FM ANALYSIS OF STRESS DISTRIBUTIONS IN EMBANKMENT OF EARTHEN DAM

Abstract

In the conventional method of stability analysis of dams a sliding surface is assumed and a quantitative estimate of the factor of safety is obtained by examining the equilibrium conditions at incipient failure and comprising the strength of the fill material on the entire surface. These procedures indicate the factor of safety of the dam with respect to instability but provide no information regarding the deformations of the dam. In recent years, however there has been a growing realization of the need to determine the stress distribution and deformations inside the dam section. Excessive settlements can lead to loss of freeboard and danger of overtopping. Excessive spreading of an embankment may lead to formation of longitudinal cracks which adversely affect its stability. Differential settlements between sections along the crest of dam may lead to development of cracks which could allow passage of water and progressive failure by erosion and piping. Differential compressibility of the core and shell of zoned embankment may result in hydraulic fracturing if the stresses at any elevation are reduced to values less than the pressure of water at the same elevation by transfer of part of the load to less compressible shells. Keeping this in mind elastic stress distribution_ is obtained inside the embankment considering isotropic plain strain condition. Results obtained are compared with those given in literature. An existing dam section is analyzed for three different load cases: Empty reservoir condition (only self weight), full reservoir condition and hydrodynamic pressure, results obtained are compared for three load cases as mentioned. In dynamic analysis modal analysis for empty reservoir condition is carried out, first ten mode shapes and corresponding natural frequencies are obtained. For computation, finite element method based software ANSYS-8.0 used.