Dams MCQ with answer and solution

Concept

Failure modes of gravity dams encompass overturning, sliding, crushing, and tension development due to uplift and hydrostatic forces.

Step-by-step solution

1. Identify the forces acting on a gravity dam: self-weight, water pressure, uplift pressure, wave pressure, and silt pressure. 2. Note that hydrostatic tension occurs if the resultant falls outside the middle third, causing tensile stresses. 3. Overturning occurs when the overturning moment exceeds the stabilizing moment. 4. Excess uplift pressure reduces the effective normal stress, increasing the risk of sliding and overturning. 5. Therefore, all listed options are valid modes of failure for a gravity dam.

Explanation

A gravity dam relies on its self-weight to resist external forces. It can fail through multiple modes including overturning about the toe, sliding along a horizontal plane, development of hydrostatic tension causing cracks, crushing due to excessive compressive stress, and instability caused by excess uplift pressure reducing the effective self-weight.

Why the other options are wrong

A: Hydrostatic tension is indeed a mode of failure. B: Overturning is a classic mode of failure. C: Excess uplift reduces stability and can cause failure.

Shortcut

Gravity dams can fail by overturning, sliding, crushing, or tension—remember the primary modes: Overturning, Sliding, Crushing, Tension (OSCT).

Common mistake

Thinking a dam fails only due to a single cause like overturning, ignoring that uplift and tension are equally critical failure mechanisms.