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Istanbul fast track

The first train is due to be lowered into the first phase of the Istanbul Metro next week. NCE reports.

Construction is progressing well on the $650M Istanbul Metro, a project which promises to become one of the world's most heavily used urban mass transit systems.

Civils works on phase one of the 7km long railway is almost complete and electrical and mechanical installation began recently. Trackwork is complete on about half the length of the system and installation of the traction power supply equipment has also started.

The first stage of the Metro is expected to be finished late this year.

Engineer for the installation of E&M services on the project is Hyder Consulting, acting for the client, Greater Istanbul Municipality. A team of Turkish, Romanian, Hungarian and British engineers is supervising the work of the contractors.

Hyder is also consultant for the commissioning of rolling stock for the Metro.

Istanbul has boomed in recent years, with consequent road traffic congestion. The Metro will cross the city centre and is designed to carry 70,000 passengers per hour in each direction. It is predicted that this figure will be reached within a few years of opening, putting Istanbul in the same class as Hong Kong for passenger densities.

The topography of Istanbul is continuously hilly, which results in some deep stations: they are all 200m long to accommodate eight-car trains of 180m nominal length.

Three stations are tunnelled in rock, with horseshoe platform caverns 200m long, 8.5m wide and 6.5m high and three are constructed in open cut. The largest stations have a shopping concourse at intermediate level between street and platform. They are huge structures which consume large quantities of concrete and steel reinforcement.

The first phase of construction has been on a fast-track schedule (18 months from E&M contract award). Hence, a proven rolling stock design - that used for the Caracas Metro in Venezuela - has been chosen to avoid potential delays due to teething problems.

The initial fleet of 32 vehicles is being supplied by Franco/British Alstom. Subsequent orders for rolling stock will be assembled in Turkey, under a licence agreement.

The logistics of the fast-track project have been challenging. So too, have the special demands on cultural interfaces at a personal level. The combination of French, Turkish and English contractors and consultants has meant that most documents have had to be translated to avoid delays and misunderstandings.

The provisional depot will be underground in one half of the 4 Levent station at the northern terminus. This unusual arrangement was necessitated by the lack of land available for the permanent depot until the next stage is constructed.

An initial fleet of eight trains will be maintained in a 200m long cavern, which is large enough to accommodate an elevated pit track which can be accessed from both ends. It will require careful management of maintenance operations during the first five years of the system.

Tunnels for the Metro system were dug in broken limestone, using road headers in a modified NATM method. The initial tunnel lining is approximately 200mm of sprayed concrete with wire mesh and rock fasteners. The final lining is 650mm of poured insitu concrete, using hydraulically positioned shuttering.

Main civils contractors are Tekfen and the Enka-Dorsch joint venture, both Turkish organisations. The tunnels were provided to French E&M contractor Cegelec in the as-poured, horseshoe shape, with a curved invert. The contractor is placing a two-pour final invert on top with STEDEF trackform, as used in the Channel Tunnel.

Taksim Square station has three entry concourses from widely separated areas of the large surface square, which is a popular area for shopping and public events. A 450m underground concourse with a travelator connects two of the entrances to the station platform level. Four, double escalator banks serve this platform.

The control centre for the Metro is in a six-storey office block above one entrance to Taksim station, which also provides space for one of the ventilation shafts.

Tunnel construction was accessed through three adits, with several vertical shafts which will become part of the ventilation system. Ventilation is designed for relief of tunnel and station temperature during summer operation, as well as smoke removal in the case of emergencies.

Signalling on the Istanbul Metro uses the SACEM system, as on the Paris Metro. It is specified for 90 second headway in later phases of operation to accommodate the predicted demand of 70,000 passengers per hour.

A trunked, fibre-optic based communications 'backbone' system will carry the radio trunking, CCTV, SCADA and signalling data links.

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