The Study On Soil Water Characteristic Curve And Permeability Curve Of Unsaturated Remolded Loess Under Different Dry Density

The compacted loess is a kind of remolded unsaturated soil.Due to the different lithology of the fill and the different rolling technology,there are significant differences in the soil water characteristics and unsaturated permeability characteristics of the compacted loess.In order to find out the characteristics of soil water and seepage of compacted loess,this paper takes L6 loess in Yan’an area as the research object,and uses 10%water content to prepare remolded soil samples with dry density of 1.5,1.6,1.7 and 1.8g/cm~3.The pore characteristics of remolded samples are tested by mercury injection method,the soil water characteristic curve of remolded samples is tested by filter paper method,and the permeability curve of remolded samples is tested by transient profile method.The results are as follows:The method of mercury injection adopts Autopore IV 9500 full-automatic mercury injection instrument.The pore volume of corresponding pore size can be known by measuring the amount of mercury in the hole under different external pressures.According to the results of mercury injection test,the PSD curve is divided into three sections:pore diameter d<0.14μm,corresponding to micropore;pore diameter 0.14μm<d<6μm,corresponding to small pore;pore diameter d>6μm,for medium pore and large pore.Through the analysis and comparison of the pore distribution curves of four remolded samples,it can be seen that in the process of increasing dry density,compaction mainly changes the distribution of small pores(pore diameter 0.14μm<d<6μm),but has no significant effect on the distribution of micropores.By measuring the moisture content of the filter paper in direct contact with the soil sample,the corresponding matric suction is obtained by using the rating equation.According to the measured data of filter paper method,the soil water characteristic curve of remolded loess can be divided into three parts:saturated section,rapid drop section and slow drop section.In the saturated section,the soil is basically saturated,and there are four groups of soil water characteristic curve intersections;the slope of soil water characteristic curve decreases with the increase of dry density;in the gentle fall section,the distribution of micropores of the four soil samples is similar,so the soil water characteristic curve is almost coincident.It shows that the pore distribution of loess controls its soil water characteristic curve.The permeability curve test adopts a small soil column test device,which combines the filter paper method with the transient profile method,it weighs the mass of the ring knife sample and the filter paper regularly to obtain the water content and head profile at different times,then calculates the permeability coefficient under different suction or water content,and obtains the permeability curve.According to the test results of transient profile method,the permeability curves of remolded samples are divided into three parts:saturation section,rapid drop section and slow drop section.In the saturated section,the permeability coefficient decreases with the increase of dry density;in the rapid drop section,the unsaturated permeability coefficient decreases with the increase of dry density;the permeability curve of the remolded sample basically coincides in the gentle drop section.