Uses and Application of a Rockfill Dam

Rockfill dams can be very economical and cheap to build

Rockfill dam
Rockfill dam. Photo J Rodriguez

Rockfill dams are embankments of compacted granular soil combined with impervious areas of the structure. They must contain an impervious zone, an area resistant to rainwater, and usually selected aggregates with filter zones that comprise a substantial volume of the dam.

These structures are effective because the force of the river or reservoir hits the core of the embankment in a downward direction and is then transferred to the solid foundation of the dam.

The dam might be called a composite dam when clay is used as the impervious material. 

Geosynthetic filters are used to prevent soil migration to reduce internal erosion. Filters are specifically graded soil that's been designed to prevent the migration of fine grain soil particles. Rockfill dams are resistant to damage from earthquakes. The three main components of a rockfill dam are:

  • The main rockfill
  • The impervious zone
  • Auxiliary supporting members

Rockfill Dam Special Considerations

If you're ever assigned to build such a damn or you decide that you want to built a rockfill dam on your property, it's important that you pay attention to the following areas:

  • Stability is critical. Both the foundation and the abutment must be stable throughout the life cycle of the dam.
  • Seepage must be controlled to ensure safe operation. Seepage control measures should be in place before the dam's initial use.
  • The spillway must be strong enough to prevent over-topping of the embankment.
  • Reservoir slopes should be carefully designed.

Advantages of Rockfill Dams

One of the most important aspects of a rockfill dam is that it can be very economical and cheap to build. Materials are most likely to be local. This type of dam can also be suitable in areas that don't present the best conditions for deep foundations.

Another key benefit is that the dam can be planned in areas that are susceptible to cold conditions, and in hot and humid climates as well. The rock placement process won't be delayed due to the weather. It's an extremely fast process because it doesn't depend on compaction operations.

How to Create a Rockfill Dam

The best way to build a dam is to start by placing the material in controlled lifts. Steel drum roller compactors are used so the material can be locked into place to reduce settlement during subsequent years. These rollers can also be used to avoid material segregation due to high lift rock fall on the slopes. 

The dam height can be naturally increased by adding more rocks behind the diaphragm without encroaching on the reservoir area. The main rockfill provides the support by its own weight and stability, while the membrane holding the water creates an impervious zone. This membrane can be made out of wood, concrete, steel, asphalt, or stone. The dam is then made water-tight by continuing the impervious face upward.

Always consult your local building codes and water regulations before proceeding.