Experimental Investigation On Water Permeability Of Unsaturated Soils Under Hydro-Mechanical Coupled Conditions

The construction of fill subgrade of express highway,landfill of anti-seepage cushion,soil tunnel and slope,etc.Mastering the seepage characteristics of unsaturated soils under hydraulic-mechanical coupled conditions is essential for the safe design and construction of the above structures.However,the hydraulic-mechanical coupled characteristics are the most distinguishing features of unsaturated soils from saturated soils.In the existing research,there are more attentions about the deformation and strength characteristics of unsaturated soil under hydraulic-mechanical coupled conditions,but few researchers have conducted in-depth research on the evolution law of the permeability coefficient of unsaturated soil under water-force coupling.Aiming at the above problems,a set of unsaturated soil seepage soil column test device considering hydraulic-mechanical coupled is developed,and using this device,a series of experiments on the seepage of unsaturated soil under the action of hydraulic-mechanical coupled on the highly weathered sandstone and sandy loess have been carried out,and the obviously innovative results can be described in the followings:(1)The test on full suction range of soil-water characteristic curve of strongly weathered sandstone and sandy loess was carried out.The soil-water characteristic curves of the soils with different initial dry densities at different suction stages were tested by the tensionmeter method,the filter paper method and the dew point water potential meter(WP4C)method.The soil-water characteristic curve of the full suction range of strongly weathered sandstone and sandy loess was obtained from the test.The test results further verify the positive correlation between the initial dry density of the soil and the intake air value.The larger the initial dry density,the larger the intake value.(2)An test device for measuring the permeability coefficient of unsaturated soil under hydraulic-mechanical coupled conditions has been developed independently.The advantages and disadvantages and applicability of the existing design of unsaturated soil column test equipment are analyzed in detail.On this basis,a new test device for unsaturated soil seepage column is developed,which consists of four parts:device frame,pneumatic system,measurement system and auxiliary devices.It can control the axial load of the soil column,accurately measure the overall axial deformation of the soil column and the water content at different positions of the soil column.(3)Based on the developed unsaturated soil column test device,a series of seepage soil column tests of strongly weathered sandstone and sandy loess were carried out by using the "wetting front advancing method".? A series of tests on strongly weathered sandstone and sandy loess have been carried out.The initial dry density of soil column was 1.40,1.54,1.60 g/cm3 and 1.40,1.55,1.65 g/cm3,respectively,at the same time,the soil column tests under the conditions of vertical load of 0,40 and 80 kPa for each initial dry density.The test results show:the volumetric water content distribution of the soil column gradually decreases as the depth of the soil column increases;the logarithm of the wetting front rate is proportional to the time logarithm;when the dry density of soil column is the same,the wetting front velocity of soil column under different axial forces tends to be the same finally;with the increase of dry density of soil column,the difference of wetting rate of soil column under different axial forces decreases;the permeability coefficient function at different sections of soil column is influenced by both dry density and axial force,the greater the axial force,the greater the difference of permeability coefficient function at different sections,the greater the dry density,and the smaller the difference of permeability coefficient function at different sections;axial deformation of soil column is positively correlated with axial force and negatively correlated with dry density.? A series of experiments on sandy loess with natural water content were carried out.Soil column tests with initial dry density of 1.40 g/cm3 and vertical loads of 0,40 and 80 kPa were earried out respectively.The test results show:the volumetric water content distribution of the soil column gradually decreases as the depth of the soil column increases;the logarithm of the wetting front rate is proportional to the time logarithm;the wetting front velocity of soil column under different axial forces tends to be the same finally;the greater the axial force,the greater the difference in the permeability coefficient function at different sections;the axial deformation of soil column is positively correlated with axial force;compared to dry sandy loess soil column,the humidification rate is greatly increased,the final stable permeability coefficient is greatly increased,and the axial deformation is greatly reduced.