Construction World April 2017

GEOTECHNICAL ENGINEERING

LESS TIME, COST AND DISRUPTION for large-bore pipelines

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.

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,

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-

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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CONSTRUCTION WORLD APRIL 2017

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