Research On Flow Regime Transition Between Unsaturated Soil Matrix Flow And Macropore Flow

Object: To analyze the influencing factors and influence characteristics of macropore flow phenomena in unsaturated soils,and to provide help for the productive application of macropore flow theory.Methods: In this study,drip irrigation experiments were conducted by indoor soil trough and soil column tests in which pores of 4 mm diameter were artificially created in troughs and columns containing chalky loam for surface and non-surface irrigation,and five variables were set in the experiments.irrigation water(50 L,60 L,70 L),Pore depth(50 cm,60 cm,70 cm),Initial soil moisture content(5.7%,9.9%,13.3%),Pore form(vertical pore,oblique pore,curved pore),Soil texture(sandy soil,chalky loam).The probability of large pore flow in the pore space was analyzed by determining the pore wall soil water content and matrix suction at different depths of the pore space and the matrix flow zone soil water content and matrix suction at the corresponding depth,and calculating the pore wall wetting front transport rate and the matrix zone wetting front transport rate at the corresponding depth.Results: The phenomenon of large pore flow in soil has a certain randomness,the probability of large pore flow in the upper part is smaller than the probability of large pore flow in the lower part;the probability of large pore flow in pores through the surface is smaller than the probability of large pore flow in pores not through the surface.Conclusion: The main findings of the study are as follows:(1)The probability of large pore flow phenomenon in the upper part of the pore(0-30 cm)is 7.8%,and the probability of large pore flow phenomenon in the lower part of the pore(40-70 cm)is 30.4%,and the probability of large pore flow phenomenon in the upper part of the pore is smaller than the probability of large pore flow phenomenon in the lower part of the pore.(2)The probability of large pore flow phenomenon in surface pores is 15.7%,and the probability of large pore flow phenomenon in non-surface pores is 28.7%,and the probability of large pore flow phenomenon in surface pores is smaller than the probability of large pore flow phenomenon in non-surface pores.(3)The mean value analysis of different variables on the probability of occurrence of macropore flow phenomenon shows that the probability of occurrence of macropore flow phenomenon under different irrigation amounts,different pore depths(lengths),different initial water contents,different pore forms,and different soil textures are 18.75%,25.3%,16.67%,22.92%,and 28.13%,respectively.(4)The conversion of matrix flow in the soil to macropore flow requires a certain transition section,and this transition section is the length required for water to move down the pore and gradually converge into gravity flow.(5)The probability of large pore flow in the soil is somewhat random and not continuous.