Minimal coverage, very restricted working space – the conditions on site made the renovation of a large-diameter interceptor sewer in the German city of Bruchsal a challenging task. HOBAS helped make this extraordinary project a full success.

The combined interceptor sewer located in Werner-von-Siemens Street in the German city of Bruchsal is a central and historical drainage channel. Earliest records date back to 1640 and in 1896, the former moat was upgraded to a man-sized channel with a height of 2 m and a width of 2.70-2.90 m. And the channel not only transported sewage: Telecommunication and electricity providers as well as potable water suppliers also passed their lines through the large profiles.

The impressive HOBAS NC Profile in the middle of the German city of Bruchsal

In 2011, an examination of the old sewer’s condition revealed severe cracks and leakage as well as serious structural instabilities on a 175 m long pipe section. Urgent action needed to be taken. Due to the many different cross-sections and the interceptor’s poor condition, a rehabilitation through relining was not an option. It was therefore decided to replace the old structure with a new one along the original route. The decision to use GRP as pipe material was quickly made, not least due to traffic-related reasons: The two busy lanes of the interurban Werner-von-Siemens Street had to remain unaffected by all means, and the use of concrete pipes would have demanded a larger trench and heavier lifting equipment, considerably narrowing the traffic space. Furthermore, a gradient of merely 0.6 ‰ and the resulting low flow rate were unquestionably a case for GRP pipes with their smooth inner surface, which helps prevent deposits.

In close cooperation with the responsible engineering office, HOBAS Germany worked out a solution involving non-circular GRP profiles with a cross-section of 3000/2000 mm, that considered all necessary structural aspects with regard to the minimal coverage of approximately 300 mm. The project was put out to tender beginning of 2013 and the construction company Michel Bau won the contract. For the entire installation period, the old interceptor was drained and put out of operation. The water was instead redirected through a temporary steel pipe structure which was specially built on support stilts, passing over the two-lane road, walk- and cycle ways as well as private property. Thanks to this solution, it was possible to divide the construction works into merely three sections and thereby increase the cost-efficiency of the construction process considerably.