Study On The Influence Of Rain Intensity And Gradient For Benggang Failure Based On The Indoor Soil Model Test

The change in water content inside the slope caused by rainfall is an important condition for the occurrence of instability and failure of collapsed hills and walls.Studying the impact of rainfall intensity and gradient factors on the internal water content change,surface soil particle composition,soil cohesion,internal friction angle,and degree of failure of collapsed slopes can reflect the influence of different factors on the failure of collapsed slopes.The soil used in this article is from Tongcheng County,Hubei Province.Red soil and sandy soil developed from granite in the field were collected,and a landslide slope model was established in an indoor soil tank.An artificial rainfall system was used to conduct a simulated landslide slope failure test under three rainfall intensities and two slope conditions.Embed moisture sensors in the model of a collapsed slope to monitor the changes in volumetric moisture content at four monitoring points during rainfall,namely the shoulder,middle up,middle down,and foot of the slope.Record the failure process of the collapsed slope,measure the soil particle composition at each monitoring point after rainfall,and make direct shear samples based on the soil particle composition and moisture content at each monitoring point on the surface of the collapsed slope after rainfall,to determine its cohesion and internal friction angle,The main experimental results of studying the mechanism of instability of collapsed slopes are as follows:(1)The trend of water content change in the slope is that the water content increases sharply in the early stage,slows down in the middle stage,and tends to stabilize in the later stage.As the rainfall intensity and gradient increase,the increment of volumetric moisture content increases.At a slope of 60°,the rainfall intensity increases from 40 mm/h to 80mm/h,and the increment of volumetric moisture content at the slope shoulder increases from 22.92%to 39.90%;When the rainfall intensity is 80 mm/h,the gradient increases from 60°to 75°,and the increment of volumetric moisture content at the slope shoulder increases from 39.11%to 41.59%.The water infiltration rate increases with the increase of rain intensity and decreases with the increase of gradient.At a gradient of 60°,when the rain intensity increases from 40 mm/h to 80 mm/h,the water infiltration rate on the slope shoulder increases from 0.006 cm/s to 0.017 cm/s;When the rainfall intensity is 80 mm/h and the gradient increases from 60°to 75°,the water infiltration rate on the slope shoulder decreases from 0.017 cm/s to 0.011 cm/s.Rain intensity,gradient,and their combined effects have a very significant effect on the changes in water content within the slope.In the upper half of the slope,the single rain intensity factor has a greater impact on water content;In the lower part of the slope,the single slope factor has a greater impact on water content.(2)As the rainfall intensity and gradient increase,the content of fine particles in the surface soil of the slope decreases,while the content of coarse particles in the soil increases.At a gradient of 60°,the rainfall intensity increases from 40 mm/h to 80 mm/h,and the content of clay particles in the slope shoulder soil decreases by 9.09%,while the content of sand particles increases by 11.96%;When the rainfall intensity is 80 mm/h,the gradient increases from 60°to 75°,and the soil clay content at the slope shoulder decreases by 0.23%,while the sand content increases by 1.34%.The variation of soil non-uniformity coefficient(C_u)and curvature coefficient(C_c)with rainfall intensity varies at different positions of the gradient under different experimental conditions.The fractal dimension of the soil on the wall collapse slope decreases with the increase of rainfall intensity.When the slope is 60°,the rainfall intensity increases from 40 mm/h to 80 mm/h,and the analytical dimension of the soil on the slope shoulder decreases from 2.8787 to 2.8212.The influence of the single rainfall intensity factor on the fractal dimension of the soil is greater than that of the single gradient factor and their combined effects on the fractal dimension of the soil.(3)The change of soil moisture content and fractal dimension on the slope surface should affect the soil shear strength index;With the increase of soil fractal dimension,the shear strength index of soil on the slope surface increases.The water content increases from22.92%to 39.90%,the cohesion of the soil mass of the slope shoulder decreases from 19.87k Pa to 7.60 k Pa,the internal friction angle decreases from 22.00°to 8.90°,the fractal dimension increases from 2.8212 to 2.855,the cohesion of the soil mass of the slope shoulder decreases from 7.60 k Pa to 16.95 k Pa,and the internal friction angle decreases from 8.90°to 19.25°.Water content,soil fractal dimension and their combined effects have a very significant impact on soil cohesion and internal friction angle,and water content has the greatest impact on soil cohesion and internal friction angle.(4)Quantify the degree of failure of a collapsed slope by measuring the geometric parameters of the cracks,the depth of the catchment surface subsidence,and the area of the failure surface.With the increase of rainfall intensity and gradient,the geometric size of cracks generated on the collapsed slope increases,and the area of the slope failure surface and the depth of the water collection surface also increase.The degree of damage to the collapsed slope also becomes more severe.At a gradient of 75°,the rainfall intensity increases from 40 mm/h to 80 mm/h,the sinking depth of the catchment surface increases from 1.10 cm to 1.70 cm,and the area of the failure surface increases from 880 cm~2 to 1600cm~2;Under rainfall conditions of 80 mm/h,the gradient increases from 60°to 75°,the length of slope cracks increases from 41.80 cm to 42.30 cm,and the depth of water collection surface subsidence increases from 1.60 cm to 1.70 cm.The instability and failure of the collapsed slope mainly occur during the stage of drastic changes in water content.In summary,the stage of collapse slope failure occurs during the stage of rapid increase in water content rate,where the soil gradually coarsens,soil cohesion and internal friction angle continue to decrease,resulting in a decrease in soil strength,thereby reducing the stability of the collapse slope and causing deformation and failure of the collapse slope.