The Study Of Water Characteristic Curve And Strength Characteristics Of Unsaturated Soil Of Granite Benggang In Anxi County

To study the water characteristic curve and strength characteristics of unsaturated granite soil in benggang,different layers' soils of collapsing wall were chosen as research objects.The basic physicochemical property test of soil,dehumidification test of saturated soil,shear strength test of unsaturated soil were employed to explore the differences of particle morphology,characteristics and influence factors of water characteristic curve,characteristics of shear strength of unsaturated soil.Results are as follows:(1)The content of organic matter and clay particles,as well as the fractal dimension of mass,decrease with the increase of collapsing wall depth,but the content of sand increases as soil depth increases.Collapsing wall soil particles are mainly block particles with many angles on the surface,roundness and the specific surface area show a decreasing trend while the soil depth increase.(2)With the increase of the depth of the collapsed soil layer,the slope of the water characteristic curve of the collapsing wall soil gradually increases gradually,the residual water content and the VG fitting parameter a shows a trend of decreasing,however the air entry value and the fitting parameter n shows an upward trend.All of them have significant correlation with soil bulk density,total porosity and roundness.Both the air entry value,the parameter of a and n have significant correlation with surface area,in addition the residual water content has significant correlation with clay and sand content.The air entry value can be expressed by total porosity,the residual water content could be expressed by capillary porosity and clay content,the parameter of a could be expressed with average shape ratio,bulk density and non-capillary porosity,specific surface area,total porosity and non-capillary porosity can express the parameter of n.(3)The shear strength of unsaturated soil is greater than that of saturated soil.All the total cohesion,internal friction angle and the adsorption strength of the unsaturated soil increase while the matrix suction increases,whereas the adsorption internal friction angle decreases. The order in changes of the total cohesion of unsaturated soils with the increase of matrix suction is:red soil layer>sand layer>detritus layer,and the internal friction angle represents as:detritus layer>sand layer>red soil layer.Under non-saturated conditions,both the internal friction angles and adsorption strength of the soil shows:red soil layer(?=24.65°,?ff =41.84 kPa)>sand layer(?b= 17.50°,?ff =50.08 kPa)>detritus layer((?b=12.50°,?ff=22.28kPa).In summary,the effect of matrix suction on the shear strength of the benggang unsaturated soil is obvious,which would affect the collapse of the benggang soil.During exploring the causes of collapsing,we should pay attention to the effect of matrix suction on shear strength and its mechanism.