The two principal types of embankment dams are earth dams and rock-fill dams.
Embankment dams are large artificial barriers constructed from compacted natural materials, designed to impound water. Unlike concrete dams, which rely on their mass or arch shape for stability, embankment dams depend on the shear strength of their constituent materials. Their classification primarily stems from the predominant fill material used in their construction.
Earth Dams
Earth dams, also known as earth-fill dams, are the most common type of embankment dam. They are constructed primarily from compacted earth materials such as soil, clay, sand, and gravel. These materials are carefully layered and compacted to create a stable, impermeable barrier.
- Key Characteristics:
- Material: Predominantly composed of soil, clay, sand, and gravel.
- Core: Often feature a central core of impervious clay to prevent water seepage.
- Flexibility: Can adapt to a wider range of foundation conditions compared to rigid concrete dams.
- Construction: Typically built by placing and compacting layers of selected earth materials.
- Applications: Widely used for water supply, irrigation, flood control, and power generation due to their cost-effectiveness and adaptability.
Rock-Fill Dams
Rock-fill dams are embankment dams where the primary structural material is compacted rock. These dams often incorporate an impervious zone or face to prevent water from seeping through the rock fill.
- Key Characteristics:
- Material: Primarily constructed from quarried rock, blasted rock, or large aggregates.
- Impervious Element: May have an upstream concrete face (concrete-faced rock-fill dam, CFRD) or an internal clay core (core-type rock-fill dam).
- Stability: Highly stable due to the inherent strength and interlock of rock particles.
- Drainage: The rock fill provides excellent drainage downstream of the impervious zone, enhancing stability.
- Applications: Often preferred for higher dams, in areas with abundant rock resources, or where seismic activity is a concern due to their inherent strength and resilience.
Classification Basis
According to the Embankment Dams, Chapter 4 (Draft Version) by FERC (Federal Energy Regulatory Commission), the differentiation between these two types hinges on the predominant fill material used. This fundamental distinction influences their design, construction methods, and suitability for various geological and hydrological conditions. For more detailed information on dam types and design, refer to resources like the FERC's technical guidelines on embankment dams.
Comparison of Earth Dams and Rock-Fill Dams
Understanding the differences between earth dams and rock-fill dams is crucial for dam engineering and design. The table below highlights their main distinguishing features:
| Feature | Earth Dams | Rock-Fill Dams |
|---|---|---|
| Predominant Material | Soil, clay, sand, gravel (compacted earth) | Quarried rock, blasted rock, large aggregates |
| Impervious Zone | Internal clay core, compacted impervious soil | Upstream concrete/asphalt face, or internal clay core |
| Flexibility | High (adapts well to varying foundations) | Moderate (stable but less adaptable to extreme foundation variability) |
| Drainage | Relatively low natural drainage (requires filters) | Excellent natural drainage through rock fill |
| Construction Method | Layered compaction of fine and coarse soils | Placement and compaction of large rock fragments |
| Typical Height | Generally medium to high | Can be very high (suitable for tall structures) |
| Cost-Effectiveness | Often more economical when suitable earth materials are available locally | Can be cost-effective if rock is abundant nearby, but face/core can add cost |
| Seismic Resistance | Good, if well-designed for deformation | Very good, due to robust interlocking rock structure |
Both types of embankment dams are vital components of water management infrastructure worldwide, each offering distinct advantages based on available materials, site conditions, and specific project requirements.
