Microtunneling Jacking Pipes for a Combined Sewage Collector in Rennes

In the face of an accelerated increase of sediments in the canal d’Ille-et-Rance and the river Vilaine in the heart of Rennes and the therefore significant impact on these waterways, the city adopted a perennial program in 2008 to improve the pipelines and hydraulic properties of its wastewater system. The aim was to reduce the amount of overflow into the river during periods of heavy rain by 50 %. A total of 8,000 cubic meters of storage capacity were to be added to the combined sewer system of which 3300 m³ have been implemented downtown, along the river Vilaine beneath a lane for public green transport. For the latter part, the technical service department of the city Rennes designed a 1340 meter-long collector with a pumping station that controls the flow to the wastewater treatment plant. A combination of an average installation depth of 7 m and high groundwater levels that partly even reach the surface asked for trenchless installation – microtunneling. HOBAS GRP Pipe Systems were a firsthand choice, for their resistance to chemical attacks by hydrogen sulfide and the products’ optimal hydraulic properties as well as internal and external leak tightness. The pipes with their, in the trenchless sector much appreciated, smooth outer as well as inner walls and precise outer diameter were designed at 1940 mm De and a wall thickness of 77 mm. Despite their comparably light body (in this case 3 tons per 3 m pipe) they easily withstand the required 800 ton axial loads which are evenly distributed along the whole length of the pipe.