WEBINAR Registration Link

Date:             27 September 2023

Time:            6:00 pm — 7.00 pm AEST

Location:       Online only

Overview

The Nant-de-Drance pumped hydropower scheme (900 MW), awarded “International Major Tunneling Project of the Year” ITA-NCE prize in 2014, connects the two existing artificial reservoirs at Emosson and Vieux Emosson in Switzerland.

Except for raising the upper dam, all works were undertaken underground. They include 16 km of tunnels, two vertical shafts of height 440m and 6 large caverns. The exceptional size of the powerhouse cavern (194m x 32m x 52m), located at 600m depth in a metamorphic rock formation of sedimentary origin, required the definition of an appropriate excavation, support and lining concept.

An advanced rock behaviour model, based on an important investigation campaign, 3D finite element modeling, and analysis of unstable blocks allowed the optimization of the support and the lining.

Monitoring during construction and back-analysis allowed the successive reduction of support measures and the streamlining of the excavation phasing. The resulting savings largely exceeded the incurred expenses for additional investigation and calculations.

The cavern excavation schedule was accelerated by reorganizing the phasing of the different stages, creating a margin to make up delays elsewhere.

Structural design was also particularly challenging due to the unusual load cases to which the structure is subjected during construction and operation, as well as the large volumes of concrete being poured.

After 14 years of work, Nant de Drance was officially commissioned on 9 September 2022. At the height of construction, up to 650 labourers were present on site without any serious accidents. By its ability to absorb or inject up to 900 MW of power, Nant de Drance is going to be a key instrument for stabilisation and regulation on the Swiss and European grid.

Speakers

Patrick Heck, CEng MICE graduated with a degree in civil, structural and environmental engineering in 2007 from Trinity College Dublin, Ireland. Patrick started his career in geotechnical engineering, first with Buro Happold in the UK, and from 2010 with WSP-BG in Lausanne, Switzerland. He has been involved in the design and construction of several hydroelectric schemes in Switzerland. He was the BG project manager for the civil & structural engineering of the powerhouse and switchgear caverns at Nant de Drance.

Etienne Garin, Civil Engineer, M.Sc.: graduated in Civil Engineering from Swiss Federal Institute of Technology in Lausanne in 1996. He benefits from vast experience in the field of underground construction and hydroelectric scheme. Since he joined WSP-BG he has actively participated in the design and construction of major tunnels in Switzerland and abroad, as well as hydroelectric power schemes. During his career, he has carried out calculations at detailed and final design stage, been responsible for site supervision, and has managed projects from preliminary design to client delivery. He was in charge of the design of the caverns for the Nant-de-Drance project. Since 2023, Etienne Garin is animator of the ITA WG 19 “Conventionnal Tunnelling”

Gérard Seingre, Civil Engineer, M.Sc.: graduated in Civil Engineering from Swiss Federal Institute of Technology in Lausanne. Gérard is an expert in deep tunnelling and site survey for construction of energy infrastructures. He has planned and played a leading role in the construction of over 40 km of deep tunnels, 3 vertical shafts over 400 m high, more than 10 big caverns and 2 descending access galleries (main projects Loetschberg-base Tunnel and Pump storage power plant Nant de Drance). He was for 12 years animator of the working 17 “Long tunnels at great depth” for the ITA. He is currently the treasurer of ITA. Gérard is also lecturer for tunnelling construction at the Swiss Federal Institute of Technology of Lausanne.