Innovation for an exceptional project

For the ten-yearly maintenance of the EDF hydroelectric power plant in Montézic (Aveyron), Serpollet Agence HTB Grands Travaux was commissioned by RTE to replace six 400,000-Volt oil-filled cables. This was a highly demanding project, both technically and in terms of tight deadlines.

Managed for Serpollet Agence HTB Grands Travaux by Alexandre Uson, Area Manager, as part of the GTSE* joint venture, the project required more than two years of engineering studies to develop operating procedures tailored to the physical constraints of the site.
The six oil-filled cables to be replaced ran along both sides of a narrow, 700-metre-long gallery that was dimly lit, damp, continuously ventilated, and buried under 500 tonnes of sand inside 2,800 cable trenches covered with concrete lids. These lines then ran through a 70-metre-vertical shaft before emerging into the plant area.

For Alexandre Uson, “spanning eleven weeks from April to June 2023, this operation was a real challenge. We succeeded because we prepared extremely thoroughly alongside RTE, EDF, and the joint venture. We relied on dedicated technical innovations and the commitment of highly professional teams led by Abdallah Samit, Cable Pulling Site Manager for Agence HTB Grands Travaux, despite difficult working conditions. It was the combination of these three aspects—preparation, innovation, and commitment—that made the project a success.”

Working in a confined space

One of the major challenges was the sheer volume of sand in the trenches, which had to be cleared, stored, and put back, even though no existing mechanized solution was suited to the narrowness and length of the tunnel. Two bespoke technical solutions were specially designed: a vacuum suction system to clear the sand from the first 350 metres of the tunnel, followed by a custom-built electric double-tipper trailer to facilitate the removal and reuse of the sand from the remaining 350 metres. These two innovations greatly simplified the teams' work on-site.

Ultimately, this project, carried out under fairly extreme conditions, went very smoothly.
Patrice Coutenceau, Project Manager for RTE, highlighted how the safety of all employees was ensured: “not a single accident was reported on a project where teams worked intensively in 2x8 or 3x8 shifts, particularly on quite arduous manual tasks. I could feel the strong cohesion among the teams on-site, and I would like to congratulate all the employees of the joint venture for their dedication.”

*Groupe de Terrassement Serpollet ETPM