Study On Water Infiltration And Hydraulic Conductivity Of Compacted Loess

To alleviate the contradiction between urban development and the shortage of land resources,cities in Northwest China have transformed mountains and valleys into farmland or construction land.Usually after rolling,tamping or vibrating compaction,loess is directly used in engineering construction as a kind of building material.The collapsible deformation of loess foundation and other geotechnical engineering problems are closely related to the water infiltration of loess.Therefore,in order to study the laws of water infiltration and the function of unsaturated hydraulic conductivity in compacted loess,constant-water head infiltration tests and rainfall infiltration tests were carried out on the unsaturated loess columns,and the unsaturated hydraulic conductivity of compacted loess was measured.The main research contents and results are as follows:(1)In the constant-water head infiltration tests,three groups of compacted loess columns tests were carried out with different dry densities(ρ_d=1.45g/cm~3,1.55g/cm~3,1.65g/cm~3),the trends of cumulative infiltration,infiltration rate and wetting front distance with infiltration time were researched in the tests,both the cumulative infiltration and the wetting front distance are in good power function relationships with time.The cumulative infiltration is proportional to the wetting front distance.Meanwhile,the influence of dry density on soil column infiltration is researched.(2)The results of rainfall infiltration model tests show the laws of water migration in compacted loess.The soilwater characteristic curves of compacted loess were obtained,the van Genuchten and Fredlund-Xing equations are used to model the soilwater characteristic curve(SWCC)for each soil.Both the models capture the curve reasonably well over the entire range of measured suction.(3)The unsaturated hydraulic conductivity calculated using the instantaneous profile method has an exponential relation to the volumetric water content.Meanwhile,Using the van Genuchten and the Fredlund statistical modeling formalism to predict the hydraulic conductivity function,respectively.By comparison,the predicted values of the van Genuchten hydraulic conductivity model are much closer to the experimental values.In addition,combined with the function of unsaturated hydraulic conductivity and the relationship between water and gas in soil,the mechanism of water migration in compacted loess is studied.(4)Based on the finite element numercial simulation,the indoor infiltration tests be verified and supplemented.the soil water infiltration process in constant-water head and rainfall soil column test is simulated.The simulation results are consistent with the experimental monitoring data.