Seismic Performance of an Earth Dam Strengthened with HDPE Geogrids by Finite Element Analysis

Abstract

Earth dams constructed in seismic areas are very susceptible to the strong ground shaking, particularly when in near-full reservoir conditions that cause increase of system requirement through hydro-mechanical interaction. The present article studies the dynamic response of Al-Adhaim Dam during El-Centro earthquake record (PGA = 0.30 g) at full reservoir level (EL = 143 m) with and without buttressing from high-density polyethylene (HDPE) geogrid during its service life. A fully coupled flow–deformation finite-element formulation was used for the analysis of the seismic displacement, acceleration amplification, stress redistribution, pore-pressure response, seepage behavior and overall stability. Results show that the unretrofitted dam undergoes large seismic-induced deformations of 0.33 m and peak crest acceleration amplifications up to 0.78 g, which result in a well FOS<1.0), indicating an unstable condition due to seismic loading. After reinforcement, the maximum displacements at the critical downstream zone are decreased by over 97% (from ~0.30 m to 8 × 10⁻³ m), whereas the factor of safety increases to stabilized values in the range between 1.69 and 1.83 for all reinforcements conditions. A one-way ANOVA test indicates that both reduction of the displacement (p < 10⁻⁴) and improving factor of safety (p < 10⁻⁴) are statistically significant, indicating that these improvements do not result from numerical variability but are due to the mechanical effect contributed by geogrid system. The stress analysis shows that the level of confinement in downstream shell is increased while pore pressure response and seepage pattern become constant without any ill effect from the reinforcement. All these results prove that HDPE geogrid reinforcement has been an effective and statistically proved approach for reinforcing and improving the seismic resistance of earth dams under extremely strong ground motion, which provides a reliable theoretical basis for seismic strengthening design of embankment dam in seismically high-risk areas.