SAFETY PERFORMANCE OF DAMS IN CHILE’S HIGHLY SEISMIC ENVIRONMENT
the country and was inspected by MOP in 2011. It was found to be in good condition[3], although no more details are available.
Cogotí dam is on the confluence of the Pama and Cogotí rivers, about 65km south of Ovalle City. It has a reservoir with a maximum capacity of 150Mm3. In the left abutment a lateral spillway excavated in rock – and without gates – allows water flow of 5000m3/sec. The dam is a concrete face rockfill dam (CFRD), completed in 1940, although the main body was completed earlier in 1938. The embankment, 160m long with a maximum height of 83m and a crest width of 8m, was built with rock from an adjacent quarry and placed in the dam without compaction. The upstream slope is 1.42-1.47:1 (H:V), while the downstream slope is 1.47-1.50:1 (H:V). A cross-section of the embankment is shown in Figure 30. In the first 15m, rock blocks with a maximum size of 1.5m were used, which were dumped by gravity at the dam site. Afterwards, the same material limited to a maximum size of 1.3m was placed by mechanical means, which induced slight compaction generated by the passing of trucks during construction. The technical specifications requested the application of abundant sluicing with water (water pressure of 60m) using a quantity of water equivalent to three times the volume of the sluiced layer. However, the available technical records of the construction indicate that most of the time the requested amount of water was not fully satisfied. Due to the construction procedure it is possible to conclude that Cogotí dam is composed of rockfill with poor densification.[17]
Figure 30. Cross-section of Cogotí dam[17]
The shape of the valley gorge is shown in Figure 31, where a non-symmetrical profile can be seen, with the right abutment less steep than the left one and with a change in its inclination. This narrow gorge is mainly constituted of andesitic rock. Three important structural alignments were recognized at the site of the dam: N450-75E0, E-W and N-S, which have been related to the leakage observed throughout the abutments and foundation of the dam.
Vol XXXI Issue 3 DAM ENGINEERING 211
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