Geoprofessional Business Associations (GBA) Tailings Engineer-of-Record (EOR) Task Force published a Business Brief to inform and educate Member-Firms of the ever-increasing levels of risk associated with tailings dams.
This webinar will continue from the Introduction to CPT and take a more in-depth look at using the CPT to evaluate soils for liquefaction. It is part one of a three part series on using the CPT for liquefaction. This will cover mostly the introduction and theory.
This webinar continues on from CPT for Soil Liquefaction, part 1 and discusses using the CPT to evaluate flow liquefaction.
This webinar will continue from parts 1 and 2 of using the CPT to evaluate soils for liquefaction and focus on real-world examples using the software program Cliq. CLiq is a commercially available software program available from Geologismiki: www.geologismiki.gr
Dr. Robertson's technical papers on Cone Penetration Testing (CPT) and liquefaction
South32 Worsley Alumina Pty Ltd operates several bauxite residue storage facilities at their refinery in Western Australia. The bauxite residue slurry is thickened and pumped onto the storage facilities which are constructed on an upstream basis using compacted earthfill embankments. BRDA 5 is the newest of the residue storage facilities, established in 1999, and has a current maximum height of embankment slope of 42 m, of which a compacted earthfill starter embankment makes up the first 22 m. Since 2010, the residue has been treated after deposition using amphirols, which assist in dewatering and compacting the residue. As part of their residue management commitments, Worsley undertook a dam break analysis entailing a review of all available geotechnical testing data, a fault-event analysis to evaluate the probability of removal of support to the residue through slope instability, overtopping, geotechnical piping or failure of a buried structure leading to liquefaction of the residue and a dam break. To model the flow of the liquefied residue, pilot-scale dam break testing was carried out from which estimates of the rheology of the residue were made. The rheology has been incorporated into a flow slide model that applies stream power entropy theory to define the energy changes due to viscous effects and frictional resistance. Benchmarking of the results against modelling using computational fluid dynamics has been made. This paper presents an overview of the dam break assessment process and results that covers a liquefaction potential assessment, a semi-quantified risk assessment based on a fault-event analysis approach, rheological testing of liquefied consolidated residue in a specially developed box rheometer and probabilistic modelling of the dam break, the outflow hydrograph, and the flow inundation areas. It is concluded that incorporation of rheology representative of liquefied consolidated residue in dam break modelling results in significantly reduced prediction of inundation area.
This manual presents guidance on procedures for use in the engineering design, construction monitoring, operation, and inspection of coal refuse impoundments and embankments in the United States.
Over the last few years, there has been a substantial increase in the degree of complexity of requirements regarding the licensing of tailings dams in Brazil. The stacking of filtered tailings is currently proposed as an alternative solution for tailings storage facilities; however, there are numerous challenges to understand and manage these structures in regions of high rainfall and high disposal rates. In this context, the objective of this article is to evaluate the liquefaction susceptibility of filtered iron ore tailings, based on field (piezocone) and laboratory tests (characterization and triaxial compression), both performed at an experimental landfill, located in the Iron Quadrangle (Quadrilátero Ferrífero), Minas Gerais state, Brazil. Therefore, a few methodologies were used to evaluate liquefaction susceptibility by means of the critical state theory, furthermore the fragility index of the material were also evaluated. Results indicated that the constructive method used in the experimental landfill (i.e., compaction energy, moisture and layer thickness) resulted in variability in the in-situ void ratio, indicating susceptibility to liquefaction for materials on depths greater than 0.75 m from compaction surface. In addition, from laboratory tests it was possible to determine the critical state line of the filtered tailings.
Engineer of Record (EoR) is a simple and resolute concept that is applied throughout the western world for civil works construction. But how can the EoR concept be applied to a transient design one that implements the observational approach with a construction life that covers decades, often exceeding a design engineers career or lifetime, and one that is directly impacted by changes in the state of practice? Tailings storage facilities (TSFs) are the necessary result of successful mining, milling and/or power production. However, unlike conventional water storage dams that are viewed as an asset by their owners, TSFs and the dams that retain them are an ever-expanding and undesirable yet necessary and ongoing liability throughout the life of operations and into perpetuity. In the wake of the Mount Polley (Canada) tailings dam failure in August 2014 and the Samarco (Brazil) tailings dam failure in November 2015, the efficacy of the EoR for TSFs has been brought into question globally. GBAs Tailings EoR Task Force is leading this important initiative in the United States.
While it is trivial to pour a thickened slurry into various forms of moulds or vessels to prepare for element testing, questions remain over whether the density that is reproduced will be relevant to in situ conditions. In particular, preparation of triaxial samples from thick slurries is particularly challenging as a number of steps are required to enable such samples to be free-standing, with each one of these steps potentially leading to slight disturbance and thus densification of the sample. Where such densification occurs, it would result in the element test results being non-conservative. This could have important implications with respect to expectations of the contractive (and potentially liquefiable) or dilative response of the tailings in situ. To investigate these issues, a series of slurry-deposited triaxial tests was carried out using a non-segregating slurry. As test methods were refined during the program, the amount of disturbance applied to the specimen was reduced. However, comparison of the triaxial tests to slurry consolidometer tests indicated that, regardless of efforts made, the triaxial tests achieved denser states at a given amount of consolidation stress. This was found to be the case using any conceivable range of assumed geostatic stress ratio to interpret the slurry consolidometer results. This outcome is speculated to be a result of the quiescent conditions used in the preparation of a slurry consolidometer specimen, which only requires pouring and then application of vertical load, first using weights, then a load frame. The implications of the increased density seen in triaxial tests compared to the likely more realistic value seen from the slurry consolidometer are discussed. Alternative preparation methods to target this looser density range are briefly discussed.