Linking pore structure characteristics to soil strength and their relationships with detachment rate of disturbed Mollisol by concentrated flow under freeze–thaw effects

In mid-high latitude areas, seasonal freeze–thaw cycles generate significant effects on pore structure of soils, and in turn, affect soil mechanical properties and soil erosion processes. Furthermore, soil particles can be detached on ridged farmland by snowmelt or rainfall concentrated flow due to topographic relief during the spring snowmelt period. To explore the changes in pore structure characteristics under freeze–thaw effects on soil detachment rates under simulating concentrated flow, fifteen soil columns and twenty soil tanks underwent a freeze–thaw pre-treatment of zero, one, five, ten, and fifteen cycles. Soil structure characteristics were quantitatively obtained by scanning soil columns with industrial computer tomography at a 25-μm resolution. Soil strength was measured by a portable vane shear instrument on the surface of soil tanks. Detachment rates of soil tanks were measured in a flume under changeless flow shear stress (τ = 2.32 Pa). Results indicated that freeze–thaw effects significantly decreased soil strength by changing pore network structure, including increasing total imaged porosity and elongated-pore porosity. The detachment rate significantly rose with the rising freeze–thaw cycles (p < 0.05) and had a power relationship with the soil strength (R2 = 0.503, p < 0.05). Thus, the increase in detachment rate was mainly caused by the decrease in soil strength, which is dependent on large and elongated pores that formed during freeze–thaw cycles and on the geometrical characteristics of the pore network. The findings improve the understanding of the generation mechanism of soil erosion as a result of changes in pore structure characteristics during the spring snowmelt period.