|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.
|Dr. Lennert Elfgren|
Guest Post by James L. Gordon, P. Eng. (Ret’d)
Sioban Coady – Minister, Department of Natural Resources, Newfoundland.
am writing to further clarify the recent letter from Stig Bernander and Lennart
type of sliding failure described by Bernander and Elfgren has not been investigated
SNC have investigated upstream and downstream surface slope failure using
average soil strengths obtained from tests. Not a sliding failure.
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.
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
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.
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
result is a safety factor well below 1.0 indicating failure. A safety factor of
at least 1.6 is required to ensure safety.
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.
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.
|James L. Gordon, P. Eng. (Ret’d)|