The main components of an earth dam are as follows :
1. Impervious core
2. Pervious shell
4. Rock toe
5. U/S slope protection
6. D/S slope protection
core shouldnot be less than 3 m and its height should be 1 m more than the maximum water levelin the reservoir.
The upstream pervious zone provides free drainage during sudden drawdown. ,
Usually following types of filters are provided :
(1) Toe filter
(2) Horizontal drainage filter (blanket)
(3) Chimney drains
Such a filter is sometimes known as inverted filter or reverse filter.
Rock toe keeps the phreatic line well within the section and also facilitates drainage.
The following measures are taken to protect the slope.
(1) Rock riprap
(2) Concrete pavement
(3) Steel facing
(4) Bituminous pavement
(5) Precast concrete blocks
Cut off is required to
(1) reduce loss of stored water through foundation and abutments
(2) Prevent sub surface erosion by piping.
Cutoff may be provided in the following ways :
• by providing concrete cutoff wall
• by providing cutoff trench filled with impervious material
• by driving sheet pile
• by curtain grouting