Guest Post By PlanetNL
PlanetNL6:
Latest Bernander Report on North Spur Leads to Terrifying Conclusion
If there is one topic in the whole of Muskrat that is truly
clear as mud, it’s the North Spur. Equally murky is Nalcor’s plan to use this
natural formation across the Churchill River as the largest dam holding back
the reservoir.
PlanetNL’s agenda has deliberately left this challenging topic
to others, choosing instead to concentrate primarily on the financial disaster
that awaits the people of this Province upon Muskrat completion in 2021. The others who have written on the North Spur
are better researched on the subject and have written passionately about the
North Spur on this blog and elsewhere.
PlanetNL would not write about the North Spur now except that
a new report issued by Dr. Stig Bernander clearly implies that a different disaster
appears imminent and will be realized before project completion. It’s no longer necessary to guess if, when or
how the North Spur may fail. Dr.
Bernander has presented us with the necessary failure analysis and Nalcor is
scheduled to meet the conditions required no later than November 2019.
It would be hard to argue that anyone could exceed Dr Stig
Bernander of Sweden as the foremost engineering authority on the behaviour of
the glaciomarine clays that underlie the North Spur. Leading Muskrat critic, Cabot Martin, in his
persistent quest to learn more about these materials and the landslides they
create, met Dr. Bernander in 2013 at a conference in Quebec. Thanks to the huge efforts of Cabot Martin
and the Uncle Gnarley blog, the public has received several papers prepared by
Dr. Bernander critiquing Nalcor’s approach to stabilizing the soils of the
North Spur.
 |
| From "North Spur Landslide and Instability Problem" Presentation by Cabot Martin March, 2013 |
Having read the prior reports and information these last few
years, many of us may have thought the North Spur could possibly fail - or
maybe it wouldn’t. Perhaps it could be a
random event many years down the road.
Perhaps it could be triggered by an upslope landslide from the suspect
land to the North. Another scenario is
an upstream slide triggered by raised river levels setting off a large wave
that may have a terrible impact on the North Spur dam. Or perhaps the Spur dam might be plagued by relatively
slow leaks and that actions to fix them, costly though they may be, could be
taken to mitigate them.
Dr. Bernander’s latest report, however, yields a moment of
clarity. The paper entitled “Summing Up
of North Spur Stability Issues”, issued November 26, 2017, is a challenging
read. It is not meant to stand alone but
it references other Bernander reports and it also directly addresses
deficiencies in Nalcor reports. The
referencing of other documents and the inherently highly technical language
make it a tough read even for engineers with some familiarity of geotechnical
issues. It therefore took a few readings
before it became clear what Dr. Bernander’s latest report was indicating.
It is a necessary convenience to readers, that the following
section is presented to summarize in relatively simple language the key
technical points of the report – this interpretation is believed to be faithful
to Dr. Bernander’s assessment of the North Spur.
A Summary
Interpretation of the November 2017 Bernander Report
Of primary concern is that project engineering reports by
Nalcor and their Consultants did not include a precise soil structure model and
they did not use soils data representative of the Churchill River Valley. Instead,
their models were based upon different formations found in Eastern Canada with
which the Project Engineers were familiar.
The key issue at variance is that Dr. Bernander finds that the
glaciomarine clays of the North Spur are virtually identical to those he is very
familiar with in Northern Europe and they exhibit properties much weaker than
those used in the Nalcor basis of design.
First is that the glaciomarine clays are especially saturation sensitive
and second is that under high strain, even absent excess moisture, the clay material
can suddenly and dramatically lose its strength or resistance to loading.
 |
| Dr. Stig Bernander |
To reduce saturation, a common engineering solution for the
Eastern Canadian soils and applied at Muskrat has been to install a water
penetration barrier known as a cut-off wall to limit water seepage and behind
it install a number of deep pumped wells behind to limit saturation below
critical levels. The Nalcor design for
the stronger soil model therefore utilizes far fewer pumped wells at much wider
spacing than would be dictated by a model using weaker clay characteristics.
The weak clay will have several times less than the minimum shear
strength required to withstand the heavy load of the full reservoir. The deflection and compression of the North
Spur, as the immense weight of water grows upon it, will introduce substantial
shear strain. At a certain strain level,
these weak clays don’t just deform, they turn into a liquid. Bernander calculates that full reservoir
impoundment at the normal operating level of +39m above sea level (36m higher
than the downstream level) will surpass the strain limit by a factor of 3. The point of onset of soil failure (factor of
1) is calculated to occur at a reservoir level of +32m.
 |
| Source: Cabot Martin Presentation March 2013 |
Also to be considered is the impact of dynamic movement as
soils settle and shift under pressure. The
Project Engineers relied on a modelling type that does not capture dynamic strain
effects that can transform the clay into a liquid. Despite the slow filling of the reservoir,
the natural varied soil type and layers within the Spur will react differently
to the rising pressure. Many sudden compressive
movements and deflection should be expected within the North Spur as it is not
a homogenous engineered structure. These
dynamic jolts are likely to be sufficient triggering events to cause soil
liquefaction in localized areas. The
concern of inadequate water removal will lower the strain capacity of the
sensitive clay.
