A berm is a flat, horizontal area at the base of a dyke, wall or slope. It serves as support and protection against erosion or undermining of the structure.
Function
A berm fulfils several functions in hydraulic engineering and soil mechanics. First and foremost, it increases the stability of the slope or dyke by adding weight at the base. This prevents the structure from shifting or sliding due to earth pressure or water pressure.
In addition, the berm protects the toe of the structure against erosion caused by flowing water, wave action or rainwater. The horizontal surface breaks the force of the water and prevents soil from being washed away at the base of the slope.
Application
Berms are used in various types of construction:
- Dykes and flood defences — On the outer side (river side) of a dyke, a berm is often constructed to increase stability and limit erosion from wave action.
- Slopes and embankments — On high slopes along roads or railway lines, berms are used to interrupt the gradient and ensure stability.
- Retaining walls — At the base of a retaining wall, a berm can be added as extra support against overturning or sliding.
Construction and dimensions
The width of a berm depends on the height of the slope and the expected loading. For dykes, a berm is typically several metres wide. The berm is constructed from compacted soil material, clay or rock fill, depending on the application and local conditions.
The design takes into account the groundwater level, soil conditions and expected water pressure. A properly dimensioned berm contributes significantly to the lifespan and safety of the structure.
Related terms
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