Effect Of Freeze-thaw On Detachment Capacity And Erodibility Of Soil Physical Crusts

Soil detachment capacity is an indicator to measure the rate of soil detachment and is the first process of soil erosion.Research on soil detachment capacity can lay a foundation for the study of soil erosion.Soil detachment capacity is affected by many factors.Physical crust is a dense layer formed on the soil surface,which affects the soil detachment capacity.Freeze-thaw destroy the physical crust and further change the process of soil detachment capacity.In this study,sandy loess in the north of the Loess Plateau was used as the research object to prepare physical crusts with different strengths(low strength crusts,medium strength crusts,high strength crusts),combined with the indoor freeze-thaw simulation,the soil detachment test was conducted to study the change of soil detachment capacity under non-freeze-thaw and freeze-thaw conditions,and the effect of freeze-thaw on the soil detachment capacity of physical crust was investigated.Through correlation analysis,the influence of crust characteristics on soil detachment capacity was analyzed.Soil erodibility was calculated,the influence of physical crust on soil erodibility under freeze-thaw condition was studied.The results are as follows:(1)To clarify the effects of freeze-thaw on physical junction cortical properties.Freez-thaw can significantly reduce the bulk density,hardness and shear strength of the crust.The bulk density of the crust after freeze-thaw changed the most when the water content was 8%,which decreased by 14%,8% and 9% compared with that before freeze-thaw,respectively.With the increase of crust strength,the influence of freezethaw on crust hardness is greater,and the freeze-thaw hardness decreases by 10%,35%and 25%,respectively.When the water content was 8%,the influence of freeze-thaw on the shear strength of crust with different strengths was the greatest,which decreased by 28%,70% and 70%,respectively.The thickness of high strength crust was significantly affected by freeze-thaw,but the difference between low strength crust and medium strength crust was not significant.There was no significant difference in crust bulk density between different strengths under non-freeze-thaw conditions,and the other crusts characteristics were significantly positively correlated with crust strength.Under freeze-thaw conditions,the bulk density,hardness and shear strength of the crust increased with the increase of the crust strength,while the thickness of the crust showed that the medium strength skin was the largest,followed by the high strength crust,and the low strength crust was the smallest.(2)The effect of freeze-thaw on the detachment capacity of soil physical crust was expounded.The soil detachment capacity after freeze-thaw was greater than that before freeze-thaw,but the difference was not significant before and after freeze-thaw.The smaller the slope and the larger the physical crust strength,the greater the influence of freeze-thaw on the soil detachment capacity.Freeze-thaw had no significant effect on the soil detachment capacity with no crust and low strength crust,with contribution rates of 1%.However,freeze-thaw significantly affected the soil detachment capacity with medium strength crust and high strength crust,with contribution rates of 2% and3%,respectively.Under non-freeze-thaw conditions,soil detachment capacity was significantly positively correlated with flow and slope,and physical crust significantly affected soil detachment capacity,contributing 4%,which gradually decreased with the increase of crust strength.Under freeze-thaw conditions,the soil detachment capacity increased gradually with the increase of flow and slope,and the physical crust had no significant effect on the soil detachment capacity,with the contribution rate of 0.34%.The influence of medium strength crust on the soil detachment capacity was the greatest,followed by low strength crust and high strength crust.There is a linear relationship between soil detachment capacity and flow shear force and flow power.(3)The influence of physical crust on soil erodibility under freeze-thaw conditions was expounded.The erodibility parameters after freeze-thaw are always greater than those before freeze-thaw,and with the increase of crust strength,the influence of freezethaw on erodibility parameters is greater.Compared with non-freeze-thaw,erodibility parameters after freeze-thaw are increased by 4%,7%,29% and 33%,respectively.Freeze-thaw can reduce the critical shear force of soil crusts,but there is no obvious change rule.With the increase of crusted strength,the critical shear force decreases by58%,22%,17% and 42%,respectively.In the non-freeze-thaw condition,the erodibility parameter was larger than that with crust,while the critical shear force was smaller than that with crust.The erodibility parameter decreased with the increase of crust strength,and the erodibility parameter was negatively correlated with crust thickness.The critical shear force is the maximum of medium strength crust and the minimum of high strength crust.Under freeze-thaw condition,erodibility parameter of medium strength crust is the largest,and the critical shear force of low strength crust is the largest.