STUDY ON DEFORMATION LAG TIME EFFECT OF TYPICAL COLLUVIAL LANDSLIDE IN THREE GORGES RESERVOIR AREA

Colluvial landslide is an important type of geological hazard during the operation of the Three Gorges Reservoir, and its deformation evolution often lag behind the change of rainfall and reservoir level, show the time lag effect, which brings a great challenge to landslide hazard prediction and disaster alert release. In this paper, firstly we construct a landslide weighted displacement vector calculation model by adopting set pair analysis method and analytic hierarchy process method, then carry out the qualitative analysis of the relationship between landslide weighted displacement evolution and reservoir water level, then look for the number of translation steps when the correlation between landslide weighted displacement and reservoir water level change rate reaches the maximum, finally calculate the time that landslide deformation lags behind the reservoir water level change. Taking Shuping landslide which is a typical colluvial landslide in Three Gorges Reservoir Area as an example, based on the analysis of the landslide deformation evolution law, the monitoring data of surface displacement and reservoir water level decreasing rate during flood and rain periods in 2012, 2013, and 2014 were respectively selected to carry out research on landslide deformation lag time. The results show that when the decreasing rate of reservoir water level is less than or equal to 0.43 m·d^-1, the deformation lag time of Shuping landslide is greater than or equal to 5 d; When the decreasing rate of reservoir water level is between 0.43 m·d^-1 and 0.7 m·d^-1, the deformation lag time of Shuping landslide is between 2 d and 5 d; When the decreasing rate of reservoir water level is greater than or equal to 0.7 m·d^-1, the deformation lag time of Shuping landslide is less than or equal to 2 d. Therefore, the decreasing rate of reservoir water level increases, the lag time of landslide deformation decreases. By analyzing the lag time of monitoring points at different spatial locations of the landslide, it is found that the closer the landslide front edge, the shorter the landslide deformation lag time. When the decreasing rate of reservoir water level is between 0.43 m·d^-1 and 0.7 m·d^-1, the deformation lag time at the front edge of Shuping landslide is between 2.4 d and 5.4 d, the deformation lag time at the middle part of Shuping landslide is between 3.4 d and 5.6 d, and the deformation lag time interval between the front and middle parts of Shuping landslide is from 0.2 d to 1.4 d. The research results can provide reference for the monitoring and early warning of Shuping landslide, and have certain reference significance for the monitoring and early warning of partly submerged landslides in major water conservancy projects.