The Research On Anisotropic Seepage Characteristics And Stability Of Red Clay Slope Containing Crack Zone

Red clay is a kind of highly plastic clay formed by the strong chemical weathering of carbonate rocks.The cracks are highly developed.Surface water is easy to infiltrate during the rainy season,causing slope deformation and instability damage.Carrying out research on seepage characteristics and stability of red clay slopes containing cracked zones under rainfall conditions has important theoretical value and practical significance for current engineering construction and slope natural disaster prevention.Based on the slope project of Changzhi Expressway in Hunan Province,this study grasped the development characteristics of red clay cracks and established simplified models through field observation and investigation,carried out a series of geotechnical tests to determine the basic physical and mechanical properties of red clay,combining the indoor scale model test and numerical analysis,in-depth research has been carried out on the anisotropic seepage characteristics and stability analysis of fractured red clay slopes.The main research contents and conclusions are as follows:(1)The distribution of cracks in the red clay of the supporting project was investigated,and it was found that the soil structure has significant cracks.The cracks are distributed irregularly on the plane,showing a chaotic distribution,with a crack rate of 0.093.In the vertical direction,the surface cracks have a high degree of development and irregular distribution,and the lower cracks have a certain regularity.Specifically,there are two sets of systematic cracks distributed along the slope and vertical.(2)Carry out a series of geotechnical tests on red clay to obtain its basic physical and mechanical properties.The main mineral components of red clay are kaolinite,quartz,mica and hematite.The uneven coefficient of red clay is 22,the curvature coefficient is 2.9,and the gradation is good;the natural moisture content is 22.8%,and the natural density is 1.90 g/cm3;the saturated permeability coefficients of red clay and cracked soil are 4.67×10-8 m/s,6.82×10-6 m/s,respectively;the cohesion of red clay is 37.20 kPa,and the internal friction angle is 15.65°.(3)Rainfall causes the pore water pressure and water content of the slope surface to increase rapidly,and form a transient saturated zone.The shape of the wet front and the transient saturated zone in the intact slope is consistent with the slope surface,and the depth of rainwater infiltration is limited.When there are cracks in the slope,the scope of influence of rainwater infiltration is significantly expanded,the pore water pressure and water content in the crack zone increase,the wet front is convex downward,and the bottom of the crack forms a transient saturated zone.The distribution characteristics of the crack zone will affect the slope seepage field to a certain extent.The position of the crack zone affects the accumulation of rainwater.The closer the position of the crack zone is to the foot of the slope,the more conducive to the expansion of the wet front and the transient saturated zone.The depth of the crack zone affects the rainwater infiltration.The smaller the depth of the crack zone,the shallower the depth of rainwater infiltration,and the greater the variation of water content.The greater the depth of the crack zone,the easier it is to cause the groundwater level to rise.The angle of the crack zone affects the vertical permeability coefficient of the crack,the smaller the crack angle,the greater the vertical permeability coefficient,which is more conductive to the seepage of rainwater and the formation of transient saturated zone.(4)The degree of development of the crack zone will affect the strength and stress state of the soil,among which the crack state and the crack depth have the greatest influence on the safety factor of the slope.Secondly,the infiltration of rainwater from the cracks will cause a decrease in the shear strength of the soil and an increase in the sliding force.When the crack zone is located at the slope foot,the resistance of the slope resistance section will be lost,and the safety factor will decrease the most.When the crack zone depth is 5m,the pressure head in the crack is the largest,the development rate of the transient saturation zone is fast,and the sliding moment of the slope is large.Comprehensive analysis shows that the depth and location of the cracks have the greatest impact on slope stability.(5)The instability of red clay slope is closely related to the development of cracks in the slope.The strength of the soil near the crack area is low.After rainfall,the crack area collapses in a small area,the slope surface forms a gully,and the slope stability decreases.In a dry environment,the surface soil of the slope loses water and shrinks,the tensile stress between soil particles increases,the original cracks in the soil further expand,and the top of the slope produces tension cracks,which form a sliding structure surface with the original crack zone in the slope.After a long period of rainfall,the crack area is saturated with water,the strength of the soil is softened,and the suction of the matrix is lost,which induces instability of the slope.