NORTH SPUR: JIM GORDON TRIES AGAIN TO GET SIOBHAN COADY'S ATTENTION

Dr. Stig Bernander

Editor's Note: Canadian Hydro Engineer, Jim Gordon has worked hard to get successive Ministers of Natural Resources, including more recently Siobhan Coady, to take seriously the geotechnical analysis conducted by Swedish scientists Dr. Stig Bernander and Dr. Lennart Elfgren in relation to the North Spur, but without success. 

The Spur is a natural formation which forms part of the dam structure for the Muskrat Falls project. The feature contains clays defined by experts as "sensitive" because under certain circumstances they have the capacity to liquefy and to collapse. The issue is increasingly urgent because Nalcor, in a matter of days, will begin filling the Muskrat reservoir to the 39 meter level. 

What follows is the text of Jim Gordon's recent email  to Minister Coady succinctly explaining the contents of a Report entitled "A Downward Progressive Failure of the North Spur at Muskrat Falls - A Possibility that ought to be investigated and mitigated" written by Drs. Bernander and Elfgren. 

Dr. Lennert Elfgren

It is important not just that the Government is warned by experts in the geotechnical sciences that Nalcor has not applied the standard of independent review warranted by the issue but that the public is aware that they have been warned. - Des Sullivan

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Guest Post by James L. Gordon, P. Eng. (Ret'd)
Honorable Sioban Coady – Minister, Department of Natural Resources, Newfoundland.

I am writing to further clarify the recent letter from Stig Bernander and Lennart Elfgren.

The type of sliding failure described by Bernander and Elfgren has not been investigated by SNC.

Instead SNC have investigated upstream and downstream surface slope failure using average soil strengths obtained from tests. Not a sliding failure.

The Spur soils were deposited in almost horizontal layers during the last ice age as winter flows alternated with summer spring floods. The deposition was not similar each year due to the variability in flood flows. The result is a Spur with layers of silts and sands of varying composition and strength. 
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Related:
Jim Gordon's Final Comments on North Spur

A Downward Progressive Failure of the North Spur at Muskrat Falls - A Possibility that ought to be investigated and mitigated by Dr. Stig Bernander and Dr. Lennart Elfgren
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At the base of the Spur there is a layer of soft soil sloping slightly downstream, where a sliding failure could easily occur. The failure would be rapid under the force exerted by the reservoir waters impounded against the Spur. There would be no warning, and no time to evacuate downstream residents.

Dr. Bernander and Dr. Elfgren have analysed the possibility of such a failure using the low strength of the soft base layer and not the average strength of the Spur soils, since the failure will occur in the weakest layer, not the “average layer”.

The result is a safety factor well below 1.0 indicating failure. A safety factor of at least 1.6 is required to ensure safety.

More tests of soil strength in the base layer are required using undisturbed samples. Such undisturbed samples are difficult to obtain, hence an experienced geotechnical engineer familiar with such tests will be required to supervise the sample work.

I would urge you to ensure that such soil samples and further analysis are undertaken before the reservoir is filled. This is of paramount importance since lives are at stake.

Regards,  
Jim Gordon.

James L. Gordon, P. Eng. (Ret'd)