Unit - 3
Arch dam
Q1) What is arch dam?
A1)
- An arch dam I usually curved in plan and its design is based on the concept of stress analysis, previously arch dams were constructed in rubble or ashalar masonry but now a days it is constructed in concrete.
- The highest arch dam I the world is Inguri dam in U.S.S.K. Constructed in 1962 and its height is 272m second highest arch dam in the world is vaiont dam in Italy built in 1961 and its height is 262m.
- In India, the arch dam named as Idukki dam is built across river Periyar in Kerala. Its height is 170m, width as 7.6m and base thickness as 19-8 m.
- Buttress dams is made of a sloping up stream membrane or small arches further supported by a number of buttresses.
- Buttress dam are not much popular in India and there is only one buttress dam called in a name of Meer Allum Dam near Hyderabad and constructed over 100 year ago. The type and dam are multiple arch buttress dams.
- The arch dams are concrete dam like gravity dams.
- In case of arch dam, a V-shape valley with strong abutments is more suitable and ideal.
Q2) Explain Idukki dam in detail.
A2)
- In India, the arch dam named as Idukki dam is built across river Periyar in Kerala. Its height is 170m, width as 7.6m and base thickness as 19-8 m.
- Buttress dams is made of a sloping up stream membrane or small arches further supported by a number of buttresses.
- Buttress dam are not much popular in India and there is only one buttress dam called in a name of Meer Allum Dam near Hyderabad and constructed over 100 year ago. The type and dam is multiple arch buttress dams.
- The arch dams are concrete dam like gravity dams.
Q3) What do you mean by constant radius arch dam?
A3)
- In such dam, radius of extrados i.e. outside curved surface of the arch is kept constant at all elevations from the top of the dam to its base towards the up stream of dam.
- Radius of the downstream face kept gradually decreasing radius so as to increase the thickness as the dept below the crest increases especially in large dams.
- Centres of extrados, intrados and middle line of the horizontal arch rings all lie at one common point. Vertical line shows the locus of the centre at various elevations, therefore such type is also termed as constant centre arch dam.
- In such type, the U/s face is vertical and the thickness of the arch is kept proportional to the height.
- For the construction of constant radius arch dams, U-shaped valley is more suitable because decrease in the central angle at the lower elevations is not large.
- Such type of dam is not suitable for V-shaped valley because reduction in the centre angle is quite large.
Q4) Give the neat sketch of constant radius arch dam.
A4)
Fig 1: Constant radius arch dam
Q5) What do you mean by constant central angle arch dam?
A5)
- Definition: The dam in which the central angle of the arch rings at various elevation is constant and radii are variable then it is called as constant angle arch dam.
- It is a special type of a variable radius arch dam.
- In such dam, central angle of the arch rings at all elevations have same magnitude from the top of the dam to its base.
- So as to have economical design of the constant angle arch dam, the central angle should be equal to 1330, 34′ based on thin-cylinder theory.
- But in the actual practice of construction, the central angle can be varied from 100° to 150° depending on the shape of valley.
- In such dam maximum arch action is set up in the arch rings at all elevations hence much amount of water load is carried by the arch action.
- The thickness of a constant-angle arch dam is smaller than that of constant radius or variable radius arch dam.
Q6) Give neat sketch of constant central angle arch dam.
A6)
Fig 2: Constant angle arch dam
Q7) Give USSR guidelines for designing arch dam.
A7)
- In case of arch dam, amount of the curvature of the dam and shape of the valley play a vital role because arch action depends upon the curvature and shape of valley.
- A V-shaped valleys are fairly suitable for the arch dam.
- U-shaped valleys are fairly suitable for the arch dam.
- In case of higher reservoir, the intrudes are kept gradually decreasing radius so as to provide the increased thickness is the deep below the crest increases.
Q8) Define arch dam.
A8)
The dam which can be seen curved in plan with its convexity to the upstream side and transfers the water pressure and other forces towards the abutments by arch action is called as arch dam.
Q9) Define constant angle arch dam.
A9)
Definition: The dam in which the central angle of the arch rings at various elevation is constant and radii are variable then it is called as constant angle arch dam.
Q10) Define constant radius arch dam.
A10)
Radius of the downstream face kept gradually decreasing radius so as to increase the thickness as the dept below the crest increases especially in large dams.
