Abstract: Based on the monitoring curves of landslide deformation, the early warning criteria are established separately by previous researchers according to the parameters such as the displacement rate, displacement tangent angle, and improved tangle angle. However, the uniformly fixed criterion is not sufficient for the early warning of the landslide, due to the significant differences in the characteristics of landslides. The applicable range of Time-time curve conversion was obtained by considering the improved tangential angle and the characteristic of creep strength. This study also analysed the developments of creep parameters during the constant velocity deformation stage, until reaching the constant or steady values by using the Nishihara model. The constant deformation rate can be regarded as a comprehensive external performance of the parameters in the creep process of the landslide. Moreover, it was inversely related to critical sliding tangential angle. The constant deformation rate and critical sliding tangential angle were obtained by dividing the stages and conversing Time-time curve of 16 typical graded landslides. There was a high correlation between them. By combing with the maximum tangential angle of the undisturbed landslide deformation process, the lower limit was used as the criterion of landslide warning to ensure the reliability of forecasting.

Key words: landslide, constant deformation rate, Nishihara model, critical sliding tangential angle, prediction criteria