Boundary-independent Finite Element Analysis of Soil-nailed Layered Slopes with Dimensionless Stability Indices Under Seismic Loading Conditions

This study investigates the stability and deformation behaviour of soil-nailed layered slopes subjected to static and pseudo-static seismic loading using a boundary-independent finite element framework in. A 6 m high slope with a weak upper layer overlying a stronger base was modelled within an extended domain to minimise boundary effects and ensure realistic failure mechanisms. Stability was evaluated using the strength reduction method, while deformation characteristics and failure patterns were analysed in detail. The factor of safety (FOS) of the unreinforced slope decreased from 1.40 under static loading to 1.12 under seismic loading (Kₕ = 0.12), whereas soil nailing improved stability to 1.56 and 1.24, respectively. Crest displacement reduced by approximately 30% under static and 26% under seismic conditions. Parametric analysis revealed that nail spacing had the most influence on slope stability (14–18% variation), followed by nail length (11–13%), inclination (5–7%), and diameter (4–5%). The novelty lies in the introduction of dimensionless performance indices, namely Stability Improvement Ratio (SIR) and Seismic Reduction Ratio (SRR), for generalizing reinforcement efficiency and seismic vulnerability. The study provided practical guidance for designing reinforced layered slopes in seismic regions.