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.________________________________________
The text of Dr. Stig Bernander's Report will be posted on Monday.