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Dynamic calculation for the dry closure of Almagrera tailings dam
Calcul dynamique pour la fermeture à sec du barrage des stériles d’Almagrera
Justo J.L., Morales-Esteban A., Durand P., Vázquez-Boza M.
University of Seville, Seville, Spain
Jiménez F.A.
Egmasa, Seville, Spain
Rossi E.
Politecnico di Milano, Milan, Italy
ABSTRACT: An original model, including dynamic calculation, has been developed for the dry closure of Almagrera tailings dam
and is described herein. A dynamic analysis of a structure requires the previous definition of the accelerograms and the structure
characteristics. A probabilistic method for selecting calculation accelerograms is presented in this paper. First, the probabilistic hazard
equation for site is solved. Based on the hazard curves obtained, the uniform seismic hazard acceleration response spectrum
(USHARS) is constructed for the location, according to the type of soil and the required hazard level (exposure time and exceedance
probability). Then, calculation accelerograms are selected. Based on this methodology, real accelerograms, for a return period of 975
years, have been obtained.
RÉSUMÉ : Un modèle original, développé pour la fermeture à sec du barrage des stériles d’Almagrera, est décrit ici. L’analyse
dynamique d'une structure nécessite la définition préalable des accélérogrammes et les caractéristiques de la structure. Une méthode
probabiliste pour la sélection des accélérogrammes de calcul est présentée dans cet article. Tout d'abord, l'équation probabiliste des
risques pour l’emplacement est résolue. Basé sur les courbes de risque obtenues, le spectre de réponse d’accélération de risque
uniforme est construit pour l'emplacement, selon le type de sol et le niveau de risque souhaité (temps d'exposition et probabilité de
dépassement). Puis, les accélérogrammes de calcul sont sélectionnées. Sur la base de cette méthodologie, les accélérogrammes réels,
pour une période de retour de 975 ans, ont été obtenus.
KEYWORDS: Tailings dam, dynamic calculation, uniform seismic hazard acceleration spectrum
1 INTRODUCTION
In Europe, there are many abandoned mines. Nowadays, when
permission is granted for opening a mine in any country of the
EU, a closure plan (including financing) must be presented by
the mining company (ITC 2000), but it was not so in the old
times. The point is that, up to now, only a small number of the
possible closures has been undertaken owing to economic
reasons.
2
TAILINGS DAMS INVENTORIES AND FAILURES
The recent (5 October 2010) Ajkai Timfoldgyar dam failure
(Fig. 1) poured 700,000 m3 of bauxite ore and formed a flow
that struck three villages in Hungary.
Figure 1. Ajkai Timfoldgyar dam failure.
This accident, jointly with the catastrophic failures of Stava,
Los Frailes and Baia Mare tailings dams, has emphasized the
catastrophic consequences that tailings dams’ accidents in EU
and the rest of the world might cause, and the need for safer
design methods.
Rico et al. (2008) have compiled a corpus of 147 cases of
worldwide tailings dam disasters, from which 26 are located in
Europe.
Davies & Martin (2000) estimate there are 3500 appreciable
tailings dams worldwide. According to Davies (2002) during
the last years, there have been from 2 to 5 “major” tailings dam
failure incidents. Referred to the worldwide inventory of 3500
tailings dams, equates to an annual probability between 1/1750
and 1/700, compared with 1/10000 for conventional dams.
Furthermore, these failure statistics are for physical failures
alone. Tailings impoundments can have environmental “failure”
(e.g. leaks) while maintaining sufficient structural integrity.
Table 1 shows the inventory of tailings dams and ponds in
extractive industry in Spain. Notice the large number of
abandoned structures.
Table 1. Inventory of tailings dams and ponds in extractive industry in
Spain.
Volume of residues (m
3
)
323 million
Number of structures
986
Dams
610
Structures
Ponds
378
Active
385
Abandoned
535
Restored
54
Present state
Closed
24
3 SAFETY FACTORS REQUIRED FOR SPANISH
LEGISLATION
Three kinds of actions are considered according to its risk and
permanence. Normal actions are persistent actions; accidental
actions are limited duration actions: e.g. rapid drawdown or
earthquakes. Extreme are actions that rarely occur. The safety
factors are indicated in Table 2.
J st de J.L., Morales-Esteban A., Durand P., Vázquez-Boza M.
