22
3) Gravity dam
4) Buttress or hollow masonry gravity dam
5) Timber Dams
6) Steel Dams
7) Arch Dams
8) Rubber Dams
Earth Dam and Rockfill Dam
Earthen Dam is constructed out of local soil even by local labour. The dam
essentially consists of a compact core (generally impermeable soil/clay), with
designed side slopes. They can be constructed on any type of foundation.
The rockfill dam is an embankment which is constructed with different sizes of
rocks and boulders. The upstream needs to be blocked by impervious
membrance to make it water tight. In a combined earth and rockfill dam, the
rockfill on the upstream side is laid by hydraulic rockfill and no derrick is
required. The impervious membrance is also not required (Fig. 2.3).
Cost of both earthen dam and rockfill dam is cheaper and may not need any
skilled labour. They need, however, good maintenance. They are also
vulnerable to flood damage.
Gravity Dam
A gravity dam may be defined as a dam of having sufficient weight to resist the
external forces like water pressure, uplift pressure, silt pressure etc. which tend
to destabilize the structure by exerting its own weight i.e. gravity forces and the
mass of the dam. Gravity dams are mostly constructed by concrete or
masonry. Masonry gravity dams have limited height, but the concrete dam may
be raised to any height, provided suitable foundations are made. Most of the
modern dams are of gravity type. Such type of dams can be constructed at any
site having strong foundation even in the steep gorges of the rivers, are stable
and needs less area than the earthen dams. Concrete spillways can also be
constructed along such dams. However, such dam sites require sound
foundation, particularly on hard rocks.
