Study On The Morphological Characteristics Of Preferential Flow In Soil Crust Cracks

In daily life,when rainfall strikes and washes the soil surface,it leads to the generation of crust.The further cracks and preferential flow will cause the waste of water resources in agricultural farming,which is more likely to cause a series of environmental problems.At present,the development process of surface crust,cracks and preferential flow is not clear,which leads to our insufficient understanding of the mechanism of water infiltration.Therefore,it is necessary to explore the morphological characteristics of preferential flow under the action of micro topography of sloping farmland.In this study,the micro terrain sloping farmland was taken as the research object.Through artificial rainfall simulation and dyeing tracer test,combined with high-definition photography and indoor component analysis,the soil physical properties of different types of crust were measured,and the opening and closing laws and geometric characteristics of cracks under different crust soil types were obtained.Based on the horizontal and vertical soil dyeing profile and three kinds of infiltration water（10 mm,30mm and 50 mm）,The influence of cracks on the morphological characteristics of preferential flow under different crust types is analyzed,and the preferential flow path is evaluated.The paper draws the following conclusions:（1）There are significant differences in soil physical properties between different types of crusts.Compared with structural crusts,the bulk density of sedimentary crusts is relatively large,which is 1.74 g·cm^-3.According to the analysis of soil particle composition,it is found that the proportion of sand particles in structural crusts is relatively high as 13.84%,and the proportion of clay particles in sedimentary crusts is relatively high as 2.86%.The fracture parameters of structural crust are significantly greater than those of sedimentary crust and transition zone crust.From the perspective of fracture geometry development,the development modes of different types of crust fractures are different.The structural crust fractures are reverse slope fractures,which are developed first,and the secondary fractures are developed and formed on the basis of this fracture;Sedimentary crust fractures are the main framework formed by mutual connection in the development process,and there is no special law;The crust crack in the transition zone is the first crack in the middle of the slope,and the direction is nearly linear in the reverse slope direction,spreading around in the process of development.（2）The crack area ratio and crack length density of crust soil increase with the decrease of water content.When the crack development is completed,the soil water content of structural crust is the lowest as 11.88%,the soil water content of sedimentary crust is the highest as16.84%,and the development duration of sedimentary crust crack is the longest as 357 h.During the wetting and closing process of soil crust,the crack area ratio and length density of structural crust and sedimentary crust decrease with the increase of water content.（3）With the increase of infiltration water,the development degree of preferential flow in crusted soil will increase.Under the condition of infiltration water of the same intensity,compared with sedimentary crusts,the dyeing area of structured crusted soil is larger,the difference of preferential flow indicators is obvious,and the development degree of preferential flow is higher.Compared with the sedimentary crust soil with low development degree of preferential flow,the change of soil water content of structured crust soil is less.Comparing the crack morphology with the preferential flow dyeing path,it is found that the coincidence proportion of structural crust is higher and is more affected by cracks,Under the condition of 10 mm,30 mm and 50 mm infiltration water,it is 9.09,3.85 and 6.67 times that of sedimentary crust.At the same time,the preferential flow dyeing area of structural crust soil corresponds to the crack morphology,and the morphology of dyeing area mainly depends on the geometric characteristics of primary cracks.