Arch dams are one of the most extraordinary pieces of architectural work. Arch dams are curved in plan, and most of their water load is carried by the abutment of the arch horizontally. The amount of water load it can withstand is determined by its arch or curvature.
The balance of the water load is taken care of by the foundation through a cantilever. The side walls of the dam and the canyon are also strengthened in order to withstand heavy wear and tear, the weight of the water, and the weather. The weight of an arch dam is not particularly a factor that is counted while calculating the resistance of resistance loads. Arch dams are primarily used as hydropower dams as their curvature and structural rigidity make for excellent resistance against the sheer force and pressure of water.
In the early times, arch dams were constructed using materials like rubble, masonry, etc., but soon concrete was adopted as a worldwide standard as everyone realised arch dams could be used on a larger scale. One example is the popular Hoover dam in the USA, constructed in 1936.
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Arch Dam: Quick facts
| Shape | Curved |
| Made from | Concrete |
| Constructed in | Narrow, steep-sided valleys |
| Types | Constant radius, Constant arms, variable radius |
| Advantages | adaptive to surroundings; constructed with moderate foundations; affordable to construct |
What is an arch dam?
An arch dam is a dam that is designed to have a single curved wall, shaped like an arch and having its convexity towards the upstream direction. The arch design allows the water pressure and other forces to be transferred to the abutments. They are suitable for narrow, steep-edged valleys.
How is an arch dam constructed?
Arch dams are comparatively thinner than other dams. Thus, less construction material is required, making them an economical and practical option in remote areas. Construction of such dams needs careful planning and engineering expertise to ensure the structure is stable and strong with the ability to sustain the force of the water over a long period of time.
- The various steps of arch dam construction are mentioned below:
- The construction of the arch dam construction begins with identifying a suitable site and clearing the site.
- A dam is constructed mainly across a river to create a reservoir. Thus, diverting the river will be a crucial step in creating dry land for the dam. For dams built across wide rivers, a dry construction pit is built on one side of the river, leaving the other side open for the water to flow.
- The next stage is the preparation of a foundation, which is excavated and levelled. The foundation should be strong enough to support the weight of the dam.
- Construction of the abutments is then carried out. These are the supporting concrete structures on either side of the dam.
- Concrete is mixed in a concrete batching plant at the site. Then concrete pouring is usually done by pouring a wet mixture of concrete into a mould designed in the required shape of the dam.
- This process is repeated layer by layer till the desired height is attained.
- The concrete is allowed to cure for many weeks. The finishing is done using techniques such as polishing or painting.
- Embankment dams are built upwards in a series of thin layers. Once the structure is raised to its full height, a protective layer is made on its upstream face for protection of the surface against damage by waves and waterproofing.
Arch dam: Types
Constant radius dams
In a constant radius arch dam, the radius of the outer side curve of the arch dam is built with a constant curvature throughout. The inner curve of the dam is constructed with decreasing radius from top to bottom.
In a constant radius arch dam, the arch centre for upstream, downstream and the centre line that goes through each horizontal level at various elevations; each lie on a straight vertical line, which passes through the centre of the horizontal arch ring of the upstream face at the crest. Because of this, this type of arch dam construction is also known as the constant centre arch dam.
The constant radius arch dam is commonly used for U-shaped canyons, the cantilever action. Due to this, the constant radius arch dam is much less economical of an option than a constant angle arch dam. It is much simpler to design a constant radius arch.
Constant angle arch dams
This type of dam is a type of variable radius arch dam that requires the central angle of the horizontal arch rings to be of the same magnitude at all levels of elevation.
It is also known that the volume of concrete used is minimum when the central angle is 133° 34’. About 42.6% more concrete is needed for constant angle arch dams than for constant radius ones. Therefore, making them a more economical approach overall.
Variable radius arch dams
In a variable radius arch dam, the radii of the arch ring corresponding to the upstream face (extrados curves) and the radii of the arch rings corresponding to the downstream face (intrados curves) vary at various elevations, being maximum at the top and minimum at the bottom.
This enables the builders to attain maximum central arch efficiency at all levels, as the central angle can be as large as possible.
The centres of the horizontal arch rings do not lie on the singular vertical line. Hence, it is also known as the variable centre arch dam. They are mostly used for V-shaped canyons since arch levels at the bottom can be quite sturdy. Due to having a higher arch efficiency, it also saves a ton of material and labour.
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Arch dam: Advantages
- In gorges with a very narrow base or even a narrow width throughout, it is easy to build arch dams as they are adaptive to whatever surroundings they have.
- Compared to a gravity dam, the cross-sectional area for any given height of an arch dam is much lesser. This means construction, labour and materials required are lesser and hence, cheaper.
- The base width is much smaller, which means that issues related to uplift pressure are miniscule.
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- An arch dam can be constructed with moderate foundations compared to a gravity dam. This is because only a fraction of the water load is transferred to the foundation through cantilever action.
Arch dam: Disadvantages
- The design of an arch dam requires skilled labour and needs quite the expertise to design and construct as well.
- The rate of construction is generally slow.
- The solid rock abutments they are built on are required for them to be super strong to withstand arch thrust. This means that constructing an arch dam is a very tricky task that can be done only in suitable locations.
FAQs
Which is the most economical type of arch dam?
The least expensive to design and construct is a constant angle arch dam.
What are the different types of arch dams?
Arc dams are mainly classified into three types: Single curvature arch dam, double-curvature arch dam and arch-gravity dam.
Who invented the arch dam?
The first arch dam was built by the Romans in the 1st century BC and it was called the Glanum dam.
Which is the biggest arch dam?
The tallest arch dam in the world is the Jingpin-I Dam in China constructed in 2013, measuring 305 metre (1,001 foot).
Why are arch dams good?
The arch shape enables the water pressure and other forces to be transferred to the abutments. The cross-section of an arch dam is nearly triangular, the way it is in a gravity dam. However, it is comparatively thinner. Arch Dams are suitable for narrow, steep-sided valleys.
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