SAFETY PERFORMANCE OF DAMS IN CHILE’S HIGHLY SEISMIC ENVIRONMENT


The date of 28th March 1965 became a milestone in the practice of design and construction of tailings dams in Chile. Because of the failure of the El Cobre tailings dam which caused more than 200 fatalities and significant environmental damage, the construction of tailings dams built using the upstream method was legally forbidden (decree N°86 of 1970)[35], and this restriction has been kept until the present time (decree N° 248 of 2007)[36]. The failures that occurred after 1965 correspond to dams that were built before 1965 using the upstream method, or relatively new dams like Las Palmas, that had a substandard design and poor operation and abandonment conditions.


The El Cobre tailings dam is a system of three copper tailings deposits located approximately 10km from the town of La Calera, in the Valparaíso Region. The oldest ones (Old Dam and Small Dam) started operation in 1930, while the third dam (New Dam) began construction in late 1963. As a result of the La Ligua earthquake on 28th March 1965, the failure of two of the dams occurred, releasing approximately 2Mm3 of tailings, covering a distance of 12km in just a few minutes and killing more than 200 people, destroying the town of El Cobre located downstream[37,39].


In Figure 38 three aerial views of the El Cobre deposit are presented (two before and one after the failure), while in Figure 39 a cross-section of the Old Dam is schematically shown.


Figure 38. El Cobre tailings dams, before and after 28th March 1965[37]


Figure 39. Failure of El Cobre tailings dam (deformed scale)[37]


Vol XXXI Issue 3


DAM ENGINEERING


221


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