Letter: North Spur — a risky business

Published on April 28, 2017

Work on the North Spur across the river from the Muskrat Falls dam site is shown in this file photo.

©James McLeod/The Telegram file photo

Generally speaking, shear stress is where the stress/force within a soil layer runs parallel to its surface. Other factors being equal, the steeper that a soil layer’s slope is, the greater the shear stress. When a soil layer’s shear stress is high enough that it reaches the shear strength of that soil, a landslide can occur.

Just out from the shoreline of the downstream slope of the North Spur is an underwater deep hole that drops off to a depth of about 200 feet below the toe of the North Spur’s downstream slope.

So, where is Nalcor’s first and foremost focus on safety, and government’s much ballyhooed evidence-based decision making?

This deep subsurface depression has, in places, a slope inclination of about 80 per cent (a slope inclination that is more than double what Nalcor considers safe for the North Spur above-surface slopes).

While the North Spur’s original stabilization plans called for that deep hole to be filled in, Nalcor’s final plans (and the existing North Spur stabilization works) has left that deep hole untouched.

One of the key reasons that Nalcor concluded that a progressive landslide failure “will never be initiated” at the base of that deep hole, as Nalcor’s Progressive Failure Study states, is because Nalcor’s “numerical analyses” showed that the shear stress at the base of that deep hole “is only about 60% of the minimum estimated undrained shear strength” (emphasis added).

Now we all know how reliable Nalcor’s “estimated” oil prices were, we all know how reliable Nalcor’s demand forecasts/estimates were, we all know how legally reliable Nalcor’s water management agreement has been, and we also all know that a life and death decision based on an “estimated” shear strength is not evidence-based.

In fact, the actual evidence points to the potential for soil liquefaction and flowslides.

The 2014 Hatch “Cold Eyes” Review stated that Liquidity Index “Values in excess of 1 are an indication of the potential for both liquefaction and flow type failures,” and the lower clay layer evidence shows that the upper range of Nalcor’s 123 Liquidity Index test results for the Lower Clay layer is “2” (double the safe Liquidity Index value of “1”).

Furthermore, the extent to which the established Liquidity Index/Shear Strength relationship applies to the Lower Clay layer shows that a Liquidity Index value of 2 correlates to a shear strength that is 10 times lower than the point at which flowslides can occur.

Yet, and notwithstanding that mathematically up to about half of the Liquidity Index test results may exceed 1 — indicating “the potential for both liquefaction and flow type failures,” Nalcor’s Progressive Failure Study concludes that because the Lower Clay layer “has a typical (average) liquidity index of 0.6 ... there would not be retrogression and flowslide.”

So, on the one hand we have “evidence” that points to a potential risk, and on the other hand we have Nalcor’s inappropriate use/reliance on “average” geotechnical test results and an “estimated” shear strength to conclude that “...progressive failure ...will never be initiated”.

So, where is Nalcor’s first and foremost focus on safety, and government’s much ballyhooed evidence-based decision making?
And if this whole $12-billion “investment” should fail, whose best interest has the newly appointed Consumer Advocate, the newly appointed members of the Oversight Committee, and the minister of Justice and Public Safety been really looking out for?

 

Maurice E. Adams
Paradise