Monday, October 1 Tuesday, October 2
Peter Robertson John Lupo
"Evaluation of Liquefaction in Tailings and Mine Waste:
An Update

Flow liquefaction can be triggered by either cyclic or static loading and is a major issue for tailings and mine waste structures.  Flow liquefaction can occur in any saturated or near saturated contractive soil such as very loose sands and silts as well as very sensitive clays. For failure of a soil structure, such as a slope or embankment, a sufficient volume of material must strain soften and show strength loss. Case histories have shown that when significant strength loss occurs in critical sections of a soil structure, failures are often rapid, occur with little warning, and the resulting deformations are often very large.  Case histories also show that most flow liquefaction failures occur in young, uncemented non-plastic or low-plastic soils that have a brittle strain softening response where peak strength is reached at small strains followed by rapid strength loss. Methods have been developed to evaluate if soils are either dilative or contractive at large strains based on Critical State concepts.  However, not all contractive soils are strain softening and not all soils that are strain softening have high brittleness.  Laboratory data, supported by field observations, shows that contractive sand-like soils become progressively more ductile with increasing stress.  In recent years, mine waste has been placed in an unsaturated state and evaluation of liquefaction in these deposits adds additional uncertainty.  This presentation will provide an overview on soil liquefaction and an update on the influence of high stress.  Case histories will be used to illustrate the main points.

"TSFs, Risk and the Human Element"

The risks associated with tailings storage facilities (TSFs) are often thought of technical issues, which for the most part is true (although there are social, environmental, and financial risks to be considered). However, the way we approach and manage risks requires us to adopt less prescriptive methods in favor of risk-based processes for the design, construction, and operation of TSFs. Intuitively, risk-based approaches should be more rigorous than their prescriptive counterparts, however adopting risk-based processes introduces the human element in the form of biases. These biases can complicate the risk-based processes resulting in a potentially flawed risk assessment.

Dr. Peter Robertson brings more than 40 years of experience as an educator, researcher, consultant and practitioner specializing in the areas of in-situ testing and site investigation, earthquake design of geotechnical structures, and soil liquefaction.  Peter is recognized as an expert both nationally and internationally in the areas of in-situ testing and soil liquefaction. He has been a consultant to various industrial clients and insurance companies in North America, Asia and Europe for projects involving liquefaction evaluation for major structures, stability of on-shore and off-shore structures, landslides, stability of natural slopes and tailings dams, and use and interpretation of in-situ tests.  He is the co-author of the primary reference book on Cone Penetration Testing (CPT).  He has also authored or co-authored over 250 publications as well a popular CPT Guide that is freely available via the several websites.  Peter has also assisted in the development of several inexpensive CPT-based interpretation software programs and has presented a series of free webinars in an effort to enhance education and practice.  Peter continues to provide private consulting to a wide range of clients Dr. John Lupo is a Senior Director of Geotechnical and Hydrology at Newmont Mining Corporation, located in Denver, Colorado, USA. He has over 30 years of experience in mining geotechnics. His experience includes deep open pit slope evaluations (+1 km), underground geomechanics, tailings storage facilities (slurry, thickened, paste, and filtered), heap leach facilities, waste rock dumps, water storage reservoirs, and plant site foundations. He has a broad experience in both civil and mining applications as well as heavy construction, project management, and water management planning.