Improving a municipality’s drainage network

Double, rehabilitate and separate

Along around 450m on Avenue des Barques, the task was to:

• Rehabilitate a T180 ovoid
• Build a stormwater collector in parallel (800mm-diameter concrete)
• Create/modify all branch connections to separate stormwater and wastewater drainage along most of this section

The DPSM teams took care of the rehabilitation, while the Poitiers-Metz RD, and more specifically the Saint-Etienne branch (Montagny Agency), saw to the creation of the new collector, at 2.5m to 4.5m deep, with ad hoc branch connections.

Disorders to be repaired in order

The existing ovoid, a mechanically structuring element, presented numerous leakage points, due to cracks or embedded roots, which all had to be methodically dealt with.

Step one: securing

In addition to its drying out by 200m³/hour pumping and rerouting mounted in corbelling, this segment of the combined collector, highly sensitive to rising stormwater, was secured by 2 automated water-level control points with an alarm. In addition, a subscription to the French meteorological alert service and close contact with the operators of an upstream dam were put in place. Such precautions are useful all year round, and more particularly during the works last summer.

Step two: rehabilitation

The DPSM team then proceeded to the actual rehabilitation of the ovoid, i.e. 

• Repairs to 207 specific points by purging, followed by wet spraying of H₂S-resistant mortar
• The pouring of an apron all along the section, and repairs to the right and left legs of the structure at a height of 50cm with the same mortar
• Waterproofing of the facility and branch connections

The birth of a co-contract

When the call for tender was launched by the local authority, and given the specificity of the required rehabilitation operations, the Poitiers-Metz RD naturally opted to co-contract this order with DPSM, for its successful outcome. A wonderful example of stronger together and collective intelligence!