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Mount Polley dam breach legal consequences will be heard for years to come. Imperial Metals (Vancouver, B.C., Canada), the owner of the breached dam, is reportedly suing the engineering companies Knight Piesold (KP) and Amec Foster Wheeler (AFW, formerly known as AMEC) for negligence and breach of contract over the August 2014 tailings dam failure at Mount Polley (B.C., Canada). The breach spilled 24Mm3 of tailings and water into nearby environment.
Reportedly Imperial Metals claim bears on:
We will of course not take any position, but discuss some elements raised by the three-pronged claim summarized above.
Decades ago in Switzerland, where we founded Riskope’s predecessor company, geotechnical engineers had a common rule of thumb. That was that investigations (boreholes/observation pit) should at least be as deep as the projected superstructure was tall (unless competent bedrock was encountered…). Even a small building required 5 boreholes/pits (one in each corner, one in the middle). We have rarely seen dense enough, deep enough boreholes performed for tailings dams. Standard practices evolved towards less safe conditions, while dams became bigger. Certainly 5 boreholes for a small building may have been too much, but one would certainly be too little. It’s a matter of reducing uncertainties in the project.
Our Alma Master (EPFL, Lausanne, Switzeralnd) mission was to foster dam engineering and train future engineers to build the largest dams in the world. There a geotechnical professor repeated simple, but efficient mantras. One of them was: “beware steep slopes, be frightened of flat slopes.” We have since seen numerous accidents occurring on flat slopes. The good old professor must have been right and apparently those mantras were lost. We know only one way to sharpen our decision making surrounded by uncertainties: perform probabilistic analyses.
As a matter of fact, the same professor used to say that there is not “one number fits all” factor of safety (FoS), but the selection of the magic number is a major endeavor. He brought Prof. Milton E. Harr (Purdue University) to Lausanne to teach about probabilities, reliability and probability of failure.
That was a life changer and we have build a career on those teachings. We are personally appalled many consider the ubiquitous FoS=1.3 as a “truth”. As a result, we keep showing whomever wants to listen that the probability of failure and FoS display a highly nonlinear relationship. Even a modest increase of the FoS means a lot in terms of reliability (generally with sustainable cost increases). These concepts seem so far from present day-to-day practice that some codes even accept FoS=1 under seismic conditions. This is equivalent to say that if a MCE hits a country, then it is ok that 50% of the tailings storage facility (TSF) are at limit state of breaching! I do not know any other method than probabilistic analyses to decide if 1.3 is reasonable or not, and in which conditions.
Finally, we get to the classic confusion generated by unclear use of risk statements. The “risk of the subsurface conditions” is not a risk. The unfavorable subsurface conditions are a hazard which may lead a structure built on them to deform and possibly collapse. If the deformation/collapse occurs there may be consequences (environmental, business interruption, H&S, etc.). The probability of that accident, with those consequences is the risk. We often forget or bias complex consequences into excessively simple statements due to these improper formulations.
Mount Polley dam breach legal consequences show it is time to “remember” where we come from. We are engineers and not lawyers arguing on words used in professional codes.
Our decisions have profound impacts on the world, society, then environment. Anthropocenic effects have already deeply modified the geosphere and our decisions have significant impacts on the anthropocene. They have to be compliant with geoethics awareness.
If we use quantitative risk assessment to polish our decision making throughout all the phases of a dam life, i.e. from investigations to design, construction and closure and properly communicate, among ourselves and to the general public, while avoiding any conflict of interest, then we will be going toward the right direction.