Large manholes for large-scale works in Rosnay L’Hôpital

We are dealing with a fairly classic and recurring problem, namely the intrusion of tree roots at the connection joints of manholes and pipes making up the wastewater evacuation network. Consequences: numerous water leaks and the continuous infiltration of parasitic clear water from the groundwater which saturates the Rosnay wastewater treatment plant.

Committed to an approach to improving water quality and preserving the environment, the Syndicat Départemental des Eaux de l'Aube (SDDEA) has therefore begun the rehabilitation of its network located under the departmental D 396, linking Rosnay- The Hospital in Vitry-le-François.

For Jean-Philippe DEPARDON, sector manager at NGE: “The main objective of the work is to restore the watertightness of the existing structure, in areas that have suffered root intrusion, but also to restore its good mechanical characteristics, while improving its hydraulic performance. »

The first two stages of the work consisted of diverting the water using two 100 m3 pumps then uprooting it at the level of the manholes and the collector. Once these operations were carried out, the NGE teams were able to replace the old concrete manholes made up of one-meter elements with joints with 7 new ones made of polymer concrete from the ACO brand.

For Jean-Philippe DEPARDON: “The initial project provided for the implementation of classic concrete structures with joints. But due to the high water table, which in winter completely submerges the network, we proposed to the SDDEA an alternative solution, much more efficient in the long term and perfectly waterproof. Our choice was then oriented towards the monoblock solutions in polymer concrete from the manufacturer ACO. »

While one-piece manholes are widely used across the Rhine (particularly in Switzerland), Rosnay-L'Hôpital constitutes ACO's first project in France.
In this specific case, in order to meet the specific requirements of the site, ACO had to provide tangential manholes with a diameter of 1000, ranging from 2 meters to 4,50 meters in height (the collector being located between 1,30 meters and 5 meters) .

After the excavation work, each area was secured by the installation of shielding allowing the introduction of the manholes which were subsequently connected to the network.
The many advantages of ACO manholes were determining factors in the decision-making. Indeed, the monolithic design, in a single piece and without joints, of the ACO manholes, guarantees the structure 100% watertightness, reduces handling and therefore the cost of implementation.

Designed to last 50 years, they are made from polymer concrete, a very light material which ensures a low weight compared to concrete products of the same density, and a certain advantage in terms of workability.

ACO manholes also display high corrosion resistance and total insensitivity to the H2S phenomenon due to their perfectly smooth coating.

In addition to the installation of 7 watertight manholes, the project also includes: the renovation of the discharge station (sealing, pumping, safety), that of 7 other conventional manholes and, the 250 meter wastewater pipe, which cannot be visited, for continuous structuring lining.