SAFETY PERFORMANCE OF DAMS IN CHILE’S HIGHLY SEISMIC ENVIRONMENT


were built in 1951. According to the limited information available these dams were repaired in 1979 after a flood caused serious damage. The secondary dam is a homogenous earth dam with a much longer crest (1000m) than the main dam. This dam did not show any evidence of damage from the 2010 earthquake.[14]


The Coihueco dam experienced significant seismic deformations during the Maule earthquake. The dam, which was built in 1971, is located approximately 28km east of Chillán. It is a zoned earthfill dam with a crest length of 1040m and a maximum height of 29m (31m∗), as shown in Figure 16. Following the earthquake a portion of the upstream slope experienced failure that generated significant deformations and cracks, as indicated in Figures 17 and 18. Maximum vertical displacements of the upstream slope were observed towards the left abutment, reaching values close to 4m. Uniform clean sand (SP) ejecta was present at the toe of the upstream earth slump.


Figure 16. Coihueco dam design cross-section, significant damage during the Maule earthquake in 2010[14]


According to the analyses performed after the earthquake[14], the foundation consisted of layers of sandy gravels with low to medium non-plastic fines content, clayey silts of medium to high plasticity (MH) and silts of low to medium plasticity. A pseudo-static slope


stability analysis applied to non-circular surfaces was performed with both horizontal (Kh) and vertical (Kv) seismic coefficients, and Kv ≤ 0.5Kh. The results showed that failure (FoS ≤ 1) occurs for seismic coefficients: Kh ≥ 0.22 and


Kv ≥ 0.11. The authors concluded that “These values are consistent with the level of shaking experienced at this site and match well with values adopted in engineering practice for


evaluating the impact of large earthquakes (i.e. MCE) on earthen structures”.


Vol XXXI Issue 3


DAM ENGINEERING


201


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