Related to this Post:
muskratinfo.ca A Web Site hosted by Cabot Martin featuring several Presentations on the "Quick Clay stability problem at the North Spur, Muskrat Falls
https://www.youtube.com/watch?v=3q-qfNlEP4A The Rissa Landslide - Quick Clay in Norway (Editors's Note: this is a must view.)
In addition to weak soil types is the importance of the
orientation of the layers of these soils which run broadly across the North
Spur while sloping downward from the upstream side toward the downstream
side. A localized failure zone, as
predicted in the paragraph above, will rapidly propagate throughout an entire material
layer. Gravity will be more than
sufficient to allow masses of material to move along the downward slope.
 |
| Source: Cabot Martin Presentation March, 2013 |
The report concludes that the Nalcor engineering approach is critically
deficient and must be revisited using the proper modelling technique and
revised with more accurate soil characteristics.
Additional
Interpretation by Jim Gordon
The root issue of the Bernander critique is in quantifying the
characteristics of the soils of the North Spur. To his credit, Bernander has visited the site
and has studied the numerous Nalcor reports and data. He finds the materials to be categorically
the same as the glaciomarine clays he has worked with and studied extensively
in Northern Europe: materials whose properties he thoroughly understands. Nalcor on the other hand has defended its
engineers who have chosen to classify it as the same type of material they are
familiar with in Eastern Canada and of which they assume considerably higher
strength.
In seeking comment on a draft of the above report summary, retired
engineer Jim Gordon, among the most experienced hydro dam engineers in Canada, and
author of several posts on the North Spur on this blog, was asked to review and
comment. He came back with these insightful comments:
“Nalcor
used partial soil characteristics based on the local geotechnical data.
However, they did not undertake sufficient tests to determine the soil
characteristics under load. In other words, the stress-strain tests were not undertaken,
and instead, stress-strain data from other similar soils was used to obtain
(assume) a linear relationship.
This is
the principal error found by Bernander. However, Bernander also assumed soil
characteristics based on his experience with similar Swedish sensitive clays,
which indicate a non-linear relationship at high strain (deformation) levels,
with a large reduction in strength from that based on a linear relationship, hence
failure.
Stress-strain
tests are essential to determine who is correct, and my opinion is that
Bernander is correct.”
 |
Site of massive February 2010 landslide located upstream from Muskrat Falls caused by liquefaction of glaciomarine clays (also known as "Quick Clay")
Source: Cabot Martin Presentation March, 2013
|
Dare We
Conjecture the Collapse Scenario?
If Bernander’s view is correct that Nalcor’s design approach has
substantially overestimated the strength of the glaciomarine clays, then Nalcor
is steadily marching toward a disaster of catastrophic proportions. It will happen in late 2019 as Nalcor raises
the reservoir toward its maximum design level of +39m. Filling likely begins slowly throughout the
summer and fall, intended to be complete before the river freezes over.
While Bernander states a reservoir level of +32m could exceed
the capacity of the sensitive glaciomarine clays, the dynamic effects could
trigger a major landslide at a slightly lower level. Alternately, if the clays are somewhat
stronger than Bernander assumes, the failure could happen at a higher
elevation, serving to release an even greater amount of water.
The failure of the North Spur would be dramatic and rapid. The layering of soils tilted toward the
downstream side would fail on a very broad front, presumably beginning at the
downstream side but rapidly progressing its way up the downstream slope. At some point the landslide will be met by the
positive force of the reservoir water breaking through the weakened dam. The onrush of water would carve its way not
only widely through the Spur, but it would deeply gouge out the soft soils of
the Spur. The post-failure upstream river level would likely drop by 14 m to
meet the downstream level.
The potential 14m drop would have a devastating effect on the
River for many kilometers upstream. The
substantial lowering of the river would increase water velocity, eroding the river
bottom. Numerous landslides of freshly exposed
riverbanks, made of the same soft and sensitive soils, would add to the mass of
silt sent downstream and into Lake Melville.
The sudden release of water downstream of the dam would
quickly scour the riverbanks and overflow all low-lying areas. Potential damage to inhabited areas could be
difficult to predict in its entirety as the massive amount of soils and debris
carried in the water could create overland flooding in areas not immediately
anticipated.
Who Can
Intervene?
At this point in time, after being challenged on this issue
for many years, it is illogical to expect Nalcor to change its position – they
deny any error on the soils. The same
can be said of the Provincial Government which, despite a change of Party,
appears joined to Nalcor’s hip. The remaining
formal body with a large stake at risk is the Federal Government which has
remained incredibly silent but evidently supportive of the Muskrat
project. The immense and foreseeable
disaster of dam failure at Muskrat in the weeks before a 2019 Federal election
could be fatal to the current Government.
It is in their interest to order a thorough review of the geotechnical
design of the North Spur and to begin controlling their political as well as
capital risk.
Failing that, the people of Central Labrador have been warned
to prepare for the worst. Or they can
cling to the hope Bernander is wrong and Nalcor is right.
________________________________________Editors Note:
The text of Dr. Stig Bernander's Report will be posted on Monday.