Future underground Sirkeci Station is located in the heart of Istanbul’s historical district, teeming with tourists, palaces and mosques. Work on the Marmaray Project to build a tunnel connecting the European and Asian sides of Istanbul is the first time this area has seen excavation, requiring special permission and offering up an underground treasure trove of ancient structures for archeologists.

For contractor Taisei and its joint venture partners Gama and Nurol, it may be harder to muster the same enthusiasm.

Understandably so—the contract originally called for 30 days of archeological investigations at the site of one of the access shafts, for example. Six years later, this particular shaft is still being surveyed and it’s unknown when a full excavation can be completed. Masahiro Iwano, project manager for Taisei points out, beneath that there may be Roman ruins.

Excavations at the future site of Yenikapi Station, once a Byzantine-era port, have revealed almost 30 ships and many have been moved to one of the city’s museums. One of these vessels is still sitting partially excavated in the middle of the worksite, as archeologists weigh their options for removal. Yenikapi is the biggest station of the project.

When Taisei started working in August 2004, its contract for engineering, procurement and construction for 13km of track works and associated structures and stations was worth USD 1,218M (assuming the current exchange rate) and would last for 56 months. This contract is part of a larger USD 3bn project totaling 73.6km of track, mostly above ground.

The client, Turkey’s Ministry of Transportation, the General Directorate of Railways, Harbors and Airports Construction (DLH), granted the Taisei joint venture an Extension of Time, extending it to 110 months and increasing the contract to USD 1,800M. The reason for this was mainly due to the extensive archeological investigations, says Masahiko Tsuchiya, design manager on the Marmaray Project for Taisei. The completion date then moved from 2013 to 2014 at the earliest.

Both Yenikapi and Sirkeci Stations are located on the western, European side of the Bosphorus Strait, which connects the Black Sea in the north with the Marmara Sea in the south, dividing Istanbul. Two other stations, Uskudar on the eastern side and Kazlicesme Station to the west are included in the contract, as well as electrical and mechanical work, diverting the existing railway and the time-absorbing archeological investigation.

Still, the Marmaray Project continues moving ahead. All 11 of the tube elements for the 1,387m immersed tunnel connecting the western and eastern underground rail lines are installed. One of the project’s five TBMs is starting the final leg of its excavation on 20 September. This TBM will dock with the most western immersed tube element and Iwano expects from early next year it will be possible to walk from one end to the other on the immersed tube’s southern track.

Making the connections
Four Hitachi Zosen slurry TBMs of 7.8m diameter fitted with roller cutters have been chosen to mine tunnels on either side of the immersed tube where the ground consists of mainly hard rock. An EPB from Lovat has been chosen to mine both of the 2,130m tubes between Yenikapi and Kazlicesme Stations where the ground has a stiff clay consistency.

Two of the immersed tube elements (E1 and E11, one at each end) are equipped with a specially-designed steel sleeve into which the four slurry TBMs drive and connect. Within each sleeve is a ring of rubber packing that inflates with hydraulic pressure to grasp the TBM and make a watertight seal. The steel sleeves on E1 and E11 also have an additional, temporary bulkhead on the end. Just before backfilling the area around the placed element with premixed soil, the temporary bulkhead is removed and jelly-like LW material is injected and frozen. Tsuchiya describes it as a kind of water and glass, developed by Taisei’s Research and Develop Center specifically for the Bosphorus Project. “It has a very interesting characteristic,” he says. “It becomes solid after casting, similar to concrete. Once it experiences the freeze/thaw cycle, it becomes liquid. This characteristic is very much suitable for docking of TBM into immersed tunnel.”

The man-made pre-mixed soil helps prevent liquefaction when the TBMs drive into each connection. Freeze rings around the steel sleeve froze the LW material as the TBM assed through, which removed most of it, requiring only a small amount around the TBM shell to actually be frozen. When it thaws, the material becomes liquid and runs away, and is replaced with a sealing grout. The TBM can be dismantled and a permanent in-situ lining is installed in the connection. Because there are no access shafts, all four TBM shells will stay behind. So far, only TBM 4, mining track 1, has been dismantled and removed.

