Partial Relining. Making the Wise Choice

The principles of relining in cost-conscious sewer rehabilitation are the same as those of minimally invasive surgery: to achieve great benefits with minimal incisions.

Driven by the obligation to check their sewer systems, local authority decision-makers face the question of whether to repair or build anew. In light of the fact that the German public sewer network is around 400,000 kilometres long, for many of them it’s a horror scenario. Video inspection shows that everything is possible from being ‘all OK’ to ‘a bottomless pit’.

[Translate to english:] Hutliner: Die Sanierung begrenzter Rohrabschnitte mithilfe von Kurzlinern ist ein technisch anerkanntes Verfahren. Foto: Schwalm

It is possible that the law may force immediate action to be taken, for the Federal Water Act (WHG) classifies the urgency of required action based on effluent quality and the potential risk to groundwater and the environment.

At first glance, a new sewer may seem the ideal solution. Counter arguments, however, are presented by the cost and the impact on traffic. As a fundamental rule, before undertaking repairs on any drainage system, you should first take a close look at its hydraulic aspects. If a sewer system turns out to be too small, then over the medium to long term there will be no getting away from a rebuild. Budgetary funds, cost-benefit considerations and trust in technical options are further factors in deciding what action to take. The role played by personal conviction and experience should also not be underestimated. The idea of cladding the original structure from the inside with a foreign substance seems to many like a botch job. This relining process is, however, recognised today in engineering terms as a procedure that represents good value for money.

A stocking in the sewer

A differentiation is made in the trade between relining a complete sewer and partial lining using short liners. The service life of a short liner is 15 years or more, with a warranty for 5 years. The cost of conventional rehabilitation using the open trench method is four to five times as much. Depending on the density of the damage, it is reasonable to fit four to six short liners within a 40 to 50-metre stretch. If there are more areas of damage, it is usually decided to use inversion. In this process, a liner is pulled like a long stocking into the sewer pipe and thus clads the entire length of a reach. Repairing damaged areas of sewers from the inside is reminiscent of procedures of minimally invasive surgery.

Here too, the fewest possible incisions are made, the patient is spared open surgery and the operation is carried out from within using a special appliance and video monitoring. Even civil engineering companies – traditionally armed with diggers and hydraulic drills – are today extending their range of services by adding trenchless procedures of repair and maintenance to their repertoire. At the IFAT trade show in 2004 a presentation was made on the City of Munich’s sewer rehabilitation plan. It has a cost of three billion Euros. In 2006, a small town in East Hesse had budgeted 15 million Euros for rebuilding its sewers. Faced with limited budgetary funds, relining with short liners is a serious alternative.

Martin Schwalm, Der Gemeinderat 01/2007

Schwalm Robotic GmbH Industriestraße 16 36251 Bad Hersfeld-Asbach Germany Telefon: +49 6621 79578-0 Telefax: +49 6621 79578-11