Raise-boring - 45° angle and 350m long shaft in rock for the penstock of the Sarenne hydropower plant

This article reports on the design, construction and outfitting of the penstock for the Torrent de la Sarenne hydroelectric scheme (France, 11 MW capacity, 735 m fall height), commissioned in autumn 2024. The particularities of this shaft are its 45° inclination combined with its length (350 m), as well as the very small deviation permitted to end up in an existing cavern of small dimensions. This article also presents the methodology used to install the penstock in one piece, using a rig designed specifically for the project.