Seismic Forces and Stability Analysis of Gravity Dam

A gravity dam is a solid structure, made of concrete or masonry, constructed across a river to create a reservoir on its upstream. The section of the gravity dam is approximately triangular in shape, with its apex at its top and maximum width at bottom. The section is so proportioned that it resists the various forces acting on it by its own weight. Most of the gravity dams are solid, so that no bending stress is introduced at any point and hence, they are sometimes known as solid gravity dams to distinguish them from hollow gravity dams in those hollow spaces are kept to reduce the weight. Early gravity dams were built of masonry, but now-a-days with improved methods of construction, quality control and curing, concrete is most commonly used for the construction of modern gravity dams. A gravity dam is generally straight in plan and, therefore, it is also called straight gravity dam. However, in some cases, it may be slightly curved in plan, with its convexity upstream. When the curvature becomes significant, it becomes on arch dam. The gravity dams are usually provided with an overflow spillway in some portion of its length. The dam thus consists of two sections; namely, the non-overflow section and the overflow section or spillway section. The design of these two sections is done separately because the loading conditions are different. The overflow section is usually provided with spillway gates. The ratio of the base width to height of most of the gravity dam is less than 1.0. The upstream face is vertical or slightly inclined. The slope of the downstream face usually varies between 0.7: 1 to 0.8: 1. Gravity dams are particularly suited across gorges with very steep side slopes where earth dams might slip. Where good foundations are available, gravity dams can be built upto any height. Gravity dams are also usually cheaper than earth dams if suitable soils are not available for the construction of earth dams. This type of dam is the most permanent one, and requires little maintenance. The most ancient gravity, dam on record was built in Egypt more than 400 years B. C. of uncemented masonry. Archaeological experts believe that this dam was kept in perfect condition for more than 45 centuries. The highest gravity dam in the world is Grand Dixence Dam in Switzerland, which is 285 m high. The second highest gravity dam is Bhakra Dam in India, which has a height of 226 m. The aim of the study is to analyse the dam for stability and seismic forces. Dam being one of the mega structures it becomes prime important to design and analyse such structure with keen observation considering various factors affecting them. As it is one of the lifesaving structures, it is again important to analyse such structure for major forces like earthquake. Keeping this in mind, in this paper the study is done for finding out the result that makes dam stable against forces acting on it with and without considering seismic forces. The study is done considering the hypnotically dam subjected to pre decided geographical factors like type of soil, its density, seismic zone etc. further this experimental work is done for dam full (with and without considering uplift pressure) and empty condition. This designing is done following IS code criteria. Further in paper work various such gravity dams subjected to different factors are analysed. The results of analysis are tabulated over here and the various forces responsible for failure of dam are highlighted in conclusion.