Introduction

Gravity dam is defined as a structure so proportioned that it derives its stability from its weight to resist the external forces. A gravity dam is most durable and requires little maintenance. It may be constructed of masonry or concrete. Concrete gravity dams are greatly preferred and their construction is common. A gravity dam is generally straight in plan and termed as straight gravity dam. However, it may also be slightly curved in plan. Nevertheless, the external forces are resisted by the weight of the dam and not by arch action. In a gravity dam no bending stress introduced at any point of the dam and as such it is called solid gravity dam. Gravity dams transfer the load to foundations by cantilever action and require strong foundation rock to resist the weight of the dam. They can be built to any height. They are most suited across narrow gorges with steep side slopes where earthen dam might slip. Bhakra Dam (Fig. 18.1) over river Sutlej is a straight concrete gravity dam.

Adavantages:

1. Strong and stable
2. Overflow spillway crest - for overflow dam
3. Can be constructed of any height
4. Constructed in areas of heavy rain
5. Least Maintainence
6. Failure - gives warning
7. Cheaper and permanent

Disadvantages:

1. Only on sound rock foundation
2. High initial cost
3. Proper plants and transport. If not available, construction may take time.
4. Skilled labour
5. Rise in height cannot be provided once constructed