Research On The Infiltration Model And Mechanism Of Shallow Red Layer Landslide In The Three Gorges Reservoir Are

The Three Gorges Reservoir Area has complex geological conditions and frequent heavy rain and floods,making it one of the high-risk areas for geological disasters in China.According to incomplete statistics,there are over 20,000 geological hazard points of various types and sizes in the area.Among them,landslides,collapses,and debris flows are the most numerous,widely distributed,and have the greatest potential for harm.Among the landslides,those generated solely by red strata geology account for over 70% of the total.Therefore,studying red bed landslides is of great significance for disaster prevention and control in the Three Gorges Reservoir Area.Compared with red rock slopes with larger individual landslide scales,shallow-buried red earth slopes have higher concealment due to their smaller slope foot,which makes them difficult to slide in their natural state.As a result,their potential danger has been seriously underestimated for a long time.However,under the influence of rainfall,red beds are prone to massive landslides,even though these landslides have smaller individual scales,they seriously affect the roads,shipping,and people’s lives and property safety in the reservoir area.Therefore,studying the infiltration model and landslide mechanism of shallow-buried red beds in the Three Gorges Reservoir Area under the influence of rainfall is of great significance for supplementing and improving the scientific theory of red bed landslides and guiding engineering practices.This paper is based on the research project "Study on Infiltration Deterioration Model of Shallow-buried Intercalated Red Bed Mudstone Landslides"(Project Number KJ202001241812591)funded by the Chongqing Municipal Education Commission Science and Technology Research Project.Taking the typical shallowburied red bed landslide in Xintian Town,Wanzhou District,Chongqing City as the research object,the physical parameters of the red earth were determined through basic physical experiments.Based on this,the deterioration of the slope under natural conditions was simulated using indoor dry-wet cycle tests.The micro and mechanical characteristics of the deteriorated slope were quantified through scanning electron microscopy tests,triaxial tests,and particle size distribution tests.Based on these experimental results,an infiltration model suitable for shallow buried red slopes was derived,and the instability mechanism of shallow buried red stratum slopes was explored using numerical simulation methods.The main research contents and conclusions are as follows:(1)This study summarizes the geological and natural conditions of the Three Gorges Reservoir Area and conducts laboratory experiments on typical shallow buried red soils.The study investigates the formation conditions,composition of material components,natural physical properties,expansive characteristics,soil-water characteristic curves,and microstructure of the red soils in the reservoir area.Through these experiments,the engineering properties of shallow buried red soils in the Three Gorges Reservoir Area are comprehensively understood.A comprehensive understanding of the engineering properties of the shallowburied red soil in the Three Gorges Reservoir area was obtained.(2)The red soil was subjected to scanning electron microscopy tests,triaxial testing,and particle size distribution analysis after dry-wet cycles.The microstructure characteristics,particle size distribution changes,and mechanical properties of the red soil under dry-wet cycles were analyzed.The research results indicate that: During the process of dry-wet cycles,the large particles in the sample are hydrolyzed into small particles under the action of water,while the small particles are carried away,resulting in a decrease in the area of individual pores.However,the number of pores will increase significantly,and the entire system will eventually reach dynamic equilibrium.The mechanical properties of the red layer soil will deteriorate with the increase of dry-wet cycles,among which the indicators such as cohesion and internal friction angle will show exponential decay.(3)The soil moisture characteristic curve(VG model)was used to calculate the water content at the wetting front,and the water content in the upper part of the wetting front was assumed to be equivalent to a trapezoid to improve the Green-Ampt model.The changes in wetting front depth and safety factor with rainfall time were then calculated.It was found that: Compared with traditional models and the equivalent model of a rectangle plus 1/4 ellipse,the depth of infiltration front advanced by the same rainfall duration is more in line with the actual situation,and the calculated landslide time is more accurate.This method is more advantageous for stability analysis of red layer slopes with long infiltration time.(4)Based on indoor experiments and relevant literature,the pore water pressure and safety factor of a typical shallow-buried red layer slope under rainfall were simulated using Geo-studio.The results showed that: Under natural conditions,the stability of shallow-buried red layer slopes is relatively good.However,as the duration of rainfall increases,the pore water pressure inside the soil mass will continuously increase,leading to a sustained decrease in the safety factor of the slope and exhibiting an accelerating downward trend.At this point,the infiltration rate at the toe of the slope will be greater than that on the slope surface,further weakening the stability of the slope,ultimately leading to landslides.