Tailings Impoundment Failures: Are Geotechnical Engineers Listening?

Abstract

Structural engineers are “technical cousins” to geotechnical engineers. The two groups have similar training in the fundamentals of mechanics and an equal ability to claim that the other “has it easy” in the design process. There can, however, be communication difficulties between the two. Speaking as an unbiased geotechnical engineer, the communication gap is personified by the structural engineer’s insistence that the ground is a linear-elastic material and geotechnical engineers are only useful if they will admit to such fact and provide a suitable subgrade reaction modulus at their earliest convenience. Alas, this is also expected while using factors of safety that are 50%, or lower, of those utilized for predictable materials like steel and concrete. Now, assume that structural engineers wanted to provide some more good-na tured fun for the i r geotechnical cousins. The nature of this fun would take the form of specifying the most challenging project conditions imaginable for the geotechnical engineer. Soliciting the assistance of learned geotechnical associates not aware of their evil intent, the structural engineers would conjure facilities for the geotechnical engineers to design and steward with the following characteristics: • All of the challenges of water retention dams (e.g. fluid storage with catastrophic results if such storage was unintentionally breached). • Cannot be breached upon project completion and must remain structurally competent in “perpetuity” (perpetuity is a long time). • Constantly changing in size and often reaching hundreds of millions of tonnes of material to utilize or store (and occasionally exceeding one billion tonnes). • Ever changing states of stress. • Typically under construction for at least 5 to 10 years but construction can be extended to periods of more than 50 or even 100 years. • Susceptible to brittle undrained loading response. • Contain real and perceived contaminants. • Have no ability to generate revenue for its owner (as opposed to a hydro-electric dam, for example) and so generally thought of in less than glowing terms as a necessary, but annoying, cost of doing business. • Seldom have owners that are familiar with all the key geotechnical issues facing these facilities and thus putting such responsibility on the consulting designer. Add to this long list of constraints the additional “just for fun” element that the factors of safety to be used are only marginally greater than unity. To meet the good-natured challenging scenario out l ined above, geotechnical engineers only has to note that many of us already deal with such challenges on a daily basis – these challenges are called tailings impoundments. Tailings impoundments are some of WASTE GEOTECHNICS