An embankment dam, also called earth dam or earthfill dam, is a water impounding structure built with natural materials excavated or sourced nearby. The construction of an embankment dam involves compacting the most impervious materials to form the core. Permeable earth or rock fragments are then placed on the upstream and downstream sides of the dam. To prevent natural elements such as wind and rain from eroding the dam’s sides, crushed stones or concrete are used to face the sides. Good dam monitoring can catch minor issues before they grow into major ones.
Earthfill dams are relatively safe but economical compared to other types of dams because they are built with readily available and obtainable materials. Since the beginning of recorded history, man has been using soil and rocks to construct dams. Some dams spanning a lifespan of over 200 years still exist in some parts of the world. Some of the most notable earth dams are the Nurek Dam in Tajikistan, Tehri Dam in India, Alberto Lleras Dam in Colombia and Mica Dam in Canada.
Components of Embankment Dam
Three fundamental parts comprise every embankment dam: the foundation, the shell, and the core. According to the type of dam, additional features may be required for the dam’s fundamental components to work correctly.
1. Foundation
This part of the dam bears the dam’s vertical and horizontal loads. The foundation of earthifll dams can be soil, sand, gravel, fine sand or rock. Rock is the best material for constructing a long-lasting foundation, provided the rock is free of faults, fissures, or seams of soft shale or clay that could weaken it. Due to the permeability issues presented when using sand and gravels as foundation materials, it is crucial to take the appropriate preventative measures to reduce seepage to the greatest extent possible.
2. Casing
The main purpose of the casing is to protect the core. However, the casing also enhances the stability of the dam. The casing can be made from reasonably permeable material that does not easily crack under normal atmospheric conditions. As a dam is erected, materials, foundation conditions, and height affect its upstream and downstream casing slopes. Less permeable materials are used to build steeper casings and vice versa.
3. Core
The dam’s core works like an impenetrable barrier, preventing water from freely leaking through the structure. As a result, it is known as an impervious barrier. The most preferred and used material for constructing the core of most embarkment dams is pure plastic clays. Clay can form a waterproof seal when adequately applied and compacted, even though it is capable of absorbing some water. Other soils with significant levels of compressibility, swelling, shrinkage and organic content should not be used for cores because of their intrinsic instability.
Types of Embankment Dam
Embankment dams can be classified in two ways:
- Based on method of construction
- Based on the section of the dam
Based on Method of Construction
Earthen dams that fall into this category are:
1. Rolled-Fill Dams
These dams are built by layering damp dirt on top of one other. Afterward, each layer is added on top of the previous one. Compaction is commonly accomplished with a sheeps foot roller. Heavy earth-moving equipment, such as bulldozers, scrapers, and draglines, are employed in excavation. Moisture levels are maintained throughout the process of compaction. During construction, the dam’s proper slope is maintained.
2. Hydraulic Fill Dams
The dam’s outer edges are taller than its center. Excavated material and water are pushed to the dam’s outer edges of the dam. If discharged at the edges, finer particles will settle in the center. This approach, which requires no compaction, is used until the dam reaches the desired height. The dam’s façade is composed of coarser material, making it permeable. In the dam’s core, clay dominates the finer particles, making it impervious.
Based on the Section of the Dam
1. Homogeneous Earth Dams
The dam is made of one material. It can only be built to low heights. A homogeneous portion can be adjusted by adding a rock toe, and horizontal filter drains. With these two methods, the dam can have steeper slopes. These approaches maintain the seepage line in the dam’s body. Impermeable or semi-impermeable soils are used to build homogenous dams. This dam’s upstream slopes are generally flat to reduce seepage and counteract rapid drawdowns.
2. Zoned Earth Dam
Different materials are often used to build this dam. The dam’s core comprises impervious material, while the sides are made of up permeable material. Dam seepage is drained by a rock toe, horizontal drains, and an inclined filter network. Dams should be zoned if different soils are available. The core should be impervious and the outside permeable. Pervious soil on the D/S side acts as a drain to control seepage. The core arrests any leaks.
3. Diaphragm Type Earth Dam
It is a hybrid of the two earth dams described above. Although most of the embankment is porous, an impermeable diaphragm prevents seepage. Clayey soil, cement concrete, masonry, or other impervious materials can be used to build the diaphragm. It can be in the dam’s middle or upstream face. Only the thickness of the impervious core or diaphragm separates zoned and diaphragm dams. Diaphragm dams have an impermeable core thickness less than or equal to their height above that level.