| Soil erosion has become a serious worldwide environmental problem,not controlled will lead to soil degradation,land productivity decline,thus affecting agricultural production and food security,severely restricts the social and economic sustainable development in the world,therefore,soil erosion has gradually become the main limiting human survival and development environment.The main influencing factors of soil erosion are different in different soil erosion areas.Freeze-thaw erosion,as one of the main types of soil erosion,is a kind of soil erosion phenomenon that intensifies the influence of other external forces under the action of freeze-thaw,and as an important type of soil erosion,it has a wide distribution area.Northeast China is one of the main freeze-thaw erosion distribution areas in China,which is mainly mild and moderate,and the impact of freezethaw erosion on human survival and development has become more and more obvious.As an important commodity grain base in China,it is very important for the national grain production and social stability to define the soil erosion and prevention mechanism in northeast China.In this paper,the typical black soil in the typical black soil area of northeast China was selected as the research object,and the impact of freeze-thaw action on soil anti-scour and anti-shear force was studied by using simulated snowmelt runoff erosion experiment.The main results show that with the increase of freeze-thaw cycle,the amount of eroded sediment increases gradually.The soil anti-scour coefficient decreases with the increase of freeze-thaw cycle times.When the freeze-thaw cycle times reach 15 times,the soil anti-scour coefficient changes stably.When the freezing and thawing cycles for 1,5,10 times,freezing and thawing cycles without significant effect on the rate of sediment erosion(p > 0.05),when the freeze-thaw cycles to reach 15,20 times,erosion sediment erosion rate is higher,the initial were 13.8 g · s-1 and 13.1 g · s-1,freezing and thawing cycles effect on sediment loss rate significantly(p < 0.05);In the repeated freeze-thaw process,aggregates of 2-0.25 mm grain size dominated the eroded sediment.With the increasing number of freeze-thaw cycles,the size of 5-2mm grain aggregates decreased and that of < 0.25 mm grain aggregates increased.Soil shear strength decreases with the increase of freeze-thaw cycle times,and there is a significant difference between the shear strength of soil samples without freeze-thaw and that of soil samples with freeze-thaw cycle for 20 times.Under the action of freezing and thawing were studied with CT scans,black soil pore structure characteristics of the change of the research results show that the overall after freezing and thawing soil porosity is greater than the freezing and thawing soil porosity,and with the increase of freeze-thaw cycles,total porosity increased,soil hole and the main form is live with extended pore,pore accounted for more than 95% of the total porosity,with the increase of freeze-thaw cycles remain obvious growth trend,and rules of porosity and irregular porosity decreases.As the number of freeze-thaw cycles increased,the total pore number first increased and then decreased.When the freeze-thaw cycles were 5 times,the pore number reached the maximum.Among them,the number of lengthened pores decreased significantly with the increase of freeze-thaw cycles,and the number of lengthened pores in unfreeze-thaw soil samples was up to 18,while only one remained with the increase of freeze-thaw cycles.The number of irregular pores accounted for 12%-17.6% of the total number of pores,and the number of regular pores accounted for 82-87.9% of the total number of pores.In this study,due to the remolded soil,the soil sample foundation has large pores,limited by the resolution,and no storage pores < 30 m after treatment.The number of capillary pores and non-capillary pores first increased and then decreased with the increase of freezing-thawing cycles.The proportion of capillary pores in total pores gradually increased and that of non-capillary pores in total pores gradually decreased.Capillary porosity first increases and then decreases with the number of freezethaw cycles,while non-capillary porosity first decreases and then increases.With the increase of freezing-thawing cycles,the total specific surface area of soil pores first rose and then decreased.When the freezing-thawing cycles reached 5 times,the total specific surface area reached the maximum and then gradually decreased.It may be that the soil sample is a disturbed backfill.When the freezing-thawing cycle is 5 times,it reaches the state of original soil,with the maximum porosity richness and strong cementing ability between soil particles.The total specific surface area reaches a critical value and then decreases with the increase of freeze-thaw cycle.In addition,the correlation between the parameters of black soil pores under freeze-thaw cycle was analyzed.Finally be most soil total porosity and the pore parameters,there were significant or extremely significant correlation between the same soil pore morphology parameters extended pore,irregular pore,rules,porosity and capillary porosity,capillary porosity,specific surface area were respectively with a significant role in other parts of the pore characteristic parameters and extremely significant correlation.In order to further study black soil pore structure characteristics of the change of soil resistance to erosion and soil shear resistance of quantitative relation by using partial least squares regression method carries on the quantitative analysis(PLSA),total porosity,irregular porosity,extended porosity and capillary porosity is under the influence of the freeze-thaw cycle impact on soil shear resistance and impact coefficient of main soil pore characteristic factors. |
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