Effects of Freeze-thaw Cycles on Gully Wall Collapse in the Black Soil Region of Northeast China
[Objective]To evaluate the contribution of freeze-thaw cycle(FTCs)to gully erosion by measuring the collapse volume of gully wall collapse during FTCs.[Methods]From 2016 to 2018,a total of 463 collapse points in 36 gullies were selected for field investigation.Based on the investigation results,there were two types of wall collapse:massive collapse and loose accumulation.The morphology parameters of two kinds of accumulations were measured at each collapse point,including the volume of the collapsed soil,the width and depth of the gull coross-section,and the shear force and hardness of soil of the corresponding gully wall soil.[Results](1)The average collapse strength of gully wall collapse caused by FTCs during the three-year study period is 16.12 m3/(km·a).The two types of collapse occurred randomly within the gully,and the single point freeze-thaw collapse mainly concentrated in 0～3 m3,but the amount of soil caused by massive collapse was larger.(2)The transverse width and depth of the gully were the main factors affecting the collapse of the gully wall,and the collapse amount increased with the increase of the width-depth ratio.When the width-depth ratio＞2.71,the collapse amount increased rapidly.(3)The amount of gully collapse was closely related to the shear force and hardness of the soil on the gully wall.[Conclusion]The freeze-thaw collapse of the gully wall was closely related to the width and depth of the gully cross-section,the freeze-thaw collapse accounted for 3.28％to 23.68％of the sediment yield of the gully erosion,and its influence was equivalent to that of the headward erosion of gully head.The research results provide data support for quantitatively evaluating the contribution of FTCs to gully erosion.
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