Gravity dam is a solid structure, made of concrete or masonry, constructed across a river to create a reservoir on its upstream. 
Modes of failure of a gravity dam: 
The gravity dam must be designed such that it is safe against all possible modes of failure, with adequate factor of safety. The dam may fail in one or more of the following modes:
1. Overturning failure 
2. Sliding failure 
3. Tension failure
4. Crushing failure (or compression failure)