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Critical gradients for tailings dam design
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
2010 (English)In: Mine Waste 2010: First International Seminar on the Reduction of Risk in the Management of Tailings and Mine Waste ; proceedings of the First International Seminar on the Reduction of Risk in the Management of Tailings and Mine Waste ; 29 September - 1 October 2010, Perth, Australia / [ed] Andy Fourie; Richard Jewell, Nedlands, Western Australia: Australian Centre for Geomechanics, 2010, 23-32 p.Conference paper (Refereed)
Abstract [en]

Knowledge on tailings dams design is often derived from conventional earth- and rockfill dams mostly designed for relatively short service periods. Tailings dams often differ in structural design and service life, where a long term stability of 1000 years or more is demanded. One of the most important factors related to tailings dams stability and performance in long term perspective is the prevention from internal erosion, i.e. particle migration initiated by seepage pressure. Internal erosion is a process not yet completely understood; it is related to the seepage rate, which is in turn is connected to the hydraulic gradient, internal structure, particle size distribution etc. The hydraulic gradient is therefore crucial for embankment stability and prevention of particle migration for a given material, and a basic research question is: Does a maximum hydraulic gradient exist in a given material? If so, what maximum gradient can we allow for a tailings dam construction in order to prevent internal erosion with respect to the long term stability of the construction? The maximum, or critical, gradient is often related to slope stability problems, heave, or blow out. Such critical values differ from a critical hydraulic gradient for erosion problems inside the soil matrix. To be able to apply critical values on internal erosion problems, clear definitions and information on the origin of a given critical hydraulic gradient is needed. The paper presents a detailed literature survey on reported values of critical hydraulic gradients for the initiation of piping shows that values range between 4,8 and 14 %. These values are derived from laboratory tests and from experiences of conventional dam constructions, i.e. they have to be looked upon in a limited time perspective. The paper discusses the use of these values for tailings dams design. To take the long term aspect into account, natural analogies to dam constructions have been analyzed. These structures are formations from the last glaciation that have fulfilled the task of damming water. Such structures are especially interesting with regard to their obvious stability against internal erosion over long time periods. Such natural formations are analyzed and presented in the paper. Results show that they are stable under a hydraulic gradient between 2 to 5 %. Current guidelines on tailings dam design in Sweden allow a hydraulic gradient where both the long term stability of the construction and the possible degradation of the construction material is not taken into account. To ensure a long term stability of tailings dam constructions, a more thorough understanding of the critical gradient in long term perspective is needed, and a modification of the present design guidelines is suggested.

Place, publisher, year, edition, pages
Nedlands, Western Australia: Australian Centre for Geomechanics, 2010. 23-32 p.
Research subject
Soil Mechanics
URN: urn:nbn:se:ltu:diva-34815Local ID: 91c2cf70-cba5-11df-a707-000ea68e967bISBN: 978-0-9806154-2-5OAI: diva2:1008066
International Seminar on the Reduction of Risk in the Management of Tailings and Mine Waste : 29/09/2010 - 01/10/2010
Godkänd; 2010; 20100929 (isajan)Available from: 2016-09-30 Created: 2016-09-30Bibliographically approved

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