The effect of earthquake characteristics on the seismic performance of slopes reinforced with soil nails

Soil-nailed walls, frequently used in excavation and slope stabilization, exhibit high performance under seismic loads due to their flexibility. Pseudo-static approaches (e.g., Mononobe-Okabe) used in the dynamic design of such systems express earthquake effects with a seismic coefficient proportional to the peak ground acceleration. However, this method, based on the limit equilibrium principle, fails to examine details such as soil-nail interaction and facing performance; furthermore, it neglects critical parameters like the frequency content and duration of the earthquake. Therefore, time-domain dynamic analyses are required for a detailed investigation of the seismic behavior of soil-nailed walls. This study investigates the effect of various earthquake parameters by examining the dynamic behavior of rock and granular soil slopes with varying degrees of weathering under ten different earthquake records. Dynamic analyses of three-dimensional slope models reinforced with soil nails were performed using FLAC3D software. To create a realistic numerical model, key components such as steel reinforcement, grout, shotcrete facing, and nail head plate were modeled. To confirm the reliability of the developed numerical model, two different studies in the literature, where the seismic behavior of soil-nailed slopes was modeled using one-dimensional shake table and dynamic centrifuge tests, were modeled in a finite difference environment to perform validation analyses. The numerical analyses revealed that displacements increased with increasing weathering levels in rock slopes, and maximum displacements occurred in sand slopes. It was determined that increasing nail spacing led to an increase in axial force values, and maximum nail forces developed in the lower rows of nails due to effective nail lengths. In regression analyses conducted to evaluate the effect of earthquake characteristics on displacements, it was observed that the Ia and CAV parameters, which are related to the energy and time domain of the earthquake, predicted deformation behavior better than peak ground acceleration. Amplification values calculated at the top of soil-nailed walls were found to be significantly higher in sandy soils compared to weathered rock environments; this was attributed to the low shear wave velocity and weak material properties of sandy soils. In weathered rocks, similar amplification factors were observed in near-surface regions, while amplification values decreased with increasing soil nail spacing in both rock types; this is interpreted as increased nail spacing reducing wall stability, increasing deformations, and triggering nonlinear behavior in the system.