New dynamic procedure for back-calculating the shear strength parameters of large landslides

Case histories of the Tsaoling landslide and the Chiu-fen-erh-shan landslide, both located in Taiwan, are used in this study to validate the procedure proposed for the dynamic back-calculation of the shear strength parameters of the sliding surfaces of large landslides. This new procedure uses the Newmark sliding model while simultaneously considering the critical displacement concept. The premise of the new procedure is that, in a stable slope, back-calculation tends to underestimate the shear strength; however, as the intensity of earthquake shaking increases and the slope approaches failure, the back-calculated shear strength will approach to the “true” value. Based on this concept, the new procedure (method) is developed and validated with the two well-documented case histories. The shear strength parameters back-calculated using the proposed method agree well with those reported in the literature. The new dynamic back-calculation procedure is especially suitable in the situation where groundwater monitoring data are unavailable. Thus, the new method is complementary to the traditional groundwater-based limiting equilibrium back calculation approach.