A critical review of dam analysis methodologies

Dams in many countries including India were primarily designed on the basis of approximate hand calculation based method. A frequent occurrence of floods due to a failure of such dams and embankments clearly points to the need of a review of the procedure of dam analysis methodologies and to suggest a reasonably accurate one. The paper is a limited effort for the same, based on three Indian dams. As a very preliminary step of the whole plan of checking the safety of Indian dams, an analysis of three dams having similar features as that of Chirpatia Dam (Rajasthan), an earthen embankment dam, Koyna Dam (Maharastra), a concrete gravity dam and the earthen embankment surrounding Ash Pond of Bakreswar Thermal Power Project (West Bengal), have been carried out with the help of two-dimensional and three-dimensional finite element discretisation under static loading conditions. The result is then compared with the corresponding results obtained from a conventional hand calculation based on approximate gravity method of analysis. The comparison of the results exhibited a considerable increase in compressive stresses in two-dimensional finite element analysis with respect to what is obtained in the conventional hand calculation based approximate gravity method. Both of these methods considered an in-plane stress distribution along a cross-section of the dam and hence, could not recognize any possibility of stress generation perpendicular to the cross-section. In this context, a three-dimensional study reveals that considerable stresses may generate even in the longitudinal direction of a dam that is generally ignored in hand calculation based gravity method of analysis and two-dimensional analysis due to the assumption of the two-dimensional nature of the problem. A rigorous finite element analysis also shows that even tensile stress may generate under static loading conditions which can hardly be predicted from the conventional method. It is also observed that hand calculation based on slip-circle method and two-dimensional analysis cannot adequately recognize the possibility of shear failure at many points in the body of the dam though their vulnerability due to itself and so it is necessary to point out by a rigorous three-dimensional modeling and analysis. Thus, the study suggests the unavoidable necessity of three-dimensional analysis for a safe design of dams.