Variation patterns of soil anti-scourability at different positions of subsidence slopes in the Northern Shaanxi coal mining area of the middle Yellow River

To clarify the variation characteristics of surface soil anti-scourability on loess slopes under coal mining subsidence, a subsidence slope in the Ningtiaota Coal Mine, Northern Shaanxi, in the middle reaches of the Yellow River is selected as the study object. The slope is divided into three positions: slope top, slope middle and slope foot, and an undisturbed natural slope is used as the control （CK）. Field sampling, measurements of soil physicochemical properties and undisturbed soil scouring experiments are conducted to analyze the differences in soil structural characteristics, runoff sediment yield and anti-scourability coefficient among different slope positions. The results show that the surface soil texture type did not change after subsidence and remained silty loam, but the particle composition and structural stability changed. Compared with the corresponding CK, the sand mass fractions at the slope top, slope middle and slope foot increase by 8.8%, 2.9% and 2.8%, respectively, while the clay mass fractions decrease by 1.1%, 6.9% and 7.0%, respectively; soil porosity increase by 4.1%, 2.1% and 1.4%, respectively. The mass fractions of ＞0.25 mm water-stable aggregates decrease by 25.3% （p＜0.05）, 15.5% （p＜0.05） and 3.1%, respectively, and organic matter contents decrease by 7.7%, 6.8% and 3.3%, respectively. The undisturbed soil scouring experiment shows that runoff sediment yield at different slope positions exhibit a three-stage pattern of “rapid increase-slow increase-stabilization” with increasing scouring time, and the sediment yield during 0-4 min accounts for more than 90% of the total sediment yield within 10 min. Compared with CK, the cumulative runoff sediment yield of the subsidence slope increases; at 1 min, the increases at the slope top, slope middle and slope foot are 14.4%, 10.2% and 6.0%, respectively. The anti-scourability coefficient decreases overall, and the degree of degradation follows the order of slope top ＞ slope middle ＞ slope foot. Correlation analysis shows that the 4 min cumulative runoff sediment yield is extremely significantly positively correlated with sand mass fraction and porosity （p＜0.01）, and extremely significantly negatively correlated with clay and organic matter contents （p＜0.01）. The 4 min anti-scourability coefficient shows the opposite relationships with these indicators. In summary, coal mining subsidence weakens surface soil anti-scourability by promoting particle coarsening, increasing porosity, reducing aggregate stability and decreasing organic matter content, with the most pronounced response occurring at the slope top. The results can provide a basis for zonal prevention and control of soil and water loss on subsidence slopes in the Northern Shaanxi coal mining area.