Atlas Copco’s portable air division is playing a crucial role in Turkey’s Marmaray project by offering uninterrupted compressed air for specialist contractor Bauer.

Bauer is currently involved with the diaphragm wall construction and sub soil jet grouting of a new 13 km underground metro station of the Yedikule-Kadikoy rail system, which forms part of the Marmaray project. The project will provide an upgrading of the commuter rail system in Istanbul, connecting European and Asian sides of the city with an uninterrupted, modern, high-capacity commuter rail system.
Bauer is currently working on a diaphragm wall as a temporary reinforced concrete structure to allow excavation works for one of three underground stations on the Marmaray project at Uksudar.
“Two Atlas Copco XAS 186 compressors are supplying air power for the bentonite plant. Prior to pouring the concrete into the trench the bentonite prevents the collapse of the open trench. Working at a pressure of 7 bar and a free air delivery of 11.1 cu m per minute, both compressors agitate the bentonite in five tanks of 60 cu m each.” says Sam Waes, divisional communications manager for Atlas Copco’s Portable Air Division.
“When completed, the north and south diaphragm walls will be 280 m long and the west and east sides will each be 35 m. Additional work is also being carried out by Bauer, which will improve the subsoil below the foundation level of the underground station with a water-cement mix injected at high pressure through a small bore hole,” he adds.
On the Marmaray project, the subsoil jet drilling is high pressure jet grouting supported by an Atlas Copco XRVS 476 portable air compressor working at 25 bar and a fad of 27.7 cu m per minute. This machine is powered by a Caterpillar C13 six-cylinder diesel engine, rated at 328KW, which is fully Tier III/Stage III compliant. The high-pressure compressor has a fully leak-free chassis and a central fluid drain system together with quick and easy access to all service points, ensuring ease of maintenance. Featuring a Zincor-treated canopy with a powder coat finish ensures improved resistance to corrosion and a higher resell value.
The sub-soil strata of the site feature a mix of medium dense sandy layers, clays and stiff clay. “Jet grouting in the medium dense sandy layers is based on proven technical procedures established by Bauer,” says the spokesman. “In view of the relatively high fines content of the silt-sand, jetting is carried out with a concentric collar of compressed air. A high-pressure fluid jet is released at high speed through a very fine nozzle.”
“The fluid jet of cementious grout cuts into the soil and breaks down the soil around the borehole. The infilling joint material and fine portion of the soil is eroded and transported upwards through the drill-hole whilst the coarse material remains in place and is mixed in-situ with the cementious grout to form the jet grout column. The drill rig allows drilling to the full depth of grouting in a single ‘shot’ without disconnecting the individual drill rods. The rig, a Bauer BG 28, has been designed to drill to depths of 39.50 m,” points out Waes.
The jet-grouted layers, which will offer lateral support, will have a thickness of 10 m. Transversal struts will be formed by triple rows of columns. This has the advantage that the primary/secondary sequence can be applied for grouting. A further advantage is the width of the jet grout struts will be large enough to provide stability against buckling through possible water seepage, says the spokesman.
Each of the rows will be cast using the ‘wet in wet’ method, where each adjacent column is jetted before initial settlement of the grout in the previous column thereby forming a monolithic grout body. As a result, when completed, large 3 m diameter jet grout columns will have been constructed to a depth of 10 m below the bottom level of the station raft foundation along the inside edge of the diaphragm wall to act as an additional retaining structure between the north and south diaphragm walls which will minimise any possible deflection.
“A total of 800 columns will be inserted at Uskudar, with work starting in December 2006 and having reached the halfway mark by April this year,” points out Serhat Memisoglu, the Bauer site manger on the project.
Atlas Copco is a world-leading provider of industrial productivity solutions products and services range from compressed air and gas equipment, generators, construction and mining equipment, industrial tools and assembly systems, to related aftermarket and rental. Portable Air is a division within Atlas Copco’s Compressor Technique business area which develops, manufactures and markets portable oil-injected and oil-free air compressors, and generators for prime or standby power worldwide, under several brands, to the construction and general industries. The divisional headquarters and main production center are located in Antwerp in Belgium with a distributorship network that also serves customers in selected geographic markets and industry segments with temporary air and power rental solutions.