Urban sewer system owners and operators frequently ask for the rehabilitation rather than renewal of the deteriorated sewers. Many of the tenders are called for sewer rehabilitation works because of various structural and hydraulic deficiencies.

The implementation of state-of-the-art trenchless rehabilitation methods, especially in urban areas and cities, is becoming more and more popular due to their unique advantages – minimal surface excavations, reduced traffic disruption, considerable reduction of noise and dust.

Linz, Austria 2007

In 2007, Linz AG awarded a contract for the sliplining of egg-shaped sewers sized 580–1,160 mm in diameter. Due to hydraulic constraints it was important to avoid a reduction in cross-sectional area and to retain maximum flow capacity.

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The old sewer had to be enlarged by reaming, using the unique Angerlehner reaming machine (AKF) 22. This hydraulically driven and computer-controlled machine reamed approximately 15 m of the existing sewer in a single day. In total, approximately 80 mm of the existing sewer body was reamed off resulting in a large increase of flow capacity.

Kolkata, India

The client called for tenders to conduct sewer rehabilitation and upgrade works in various egg-shaped trunk sewers, including CCTV surveys, removal of silt, local repairs and installation of GRP liners, to enhance the structural integrity and life span of the system.

Angerlehner was awarded Phase I – rehabilitation of 6,647 m of trunk sewers with sizes ranging from 750 and 1,120 mm to 2,210 and 2,857 mm, and Phase III – rehabilitation of 4,154 m of trunk sewers in similar sizes.

The lining design, taking into account the structural condition and cross section, was completed according to the WRc Sewer Rehabilitation Manual. Due to heavy infiltrations at certain locations and better workability, a self-supporting Type II lining was more suitable for the rehabilitation.

GRP liners with durable spigot-gasket-socket joints were installed through installation shafts and transported by tailor-made trolleys pulled by high precision cable winches. After completion of the installation of the liners, a cement-mortar based grout was pumped into the annulus through pre-installed grout nozzles in the liners. In order to avoid buckling or stresses to the lining, the grouting was conducted in stages.

Due to the high demand of GRP liners (ISO 9001:2008 certified) a production plant capable of processing up to 750 tonnes of materials monthly was erected.

The project commenced in 2008 and was completed in 2011.

Conclusion

The implementation of this method resulted in a higher flow capacity, a structurally sound sewer system with a strong chemical and abrasion resistance, longevity, and a minimal requirement for maintenance.