Guest Post Written by James L. Gordon, P.Eng. (Ret'd)
Dear Mr. Marshall,
OPEN LETTER TO NALCOR CEO STAN MARSHALL
Dear Mr. Marshall,
I write
concerning safety issues with respect to the Muskrat Falls Project, and
specifically concerning the North Spur.
You have
probably been advised by your staff that, while the North Spur does indeed
present significant technical challenges, they have been addressed by competent
professionals, and so are no cause for concern.
In my
professional opinion, such a conclusion is incorrect, and dangerously so.
Let me
summarize the current situation at the North Spur, as I see it:
The North
Spur Dam at Muskrat Falls will be the first dam ever built containing quick (or
marine) clay in the dam body, and on a quick clay foundation.
To date,
these clays have been avoided like the plague by dam designers, due to their
propensity to liquefy if disturbed or fully saturated.
The dam
design has been undertaken by SNC using the FLAC program, generally used on
embankment dams.
The FLAC
program has never before been used on a dam built on quick clay.
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| James L. Gordon, P.Eng. (Ret'd) |
Two other professors are known to have reviewed the North Spur, one was an earthquake specialist, but neither issued a report.
The North
Spur dam design has also been reviewed by MWH, using the same FLAC program,
with the same results.
One might
argue that, since FLAC is the state of the art regarding soil stability, the
concerns have thus been put to rest.
Unfortunately, this is not the case.
The
scientific critique of the application of traditional methodologies to quick
clays comes from an unlikely source. Dr.
Stig Bernander was, for many years, Chief Engineer for SKANSKA, an
international Swedish contractor with over 55,000 employees. He and his team
were asked by the Swedish government to determine the stability of several
quick clay deposits being farmed in Sweden, due to the loss of life when
several liquefied. Unfortunately, despite working on the problem for several
years, they could not determine the safety with any precision, due to the lack
of a reliable computation methodology.
When Dr.
Bernander retired in 1991, he returned to the Lulea University of Technology to
conduct research on quick clay stability.
In his doctoral research (Published in 2011 and updated in 2012), he
developed a reliable computation methodology for determining quick clay
stability, and successfully defended his 252 page thesis titled “Progressive
Landslides in Long Natural Slopes”, before a geotechnical panel.
While I am
not a geotechnical specialist, at times in my career I have worked with many
geotechnical experts, including Dr. A. Casagrande from Harvard, and Dr. N.
Morgenstern from U of A. I have read Dr.
Bernander’s thesis carefully, and I find its critique of applying traditional
methodologies to quick clays to be persuasive. He demonstrates that the normal
methods used to calculate the stability of embankment dams cannot be used where
quick clay is involved, as they lead to inaccurate results. His methodology,
which has accurately predicted instability in several cases, requires certain
geotechnical data not normally obtained for dam analysis.
I called Dr.
Bernander and asked him his opinion regarding the reliability of the FLAC
analysis for quick clays. He said that he had compared results from FLAC with
those of his own methodology, and found that they were not compatible, even
after altering the FLAC program to account for a new variable.
Dr.
Bernander has reviewed the reports and data made public so far concerning the
North Spur, and finds it unpersuasive.
He visited the North Spur in October 2014. He has prepared a report,
based on the data he has been able to consult, which has been filed with the
Public Utilities Board in the context of the post-interconnection reliability
review. In this report, Dr. Bernander
was unable to determine whether the proposed design was safe because there was
insufficient geotechnical data and inadequate soil testing. One of his
conclusions stated “The likely liquefaction of this kind makes the results of
standard type soil investigations and the associated determination of the
factors of safety in respect to slope stability, very unreliable. This applies
in particular if calculations are based on the Plastic Equilibrium mode of
analysis”, which underlies the FLAC program.
Dr. S. Bernander
is currently working on a second report reviewing the SNC North Spur report
issued this year. Unfortunately, he still cannot determine the safety factor
due to the lack of the appropriate geotechnical soil tests.
The bottom
line – the methodology used thus far to determine the safety of the North Spur
Dam is not reliable for these types of soils. Until new analyses are performed
by geotechnical engineers familiar with Dr. S. Bernander’s methodology, the
possibility of catastrophic failure of the Muskrat Falls dam after impoundment
cannot be ruled out.
Determining
the North Spur dam safety factor is essential, in order to avoid both a
financial disaster for NALCOR, and a fatal disaster engulfing the communities
downstream of the Muskrat Falls Dam. Due to the deep
deposit of quick clay below the North Spur, a failure would leave the Muskrat
powerhouse high and dry, with no possibility of an economic repair.
Given the
enormous human and economic cost of such an event, I strongly encourage you to
give this issue your full attention.
The point I
am trying to make is that the existing design is based on a discredited
procedure. To bolster confidence in the design, it would be invaluable for someone familiar
with Bernander's methodology review the work and determine the safety factor
using the Bernander procedure. The cost, at something less than $50,000, would
be insignificant compared to a failure.
For all I
know, the design may be safe, but added reassurance would assuage the
anxiety of the residents downstream, since they are convinced that the North
Spur dam is not safe.
Sincerely,
James L. Gordon P.Eng. (Retired)
James L. Gordon P.Eng. (Retired)