Performance-Based Forensic Evaluation of Reinforced Soil Structures Using Displacement-Based Back Analysis and Seismic Resistance Curves

This study presents a performance-based forensic investigation of the Tanada wall, a geosynthetic reinforced soil wall with a full-height rigid facing that experienced strong shaking during the 1995 Hyogoken Nambu earthquake in Japan. The analytical framework integrates a compiled soil stress–displacement dataset, limit equilibrium constraints, displacement-based back analysis, reconstruction of the displacement (Δ3h)–seismic inertial coefficient (kh) curve, and systematic parameter sensitivity evaluation. The displacement-based seismic resistance curves developed using representative soil parameters show that the Tanada wall maintains strong seismic resistance up to HPGA ≈ 0.7–0.8 g, with displacement trends that remain physically consistent across three logarithmic cycles. Sensitivity analyses demonstrate that only three parameters—the soil stiffness number K, peak friction angle φpeak, and the initial pullout stiffness number Kt—produce variations of approximately ±0.8–1.5 × 10−3 m in the final displacement Δ3h. All remaining soil, reinforcement, and facing parameters contribute only minor variations on the order of a few 10−4 m. These findings show that the force-equilibrium-based finite displacement method (FFDM), supported by laboratory evidence and displacement-based inference, provides a rigorous and physically grounded methodology for forensic evaluation of reinforced soil structures.