Advancements within static and dynamic Finite Element Analyses of large Embankment Dams

Assessing the stability of large embankment dam structures used for water storage purposes is of great importance. Due to the enormous hazard potential in case of breaching, static and seismic loading conditions must be considered. Traditional static stability assessment for em-bankment dams is based on limit equilibrium methods such as slip-surface analyses introduced by Bishop (1952). To estimate the seismic performance and associated permanent displacements, coupled, and decoupled analyses (Jibson et al. 2013) employing the linear equivalent method accounting for shear-strain dependent stiffness degradation are used (Monobe et al. 1936), (Am-braseys (1960), (Newmark 1965), (Seed and Idris 1970), (Makdisi & Seed 1978). Due to the low computational effort, these methods allow for time-effective first estimates of the seismic dam performance. However, slip surface methods cannot consider non-associated plasticity and are limited to the linear-elastic, perfectly plastic material behaviour. Also, information on stress-re-lated deformation patterns cannot be provided. Within a master’s thesis, conducted at the Graz University of Technology, Institute of Soil Mechanics, Foundation Engineering and Computa-tional Geotechnics, static and dynamic finite element assessments of large, zoned embankment dam layouts were done (Scheikl, 2022). Dynamic structure responses and associated plastification of dam zones are discussed using the Hardening Soil Small (HSS) (Benz 2007) and the Mohr-Coulomb (MC) material models. Effects on the results from strength reduction finite element analyses (Tschuchnigg et al. 2015), considering non-associated plasticity at relatively high fric-tion angles, and steep embankment slopes involving pore water pressure are discussed. The HSS constitutive material law, which features a hyperbolic stress-strain formulation and a strain-re-lated stiffness degradation approach based on the work of Atkinson & Sallfors (1991) is discussed regarding disproportionate structure responses from cyclic loading at very small strains. A first approach to solving this problem considers stiffness-proportional damping parameters. These pa-rameters are evaluated to eliminate unrealistic extreme accelerations and higher mode oscilla-tions. Also, missing plastic strain accumulation during dynamic calculation sequences using the HSS material model and required visualization of shear-strain and plastic point patterns for all time steps calculated with a temporal discretization of 0.005s are discussed to interpret onsets of seismically induced dam failure. Seismic structure responses are compared with results from Cascone and Rampello (2003).