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Risk minimisation in construction of upstream tailings storage facilities based on in-
situ testing
Minimisation du risque sur base d’essais in situ lors de la construction de digues de stockage des
résidus miniers par la méthode amont.
Fourie A.B.
University of Western Australia, Perth, Australia
Palma J.H., Villavicencio G., Espinace R.
Geotecnia Ambiental, Valparaíso, Chile
ABSTRACT: Tailings storage facilities (TSFs) in Chile are now built using the downstream method of construction, an approach that
was triggered by the failure of a number of upstream constructed facilities during or immediately after large seismic events. In
Australia, the upstream method continues to be used, because of the significantly lower cost and the perceived lack of a credible
seismic risk. The design of TSFs in Australia is moving towards the adoption of maximum credible earthquake (MCE) considerations,
particularly for closure, where the design life is increasingly expected to be ‘in perpetuity’. Recent research in Chile has shown the
viability of using a lightweight penetrometer, the PANDA penetrometer, as a tool for rapid, inexpensive and regular in-situ
determination of the state of deposited tailings. The PANDA has been calibrated against density measurements and is frequently used
to estimate the relative density, which is a useful indication of liquefaction susceptibility. This paper describes an approach for
managing upstream TSFs in Australia using the PANDA penetrometer for regular in-situ testing which, when coupled with the results
of laboratory compressibility measurements, can be used to predict the future state of tailings once buried to a significant depth.
RÉSUMÉ : Aujourd’hui les digues de stockage de résidus miniers (DSR) au Chili sont construites par la méthode aval, une approche
qui a été déclenchée par la rupture de plusieurs ouvrages contruits par la méthode amont, pendant ou immédiatement après
d’importants événements sismiques. En Australie, la méthode amont continue d’être utilisée, du fait de son moindre coût et de la
perception de l’absence de risque sismique crédible. La conception des DSR en Australie avance vers l’adoption de considérations
d’un tremblement de terre maximum crédible, en particulier dans le cas de fermeture de site minier, pour laquelle la durée de vie de
l’ouvrage est considérée être à perpétuité. Des recherches menées au Chili ont montré qu’un pénétromètre léger, le pénétromètre
PANDA, peut être utilisé comme outil pour déterminer l’état des résidus déposés dans les digues, de manière rapide, peu coûteuse et
régulière. Le PANDA a été étalonné vis-à-vis de mesures de densité et est utilisé fréquemment pour estimer la densité relative,
donnant ainsi une indication de la tendance à la liquéfaction. Ce papier décrit une approche de la gestion des DSR en Australie basée
sur des essais in situ réguliers à l’aide du pénétromètre PANDA qui, combinés aux résultats de mesures de compressibilité en
laboratoire, permettent de prédire l’état atteint par les résidus une fois enfouis à une certaine profondeur.
KEYWORDS: tailings, liquefaction, earthquake, penetrometer, in-situ testing.
1 INTRODUCTION
Tailings storage facilities represent some of the largest man-
made structures in the world, with many reaching heights in
excess of 100m and volumes in excess of 1 billion cubic metres.
The risks associated with these facilities are associated with the
storage of large volumes of material that is often at a very low
density. Loading due to events such as earthquakes can be
particularly devastating for these facilities, and there are
numerous records of failures of Tailings Storage Facilities
(TSFs) resulting from earthquakes. Nowhere has this been more
apparent than Chile. In Chile, failures have mainly occurred
due to seismic liquefaction, followed by slope instability and, in
some cases, overtopping. These failures have mainly been in
operational tailing dams constructed using the “upstream”
method, located in areas with an average rainfall regime,
including Valparaíso, Santiago, Rancagua (central zones) and
Maule (southern-central), (ICOLD 2001, Carvajaly and Pacheco
2005, and Rico et al 2008).
Failure of the El Cobre TSF, which occurred in 1965,
resulted in the deaths of more than 300 people. A consequence
of this failure was significant changes to the practice of tailings
management in Chile, with the tendency to adopt downstream
construction as the preferred method of construction. This trend
accelerated after the failures in Chile in 1985, which resulted in
further fatalities. Today, no new large TSF in Chile is
constructed using the upstream method, although this is not
necessarily true for some of the smaller operations. The very
large earthquake that occurred in 2010 (magnitude 8.8), resulted
in the failure (due to either slope instability or liquefaction) of
five TSFs, all of which had been built using the upstream
technique; of these, only one was operational at the time of the
earthquake. The other four could be considered to have been in
a state of closure, indicating that the risks associated with
upstream construction do not necessarily go away once
operations cease. There were no failures of downstream TSFs,
although anecdotal evidence suggests that in some cases the
contents of the TSF (consisting of cyclone overflow usually) did
indeed liquefy, but the downstream shells retained their
integrity.
2 AUSTRALIAN PRACTICE
The upstream method of construction is still the most
common method of TSF construction in Australia. This is
justified on the basis that levels of seismicity in Australia are
generally low and there have been no recorded failures of TSFs
in Australia due to earthquakes. The relatively low cost of this
approach is a strong consideration for its continued use.
Events such as the failure of a number of non-operating
TSFs during the 2010 earthquake in Chile have recently focused
attention in Australia on the adequacy of current design
approaches in the country. A number of peer review exercises
led by tailings experts from outside Australia have highlighted
potential concerns with techniques used for both design and
monitoring. In addition, the recently released ANCOLD
