Modes of failure of Gravity dam
The modes of failure of gravity dam are:-
- OverTurning or Rotation about toe:- When the resultant force acting at any section if it passes outside the toe, the dam shall rotate or overturn about the toe. In other words, it means that if horizontal forces dominate over vertical forces the dam will definitely rotate. At such condition we mainly use a factor of safety, it is the ratio of righting moments(anticlockwise) about toe to the overturning moments(clockwise) about the toe. The factor of safety should not be less than 1.5.
- Crushing:- It generally happens when the compressive stress exceeds the allowable stress of the material of a dam, hence the dam may fail. The total normal stress = Direct stress + Bending stress, Pmax will be produced on the end which is near to the resultant force, if Pmin is negative then tension is produced at that end.
- Sliding or also called shear failure:- When horizontal forces responsible for sliding dominate frictional resistance of dam at that level. To prevent sliding the horizontal forces(∑H) should be less than shear resistance(μ∑V). i.e. ∑H <μ∑V
- Tension: If eccentricity e> b/6, then tension will be developed at the heel of the dam. Since concrete cannot resist tension. Hence, no tension is permitted at any point in dam.