SAFETY PERFORMANCE OF DAMS IN CHILE’S HIGHLY SEISMIC ENVIRONMENT
consists of a core of fine soils with supporting shoulders made of gravelly sand. It is resting on fluvial soil deposits constituted from sandy soil materials. Both abutments are constituted by weathered granite that improves with depth. A plastic concrete wall, 80cm thick, was built through the fluvial foundation down to a maximum depth of 22.5m, but without reaching bedrock.
Figure 19. Aromos dam design cross-section
It has been described that near the end of construction some equipment accidentally sunk into the loose sand which had suffered localized liquefaction due to the vibrations produced by the equipment. This fact implied the development of a comprehensive geotechnical investigation which concluded that the foundation ground was liquefiable, so the dam requested a significant re-design. Due to economic reasons, no changes to the dam were performed, and only wells were constructed near the toe of the dam with the intention of providing a dissipation system for any excess pore pressure in case of dynamic loadings[17].
The dam did not suffer any serious damage during the earthquake of 1985, although the acceleration level around the dam is estimated in the range of 0.3g to 0.4g. The data showed that the earthquake induced in the embankment vertical settlements smaller than 10cm, which implied that the foundation ground did not suffer any major liquefaction. Therefore, new studies were carried out which concluded that the areas of low N-SPT (liquefiable sandy soils) are surrounded by areas with high N-SPT (no-liquefiable soils). It was interpreted that the areas of high N-SPT, which are stiffer, probably took most of the dynamic shear stresses, reducing in this way the disturbances of the loose confined zones[17]. Convento Viejo dam is located 160km south of Santiago, near the town of Chimbarongo. This embankment dam, 32m in height, is separated by a small hill of a rolled concrete dam where spillway and gates are located. The two dams allowed the formation of a reservoir with a storage capacity of 237Mm3. The dam has a central impervious clay core, upstream
Vol XXXI Issue 3
DAM ENGINEERING
203
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