Study of an Effective Rainfall Calculation Method for Early and Medium Term Forecasts of Accumulation Landslides Induced by Rainfall

The rainfall threshold is a key indicator for the early warning and prediction of accumulation landslides induced by rainfall.A reasonable and effective rainfall calculation method is an important means to obtaining an accurate rainfall threshold and a premise for accurate early warning and forecasting.In this paper,the Xuwa,Wangjiapo,Tanjiawan and Tudiwan landslides were taken as research objects,representing small,medium,large and super-large rainfall-type accumulation landslides,respectively.First,the deformation characteristics of rainfall-type accumulation landslides under the action of rainfall were analyzed.Then,a “one rainfall process” was introduced to unify the rainfall processes affecting landslide deformation,and combined with the concept of a “displacement rate impact degree”,a set of calculation methods for early effective rainfall were designed and compared with traditional calculation methods.The research findings showed that (1) the deformation of small,medium,large and super-large rainfall-type accumulation landslides is closely related to the rainfall process.After entering the creep deformation stage,the cumulative displacement curve of landslides has obvious “step” characteristics.(2) There is a “lag decay” phenomenon in the displacement rate of the rainfall accumulation layer,and the “lag decay” time T of a single landslide is an approximately fixed value,which is basically consistent with the stability evolution characteristics of landslides.(3) Combining the “one rainfall process” and the “displacement rate impact”,the calculation method of early effective rainfall considering “lag attenuation” has a good fit with the duration of landslide deformation and the landslide deformation rate,which has obvious advantages in the landslide early warning process.