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Dam Engineering Essentials

Dams are large structures built across waterways that serve several purposes: storing water, irrigating farmland, controlling water flow/level, generating power, supplying water, and creating recreation areas. Dams experience vertical forces like their own weight, water weight, and structure weight, as well as horizontal forces such as hydrostatic pressure, wind, waves, floating debris, and earthquakes. Their stability is ensured by factors of safety against overturning and sliding being greater than 1, which are calculated using resisting and driving moments and forces. The location of the resultant force acting on the dam depends on how pressure is distributed at its base.

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136 views8 pages

Dam Engineering Essentials

Dams are large structures built across waterways that serve several purposes: storing water, irrigating farmland, controlling water flow/level, generating power, supplying water, and creating recreation areas. Dams experience vertical forces like their own weight, water weight, and structure weight, as well as horizontal forces such as hydrostatic pressure, wind, waves, floating debris, and earthquakes. Their stability is ensured by factors of safety against overturning and sliding being greater than 1, which are calculated using resisting and driving moments and forces. The location of the resultant force acting on the dam depends on how pressure is distributed at its base.

Uploaded by

Rochelle
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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𝐷𝐴𝑀𝑆 − 𝑙𝑎𝑟𝑔𝑒 𝑠𝑡𝑟𝑢𝑐𝑡𝑢𝑟𝑒𝑠 𝑐𝑜𝑛𝑠𝑡𝑟𝑢𝑐𝑡𝑒𝑑 𝑎𝑐𝑟𝑜𝑠𝑠 𝑤𝑎𝑡𝑒𝑟𝑤𝑎𝑦𝑠

Uses of Dams:
𝑎) store water during rainy days
𝑏) irrigate farm lands
𝑐) control the flow or raise the level of water
𝑑) generate electric power
𝑒) control the flow of water
𝑓) supply industrial and public water necessities
𝑔) create lakes for recreation
Forces acting on Dams
A. Vertical forces

a.1 Weight of the dam


a.2 weight of water in the upstream and downstream
side if any
a.3 weight of permanent structures
a.4 Hydrostatic uplift

B. Horizontal Forces

b.1 Total hydrostatic force acting at the vertical


projection of the submerged portion of the dam
b.2 wind pressure
b.3 wave action
b.4 floating bodies
b.5 earthquake load
Factor of Safety
a. Against overturning
𝑅𝑀
𝐹𝑆𝑜 = >1
𝑂𝑀
b. Against sliding
𝝁𝑹𝒚
𝑭𝑺𝒔 = >𝟏
𝑹𝒙
Where:
RM = righting moment
OM = overturning moment
𝑅𝑦 = net normal force
𝑅𝑥 = net sliding force
μ = coefficient of sliding friction

Location of 𝑅𝑦 (𝑥)ҧ
𝑹𝑴 − 𝑶𝑴
ഥ=
𝒙
𝑹𝒚
Pressure distribution at the Base of a Dam
1. Resultant coinciding with the middle of the base

R = PB
𝑅
P =𝐵
P

𝑹𝒚 𝑥ҧ = 𝐵/2

2. Resultant is at the middle third nearer the toe

1
𝑅= 2𝑃𝐵

𝑩Τ𝟑 𝑩Τ𝟑 𝑩Τ𝟑 𝑃 = 2( 𝑅𝐵)


heel toe
P
𝑹𝒚
3. Resultant outside the middle third
1
𝑅 = 2(3𝑥)𝑃
ҧ 𝑚𝑎𝑥

2𝑅
B 𝑃𝑚𝑎𝑥 = 3𝑥ҧ
𝐵 − 3𝑥ҧ 3𝑥ҧ
heel toe

𝑃𝑚𝑎𝑥
𝑹𝒚 𝑥ҧ

4. Resultant within the middle third

𝑅𝑦 6𝑒
𝑃𝑚𝑎𝑥 = (1 + )
𝐵 𝐵
𝑅𝑦 6𝑒
𝑃𝑚𝑖𝑛 = (1 − )
𝐵 𝐵
heel toe 𝐵
𝑒 = − 𝑥ҧ
𝑃𝑚𝑖𝑛 2
𝑃𝑚𝑎𝑥
𝑹𝒚
B/2 e 𝑥ҧ
1. The section of a concrete gravity dam is shown in the figure. The
depth of water at the upstream side is 6m. Neglect hydrostatic uplift
and use unit weight of concrete equal to 23.5 𝑘𝑁Τ𝑚3 . Coefficient of
friction between the base of the dam and the foundation is 0.6.
Determine the following: (a) factor of safety against sliding, (b) the
factor of safety against overturning and (c) the overturning moment
acting against the dam. (CE Board May 2002)
2m

8m

6m

4m

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