A rockfill dam is a type of embankment dam which comprises primarily compacted rock materials. Shaped much like a bank or hill, rockfill dams are effective because the force of the river or reservoir hits the core of the embankment, is exerted in a downward direction, and transferred to the solid foundation of the dam.
Rockfill dams tend to use aggregate extracted from nearby mining sites to make them impermeable. The parts of a rockfill dam include the main rockfill, which is the structural support; the impervious zone, which combats against the force of the reservoir; and the central core, which transfers the force and maintains stability.
Consisting of at least 50 percent rock, these types of dams are economical and the rocks make an effective barrier against the strong forces created by rivers. Unlike earth or concrete dams, workers can work in wet weather conditions and still construct a strong and durable dam.
Consideration must be given to the type of rock being used for the dam, however, as some rocks have stronger properties than others. Quartzite, for example, is a rock with ideal properties for dam building, but it is also an expensive material to drill. The way rocks break away when they are drilled must also be considered. Some rocks, such as sandstone, are ideal for compaction but many others are not.
Whether a certain type of rock is durable to stand the test of time cannot be proven in the long-term, but many engineers of rockfill dams tend to look at the oldest dams in the world and whether the materials have held up successfully. Compression testing, as well as freeze-thaw and wet-thaw tests can be carried out on the rock type, but ultimately it is time that will tell if the dam will hold.
Other types of embankment dams include earth dams.