Inverted siphons

In the early 1980s, the authorities in the German city of Lübeck discovered that a wastewater inverted siphon under the river Trave was in a very bad condition. Already back then Aarsleff Pipe Technologies was a market leader in No-Dig renewal of pipe systems, and we accepted the challenge of renewing the inverted siphon using the latest No-Dig technologies; even though it would be the first time ever that this had been done.

Inverted siphons, sometimes called depressed sewers, allow storm or wastewater pipelines to pass under obstructions, such as rivers. They flow under pressure of about 2 to 2.5 bar and generally need a high flow velocity to keep material suspended.

Renewing inverted siphons is a complicated matter. Typically, they cannot be emptied for water due to leaks or due to the risk of them lifting if emptied. Add to this the fact that renewing inverted siphons is basically an underwater project, which often involves highly skilled divers. 

Since we renewed the inverted siphon in Lübeck in the early 1980s, we have continuously developed new methods and technologies that enable us to renew inverted siphons in dimensions of DN 150-DN 2000 under even very extreme conditions. The typical length of an inverted siphon is 200-300 m. However, we have worked with pipe lengths of up to 750 m.

Today, the demand for renewal of this special kind of underwater pipelines is increasing, not least because of the cost of the few alternative solutions. Our approach is highly competitive seen from a financial point of view. To many of our clients, the only real alternative is to install new pipes in the ground under a river.