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Evaluation framework for technique choices in water mains rehabilitation

The Netherlands has almost 120,000 km of buried water mains. An increasingly large portion of these will now, and in the decades ahead, have to be replaced. Since digging trenches is expensive and creates significant nuisance, water companies are looking for better replacement approaches, such as trenchless techniques. But their experience with the different techniques is still too limited for them to decide which technique is the best for which mains. This is why KWR, together with the WML, Vitens, Brabant Water and PWN water companies, and the construction companies Heijmans and BAM, have worked, within TKI Water Technology, on developing an evaluation method with which projects can be assessed and compared. The result is an evaluation framework with which companies, early in their decision-making process, can evaluate the different techniques.

Which technique where?

Drinking water mains have traditionally been rehabilitated almost exclusively by means of open excavation. But this method is not always possible or desirable. The smart application of a suitable (trenchless) rehabilitation technique means that customers, neighbouring residents and traffic are subject to less inconvenience, and costs might be reduced. But which is the best technique for a particular situation? Current experience with trenchless rehabilitation techniques is so limited and piecemeal that it is impossible to make a well-founded evaluation of the different available techniques for any given water main.

Structured evaluation

In TKI’s ‘Smart Rehabilitation of Water Mains’ project KWR, along with WML, Brabant Water, Vitens, Heijmans and BAM Infra, Energie & Water, have developed a method for the transparent and uniform evaluation of projects using different rehabilitation techniques. The method has been tested in a number of pilot projects, both within the TKI project and in a PWN pipe cracking project at Middenbeemster (pipe cracking is a trenchless technique in which an existing pipe is fractured from the inside and replaced by a new one). The evaluation method has proven effective. On the basis of the results, an evaluation framework has been developed which consists of questions addressing distinct aspects of evaluation decisions, and includes an indication chart offering insight into the application possibilities of trenchless techniques in the Dutch distribution network. This evaluation framework represents a first step in the structured inclusion of an evaluation of rehabilitation techniques early in the decision-making process.

Trenchless renovation might for instance involve introducing a folded new pipe into the old pipe and then unfolding it, as in the Zwaagwesteinde pilot.