Investing in a reliable functioning sewer system with the right rehabilitation technology has been made easier with the Janssen lateral rehabilitation process, that can be used even with groundwater ingress and the formation of voids.

Last October in the Westphalian city of Minden, located in Germany, the main sewer was comprehensively repaired at a length of 190 m, including leaking joints, shards, and original improper connected laterals. At a depth between 4.8 and 5.2 m with the local soil conditions of heavy clay and gravel sands, initially there was no detailed information about the existing compaction of the sewer line.

Here the CCTV inspection of the main line and the laterals helped. Soil reports in connection with a geo-physical process by way of geo-radar were to give additional information about voids and bedding problems.

Quick solution needed

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Ulrich Schmit of the City Works Minden (SBM) said “It turned out that there was no serious compaction problem, yet at the leaking joints and above the lateral connections there was a large infiltration of groundwater.”

In co-operation with the engineering firm IWA of Minden, the option of constructing a new pipe in an open trench was quickly dismissed as it would be too costly and complex. A new construction would have meant the need for costly groundwater management.

“It was for this reason, and because there were no major hydraulic load problems, we decided for a repair from the inside.

“With this option we used a close-fit-liner, which meets the on-site structural requirements and can be installed under the given circumstances. At the same time we trusted the Janssen Lateral Rehabilitation Process. No other lateral repair system can connect and seal these laterals so well,” Mr Schmit said.

This solution is based on a special packer and two component resin. After a series of protruding laterals, and other obstructions were removed using a cutting robot, the actual rehabilitation could begin.

The packer was placed at the damaged spots and inflated by compressed air. Then the liquid two component resin was injected through the damaged areas.

Managing Director of the Goch-based service company Janssen Umwelttechnik said “The resin fills the voids, displaces the groundwater and bonds with the bedding material – this way the actual sealing and stabilising happens on the outside of the pipe.

“Even the annulus between the close-fit-liner and the host pipe is filled and sealed up to 1 m to the left and right of the lateral.”

The freshly sealed laterals could then be connected to the HDPE liner, the so-called close-fit-liner – now there will be nothing standing in the way of unproblematic sewer discharge in Minden-Letelen.

“Because the sewer lines and the laterals are now tight, there will be no more sand washed into the pipe through the damaged areas,” Mr Schmidt said.

The total wastewater volume was reduced from 900 cubic m to around 300 cubic m with this constructive measure. The reduction by two-thirds has positive effects on the life of the pumps and leads to more economical operation of the pumping station.

“Thus a cost reduction at the pumping station comes hand in hand with the rehabilitation of the sewer system,” Mr Schmidt said.

Special resin against ground water ingress

In 2009, the sewer had been inspected by CCTV according to the existing ordinance (SuewVKan). Five damages with significant ground water ingress were found making an immediate repair inevitable. The service company from the Lower Rhine Janssen Umwelttechnik applied its lateral repair process here as well.

“This way all damages could be sealed and repaired,” said Norbert Fischer of Grid Service Waste Water of the City Works Roesrath.

The data of the running times at the pumping station prove the successful repair of the sewer pipe. While the pumping station was operating for eight to nine hours prior to the repair, it needed to run only three to four hours after. The volume of the wastewater pumped showed a significant difference – it was reduced from about 200 cubic m to 90 cubic m per day.

By reducing the external water inflow into the wastewater stream, the city works not only profited in the short term from the reduction of cost and the well functioning wastewater system, but also long term from a safe wastewater management without the danger of streets subsiding.

Head of the Department of Water and Wastewater Grid in Roesrath Rainer Witte said “Without this technology all this combined would not have been possible in such a short time. Therefore in future we will always rely on the Janssen Lateral Connection Rehabilitation Processor whenever necessary."