on a big project for Bordeaux Métropole with the SADE Special Works teams.

Two project aims

• Increase the treatment capacity of the Cantinolle and Lille wastewater treatment plants, located in Eysines and Blanquefort respectively, in response to the growing population of these two municipalities;
• Preserve the sensitive natural environment of the River Jalle by discharging treated water into the River Garonne, which has a higher flow rate.

The works

Since August 2020, 18km of additional networks have been built to link these two wastewater treatment plants located in the Bordeaux metropolitan area and enable the transfer of wastewater from Cantinolle to the Lille plant.

Two parallel pipes are currently being laid along 9km each, including around 2.6km laid using an 800mm-diameter micro-tunneller.

The STS – Valentin consortium (agent) is carrying out this section of trenchless works.

Several reasons explain the choice of the micro-tunnelling technique for this section:

• Passages under departmental roadways and railway lines
• Proximity to Padouens Lake, a few metres from the worksite, implying a strong presence of water and unstable ground unsuited to conventional open excavation works.

The drilling plan required seven entry shafts and eight exit shafts, all located at a distance of 100m from each other.

At this stage of the works, 5 drilling operations of over 100m have already been executed, out of a planned total of 25, including beneath railway lines.

Works are scheduled to continue to August 2022.