Test: Gravity Dams, Earthen Dams & Rock Fill Dams - 1 - Civil Engineering (CE) MCQ

Zoned embankments are usually provided with a central impervious core, covered by a comparatively pervious transition zone, which is finally surrounded by a much more pervious outer zone. Clay inspite of it being highly impervious, may not make the best case, if it shrinks and swells too much. Due to this reason, clay is mixed with fine sand or fine gravel so as to use it as the most suitable material for the central impervious core.

In hydraulic -fill method, the dam body is constructed by excavating and transporting soils by using water. Pipes called flumes, are laid along the outer edge of the embankment. Since the fall is saturated when placed, high pore pressure develop in the core material, and the stability of the dam must be checked.

Rockfill dams have characteristics lying somewhere between the characteristics of gravity dams and those of earthen dams. They are less flexible than earthen dams and more flexible, then gravity dams. Their foundation requirements are not a strict and rigid as are required for gravity dams. But the foundation requirements are more rigid than those for earthen dams which can be constructed almost on any types of foundations.

Rockfill dams are very useful in seismic regions, as they provide high resistance to seismic forces because of their flexible character

The wave pressure acting on the dam due to the wave of height h_w can be calculated using the following formula:

p = 1/2 * ρ * g * h_w * (1 + cos(2πx/L))

Where:

• p is the wave pressure
• ρ is the density of water
• g is the acceleration due to gravity
• h_w is the wave height
• x is the horizontal distance from the dam
• L is the wavelength

The center of pressure of this wave pressure distribution is located at a height of 2/3 * h_w above the maximum still water level.

This is because the wave pressure distribution follows a sinusoidal pattern, and the centroid of this pressure distribution is located at 2/3 of the wave height above the still water level.

Therefore, the correct answer is that the center of pressure of the wave pressure due to a wave of height h_w acting on a gravity dam is located at a height of 2/3 * h_w above the maximum still water level.

Hence, if B is taken equal to or greater than  no tension will be developed at the heel 
with full reservoir.
When, C = 1

If uplift is not considered,

For the dam to be safe in sliding,


If C = 0, i.e., no uplift is considered then,

If f_c represents the allowable stress of the dam material, then the maximum height (H_max) which can be obtained, without exceeding the allowable compressive stresses is given as: