A gravity dam may fail in following ways:

1] By overturning.

2] By crushing or compression.

3] By development of tension.

4] By shear failure or sliding.

1] Overturning:

• If resultant of all forces acting on a dam at any of its sections, passes outside its tow, the dam shall rotate and overturn about the toe.

• Practically, such a condition shall not arise.

• The ratio of righting moments about toe (anti – clockwise) to the overturning moments about toe (clockwise) is called factor of safety. Its value ranges between ?

2] By crushing or compression:

• A dam may fail by failure of materials i.e. the compression stress produced may exceed allowable stress and dam material may get crushed.

P = Direct stress + Bending stress.

$= \frac{\sum V}{B} + \frac{M}{I} Y = \frac{ \sum V}{B} \pm \frac{\sum V. e}{B^2/6}$

$\frac {P_{max}}{min} = \frac{\sum V}{B} [ 1 \pm \frac{6e}{B}]$

• If Pmin comes out to be negative, it means ? shall be produced at the appropriate end.

• If Pmax exceeds allowable compressive stress of dam material, [generally taken as 3000 KN the dam may crush and fail by crushing].