A dam that is built in an arch to assist in bearing the intense water pressure against the abutments at either side of the dam.
An arch dam is a concrete dam that is curved upward in a plan.
Here we will learn about arch dam, types of arch dam, advantages & disadvantages of arch dam.
Introduction to arch dam:
The arch dams are designed in such a way that the water pressure toward the arch is commonly known as hydrostatic pressure, to compress and strengthen the structure it pushes into its foundation or abutments.
An arch dam is best suited for narrow valleys or valleys with steep walls of stable rock to assist structure and stress.
Types of Arch Dam:
1.Single Curvature Arch Dams:
There are three types of single-curvature arch dams as follows:
Constant-radius arch dams:
In this type of dams, the radius of the extrados (i.e. outside the curved surface of the arch is kept fixed at any elevations, from the top of the dams towards its base).
However, the radius of the Intrados i.e. the radius of the downstream face gradually increases with decreasing radius, to increase the thickness because the depth below the crest will increase particularly in bigger dams.
The center extrados, Intrados midline of the horizontal line are all located at a typical level.
The vertical line exhibits the placement of the centres at completely different heights, it is called as the continuous center arch dam.
On this type, the U-shaped face is vertical and the thickness of the arch is proportional to the peak.
For the development of continuous radius arch dams, the U-shaped valley is extra suitable because at low elevations the central angle reduction is not large.
Any such dam is not suitable for V-shaped basins as a result of the central angle reduction is kind of large.
Variable radius arch dam:
The dams in which the radius of the extrados and intrados curves diverges at different heights is called the variable radius arch dams.
In such a dam, the radius at the top of the dam are maximum while it is minimum at the base.
These types of dams are suitable for both U-shaped and V-shaped basins for their proper construction.
Such a dams is generally more economical than a stable radius arch dams.
The dam in which the middle angles of the arches are constant and radial at different heights is called the constant angle arches.
Constant angle arch dam:
The dams in which the central angle of the arch rings at different heights are fixed and radius is variably known as a constant angle arc dams.
In such dams, a central angle of the arch rings at all elevations is identical magnitude from the highest of the dams to its base.
For economical design of constant angle arch dams, the central angle should be from 133°- 134° based on the thin cylinder principle.
But in the actual practice of construction, the central angle can vary from 100 ° to 150 ° depending on the size of the valley.
In such dams the maximum arch action is established in the arch rings at all elevations.
The thickness of a constant-angle arch dams are smaller than that of a constant radius or variable radius arch dams.
A continuous angle arch dams are suitable for a narrow angle valley.
2.Double Curvature Arch Dam:
This type of dams is also called a cupola dams or shell arch dams because it looks like a rock structure, it is curved in elevation along the plan.
In comparison, this dams has a slight thickness compared to a single curvature arch dams.
Due to the smaller thickness, it is more economical in India; Idukki dam in Kerala is the type of the double curvature arch dams.
When the thickness of the arch is more than such dams are termed arch-gravity dams, it is constructed in the combination with gravity dam.
In such dams, there is extrados of the arch rings with gradually increasing radius in the lower portion of the valley.
There is batter on the upstream face at the base of the dam hence due to significant batter at the base, the base width becomes quite large.
Due to the thick arch with the combination of gravity dams, this type of dams structurally behaves as both gravity and arch dams.
In the U.S.A. the famous floorer dam is type of arch-gravity dam.
Advantages of Arch Dam:
- The uplift pressure problems are minor due to the very low width.
- When the length is smaller than the height, arch dams are more suitable.
- Arch dams require less material, therefore they are more economical.
- This dam can be constructed on a moderate foundation.
Disadvantages of Arch Dam:
- The construction speed is generally low.
- These dam construction requires skilled labour.
- It needs classy formwork.
- Also, requires a special design.
- It is not suitable in places where strong abutments are not available.
This dam body usually made of cement concrete, although debris and stone masonry have also been used.