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Report dismisses Muskrat Falls stabilisation criticism

Muskrat Falls

A geotechnical peer review panel (GPRP) report has confirmed the design approach for stabilisation work at Muskrat Falls North Spur in Canada after critics voiced concerns over the work.

The Muskrat Falls Hydroelectric Development forms part of the Lower Churchill Project (LCP) in Newfoundland and Labrador in Canada and is using the natural geomorphology and dam construction to impound the water.

The 824MW generating station is located between a 34m high and 430m long concrete dam at its north side, and a 15m high and 350m long rockfill dam at its South side. The area north of the river forms a natural dam, known as the North Spur.

It is the stabilisation works of the naturally-occurring dam North Spur that has drawn criticism from experts and has driven Nalcor, the organisation responsible for the development, to convene a GPRP to counter the critics and local people against the scheme.

SNC-Lavalin (SLI), who has been working on the development, had undertaken several studies of the North Spur and evaluated the stability and integrity of the natural dam.

The work included stabiliation activities on the upstream and downstream portions of the North Spur such as: regrading slopes; excavating and removing high sensitivity clay and sandy, silty and clayey soils; installing cement bentonite cut off walls down to the lower clay layer; building protective rock berms along the shoreline; installing drainage and relief wells; and, installing monitoring equipment.

However following the publication of SNC-Lavalin’s report on the North Spur works, there have been critical reports written by a number of academics who have questioned and criticised the findings.

The critics claimed that the stablisation works had not considered a number of factors, including the type of the landslides in the study area; the “extreme sensitivity and particular structure” of the soils in the North Spur; the application of the limit equilibrium approach to evaluate stability of the North Spur; aspects of progressive failure; and the consequences of a potential landslide and downstream flood.

The GPRP examined the engineering documentation available for the North Spur and concluded that “the overall approach, concepts and methods used for checking the stability and integrity of the North Spur follow the current standards and state of the art practice”.

The GPRP report states that the clays found in the North Spur are similar to many of the clays found in Eastern Canada and in Norway, and the observed landslide features are also comparable to landslides observed in sensitive clays elsewhere.

It argued that the ”methodology used to evaluate the stability of an initial slide on the North Spur slopes corresponds to the current state of practice” and “the analyses by SLI are conceptually acceptable to take into account the initiation of progressive failure and to ensure a proper design of mitigation measures”.

The report went on to say that suggestions by the critics had been ”based on several incorrect assumptions and that the results are therefore not realistic”

Read the full reports here

Members of the GPRP were Memorial University professor Bipul C Hawlader, retired Université Laval professor Serge Leroueil, Norwegian Geotechnical Institute technical lead landslides Jean-Sébastien L’Heureux and Université Lavalp professor Ariane Locat.

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