The Dieppe-Maritime Urban Community recently undertook the rehabilitation of its main concrete stormwater collector dating from the 19th century which is located under the ‘Cours de Dakar’ road behind the harbour, running at a depth of 5 m over a length of 1 km. The ovoid network had major structural weaknesses that led, between 2014 and 2018, to three roadway collapses; a roadway on which trucks and cranes weighing up to 490 t regularly travel to handle onshore wind turbine blades and heavy equipment at the quayside. Between October 2019 and June 2020, the Cours de Dakar, main road in the harbour, was the scene of extensive renovation works to reinstate the network to its full structural capacity, restore its watertightness, and protect it against abrasion and corrosion.
To give a new lease of life to this 1.20 m wide, 2.20 m high structure, the Dieppe-Maritime Urban Community chose the relining trenchless method to complete the works.
This less invasive method allowed the contractor, Sade, to install nearly 500 Amiblu NC pipes measuring 1,024 x 1,923 mm and 2.50 m long without opening a trench. In addition to enabling the project to be on time, this method made it possible to reinforce the structure from the inside using GRP pipes and limit inconvenience to local residents. It also monopolised only one part of the road, avoiding closing this very busy road completely.
The NC pipes were inserted one by one into the concrete ovoid network, then transported on a specially manufactured trolley to the installation site where they were joined together to rebuild the inside of the pipeline. The annular gap between the old and new pipes was filled with bentonite grout, forming a complete restructuring composite system.
The other aspects of the project included the replacement of a grey cast iron wastewater conveyance pipe with a 350 mm diameter, which was supported by concrete sleepers inside the network and over a length of approximately 850 m. This pipe was removed and a new one created under the Cours de Dakar over a length of 1.350 km.
Also, diversion of rainwater usually carried by the network required extensive preparatory work. The water had to be diverted outside the network to allow the work to be carried out inside.
Implementation of an anti-flooding pumping station was also necessary and was subject to the tides, the ovoid network is quickly saturated, which causes flooding. The anti-flooding station will be able to handle up to 4,500 m3 of water per hour.
