Stability Analysis Of Loess Slopes Under Different Rainfall Patterns And Monitoring And Early Warning Research

Loess landslides are one of the most frequent and serious geological hazards in the western region of China,and their occurrence seriously affects the safety of people’s lives and property and social development.Based on the obvious trend of"warming and humidification"of the western climate in recent years,the frequent occurrence of discontinuous rainfall such as intermittent and paroxysmal rainfall,coupled with the implementation of strategies such as ecological protection and high-quality development of the Yellow River basin,have put forward higher requirements for disaster prevention and mitigation work in the western region.At the same time,there is currently no extensive coverage of geological hazards such as landslides,some landslide hazards have a low pre-identification rate,and research on early warning models and thresholds still needs to be further deepened.The study of the influence of different rainfall patterns on the stability of loess slopes and the prevention and forecasting of rainfall-type landslides is thus of great theoretical significance and application value to the work of optimising monitoring and early warning and enhancing disaster prevention capacity in the western region.Based on the saturated-unsaturated soil seepage and strength theory,this paper establishes a computational model for loess slopes by using the finite element Geo-studio numerical simulation software to consider different rainfall influencing factors that induce landslides,i.e.to analyse the effects of rainfall intensity,rainfall duration and rainfall type on the seepage and stability of loess slopes.At the same time,for the monitoring and early warning of rainfall-type landslides,a slope in Wujiawan Village,Longnan City,was selected for the study of rainfall thresholds,with a view to providing reference for the early warning and forecasting of slope instability and sliding.The main findings of this paper are:（1）Under the influence of different rainfall intensities,the pore water pressure of the slope soil increases with the increase of rainfall intensity,and the greater the rainfall intensity,the more the amount of rainwater infiltrated into the soil,and the more unfavourable to the stability of the slope.Under different rainfall intensities,the pore water pressure at different locations on the slope varies in magnitude,with the greatest increase in pore water pressure at the top of the slope,and the increase in pore water pressure from the top of the slope,the slope surface to the bottom of the slope gradually decreasing.Generally speaking,the change in pore water pressure at each characteristic point on the slope top,slope face and slope bottom is basically the same under different rainfall intensities.（2）Under the influence of different rainfall patterns,the pore water pressure of the slope soil varies with the rainfall time.The pore water pressure rate changes under the influence of different rainfall patterns were analysed,and it was concluded that under the effect of pre-peak rainfall,the change rate of pore water pressure showed an upward convex pattern,uniform rainfall showed a linear pattern,post-peak rainfall showed a downward concave pattern,and step rainfall showed a convex and then concave pattern;and according to the influence of different rainfall patterns on the slope of Wujiawan Village in Longnan City,it was further concluded that the degree of influence on the stability of the slope was:post-peak type>step type>uniform type>Front-peak.Therefore,when rainfall occurs in the area and its intensity increases with the time of rainfall,it is more important to strengthen the monitoring and prevention of slopes.（3）When the rainfall intensity and rainfall type are certain,the longer the rainfall time,the greater the infiltration of rainwater,and the greater the increase in the pore water pressure of the soil inside the slope,which further reduces the matrix suction value of the slope;based on the changes in the pore water pressure of the slope,the longer the rainfall time,the greater the decrease in the safety and stability coefficient of the slope,which is not conducive to the stability of the slope.（4）According to the I-D curve,the rainfall threshold for the slope of Wujiawan Village in Longnan City is proposed:I=69.12D^-0.64,which yields an inverse relationship between the rainfall intensity and the rainfall calendar time for the occurrence of landslides on rainfall-type loess slopes.When I≥69.12D^-0.64,landslides are likely to occur on the slopes;when I<69.12D^-0.64,the probability of landslides occurring on the slopes is relatively small.In the process of rainfall dynamic monitoring,when the dynamic curves of rainfall intensity I and rainfall time D in the rainfall process are close to this threshold curve,timely warning is issued to prevent landslide disasters.