Study On Mechanical Properties And Water Sensitivity Of Purple Soil In The Three Gorges Reservoir Are

The purple soil in the engineering environment is often affected by the coupling of groundwater seepage,self-weight and other factors.The purple soil is a special soil with unique water sensitivity and collapsibility.If the civil construction activities are carried out on the untreated and directly exposed purple soil,once the water intrusion occurs,it is easy to cause collapsibility and reduce strength,and induce engineering accidents such as slope instability,pavement subgrade collapse and uneven foundation settlement.In this paper,the mechanical properties of purple soil in the Three Gorges Reservoir area under the influence of multiple factors were studied,and the disintegration characteristics of purple soil under different water content and consolidation degree were analyzed.The shear strength characteristics of purple soil under triaxial shear and plant root reinforcement;with the help of SLB-1A stress-strain controlled triaxial shear permeability tester,the permeability characteristics and shear strength characteristics of purple soil stress-seepage coupling under the action of multiple factors are analyzed,and the stress-seepage coupling relationship of purple soil is explored.The mechanical properties and water sensitivity of purple soil in the Three Gorges Reservoir area are analyzed at multiple scales.The main conclusions are as follows:(1)High consolidation pressure corresponds to high soil compression and low optimal water content.The average disintegration speed of soil can be divided into three stages.Under the same consolidation pressure,when the water content ω≤15%,the average disintegration rate decreases significantly with the increase of water content.When the water content ω≥19%,the effect of inhibiting soil disintegration is no longer significant by increasing the water content.(2)Under the influence of water content,the pure shear effect and seepage-shear effect of purple soil in the Three Gorges Reservoir area have obvious changes in its shear strength index,and the change rules are similar.The cohesion c increases first and then decreases with the increase of water content,and there is an obvious peak value.The water content at the peak is about 11%.The internal friction angle φ decreases with the increase of water content,and the shear strength of purple soil in the Three Gorges Reservoir area is water sensitive.(3)Under the action of seepage-shear,the water content and confining pressure greatly affect the shear strength of purple soil.The cohesion reaches the peak at the water content of 11%,and the change of cohesion and internal friction angle conforms to the linear change.Under the same conditions,the greater the control value of principal stress difference,the more significant the decrease of permeability of purple soil with different water content,and the contribution rate of principal stress difference is higher than that of water content.The contribution rate of each factor to the permeability of purple soil from high to low is osmotic pressure> principal stress difference> confining pressure> water content.(4)The tensile strength of three kinds of herbaceous plants in the test area from large to small are : Bidens bipinnata,Setaria viridis,Liquor grass;the bending strength and tensile strength from large to small were : Setaria viridis> Bidens> Liquor grass;the tensile strength from large to small is : Setaria viridis> Liquor grass> Bidens bipinnata.Bidens pilosa and Setaria viridis showed good adaptability and could be used as key herbs to maintain the stability of purple soil slope.