Articles & Case Studies


Posted: Friday 5th November 2010

It was a mammoth task the PIASIO company, a subsidiary of COLAS SWITZERLAND, had ahead of them in Geneva Meyrin. Using a GRUNDOBURST type 2500 G (250 t pulling force), an over-aged and under-dimensioned 500 mm drinking water transport pipe made of grey cast iron had to be replaced by a 730 mm concrete pipe with a steel core, manufactured by BONNA.

In Geneva, when extending public traffic routes, in this case for the highways network, it is the normal procedure to check all underground supply networks and, if necessary, renew or repair them. Generally, up to 5 years after completion of work on public roads the authorities are not allowed to excavate any subsequent excavations. The aim is to prevent any danger areas, ugly road patchwork and constant repair procedures, which could cause further accidents on the extended highways network

The supply networks are supervised by the Geneva Public Utility Company (SIG) who oversee the water supply, as well as the gas and power supply of the whole city. This ensures an efficient and co-ordinated planning and execution of any road repair and remedial pipe and cable measures.

The choice of new pipe materials rests with the SIG with clear requirements:

- Polyethylene for pipes below 300 mm diameter

- Cast iron for pipes from 300 to 400 mm diameter

- Concrete for pipes above 400 mm diameter

This project was to cause as little disruption as possible to the adjoining property owners and traffic flow. This was also one of the reasons for the use of the pipe bursting replacement method, whereby the old pipe is broken and the new pipe, which is often of an increased diameter, is directly pulled into the existing pipeline bore path. This replacement method is suitable for most pipe materials with the main advantage being the trenchless installation of a new pipe with a relevant, extended service life. In this case the renewal of the pipe stretched over several sections with a total length of 450 m.

Jean-Michel BALMAT, responsible for "No-Dig" at COLAS SWITZERLAND commented that his company had been involved with pipe bursting technology since 1998 and had already gained very good experiences with the GRUNDOBURST 400 G and 800 G versions." ˇ°This larger project using a 2500G was a first for us and our experience gave us an extreme advantage, particularly for a task of this magnitude.. The challenge was in the difficult replacement section of 125 m in length, which had slight bends laid at a depth between 1,70 m and 3 m further complicated because the pipeline ran beneath a petrol station."

The adjoining property owners each received brochures in advance, giving them information and explanations regarding the Grundoburst pipe bursting method and the separate working steps. Numbered signposts were set up on the footpath to indicate the progress of working steps. This exemplary measure was highly acclaimed by the affected adjoining property owners and was much appreciated by them.

For the GRUNDOBURST 2500 G (Manufacturer: The TT Group - Tracto-Technik) a pit was excavated with a length of 10 m. With its formidable pulling force of 250 t old pipes from ND 300 to ˇÜ ND 1000mm can be renewed. The GRUNDOBURST rig, even with the highest pulling force demands, has to be stabilised securely inside the machine pit. A stabiliser made of steel reinforced concrete fitted to the front of the rig was specially produced to ensure its stability.

The proven QuickLock principle with the bursting rods being simply linked in place is a major assembly advantage, taking the individual rod weight of 225 kg into consideration. Lowering and retrieving the QuickLock bursting rods was easily accomplished using a special fast attachment lifting device.

When pulling in the new pipes, a pit with a length of 15 m was required at the opposite end of the pipe run, with enough space for 2 pipe sections welded together, each with a length of 6,5 m. With two pipe sections the pipe weight was almost 4 t, which meant an overall pipe weight of 37,5 t over the whole length of 125 m. After the steel pipe welding process, an insulated protective sleeve was pulled over the welded joint. The welding work took approximately 2 hours for each pipe joint and was carried out by a specialist welding company.

After the QuickLock rods had been pushed in through the old pipe, the expander head with cutting blades and the new pipe were connected.

The bursting process and the pulling-in process of the new pipe were carried out while adding a mixture of Bentonite to decrease any pipe surface friction. Furthermore, it was necessary to make sure and observe the pulling forces and not to exceed the recommended maximum values stipulated by the pipe manufacturer.

Without taking into account all the preparatory and auxiliary work the actual bursting and pipe replacement process took just 3 days.

After completion of the work, the numerous representatives from the public utility company were highly satisfied with the technically and economically well planned and executed pipe bursting project.

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August 2021

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