EARTHFILL DAMS & ITS CLASSIFICATION
Earthfill dams are the most common type of dam built to any height. They are designed as a non-overflow section with separate spillway. The reason for such wide spread use of earthfill dams are:
- The foundation requirements are not as rigorous as other dams
- Local available soil is the main construction material
- High skill not required
- No special plants are required. Most earth-moving machines can be used
Fig. 1. General view of an Earthfill dam
Figure 2: General view of an Earthfill dam
Classification of earthfill dams
Earthfill dams are classified by many factors.
1. Based on the method of construction
- Rolled fill earth dams
- Hydraulic fill dam
2. Based on mechanical characteristics of earth materials making the section of the Dam
- Homogeneous earth dams
- Non-Homogeneous (zoned) earth dams
i) non-homogeneous with inclined impervious zone (ekran) of artificial material
ii) with impervious zone of soil with low permeability
iii) with central core soil material of low permeability
iv) with a central thin diaphragm of impervious material
Rolled Fill Earth dams
In this type of dams, successive layers of moistened or damp soils are laid one over the other. Each layer not exceeding 20 cm in thickness is properly consolidated at optimum moisture content, only then is the next layer laid.
Hydraulic Fill dams
In this type of dams, the construction, excavation, transportation of the earth is done by hydraulic methods. Outer edges of the embankments are kept slightly higher than the middle portion of each layer. During construction, a mixture of excavated materials in slurry condition is pumped and discharged at the edges. This slurry of excavated materials and water consists of coarse and fine materials. When it is discharged near the outer edges, the coarser materials settle first at the edges, while the finer materials move to the middle and settle there. Fine particles are deposited in the central portion to form a water tight central core. In this method, compaction is not required.
Homogeneous Earthen Dam
These dams are constructed with uniform and homogeneous materials. It is suitable for low height dams (up to 10m). These dams are usually constructed with soil and grit mixed in proper ratios. The seepage action of such dams are not favourable, therefore, for safety in case of rapid drawdown, the upstream slope is kept relatively flat (3:1)
Homogeneous section is modified by constructing rock toe at the downstream lower end and providing horizontal filter drain.
Zoned Earth Dams
These are dams with the central portions called core or hearting made from materials which are relatively impervious. The thickness of the core wall is made sufficiently thick to prevent leakage of water through the body of the dam.
Dam with a Diaphragm
This type of dam is constructed with pervious materials, with a thin impervious diaphragm in the central part to prevent seepage of water. The thin impervious diaphragm may be made of impervious clayey soil, cement concrete or masonry or any impervious material The diaphragm can be constructed in the central portion or on the upstream face of the dam. The main difference in zoned and diaphragm type of dams depend on the thickness of the impervious core or diaphragm. The thickness of the diaphragm is not more than 10 m.