EARTHEN DAM

 

Types of Earthen Dam

 1. Homogeneous Embankment Type

 2. Zoned Embankment Type

 3. Diaphragm Type Embankment

 1. Homogeneous Embankment Type :-

• The simplest type of earthen dam consist of a single material and homogeneous throughout.

• Such section is used for low to moderately high dams when only one type of material is economically available.

• A purely homogeneous section poses the problems of seepage and huge sections are required to make it safe against piping, stability etc.

• Due to this, a homogenous section is generally added with an internal drainage system, such as a horizontal drainage filter.

• The internal drainage system keeps the phreatic line (i.e. Top seepage line) well within the body of the dam and permits steeper slopes and thus smaller sections can be used.

• The internal drainage is, therefore always provided in almost all types of embankments.

2. Zoned Embankment Type :-

• Zoned embankment are usually provided with a central impervious core, covered by a comparatively pervious transition zone, which is finally surrounded by a much more pervious zone.

• The central core checks the seepage. The transition zone prevents piping through cracks which may develop in the core. The outer zone gives stability to the central impervious fill and also distribute the load over a large area off foundations

• Silts or silty clays may be used for central core.

• Freely draining materials, such as coarse sands and gravels are used in the outer shell.

• Transition filters are provided between the inner zone and outer zone as there is an abrupt change of permeability from one zone to another.

 3. Diaphragm Type Embankment :-

• Diaphragm type embankments have a thin impervious core, which is surrounded by earth or rock fill.

• The impervious core, called diaphragm is made of impervious soils, concrete, steel, timber or any other material.

• It acts as a water barrier to prevent seepage through the dam.

• The diaphragm may be placed either at the centre as a central core or at the upstream face as blanket.

• Diaphragm must be tied to the bed rock to avoid excessive seepage through the pervious foundation material.

• The diaphragm type of embankments are differentiated from zoned embankments depending upon the thickness of core.

• If the thickness of the diaphragm at any elevation is less than 10 meters or less than the height of the embankment above the corresponding elevation, the dam embankment is considered as ‘Diaphragm Type’, otherwise it is called as zoned embankment.