Abstract：The Daguangbao landslide(12×108 m3) is the largest landslide triggered by the Wenchuan Ms8.0 magnitude earthquake in 2008. The seismic records show that the landslide area not only suffered strong horizontal ground motions，but also received almost equal vertical ground motions. In this paper，an improved Newmark model considering vertical seismic force is used to study the influence of the shear strength parameters of the sliding surface on the earthquake permanent displacement response of the landslide. The results show that vertical ground motions increase the cumulative permanent displacement of the landslide(the maximum increase is 903%)，and the contribution of vertical ground motion to the permanent displacement(cumulative total amount and cumulative rate) is significantly affected by the friction angle of the sliding surface(the influence level ranges from 87.8% to 90.7%)，but is less affected by cohesion(the influence range is only 5%–27.4%). The maximum cumulative rate and duration of the permanent displacement of the landslide during the seismic process are determined by the concentrated release period of the seismic energy，and 50% of the energy is released within 30–50 s during the 120 s earthquake holding time in the Daguangbao landslide area. It is inferred that the instability of Daguangbao landslide may be in the early stage of earthquake. The improved Newmark method used in this paper can be used to evaluate the contribution of vertical ground motion to the initiation of the seismic landslide.
2021, Vol. 40 
