Experimental Study On Water Conductivity Of Surface Crust Soil In Sloping Farmland

During the rainfall process,due to the splashing action of raindrops,the surface of the soil will form a dense crust surface.The existence of crust restricts the movement of soil moisture.In order to study the effect of crust formed by different rainfall durations on soil hydraulic conductivity,In this paper,bauxite was used as the research object,though the surface of the sloping farmland was formed by artificial rainfall and the modified Mini-Disk Infiltrometer portable permeameter was used to determine the change of soil hydraulic conductivity under different rainfall durations.The results show that:(1)Under the condition of rainfall,the structure is crusted on the ridge,and the deposited crust is produced between the ridges.During the 30min rainfall process,the soil crust experienced the development process from thinning to thickening,reflecting the process of crust formation and development is a dynamic cycle process of continuous erosion and compaction and reorganization.The thickness of the structure crust was respectively the peaks appeared at 10min and 20 min,and the thickness of the deposited crust continued to increase throughout the rainfall and stabilized after 20 min.(2)The cumulative infiltration of crust soil with crust thickness less than 5mm is higher than that without crust soil,the crust thickness is about6mm,the crust is fully developed and the cumulative infiltration of crust soil is much lower than that without crust soil and the stable infiltration rate of the skin is about twice that of the deposition crust.Compared with the non-crusted soil,the structural crust barrier effect formed by the 30min rainfall period was 52.98%,and the sedimentary crust barrier effect was 61.76%.The sediment density of the sedimentary crust during the whole rainfall duration is higher than that of the contemporaneous structural crust,and the soil crust becomes more compact as the rainfall lasts.(3)The soil crust development tends to be stable after 20 min of rainfall,and the stable water conductivity of crust-structured crust soil is higher than that of ridge intercropped crust soil,and the increase of crust thickness reduces the stable hydraulic conductivity of crust soil.The stable hydraulic conductivity of soil without crusts was14.83×10~-44 cm/s.The lowest value of stable soil hydraulic conductivity was 3.35×10~-44 cm/s during 30min rainfall,and the stable hydraulic conductivity of sedimentary crust soil.The lowest value is 2.97×10~-44 cm/s,and the soil hydraulic conductivity of the crust-free soil is about 5 times of the soil hydraulic conductivity of the crust.(4)During the rainfall process,the soil crust undergoes three developmental stages:the first stage rainfall is less than 5 min,the soil crust is in the unstable stage of development;the second stage is 5 min to 20 min,the soil crust is disturbed and compacted.The cycle of the cycle;the third stage of 20min to 30min,the soil crust is basically fully developed,the thickness of the structure crust reaches 6.58mm,and the thickness of the deposited crust reaches 5.78mm.The research can provide an important basis for accurate and effective forecasting of slope land flow.