Wloclawek, April 2017

A customized one-of-a-kind solution: Trenchless egg-shaped section helps rehabilitate a main sewer

The unique project to rehabilitate the sewage system in the agglomeration of Włocławek began in January 2016 when a contract was signed between the supplier F.H.I. “Instbud Stanislaw Boguta” and the Polish city of Włocławek following an open tender. The aim of the project was to develop a complex rehabilitation concept and carry out the planned rehabilitation work in expert fashion.

In addition to cleaning, conducting a TV inspection, evaluating the state and technical efficiency of the existing pipes, and taking recordings, the comprehensive package of services included selecting rehabilitation technology and carrying out the rehabilitation work itself. The plan was to rehabilitate two sections of the sewage system with house connections and manholes. The first construction phase in ul. Kapitulna involved the following work on over 600 m of the main sewer:

  • · Rehabilitating a waste water pipe with an egg-shaped section of 1,000/1,500 over approximately 470 m with the SAERTEX-LINER® type S+
  • · Rehabilitating a waste water pipe with an egg-shaped section of 600/900 over approximately 130 m with the SAERTEX-LINER® type S+
  • · Rehabilitating waste water pipes DN 150 and DN 200 with a total length of 113 m
  • · Rehabilitating a total of 13 manholes 

Existing transport structure raises organizational challenges

This unique project unfolded in ul. Kapitulna and ul. Zielony Rynek in the city of Włocławek. With almost 120,000 inhabitants, the city lies in the Kuyavian-Pomeranian voivodeship of Poland. Ul. Kapitulna is one of the main roads in the western part of the city and one of the primary thoroughfares into the city center. It sees a very large volume of traffic, since the western part of the city is cut off from the center by a railway line running from Toruń to Kutno. The road has four lanes – two heading west and two east – and is one of the few access routes to pass under the railway line. Ul. Zielony Rynek, on the other hand, is right in the city center and has two lanes that are still paved with ancient cobblestones.

Picture one: The traffic had to continue to flow unhindered while rehabilitation work was carried out on these major traffic routes.

The main sewer in ul. Kapitulna was designed by an engineering firm from Danzig back in 1959 in order to drain waste water from all southwestern quarters of the city on the River Vistula over a total length of around 2,000 m. Prior to this, parts of Włocławek were either not properly connected to the existing sewage system or only had substandard drainage pipes in certain buildings. The project included an underpass beneath the railway line at a depth of 8 m so as not to disrupt the functionality and operation of the sewage system. The main sewer was built from brick over 50 years ago in the 1960s. 

Picture 2: Existing collection of partly historical planning documents.

A legal ruling on traffic was requested in order to carry out high-pressure cleaning on the sewage pipes. Since the roads involved were very busy, the project coordinators had to guarantee that a single lane of traffic could continue to flow while the work was being done.

New surprises accompanied the project from start to finish

The process to gage the current state of the network was initiated after the project was given the go-ahead in May 2016. The build-up of sludge in some sections of the pipe had led to a 70% reduction in diameter. A high-pressure cleaning vehicle was brought in to clean and remove the deposits in the pipe over a period of 30 or so days, during which project workers stumbled across some surprising finds: Colossal mounds of trash that should never have been sent through the sewers in the first place were only the beginning. Troublesome little rags and disposable towels also caused issues and became notorious for stubbornly blocking up the vehicles’ sieves and pumps’ baskets. This interrupted the flow of work, which kept having to be broken off in order to clean the machines at short intervals. This posed a major challenge right through to the end of the project.

After cleaning and exposing the surfaces of the existing pipes, the project workers took an inventory and evaluated the technical condition of the pipes. The deposits in the base of the pipe had left the bottom section in very good condition, while the upper portion had been corroded by aggressive waste water vapors. The evaluation of the pipe revealed that almost no deformation had taken place, placing it in category II. As part of the inventory, a full review was conducted and recordings made using a self-propelled TV camera unit.

Precision planning, organization, and implementation

Due to the design and choice of technology, the single pipe lining made of GRP pipes (GRP modules) was dropped in favor of pipe lining technology that could be cured on site by means of a resin-soaked GRP pipe liner. The main argument for choosing this type of rehabilitation technology was that the cones in the top of the manholes did not need to be dismantled. When it came to laying the pipe liner, the SAERTEX-LINER® type S+ was chosen for its excellent mechanical properties, including its significantly higher elastic modulus (short-term elastic modulus = 20.500 N/mm2) in comparison to other GRP products. This meant a GRP liner with the lowest possible wall thickness could be used and thus optimally meet the customer’s stringent requirements.

Picture 3: Hauling in the SAERTEX-LINER® using the SAERTEX® multiBelt belt conveyor developed for large sections.

The implementation work began in October 2016, whereby the rehabilitation project on the main sewer was divided into three construction phases. Waste water was successfully diverted using pumps and monitored by means of a three-shift system. Each construction phase was not permitted to exceed a working length of 110 m. The work had to be split up this way because of the high volumes of traffic and the associated requirements of the legal ruling on traffic to ensure minimal disruption to public transport. Another key aspect of the work was delivering the GRP pipe liner itself: An ideally suited loading position had to be found as the work had to be carried out using a crane on a very busy road. The heaviest GRP pipe liner weighed 15 metric tons.

Picture 4: Challenge accepted: 15 t SAERTEX-LINER® delivered to the construction site with great precision.

The SAERTEX-LINER® type S+ with egg-shaped sections of 1,000/1,500 over approximately 470 m and 600/900 over approximately 130 m was cured using a chain of 12 x 1,000-Watt UV lights at a speed of 15 cm a minute. It took 16 hours to fully cure the longest GRP pipe liner.

While this work was taking place, the manholes also had to be rehabilitated. The rehabilitation work on the main sewer took six weeks before it was successfully completed, once again proving the outstanding quality of the SAERTEX-LINER®. After the liner samples had been removed, they were sent to a testing institute and achieved excellent results.


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