The Telegram (St. John's)
Nalcor mum on questions about the North Spur
Let me say up front that I am all for Premier Dwight Ball’s oftexpressed policy position that his government will “open the books” on Muskrat Falls, and that he will make “evidence-based” decisions.
With this in mind, below are some facts, some preliminary evidence, related to the North Spur’s exposure to, and risk of large, retrogressive landslides:
• Portions of the downstream, below surface slope that is in contact with the lower quick clay layer has a grade ratio (vertical to horizontal) approaching 1:1.25 (80 per cent) — a grade that is near or higher than Nalcor’s chosen, above water level, worst case section B-B “reference case.”
• Based on the extent that the large downstream 1978 landslide retrogressed (ate into the narrowest part of the North Spur), the stability number for the downstream side of the North Spur would be 12.
• A stability number of 12 is twice as high as the stability number 6 — the number that engineering experts Mitchell & Markell say can allow large, retrogressive (multiple failure surface) landslides to occur in Eastern Canada.
• A stability number of 12 is up to four times as high as stability number 3. When the soil’s plasticity index is below 10, a stability number above 3 can allow large, retrogressive landslides to occur, and when the plasticity index is as high as 40 a stability number above 7 to 8 can allow large, retrogressive landslides to occur.
• All of Nalcor’s 123 plasticity index test results for the lower quick clay layer are below 40, and some below 10.
• Nalcor’s 123 test results for the lower quick clay layer show some liquidity indices that exceed 1.2 and correspond to shear strength values below 1 kPa (a liquidity index above 1.2 or an undrained remolded shear strength value below 1 kPA can allow large, retrogressive landslides to occur).
• Nalcor’s 123 liquidity index test results for the lower quick clay layer have some values corresponding to shear strength values that do not correlate with the normal liquid index/shear value relationship. This appears to be a significant and yet unexplained anomaly in Nalcor’s test results.
• Nalcor reports that some lower shear strength values were detected in the southern, narrowest section of the North Spur downstream toe — but that the data/analyses was “not retained.”
My request to Nalcor for the number, location and values of its North Spur shear strength test results has gone unanswered. Maurice E. Adams Paradise
“Nalcor reports that some lower shear strength values were detected in the southern, narrowest section of the North Spur downstream toe — but that the data/analyses was ‘not retained.’”