Canadian Consulting Engineer

Feature

The Great Man Made River

It is difficult to imagine that the Sahara Desert was once a fertile landscape with enough natural abundance to nourish the Roman Empire. Today it is more horizon than landscape, but Libyan officials ...




It is difficult to imagine that the Sahara Desert was once a fertile landscape with enough natural abundance to nourish the Roman Empire. Today it is more horizon than landscape, but Libyan officials have known for over 30 years that their portion of the Sahara hides the largest ancient subterranean aquifers ever discovered, containing nearly 35,000 cubic kilometres of fresh water.

The Great Man Made River (GMMR) project, launched in 1983, aims to drill for, pump and convey water through a network of pipes to get it from the desert in the south to where it is most needed: the heavily populated coastal belt in northern Libya.

The project has been called everything from the greatest feat of engineering ever attempted, to the eighth wonder of the world. When it is finished, its underground pipeline network will cover a distance equivalent to that between Montreal and Vancouver — nearly 4,000 kilometres.

SNC-Lavalin has won several key contracts for the Great Man Made River project.

The first, 15 years ago, was a mandate to drill and construct 117 water wells, 36 piezometer wells and 23 exploratory wells in the Tazerbo area in east-central Libya. Some of the wells had to be drilled to a depth of 1,200 metres, the length of 11 regulation football fields. To do this, SNC-Lavalin procured a fleet of heavy drilling and production equipment, 17,000 tonnes of cement and 8,500 tonnes of bentonite.

“We completed 117 wells with a total capacity of one million cubic metres of water per day,” says Riadh Ben Assa, Executive Vice-President of SNC-Lavalin. “We drilled over 61,000 metres in loose sand and sandstone, installed and cemented casings, gravel-packed screens and worked over four million person-hours with no accidents.”

After this, in 2001 SNC-Lavalin was awarded a contract for the restoration of 3,500 pre-stressed concrete cylinder pipes (PCCP) in the Sarir-Sirt/Tazerbo-Benghazi conveyance system. After 15 years underground, diurnal and seasonal temperature variations had caused water condensate to form around the conveyance pipeline. The condensate reacted with salts in the soils to form an acid solution which penetrated the thin layer of concrete covering the tensiled wires that served to strengthen the pipes. The acid corroded the wires to such an extent that they broke, weakening the pipes in some areas. The repairs covered a stretch of over 400 kilometres, and SNC-Lavalin’s construction crews used 450-tonne cranes to handle pipes weighing more than 70 tonnes.

The Great Man Made River is made up of over half a million of these PCCP pipes, each of which is 7.5 m long, 4 m in diameter, and 25 cm thick. Many more of these pipes will be required before the project is complete. In 2002, SNC-Lavalin was awarded a contract to design and manufacture PCCP using existing facilities in Sarir in east-central Libya. The project required a restart of a number of facilities such as batching, oxygen, acetylene, ice and power generation plants. SNC-Lavalin completed the revamp and start-up of the Sarir facility in 2003 and has been producing the massive water conveyance pipes ever since.

As well, SNC-Lavalin continues its drilling work, with contracts under way for 298 wells in the Sarir well field, and for well fields in Ghandames and Kufra.

“You have to admire the long-term vision of the Libyan government for launching this project over 25 years ago,” says Ben Assa. “Agricultural development in Libya has been hindered by the lack of adequate and reliable water resources. Once it is completed, the Great Man Made River will provide close to six million cubic metres of water per day for residential, commercial and agricultural use.”

The system will eventually irrigate about 74,870 hectares of land, and help Libya attain its goal of becoming agriculturally self sufficient. The rest of the water will continue to supply Libya’s urban centres.

Noel Rieder is a writer in SNC-Lavalin’s global corporate communications department. The project director at SNC-Lavalin in charge of the GMMR is Andr Bland, ing.

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An Engineering Wonder

Eight kilometres of carbonized metal wire is wound around each 7.5-m long pipe segment in the GMMR. The length of wire required for the first phase of the project alone could encircle the globe 230 times.

The stone and sand used to manufacture its pipes would be enough to build 16 of the Giza Pyramids in Egypt.

The quantity of cement used in this project could build a highway from Tripoli to Mumbai.