SAFETY PERFORMANCE OF DAMS IN CHILE’S HIGHLY SEISMIC ENVIRONMENT


reported that the main damage occurred at the location where the intake structure becomes physically separated from the dam, indicating a possible structural drift and possible out-of- phase movements between adjacent structures[20]. There was a rise in the infiltrations coming from the upstream zone of both spillways, from 28l/sec in November 1984 to 78l/sec after the earthquake. At that time it was estimated that this was due to damage in the water tightness plaques caused by relative movements between the upstream spillways blocks during the earthquake, and a gradual diminishing of flow could be expected. The dam was designed in 1960 for a horizontal seismic coefficient of 0.12g. The critical load case was found at the time to be a transverse (upstream-downstream) earthquake with the reservoir empty. Although no dynamic analyses were performed before or after the earthquake, comparisons were made with the results of finite element analyses from a similar dam (Sir dam, Turkey). This comparison indicated that Rapel dam should have performed satisfactorily under seismic loads similar to those induced by the 1985 earthquake[20]. The Maule earthquake of 2010 also affected Rapel dam, but less intensively than in 1985, even though it was relatively near to the fault trace of the earthquake. The maximum PGA registered by an accelerograph located in the dam was 0.21g (horizontal). The joint between the two adjacent concrete blocks next to the left abutment of the dam showed a rise of 0.5mm. Seepage increased, as it did in 1985, along the right abutment; in this case from a normal 11l/sec to 40l/sec. Some concrete pavements at the dam crest cracked. It is understood that with time seepage returned to more normal values[20].


5.3 Rolled compacted concrete (RCC) dams


The 121m high Pangue dam, built in 1996 by the Endesa-Pangue company, was the first rolled compacted concrete dam to be constructed in Chile. The dam is in the VIII Region and relatively near to the fault trace and epicentre of the 2010 Maule earthquake, but no damage was reported as a consequence of this earthquake (the world’s 6th highest in terms of magnitude). Ralco dam (155m high), built by Endesa in 2002, is also an RCC dam. Located approximately 20km to the south of Pangue dam it is, as a consequence, also relatively near to the epicentre of the Maule earthquake. As with Pangue dam, no damage was reported as a consequence of this major earthquake.


Convento Viejo RCC dam (23m high) was built in 2006 in parallel with the Convento Viejo earth dam, forming the new Convento Viejo reservoir. It has the spillway and water discharge of the reservoir, and is also associated with a hydroelectric plant. This RCC dam, and the neighbouring earth dam, are located almost over the fault trace associated to the Maule earthquake, as shown in Figure 15. Although the earth dam suffered some damage, as previously mentioned, the RCC dam remained unaffected.


Mauro RCC dam (29m high) was built about 2006 by a mining company to store and deviate water from entering a tailings deposit. This dam was subjected to the Illapel earthquake of 2015 and although it is situated relatively near to the earthquake’s epicentre (around 80km), no damage was reported.


Vol XXXI Issue 3 DAM ENGINEERING 217


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