Performance-Based Seismic Resistance Assessment of Reinforced Slopes Using the Force-Equilibrium Finite Displacement Method

Performance based evaluation of reinforced soil retaining structures often relies on numerical analyses that demand substantial time and expert effort, largely due to the complex interactions among soils, reinforcements, facings, and seismic loading. This study introduces an efficient approach for developing seismic resisting capacity curves for geosynthetic reinforced slopes with rigid facings, using a computer program built on the Force Equilibrium based Finite Displacement Method (FFDM). Positioned between conventional, non performance based limit equilibrium methods (LEM) and the more computationally intensive finite element method (FEM), the FFDM offers a practical platform for performance based seismic assessment in engineering design. The method is demonstrated through a re examination of the Tanada Wall, a geosynthetic reinforced soil retaining wall with a full-height rigid panel facing (GRS-FHR) that experienced strong shaking during the 1995 Hyogoken Nambu earthquake (ML = 7.2). Using only parameters available in published databases, the FFDM generates realistic seis-mic resistance curves and directly computes seismic displacements. Three advantages distinguish the FFDM from traditional LEM based Newmark approaches: (1) explicit incorporation of peak soil strength and post peak degradation along the slip surface, eliminating the need for empirical “operational” strength adjustments; (2) direct use of peak ground acceleration (HPGA/g) as input, avoiding reliance on empirically selected seismic coefficients; and (3) capability for back analysis, enabling soil strength and de-formation parameters to be calibrated from small observed displacements (on the order of 10⁻³ m) during medium scale earthquakes and subsequently used to predict structural response under more severe ground shaking.