Gulf Construction Online - Putzmeister helps tunnel link continents

Turkey Review

Long-reach boom pumps ... concreting the upper part of one of the giant tunnels.

Putzmeister helps tunnel link continents

01 September 2009

PUTZMEISTER concrete pumps and a concrete wet-spraying machine are playing an important role in the Marmaray Project, a spectacular multi-billion-dollar undersea rail tunnel which will link the Europe and Asian sides of the Turkish city of Istanbul, which are separated by the Bosporus Strait.

The equipment is being used to produce huge elements for the tunnel’s underwater section, more specifically in tunnel lining with shotcrete and in backfilling tunnel formworks on land.
Istanbul, with a population of 15 million, is home to around a fifth of the Turkey’s population. “Traffic planners are focusing on modernising public transport and developing the infrastructure in order to relieve the burden on the city's chronically-congested bridges over the Bosporus and the associated access roads,” explains a spokesman for Putzmeister. “The Marmaray Project is an integral component of this measure.”
Tenders for the project were approved in May 2004 following which the project was started. An important section of the structure is a 1.4-km tunnel segment, which lies on the floor of the Marmara Sea at the southern end of the Bosporus. “This segment consists of enormous prefabricated concrete elements that are lowered to a depth of up to 58 m, sealed and interconnected. The tunnel connects the European suburb of Halkali with Gebze on the Asian side of Istanbul,” he says.
The project is being undertaken by a Japanese/Turkish consortium under the management of the Taisei Corporation, together with Kumagai, Gama and Nurol for the Turkish General Directorate for Rail, Port and Airport Construction (DLH), at an estimated cost of $3.5 billion.
Work is being conducted on both sides of the waterway to establish a connection between the tunnel and the existing rail and metro network. The construction scope includes 9.8 km of driven tunnel sections, 2.4 km of open-cut tunnel sections, three new underground stations and 37 stations located above ground, which are currently undergoing a comprehensive modernisation programme. A 63-km existing railway line is being expanded.

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He continues: “Con-creting of the eleven 135-m-long, 15.3-m-wide and 8.6-m-high tunnel segments is being conducted in a dry dock on the Asian side of Istanbul in the suburb of Üsküdar. This is where Oyak Beton, one of the largest readymixed concrete producers in Turkey, is utilising several of its Putzmeister truck-mounted concrete pumps (with boom sizes M 24-4, M 36-4 and M 47-5) to fill the base, wall and ceiling formworks of the caissons from the edge of the dock.”
Approximately 5,000 cu m of concrete in varying strength classes (up to C40) is required for each tunnel element. The upper segment is concreted with a flooded basin.

Lowering the elements
Sturdy tugboats have been used to tow the finished and sealed, reinforced tunnel segments from the dock to a floating platform in the Marmara Sea in a catamaran construction. The 30,000-tonne reinforced concrete constructions are carefully towed between the two hulls. The catamaran is manoeuvred to the exact pre-calculated position above the seabed, in which dredgers have excavated a deep channel. The special ship is held in place by thick steel coils, which are secured to 13 buoys anchored on the seabed.
The catamaran houses huge cranes with cable winches, which are used to lower the tunnel sections into the artificial ditches. Cameras and measuring instruments monitor the precise alignment of the tunnel segment, which is achieved by filling and emptying ballast tanks in a similar manner to a submarine.
“The critical period is during the final phase where there is a risk of the large rubber seals being damaged. This is because these are required to produce a watertight connection between the segments. The top of the tunnel element is subsequently protected against damage with a 4.5-m-thick sediment layer,” the spokesman says.

Natural hazards
Experts are taking into consideration two serious factors in the project. First, a dangerous current runs through the passage between the Black Sea and Mediterranean Sea. And second, that more than 10,000 earthquakes are registered in the region every year (most of which, however, are barely perceptible).
Safety measures include, for example, special protection for the connection points of each individual segment under water. And where the Marmaray tunnel merges with the land tunnel, particularly powerful, flexible and elastic rubber seals are used, which will not break in the event of an earthquake, he points out.

Versatile methods
While the 1.4-km tunnel section is being established from caissons at the bottom of the Marmara Sea, entirely different tunnelling methods are being utilised at other sections of the 76.3-km Marmaray Project. Tunnelling in areas along the banks and those susceptible to soft ground conditions, for example, is conducted in a shield tunnelling process with tubing support.
In other sections, the inner formwork is concreted by stationary Putzmeister concrete pumps, which are made up of both modern BSA 1408 E units and older fully functional pumps.
Other sections are built using an open construction method, often involving the use of PM truck-mounted concrete pumps. For shotcreting, Putzmeister’s compact SPM 400 wet spray manipulator has been used. The spray arm of these machines has a working range of 2 m to 8.5 m and its spraying capacity is up to 20 cu m per hour.
With an annual production capacity of 4.5 million cu m, Oyak Beton is one of the largest readymixed concrete producers in Turkey. The company has its own concrete laboratory and is represented throughout the country by mobile and stationary mixing plants. Besides numerous truck mixers, the company also operates a fleet of around 70 Putzmeister truck-mounted concrete pumps in varying sizes.
In addition to concreting the tunnel segments, the company also delivers and pumps concrete to other sections of the Marmaray Project.