Various approaches adopted for the analysis of rock foundations are based on the Theory of Elasticity and Plasticity. Limit Equilibrium Analysis using the concept of perfect plasticity is generally adopted because of its simplicity to estimate factor of safety against plastic failure by sliding keeping in view the loads imposed on the foundations, drainage conditions and shear parameters operating in the field established through field/ laboratory testing on samples from weakest zone present in the rock foundation. Limit Analysis is extended to three dimensional analysis for better accuracy besides being economical. With the consideration of load variation and strength deterioration due to progressive failure, a factor of safety of two is considered adequate.

The choice of Limit Equilibrium Analysis is mainly controlled by the geological features. How these features i.e., their orientation and location, influenced the location of failure zones for foundation analysis of some of the dams are examined. The influence of shear strength parameters assessed from field and laboratory tests in estimating factor of safety is presented. Modifications in the design to achieve a desired factor of safety are described. Satisfactory functioning of the foundations of these dams suggests the reliability of this simple technique of analysis.

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