Opposing effects of the vertical seismic coefficient on cohesive and frictional contributions to seismic slope stability

The influence of the vertical seismic coefficient (k_v) on pseudo-static (PS) and permanent displacement analyses remains underexplored. This study introduces a novel perspective by decomposing the factor of safety (F) into cohesive (F_c) and frictional (F_ϕ) components, revealing that k_v exerts opposing effects on these two components. The extent and critical direction (upward or downward) of k_v’s impact depend on the relative contributions of F_c and F_ϕ to slope stability. This perspective is first demonstrated analytically using a planar failure mechanism and further validated through a physics informed regression model (PIRM), which achieves accuracy comparable to log-spiral upper bound limit analysis (UBLA) and finite element limit analyses (FELA) for homogeneous slopes. The opposing effects are also confirmed for inhomogeneous slopes via finite element analyses (FEA). Additionally, the PIRM is reformulated to predict the horizontal yield coefficient (k_hy), a key input parameter in permanent displacement analysis. Parametric studies indicate that neglecting k_v can overestimate F by up to 35 % and k_hy by up to 53 %, leading to unsafe designs. These findings highlight the necessity of incorporating k_v into seismic slope stability assessments. The proposed PIRMs offer an efficient and reliable tool for preliminary and regional-scale evaluations.