Seismic Failures of Chilean Tailings Dams

The Chilean earthquake of March 28, 1965, affected a copper mining zone where there are many tailings dams. The writers visited ten locations and observed 22 dams, 11 of which were badly cracked or failed. Except for their sizes, almost all of the failed dams were similar; namely, they were constructed on rather low permeability soils by the hydraulic-fill method; with central ponds usually a few meters from the borders and with uncompacted sandy shells with exterior slopes of about 35○. The typical failure was produced during or immediately after the quake, and included the slope slide and the flow of the liquefied core. The behavior of each dam is described, and core and shell sampling information is given. The failure of the El Cobre dams, where 2,400,000 tons flooded the valley, is studied in more detail, and the safety factors are evaluated. It is concluded that tailings dams of this kind are seismically unstable, and some recommendations are given.