Galleries have to be left in the gravity dams during their construction.
The size of the galleries depends upon the purpose, they have to perform.
The galleries may be aligned both along the axis and across the axis of the dam.
They are provided at all the levels of the dam.
All the galleries are given some longitudinal slope and small channels along both the edges of the galleries are formed.
Seeping water through the dam section is collected by the channels running along the galleries.
Since channels have longitudinal slope, the collected water in channels keeps on flowing automatically and is collect at some central place from where it is discharged into the D/S side of the dam.
Galleries are constructed to perform the following functions.
1. It may be cement concrete or masonary dam, some water definitely seeps through the joints and pores of the dam.This seeping water, if not intercepted
would create internal stresses in the dam and may cause its failure.
Galleries intercept the seeping water and relieve the dam from interval stresses.
2. They form a measure to reach each and every part of the dam.
3. They are use for dissipation of heat, developed by setting action of the cement concrete during construction of the dam.
4. They are use for plugging the longitudinal joints of the dam, after the dam has been completed.
5. They are use to carry out drilling and grouting of the dam or the foundations.
6. They are use to study the behaviour of the dam after completion.
7. They are use for fitting mechanical equipment's like pumps etc. in them.
8. Galleries are also essential for operation of sluice gates, outlet gates etc. Shape of the gallery is generally rectangular but it may be oval shape also.
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