Built into the steel sleeves is a seismic joint for each end of the immersed tunnel. The alignment is roughly 16km away from the North Anatolian Fault line and the employer, DLH, expects with a 65 per cent probability that there will be an earthquake in the region, registering 7.5 on the Richter Scale. Taisei had included its decision to use the joint when bidding for the project. The flexible joint consists of two omegashaped rubber gasket rings sandwiched between steel segmental linings, measuring 30cm thick and 100cm long to the longitudinal direction of the tunnel. The joint has been designed to accommodate seismic motion up to a 7.5 on the Richter Scale, handling plus or minus 10cm in longitudinal direction, and plus or minus 5cm in other directions.

The in-situ lining will only be used in the four connections. The rest of the tunnels are being lined with pre-cast reinforced concrete segments, manufactured by Taisei, which estimates approximately 13,000 segmented rings will be used in total. Each ring has a configuration of six segments and one keystone and a 7,040mm internal diameter. The segments are 1,500mm wide and either 300mm to 320mm thick.

Station location
On the eastern side, Taisei is building Uskudar Station by cut and cover, and on the western side, Kazlicesme is being built above ground, and Yenikapi by cut and cover.

At Sirkeci Station the platforms, access passages shafts, main passage and ventilation shaft are being built using NATM, excavating vertical and horizontal tunnels ranging in width from 6m to 10m. This had been chosen because space on the surface is restricted by the station’s location in the city centre—though the station’s entrance will be built by cut and cover. Emergency passages between the TBM tunnels will be excavated roughly every 200m by NATM.

Muck removal is restricted to four hours from 20:00 to 0:00 for the NATM at Sirkeci. With its prime location in the historic district, it’s against the law for removal to happen during the day, explains Iwano. The muck is stored in a temporary stock area and one or two days a month it is transported away from site. The historic nature of the neighbourhood also meant 104 buildings needed to be checked for whether or not they needed reinforcement before the construction started, near Sirkeci alone. Across the project, in total, some 170 buildings have been checked.

Sirkeci is also the only station of the four that will have two side platforms rather than one central platform. Originally its excavation had been planned using two access shafts, but with an embargo on any further work at the east shaft, the excavation has been changed.

At the time of T&TI’s site visit TBM 3 had finished its run from Yenikapi to Sirkeci Station and was having cutter heads replaced and other maintenance before it passes through Sirkeci Station’s southern portion, which has had its concrete in-situ lining completed. TBM 3 should begin tunnelling through to its connection with immersed tube element E1 by the start of October. Taisei is working 24-hours-a day and the TBMs are stopping on average for scheduled maintenance every 200m to 300m, which usually works out to be once a month. TBMs 2 and 3 both have 57 disc cutters on the face. On the centre there are 17 pieces of 17in (43.18cm) and on the gauge cutter there are 7 pieces of 19in.

In the Sirkeci’s northern side, the cutting faces are working on excavations on both ends and it should be another three to four months until the concrete lining will be put in place before TBM 2 can pass through.

Consulting with archeologists from U.S. and UNESCO, among others, Taisei has spent at least six months discussing various options for deconstructing and moving the various artifacts discovered at the eastern access shaft site. For now they are wrapped in cloth or Styrofoam, with the expectation that it will take several months to remove them, and then shaft excavation can start again.

The delay affects not only the construction schedule for Sirkeci Station, but also the tunnelling schedule because the east shaft was to provide access to bring in equipment like cabling and pipes for areas around the tunnels like walkways. Tsuchiya says client DLH assumed at the beginning of 2010 all archeological excavations would be completed by April, which they are not, entitling Taisei to yet another EOT.

Only time will tell if 2014 marks the year Istanbul’s commuters first board trains running under the Bosphorus—not to mention how much additional display space will be in needed in the city’s museums.


Steel sleeves for elements E1 and E11 The route for the immersed tube and underground rail line The alignment and TBM routes for the Marmaray Project in Istanbul TBM 4 breaks through at immersed tube element E11 The TBM joins with the immersed tube after mining through backfilled premixed soil and entering the stell sleeve. The steel shell of the TBM will be left in place The flexible seismic joint on the steel sleeves attached to element E11; there is one for E1 as well