Revisit the classical Newmark displacement analysis for earthquake-induced wedge sliding of a rock slope

Newmark displacement analysis (NDA) has been widely used to study the initiation and kinematics of earthquake-induced landslides. The classical NDA for earthquake-induced wedge slides assumes that the wedge is a rigid block (assumption A1). The vertical and horizontal accelerations perpendicular to the sliding direction are neglected (assumptions A2 and A3). Moreover, the friction angles (friction coefficients) of the sliding surfaces are assumed to be constant during sliding (assumption A4). This study evaluates the influences of these four assumptions on the kinematics of huge wedges adopted, where the shear stress could not be identical to the sliding direction. Different rock wedge shapes subjected to synthetic seismic loads are modeled, and the sensitivity of removing unnecessary assumptions from the analysis is evaluated. A case study of the earthquake-induced Daguangbao landslide (wedge slide) is provided to assess the influence of the rigid wedge assumption and adopted strengths along wedge planes on the sliding kinematics. Our study shows that the rigid wedge method (RWM) incorporated into NDA (A1) always yields an unconservative prediction of permanent displacement comparing to maximum shear stress method (MSSM), particularly for huge, narrow wedges. The MSSM, which assumes that the shear stress perpendicular to the sliding direction equals the shear strength, should be considered owing to wedge deformation if huge rock masses are involved. Neglecting the vertical acceleration (A2) induced an underestimation of permanent displacement, particularly for narrow wedges with a gentle plunge of the intersection line. Although horizontal acceleration perpendicular to the trend of I-Line does influence the NDA results for asymmetrical wedges, the effect (A3) is insignificant. Assuming a constant strength on the wedge plane (A4) only predicted stick-slip behavior but not a frequently observed high-mobility phenomenon of huge landslides. Finally, the rapid and long run-out sliding of the Daguangbao landslide can be successfully predicted if the velocity-displacement dependent friction law is appropriately incorporated into NDA using MSSM.