Estimation of Natural periods of Earth Dam-Flexible canyon systems with 3D coupled FEM-SBFEM

Abstract The geometry and flexibility of a canyon are the parameters that greatly affect the value of natural periods in earth dams. The canyon surrounding dams can be assumed as an unbounded domain. To take into account these two effects, the canyon was modeled by SBFEM and the earth dam, which has limited geometry, by FEM. The hybrid technique of SBFEM-FEM for dynamic three dimensional analysis of soil-earth dam interaction was validated with available results in the literature. Because the dynamic-stiffness matrix of the unbounded domain is complex and frequency dependent, the classical mode-superposition method is not straightforward for the soil-structure interaction system. Thus, to obtain the fundamental natural frequency, the dam was excited in the upstream-downstream direction. The natural period of the earth dam for canyons with different geometry shapes and impedance ratios were obtained. They were found to have significant effects on the natural period. The results were compared with actual recorded data. It was found that the proposed graphs in this study may be used by practical engineers for the estimation of natural periods of earth dams in canyons with different shapes and material properties.