Gravity dam is such a dam, which resists all the forces acting on it, with the help of its own weight.
This dam is considered as one of the most permanent dams.
It requires very little maintenance.
This is the most common type of dam, both for low heights as well as very large heights.
Gravity dam may be made of either masonry or cement concrete.
However, with the advent of most improved methods of construction, quality control, and curing, cement concrete is mostly used.
Gravity dams mostly have their alignment straight, but they can have their alignment a bit curved also.
In both the cases, the dam resists all the forces acting on it, by the aid of its own weight. Arch action developed, in slightly curved dams, is not considered in its design.
The gravity dams are mostly solid.
However they can be constructed hollow also.
Favourable conditions for the construction of gravity dams are the following:
(i) The foundation at the site should be solid.
(ii) The valley, across which dam is to be constructed, should be deep, narrow gorge, with very steep side slopes. Earth dams might slip on such steep slopes.
(iii) The materials required for the construction should be locally available.
(iv) Skilled labour in cement concrete should be available.
(v) The height of the banks should be large so that dam of required height and capacity could be constructed.
(vi) The valley should be narrow so that length of the dam is the shortest.
(vii) Site for installation of power house should be available.
(viii) The basin of the reservoir that will be formed U/S due to dam, should be free from faults like fissured rocks etc.
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