FINITE ELEMENT ANALYSIS OF GRAVITY DAMS USING SUBSTRUCTURE TECHNIQUE

Abstract

Dams are an essential element for providing the facilities for hydroelectric power generation and flood control. Present production of hydroelectric power in India is about 20,000 MW which has to be increased to meet the future power demand. Therefore it is required to construct a large number of dams in the country. Though a number of the geologically sound sites, suitable for dam construction has already been utilized, yet there exist a large number of sites, where all the facilites of hydroelectric power production are available. However many of them are not geologically very sound. Detailed analyses of dams, feasible at such sites, may provide good and economical solutions for such conditions. Analysis of. dam-foundation systems as a whole, which is necessary for high gravity dams on geologically weak sites, is not possible using conventional methods because these are incapable from the point of view of consideration of foundation properties. Analysis problem also arises for arch dams and gravity dams with powerhouse cavity. Finite element method can provide the solution to all such complicated problems, but when the size of the dam-foundation system increases, it requires large computer memory for the solution. In this dissertation, substructure technique for the analysis of dam-foundation systems has been presented. In this technique, the structure is divided into two or more parts, known as substructures, in such a way that at a time, one part can be handled separately and easily within the available range of computer memory. These substructures can be analysed either using iterative approach or using reduced stiffness matrix approach. Formulations for both the methods have been presented and computer programs in FORTRAN-77 have been written using the both in this dissertation work. Subroutines written for the substructure assembly and solution are general, in both the programs and these can be easily incorporated in any other program also. Two dimensional analysts of a proposed high gravity dam has been carried out using these programs. Foundation of the dam is non-homogeneous and modulus of elasticity of foundation rock is very low as compared to that of dam concrete. For the purpose of analysis, dam-foundation system has been discretized into two substructures, one as the dam itself and foundation as the other. The dam has been analysed for full and empty reservoir conditions, with and with out earthquake. Results obtained for all the loading conditions have been found to be in good agreement With one stage analysis. Effect of foundation material properties on the convergence of iterative method has also been studied hY changing the foundation material properties. It has been observed' that the use of substructure technique considerably reduces' execution time and hard disc/memory requirements. On the basis of this study, it has been concluded that in general, substructuring is more efficient with respect to time and storage requirements as compared to one stage analysis. In case of three dimensional problems and dam-foundation-reservoir interaction problems etc, use of substructure technique can be much more advantageous.