Rock-fill dams are embankments of compacted free-draining granular earth with an impervious zone. The earth used often contains a large proportion of large particles, hence the term rock fill. The impervious zone may be on the top face and made of masonry, concrete, plastic membrane, steel sheet piles, wood or other materials. The impervious zone may also be within the embankment in which case it is called the core. In the instances where clay is utilized as the impervious material, the dam is referred to as a composite dam. To prevent internal erosion of clay into the rock fill due to seepage
forces, the core is separated using a filter. Filters are specifically graded soil designed to prevent the migration of fine grain soil particles. When suitable material is at hand, transportation is minimized leading to cost savings during construction. Rock-fill dams are resistant to damage from earthquakes. However, inadequate quality control during construction can lead to poor compaction and sand in the embankment, which can lead to liquefaction of the rock fill during an earthquake. Liquefaction potential can be reduced by keeping susceptible material from being saturated and by providing adequate compaction during construction.
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