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When the Columbia River was dammed by glacial ice, sediments deposited in the deep valleys of northern Washington State. Amax sought to develop a molybdenum mine just off the Columbia in the Colville Tribe reserve. I was brought across to design the tailings impoundment at the selected site. I was brought across because preliminary surveys had revealed up to 30 meters of soft, unconsolidated mud filling the selected valley, and after all, I had just succeeded with a similar soil deposit in South Africa.
To contain the calculated volume of tailings from the proposed mine, the impoundment would have to be 1,000-ft high, an unprecedented height in 1980, but more common now. A quick calculation revealed that the rate of rise was so fast that no amount of expedited drainage of excess pore pressure would yield a fast enough gain of strength to provide the required stability. We had to find another way.
