A consortium including Vinci and Bouygues has won the € 264 million (US$ 282 million) contract to extend Line 3 of the Cairo, Egypt metro system. Other partners in the contracting consortium include Orascom Construction and Arab Contractors.

The new phase - Phase 4A - continues on from Phase 2, which was brought into service in May 2014 some than six months ahead of schedule. It consists of 5.15 km of tunnel sand five underground stations on Line 3, the east-west link across the Egyptian capital.

The design-build contract stipulates just a 34 months construction period. It will see the earth pressure balance (EPB) tunnel boring machine (TBM) supplied by NFM for the previous phase reconfigured to operate as a slurry TBM. The machine is called Imhotep after the ancient Egyptian priest and philosopher.

Vinci said the reuse of the TBM would, “generate savings for the joint venture on both its execution time and budget.” It also claimed this was the first time a TBM had been reconfigured in this way.

Slurry TBMs inject a stream of bentonite between the front shield and the cutter-head of the TBM to balance the pressure exerted by the ground. The excavated material is extracted within the return flow of the slurry. In contrast EPB TBMs use the mass of the excavated material itself between the shield and cutter to maintain equal pressure with the ground. EPB TBMs are often used in soft and unstable material such as silt, clay, sand and gravel, while slurry TBMs are best-suited to unstable and highly permiable ground.

The contract is expected to employ some 3,2000 people, mostly Egyptian.

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