CIPP technique restores pipeline under River Moscow

The Pipe Technologies division of Per Aarsleff A/S, the leading Danish civil engineering contractor, successfully completed on schedule and on budget, one of its most challenging pipeline restoration projects under extreme weather conditions in the center of the Russian capital Moscow.

Danish contractors worked in freezing temperatures during the Russian winter in Moscow to clean and inspect a wastewater inverted siphon before installing a new liner in a 300-meter-long pipe under the River Moscow.

The Pipe Technologies division of Per Aarsleff A/S, the leading Danish civil engineering contractor, successfully completed on schedule and on budget, one of its most challenging pipeline restoration projects under extreme weather conditions in the center of the Russian capital Moscow.

Working in temperatures down to minus 20 degrees Centigrade (C), Aarsleff Pipe Technologies cleaned and inspected the inside of a 300-meter-long section of a low-pressure, wastewater inverted siphon under the River Moscow, prior to installing a new thin-walled resin impregnated felt lining in the flooded 1.4-meter-diameter pipe, using its novel cured-in-place pipe (CIPP) restoration technique without any disruption to road or river traffic.

The special lining, resembling a flattened flexible tube, was tailor-made from layers of felt and impregnated on site with resin. A polypropylene skin coats the outer layer. This was done because, during the novel installation process on site, the liner was turned inside out as it was inverted and pushed by water pressure into the existing flooded rigid siphon. The wall of the existing Savinskiy steel siphon, built in 1956, acted as shuttering and the polypropylene coating became the inside surface of the new lining. After installation water inside the siphon was heated to about 85 degrees C to cure the resin, transforming the inverted flexible tube into a rigid, thin-walled smooth bore lining, capable of lasting over 100 years.

Aarsleff Pipe Technologies set up site in front of the Ministry of Defence building and about 2,000 m from the Kremlin on the north bank of the river next to the major Krymski Bridge, which is part of the Garden Ring Road round the city. The company split its approximately €1-million pipe repair contract into two separate visits: one of three weeks in December 2005 for cleaning and the second of two weeks in March 2006 for installing the new lining. Aarsleff Pipe Technologies opened up a 5-m-deep launching pit on the northern side of the Prechistenskaya Road, which runs alongside the north bank, to expose a section of the wastewater sewer pipe just before it dropped down into the pressure siphon under the river.

The line was temporarily isolated and sections of the steel pipe removed from both access pits to provide an entrance and exit to the main inverted siphon, which had about 1.5 m of cover to the river bed. Inverted siphons, sometimes called depressed sewers, allow storm or wastewater pipelines to pass under obstructions, such as rivers. They flow under pressure of about 2 to 2.5 bar and generally need a high flow velocity to keep material suspended. The siphon was left full with its ballasting water acting as negative buoyancy, preventing the pipe from the possible risk of lifting into the river bed if it was emptied.

Divers, working in air temperatures of -10 to -20 degrees C, carried out a final detailed inspection of the siphon after sludge and scale was removed from the wall of the pipe by a truck-mounted, high-pressure water cleaner.

The cleaning and inspection process took three weeks and the siphon was then temporarily sealed while Aarsleff Pipe Technologies went away to design and tailor make the new lining prior to returning in March for the installation. “Planning and preparation for impregnating the liner with resin and its installation was critical to cope with the extreme weather conditions on site,” Project manager Svend Erik Jensen said. “It could take up to four hours to heat up our machines and everything needed to be kept warm. We set up a mobile, covered factory next to the launching pit and heated it to 20 degrees C, although it was -20 degrees C outside, so we could store the resin and impregnate the lining.”

For the Moscow project Aarsleff Pipe Technologies used a twin lining system, with a preliner followed by the main lining. Aarsleff Pipe Technologies first impregnated the single layer felt preliner with the special resin that also had a watertight coating of polypropylene on the outer skin. The continuous, one piece 300-m-long resin impregnated preliner, with its closed, sealed end, was pulled by a rope, anchored to a winch in Gorky Park, from the launching pit and through the water-filled siphon and into the dry receiving pit. The liner was freely suspended in the flooded siphon and rope removed and end opened ready to accept the main multi-layered lining.

The Aarsleff Pipe Technologies’ crew followed on with the next sequence of extracting all the air from the main lining prior to injecting resin, which was evenly distributed by passing the liner through a series of rollers and folded ready for installation. The resin-impregnated liner was guided on a conveyor belt up to the top of an approximate 2-m-high trestle tower directly over the launching pit. The tower incorporated a short vertical steel section of a 1.4-m-diameter guide tube to match the diameter of the inverted siphon. The front section of the liner was turned inside out and pushed into the tube and then folded back and over and down the outside of the tube and clamped in place with circumferential straps.

Clean mains water was then pumped into the liner. The pressure and weight from the head of water in the approximate 7-m-high water column slowly pushed and extruded and inverted the liner inside out, down into the pit bottom. Here it was guided horizontally into the open-ended preliner at the mouth of the exposed inverted siphon. Pumping continued in a non-stop controlled operation, slowly inverting and advancing the liner into the preliner, expanding and forcing them both out against the siphon wall. The water in the flooded siphon was steadily exhausted into the receiving pit and pumped away as it was replaced by the clean water driving the inversion.

The tail end of the 300-m-long main lining was connected to several hoses, which were pulled through as inversion progressed to the opposite end of the siphon. The inversion and resin impregnation was a continuous process that took about 38 hours. When inversion was complete, the hoses pulled in during the process were connected to a 3,000-kW boiler. In a 40-hour continuous operation, the approximate 4,600 m3 of water in the siphon was heated to 85 degrees C to cure the resin-impregnated lining. Both waste ends of the new 21-mm-thick smooth bore lining protruding from the siphon were cut off, steel infill sections replaced and pits reinstated prior to reopening the wastewater sewer.

The Savinskiy siphon is just one of over 100 in the city and forms part of a vast 10,000-km network of wastewater pipelines, foul sewers, potable mains, pumping stations and treatment plants, which are owned, controlled and maintained by Moscow’s municipal enterprise Mosvodokanal. The Savinskiy siphon is part of the city’s southwest main sewer, which collects sewage water from the southwestern part of Moscow at the Savinkkaya pumping station for transfer to the Kuryanovskaya sewage treatment plant. Mosvodokanal is using the Savinskiy project as a trial to evaluate Aarsleff Pipe Technologies’s lining technique for possible future siphon repairs as Mosvodokanal is planning to repair four similar inverted siphons in 2007.


Author’s Note

Rodney Byles is a freelance journalist who specializes in construction and environmental issues. For more information, contact Tina Lægaard of Per Aarsleff, based in Aabyhoej, Denmark, at email: til@aarsleff.com or visit the website: www.aarsleff.com.

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