Explanation Gravity Dams ● It is a masonry structure that increases stability against all applied loads by its weight alone.
● It is a permanent type of dam.
● It is mostly straight in plan and approximately triangular in cross-section.
● The thickness of the dam provides resistance to sliding.
Forces acting on a gravity dam: 1. Dead load or self-weight of the dam ● Includes weight of concrete and accessories like piers, gates, bridges, etc.
● It is the main stabilizing force.
● Acts vertically downwards.
2. Water pressure ● Major external force.
● When the dam is horizontal, acts horizontally and intensity varies with depth.
3. Uplift pressure ● Occurs due to internal hydraulic pressure in pores, cracks within the body of the dam.
● Assumed to vary linearlyfrom full reservoir pressure at upstream face to zero or tailwater pressure at downstream face.
4. Earthquake forces ● Generates due to earthquake waves in the earth's crust.
● These waves impart accelerations and cause movement of the foundation of the dam.
5. Silt Pressure ● Occurs when dams are constructed across the river carrying sediments.
6. Ice pressure ● Important in cold countries where ice formed on the water surface of the reservoir subjected to expansion and contraction.
7. Wave pressure ● Due to the generation of waves on the surface by blowing winds.
Note: All the forces due to water, wave, uplift, etc. are resisted by the weight of the dam