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The boring of the two tunnels was carried out using a TBM from the Metro projects.
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The meandering of
the river throughout the ages, has been the major source of soils deposited in the Cairo area. Appreciable fluctuations in the level of the Nile, combined
with the shifting of the water courses, has resulted in sand deposits, with layers and pockets of silt and clay. Also, as a result of the infilling of
some old branch channels and lakes, during the nineteenth century, a mixed layer of silt, clay, sand bricks, pottery and blocks of limestone is commonly
encountered.
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Fortunately, Since the construction of the Aswan High Dam, the fluctuation in ground water level is limited
to +0.5m. The ground water has a high sulphate content.
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The lining to the bored tunnels is formed with precast reinforced concrete segments, bolted together, with grout
injected to ensure a waterproof structure. The boring was carried out in a generally sandy layer, containing occasional thin layers of silty clay and boulders,
except at Port Said Street, where a thick layer of hard boulders was encountered. Fortunately, the TBM incorporated a stone crusher. The pits of
the ventilation stations, Gohar El Kaed and Attaba Square, were used as the entry and exit shafts for the Tunnel Boring Machine. At the lowest point, the tunnels
are 32 metres below ground level. The road structure comprises precast reinforced concrete and the road is surfaced with
tarmacadam. The void under the road slab contains the ducts for the services, ventilation duct and escape passages leading to the emergency exits at the Ventilation Stations.
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There are two main ventilation stations at El Hussein and Port Said Street and two stations at Attaba and Gohar El Kaed, for emergency smoke
extraction, which have been specifically designed for this Project, not only from the technical point of view but also to make their appearance harmonise with
the Islamic features of this historic area.
Ventilation Systems
The ventilation is divided into two main types, namely:-
a)
Tunnel Ventilation, for supplying fresh air to and evacuating hot stale air and noxious exhaust fumes from the two tunnels and
b) Auxiliary Ventilation.
El Hussein and Port Said Street Ventilation Stations are the
main stations and each has the following equipment installed:-
a) 6 exhaust fans ( 2 operational and 1 stand-by for each tunnel). The fans are vertical axial fans 400 volt 3 phase, variable speed,
providing up to 100 cubic metres of air per second at 990 rpm and equipped with dampers, sound attenuators and all necessary protection and control measures.
b) Air conditioning system.
c) Auxiliary ventilation apparatus.
d) An elevator of 2 tons capacity.
e) 2 low voltage distribution cabinets supplying lighting and station power.
f) 1 CCTV transmission cabinet.
g) 2 sewage pumps, of 16 cubic meters per hour capacity.
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