SAFETY PERFORMANCE OF DAMS IN CHILE’S HIGHLY SEISMIC ENVIRONMENT


maximum horizontal accelerations recorded at the crest of the dam were 0.226g and 0.124g, in the E-W and N-S direction, respectively[17].


Taking advantage of the high seismic activity in the region, and the accelerometers installed on the crest and toe of Santa Juana dam, the natural period of the dam was evaluated through the transfer functions between the ratio of Fourier transforms of the motions recorded at the crest and toe.


The result of the Spectral Ratio is shown in Figure 34, where a peak is clearly identified at a period of 0.43sec, which would be associated with the fundamental period of the dam. It is important to mention that this value is consistant with the classical relationship for a dam (simplified as a triangular shape above a rigid half-space) if an average shear wave velocity of 700m/sec is considered for the compacted rockfill material[17].


Figure 34. Spectral ratio crest – toe, Santa Juana dam


5. Concrete Dams 5.1 Concrete gravity dams


There are only seven concrete gravity dams in Chile, with two of them constructed as early as 1911 in the northern region of the country: Laguna del Huasco dam (15m high), built by MOP and operated for many years by an irrigation association in the III Region. It remains in use but not in optimum condition; and Sloman dam (40m high) a private initiative that operated for many years under different hands for different purposes and today is abandoned and full of sediment, although with the structure apparently intact according to recent aerial photographs. There is no evidence to suggest that these dams have suffered any significant damage from earthquakes, but there is evidence that Laguna del Huasco did not suffer any damage from the Punitaqui earthquake of 1997 (Mw = 7.1).


Vol XXXI Issue 3


DAM ENGINEERING


215


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