plant project, the rig could achieve a
horizontal distance of at least 30 metres on
an average day and 45 metres on a good
day. With traditional trenching, involving
digging, laying, backfilling and perhaps even
blasting, such daily rates could take a week
or more to achieve.
Not having to dig from surface to lay
and bury large diameter pipes means that
many of the normal challenges of pipeline
installation are sidestepped altogether.
Where a pipeline crosses a watercourse,
for example, a water use licence may be
required. This a process could take up to
18 to 24 months and possibly delay a
project significantly.
Other permissions usually need to be
secured wherever a trench will intersect a
gas, power, telecommunications or water
line. In the case of HDD, the drill path simply
goes under these facilities and safely
avoids them.
Safety risks on a project are reduced,
as the absence of trenches means less
danger to workers and the public. Inclement
weather, which can often threaten the
timeline of a project by flooding trenches
and stopping construction work, is no
longer a factor, as most of the activity in an
HDD project is carried out underground.
Fuel consumption
Fuel consumption is vastly reduced, as
comparisons show that the Maxi-Rig will
tend to use as little as 5% of the diesel
normally consumed by earthmoving
equipment, including excavators and trucks,
over the life of a project.
According to Carnicelli, there are
also substantial savings in reducing the
pipeline length by installing it ‘as the crow
flies’ through a horizontal drill hole, rather
than the more circuitous route required
by trenches which have to avoid objects,
With 30 years of experience laying pipelines for the civil engineering
sector, Raubex Group company LR Civil and its partners have imported
a well-established technology for unobtrusively installing large bore
pipelines – proving its value on South African soil.
LESS TIME, COST AND DISRUPTION
for large-bore pipelines
The 24 ton Maxi-Rig with the
control tower in view.
The rig drilling 650 metres under existing
sand dunes towards the connection point.
Differential in heights is 60 metres from the
rig position to the connection point.
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