LUIS VALENZUELA P, RAMON VERDUGO A, JOSE CAMPANA Z & CARMEN G OPAZO A


Las Palmas tailings dam experienced the most catastrophic seismic failure, triggered by the 2010 Maule earthquake. The mine was operational from the early 1980s until 1997, when mining activity finished, and the tailings pond was partially covered with a 15cm layer of gravelly material. The tailings deposit consisted of two dams (a lower one and an upper one). Both dams were constructed in stages using the upstream construction method. During the Maule earthquake the tailings deposits retained by the lower dam of Las Palmas liquefied, the eastern portion of the tailings impoundment nearest the mine facilities was breached, and a tailings volume in excess of 100,000m3 flowed a distance of about 0.5km, killing four people in a house that was buried under 4m of tailings (Figure 40).


Figure 40. Failure of Las Palmas tailings dam during the Maule earthquake of 2010[14]


The tailings liquefied again (less severely) during the aftershocks of M > 5.0. During these aftershocks new evidence of sand boils and ejecta, as well as water draining from the sub-surface, was observed. A number of these liquefaction features were observed in the terraces associated with the upstream construction method at the western end of the tailings impoundment area, even though no full breach of the structure occurred at that location. Field surface wave measurements conducted on the non-failed tailings indicated shear wave velocity in the order of 250m/sec, and dynamic cone penetrometer soundings performed in both non-failed and failed tailings materials yielded blow counts of about 10[14].


6.2 Tailings dams built after 1965


After 1965 no upstream tailings dams have been built in Chile, although a few older upstream tailings dams are still in existence but not in operation. Gradual removal, and in some cases re-mining, of the tailings is underway. Table 4 presents a list of the main tailings dams built after 1965. All of them use the downstream construction method (explained in Figure 34) except for El Torito dam which at a certain height changed from the downstream to centerline construction method. This table does not include those tailings deposits that do not necessarily require a dam – or at least an important dam – such as deposits with paste tailings or filtrated tailings.


222 DAM ENGINEERING Vol XXXI Issue 3


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