A Major Pipe Bursting Task in Geneva
It was a mammoth task for the PIASIO Company, a sister company of COLAS SWITZERLAND, had ahead of it in Geneva Meyrin. Applying 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 was to be replaced by a 730 mm concrete pipe with a steel core, type BONNA.
In Geneva, when extending public traffic ways, as in this case for the road network, it is the normal procedure to check all underground supply networks and, if necessary, renew or repair them. Generally, it is up to five years after completion of work on public roads before they are allowed to excavate any pits. The aim is to prevent any danger areas, ugly road patchwork and constant repair procedures, which could cause accidents for a foreseeable period.
The supply networks are supervised by the Geneva Public Utility Company (SIG) and cover the water supply, as well as the gas and power supply of the whole city. This, on the other hand, allows for an efficient and co-ordinated planning and execution of these repair measures.
The choice of 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
The construction measure was supposed to influence the abutting owners and traffic as little as possible. This was also one of the reasons for the application of the pipe cracking method, whereby the old pipe is destroyed and the new pipe, which often as a larger diameter, is pulled into the existing bore path. This method is suitable for most pipe materials. The main advantage being the trenchless installation of a new pipe with a relevant, long service life.
In this case, the renewal of the pipe stretched over several sections and a total length of 450 m.
“We have been involved with this pipe bursting technology since 1998 and have already gained very good experiences with the GRUNDOBURST 400 G and 800 G versions.” commented Jean-Michel BALMAT, responsible for “No-Dig” at COLAS SWITZERLAND. “This is an extreme advantage, especially for a task of this measure, which is also a novelty task for us. The challenge lies in the partial section from 125 m length, which has slight bends in a depth between 1.70 m and 3 m beneath a petrol station.”
The abutting owners each received brochures in advance, giving them information and explanations regarding the pipe-cracking method and the individual working sections. Numbered signposts were set up on the footpath to indicate the progress of each working step. This measure was highly acclaimed by the abutting owners as exemplary, which they appreciated.
For the GRUNDOBURST 2500 G, manufactured by TRACTO-TECHNIK, Lennestadt, a pit was excavated with a length of 10 m. With its formidable pulling force of 210-t old pipes from ND 300 to ≤ ND 1000 can be renewed. The GRUNDOBURST rig, even with the highest pulling force demands still has to be stabilised securely inside the machine pit. A stabiliser made of steel concrete at the head of the rig was specially produced to secure it.
The proven principle with the QuickLock bursting rods, by simply linking them in place is a major assembly advantage, taking the rod weight of 210 mm into consideration. The lowering and retrieval process of the QuickLock bursting rods was carried out with a special lifting device.
When pulling in the pipes, a pit with a length of 15 m was required on the opposite side, with enough space for two pipe lengths, welded together, each with a length of 6.5 m. With two pipe lengths the pipe weight was almost 4 t, which meant a weight of 37.5 t considering a length of 125 m. After the welding process, an insulated socket was pulled over the welding seam. The welding work took approximately two hours for each pipe 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 the new pipe and a cutting blade 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 friction. Furthermore, they made sure to observe the permitted pulling forces and not to exceed the recommended values of the manufacturer.
After deducting all auxiliary work the bursting and pipe installation process took 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-cracking assignment.
This article was submitted by TRACTO-TECHNIK, Lennestadt, Germany.