Characteristics Of Rainfall-Induced Landslides And Its Application In Slope Classification Method In Shenzhen

In recent years,severe weather events such as extreme heavy rainfall have become more and more frequent and serious.Geological disasters such as landslides have attracted social attention,and the safety of urban slopes has attracted more and more attention.It is particularly important to explore the mechanism of rainfall-induced landslides and to establish a classification method suitable for slope stability evaluation in Shenzhen.Based on the analysis of the applicability of the Hong Kong Slope Priority Ranking System(NPRS)in slope stability assessment in Shenzhen,this paper explores the instability mechanism and stability change laws of different types of slopes under the action of extreme rainfall,and combines the results of numerical simulation analysis.According to the problem indicators,an improved slope stability classification method is proposed.Based on the case of rainfall-induced landslide in Shenzhen,the applicability of NPRS in slope stability assessment in Shenzhen area is explored.The results show that the geometric feature classification of NPRS is not suitable for slopes less than30°,one is that the grade is inconsistent with the actual situation,and the other is that it is unable to distinguish the stability differences of different slope heights.In the classification of geological and hydrological conditions of the site,in case of extreme rainfall,if the characteristics of discontinuity surface or complex obvious adverse groundwater conditions cannot be judged,the mild and moderate levels cannot accurately reflect the actual situation,and other characteristics need to be used to assist the evaluation.Therefore,it is necessary to modify the geometric shape characteristics,geological conditions and hydrological conditions indicators to be suitable for the evaluation of slope stability in Shenzhen area.Through finite element numerical simulation,the mechanism of slope instability of different types of slopes in Shenzhen under the action of extreme rainfall,as well as the influence of factors such as geometric characteristics,geological and hydrological conditions,on the stability of slopes are explored.Combining the law of seepage deformation and the decrease of slope safety factor,the most unfavorable working condition combination is: low permeability slope under long-term light rain and high permeability slope under short-term heavy rain.For multi-layer weathered rock-soil mixed slopes,under the action of extreme short-term heavy rainfall,the shallow soil has obvious horizontal displacement and settlement to the open surface,and obvious strain concentration appears at the interface between the clay layer and the strongly weathered rock layer.Shallow sliding deformation and instability trend occurs;under the action of extreme long-term light rain,the soil displacement of the deeper weathered rock layer also gradually develops.The potential sliding surface is affected by the change of the soil suction of this layer and the weathered bedrock surface in the lower layer,and the strain is concentrated.From the toe of the slope through the top surface of the weathered rock layer to the back of the slope,there is a tendency of overall sliding instability.Based on 45 samples of Shenzhen slopes,NPRS and improved methods were used to evaluate and grade the stability,and compared with the empirical grading method.The results show that: compared with NPRS,the stability grade prediction result of the improved method is closer to the empirical grading result,the average relative error and the maximum absolute error are both smaller,and the misjudgment rate is lower.From the sample verification results,the improved classification method is closer to the actual stability of the slope than NPRS,and can meet the needs of slope stability evaluation in Shenzhen.