519
Stability of chilean’s tailings dams with the Panda® penetrometer. Experiences of
the last 10
th
Dix ans d’études de la stabilité des barrages de résidus miniers chiliens à l’aide du
pénétromètre Panda®
Espinace R., Villavicencio G., Palma J.
Grupo de Geotecnia. Escuela de Ingeniería en Construcción. Pontificia Universidad Católica de Valparaíso, Chile.
Geotecnia Ambiental, Chile.
Breul P., Bacconnet C.
Institut Pascal – Polytech’Clermont-Ferrand. Université Blaise Pascal, Clermont-Ferrand, France.
Benz M.A., Gourvès R.
Sol-Solution Géotechnique Réseaux, Riom, France.
ABSTRACT: In Chile, since the beginning of the 20
th
century, about 40 cases of mechanical instability of the tailing dams have been
reported mainly due to liquefaction, slipping of banks or settlement. In order to solve this problem, a scientific and technological
cooperation has been established in 2001 between the geotechnical of groups at the Catholic University of Valparaíso (Chile) and
Blaise Pascal University Clermont-Ferrand (France) whit the support of two companies, Sol-Solution in France and Geotecnia-
Ambiental in Chile. This article presents the main results that have allowed to propose a methodology for control and diagnosing of
tailing dams and its application in the medium mining sector. It is based on in-situ determination of geomechanical parameters
(internal friction angle and density index) using the Panda® lightweigh penetrometer in order to characterize the constituent materials,
the variability of these materials and their implementation in the works. Finally, this methodology allows taking into account this
variability in the study of stability and the risk of liquefaction of these structures in a probabilistic approach.
RÉSUMÉ: Au Chili, depuis le début du XX
e
siècle, environ 40 cas d'instabilité mécanique de ces dépôts, principalement par
liquéfaction, glissement des talus et tassements, ont été rapportés. C’est dans ce contexte et pour apporter une réponse à ce problème,
qu’une coopération scientifique et technologique a été établie en 2001 entre les groupes de géotechnique de l’Université Catholique
de Valparaiso (Chili) et de l’univeristé Blaise Pascal Clermont-Ferrand (France), avec le soutien des entreprises Sol-Solution (France)
et Geotecnia Ambiental (Chili). Cet article présente les principaux résultats qui ont permis de proposer une méthodologie pour le
contrôle et le diagnostic des barrages de résidus miniers de relave ainsi que son application au secteur de l’industrie minière moyenne.
Elle s’appuie sur la détermination in situ des paramètres géomécaniques (angle de frottement interne et densité relative) à l’aide du
pénétromètre Panda® en vue de caractériser les matériaux constituants, de la variabilité de ces matériaux et de leur mise en œuvre au
sein des ouvrages. Finalement, cette méthodologie permet de prendre en compte cette variabilité pour l’étude de la stabilité et du
risque de liquéfaction de ces ouvrages dans une approche probabiliste.
KEYWORDS: soils and site investigation, structures in seismic areas.
1 INTRODUCTION
Mine tailings are frequently stored in dams. This is the case for
copper for which the coarse fraction (fine sands) of the tailings
form the body of the dams, while the fine saturated fraction
(sludge and silts) is poured by cycloning into the reservoirs of
the dams thus formed.
Chile has a very large number of tailings dams built in this
way. Due to the construction methods and materials used, these
dams comprise failure mechanisms such as loss of stability,
liquefaction, and internal and external erosion leading to major
risks for the populations and their environments. Such risks are
highlighted by the accidents that have occurred around the
world and recently in the case of failures occurring during the
earthquake of 27 february 2010 in Chile, with fatal
consequences (Dobry and Alvarez 1967, ICOLD 2001, GEER
2010). In order to manage these risks, it appears necessary to
employ a probabilistic approach to predict their behaviour
during construction and after closing. However, applying such
an approach in practice at present is limited by the difficulty of
managing the data (random variables and stochastic fields) to be
introduced in the reliability calculations for the limit conditions
involved and conditioned by the relevance of the probability
models chosen to represent the variability of tailings dam
properties (Villavicencio et al. 2011). This is the reason why,
this article presents an approach of estimating calculation
parameters (friction angle
’ and density index ID%) governing
the stability of these dams, and its variability from dynamic
penetration tests. Then models are proposed for all dams
composed of the same mine tailings types, making it possible to
link a probability law to the calculation parameters
’ and ID%.
This method, applied to Chilean dams constructed from copper
mine tailings, proposes a single model for all tailings dams so as
to associate a probability law to the
’ and ID%.
2 ESTIMATION OF THE DENSITY INDEX (ID%) AND
THE FRICTION ANGLE (
’)
1.1
The objective
In mine tailings with non plastic fine particles (size < 80 µm)
ID% and
’ are very important parameters, related to the in situ
penetration strength (N, qd, qc, etc), the input parameter of
static and dynamic stability models and for the evaluation of the
liquefaction (Troncoso 1986). These parameters are greatly
influenced by the origin and mineralogy of the particles, by the
physical characteristics and state of arrangement of the grains
determined by the state of compacting and by the extent of
stresses in-situ (Bolton 1986).
The methods used to implement mine tailings lead to the
prevalence of stratified internal structures that can be
heterogeneous. This can result in variations of resistance
properties, especially
’ and ID%, as a function of depth. Thus
it is important to estimate the values and variability of these
