By Carola Shmich
Tracto-Technik’s trenchless water and sewage pipe replacement technology allows Polish capital to avoid sinkhole while traffic continues unabated.
In the old historical part of Warsaw, Poland, an ND 400 mm clay pipe required replacement over a length of 30 meters. Mains inspection by the city’s water and sewerage company showed sand on the bottom of the mains, such that it was apparent the main was fractured and bits and pieces had fallen to the pipe floor. This presented a permanent problem of “undercarving” the road surface and creating a potential sinkhole – an imminent danger to the public. To verify the problem, an inspection of the pipe by camera was planned but couldn’t take place because the camera was unable to overcome the sand and other debris lying on the pipe’s bottom.
The Warsaw water and sewerage company, therefore, chose to replace the section of the main completely, but decided to find a trenchless way since the pipe replacement using an open trench method at a depth of 6m would have created enormous costs coupled with a high degree of traffic disturbance. Due to the density of vehicles traveling on the road, it was impossible to close down traffic– even finding an alternate route via neighbouring roads was ruled out. The city expected complete traffic chaos.
The only alternative to solve the problem was found by way of a hydraulic burst lining procedure from Tracto-Technik. This wasn’t only from the handling side, but also because the inner diameter of the main and the flow weren’t to be decreased.
Static Pipe Bursting
Using a hydraulically operated Grundoburst 1250 G system, after the push-in process of the QuickLock rods into the target pit or into the target manhole to renew the pressure on sewage pipes (static berstlining or pipe bursting), the guiding calibre is exchanged against a roller blade with guiding cone and expander as well as the attached new pipe. Assembly is very simple. A link piece makes the connection of the pipe lengths easier and guides them at the required radius. When pulling the rods back, the old pipe is fractured by the roller blade running at the front.
The roller blade cuts grey cast iron pipes, asbestos, plastic, concrete and stoneware pipes, which are then replaced by PVC/HDPE long or short pipes. Contrary to the standard bursting heads the roller blades can cut open even the most difficult to destroy materials, such as steel pipes and ductile cast iron pipes with connection sockets and repair sockets.
On the Warsaw site, the city turned to contractor J.T. Zaklad Budowy Gazociagow using a Grundoburst Type 1250 G with 125 tons of pull-back. When site preparations were made, the sandy soil around the main, coupled with a high level of groundwater required a well-prepared starting pit. To complicate matters, working space was restricted because of an existing ND 800 cast iron water main found over the suggested working pit.
The ND 400 clay pipe main to be replaced ended in a 2m-x-1.2m brick collector. Due to these further space restrictions, the pipes to be installed from inside the collector couldn’t be the usual butt-fused long HDPE pipes, prompting selection of short-length pipe modules made from polypropylene, PP-HM OD 450.
Remote Control Fix
The only possibility to enter into the collector was positioned about 100m away from the suggested pipe replacement. Therefore, the contractor was looking at a set of tooling that was lightweight and could be easily transported to the site inside the collector. What he found among the Tracto-Technik equipment was the Burstfix, a tensioning device to connect short-module pipes to form a solid pipe during pipe bursting applications.
This tensioning system is operated with a portable hydraulic power unit – the functions operated via remote control. The indicated pressure allows itself to be converted into the permissible thrust force.
Once the Warsaw preparations were done, the short pipes connected and equipment in place, it took barely three working hours to replace the old pipe with the new PP-HM OD 450 pipe. With friction on the new pipe increasing during the replacment, a pulling force of up to 80 tons was required, showing that the choice of the Grundoburst 1250G with 125 tons of thrust were the right decision.
The underground pipe replacement was done virtually unnoticed from the general public and without traffic disruption.
The Warsaw water and sewerage company showed its total satisfaction by advising the contractor of more sites to deploy the pipe bursting technology in the near future.
Carola Schmidt is export manager at Lennestadt, Germany-based Tracto-Technik GmbH & Co. KG, a family-owned company specializing in underground pipe installation and pipe bending technologies.
Contact: +49 (0) 2723 8080 or www.tracto-technik.de