Development Characteristics Of Soil Crust And Its Effect On Infiltration

The process of soil infiltration is affected by the intensity of water supply and soil infiltration capacity.The existence of crust reduces the infiltration capacity of soil surface layer and determines the water supply intensity of relatively loose soil in the lower layer.The crust in the process of rainfall is in the process of dynamic development,and the degree of crust development is different under different rainfall duration,which leads to the difference of soil infiltration process.According to the different formation mechanism,the crust can be divided into structural crust and sedimentary crust,and the infiltration ability of structural crust is stronger than that of sedimentary crust.The undulating micro-topography is formed under tillage measures.in the process of rainfall,structural crusts are formed in high-lying areas and sedimentary crusts are formed in low-lying areas.The area proportion and development degree of the two types of crusts under different tillage measures are different,which leads to differences in the process of slope infiltration and runoff production.In this study,the artificial simulated rainfall method was used to measure and analyze the basic characteristics of structural crust and sedimentary crust under five rainfall periods(5min,10 min,15min,20 min,30min).At the same time,a micro-disc infiltration meter was used to calculate the crust infiltration index under different rainfall duration,and the variation process line of crust infiltration performance with rainfall duration was obtained,and three measures of contour tillage,manual excavation and straight slope were designed.Different crust spatial distribution is formed.Combined with the change process of crust infiltration capacity in time series,the influence of crust spatial distribution on slope infiltration in the process of rainfall is analyzed.The main conclusions are as follows:(1)In the process of 30 Min rainfall,crust develops rapidly at the initial stage of rainfall and becomes stable with the prolongation of rainfall duration.The process of crust development is mainly concentrated in the pre-20 min rainfall process,showing that the thickness,bulk density and intensity increase with the duration of rainfall,in which the structural crust is destroyed and reorganized in the 15-20 min stage.(2)The measurement of saturated hydraulic conductivity by fixed head method is repeatable and accurate,and the infiltration indexes of soil cumulative infiltration,steady infiltration rate,infiltration rate and hydraulic conductivity of two kinds of crusts are measured by micro-disc infiltration meter,and the measured results decrease with the increase of negative pressure setting of the instrument.When the saturated hydraulic conductivity of various types of soil is measured by micro-disc infiltration meter,the parameter groups suitable for specific soil should be obtained through previous experiments to ensure the reliability of the results.(3)The infiltration process of crust is roughly divided into three stages.the initial infiltration rate of soil is larger in the initial stage,and decreases with the infiltration process,and finally reaches the stable stage.The time required for sedimentary crust to achieve stable infiltration is shorter than that of structural crust.The infiltration indexes of the two kinds of crusts,such as initial infiltration rate,stable infiltration rate,cumulative infiltration amount,absorption rate and saturated hydraulic conductivity,all decreased in different degrees with the prolongation of rainfall duration.The soil surface layer has formed crusts that seriously affect the infiltration capacity after a short period of rainfall,and the seepage reduction effects of structural crusts and sedimentary crusts are 62.36% and 82.81%,69.06% and 84.68%,respectively.The anti-seepage effect of sedimentary crust is higher than that of structural crust.(4)There is a good linear relationship between crust thickness and infiltration indexes such as initial infiltration rate,absorption rate and saturated hydraulic conductivity.Contour tillage,manual excavation and other tillage measures can intercept runoff and increase soil infiltration,and the spatial distribution of slope crust is different under different measures.The slope yield and discharge is calculated by coupling crust infiltration capacity and the process line and crust spatial distribution characteristics with rainfall duration.Compared with the measured value,the relative error is 2.67% and 5.28%.