Abstract
This paper deals with the index for risk evaluation of landslides, focusing on surface displacement at main scarp to collapse. Rainfall experiments indicate the existence of critical cumulative displacement at which a slope starts to collapse rapidly after the creep movement. A statistical analysis of various field and experimental data show that the critical cumulative displacement is in proportion with the length of the source area, and the ratio of critical cumulative displacement to the length of the source area (critical strain) ranges approximately from 0.006 to 0.02. Then an index of four-stage evaluation on the basis of the above range is proposed: precursor stage (<0.003), warning stage (0.003-0.006), failure stage (0006-0.02), and perfect failure stage (>0.02). Finally the wide validity of the proposal is verified by applying to several active landslides and old landslides.
