黄河中游陕北煤矿区沉陷坡面不同部位土壤抗冲性变化规律

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

    • 摘要: 为明确采煤沉陷条件下黄土坡面表层土壤抗冲性变化特征,以黄河中游陕北柠条塔煤矿沉陷坡面为对象,将坡面划分为坡顶、坡中和坡脚,并以未沉陷自然坡面作为对照组(CK),通过野外采样、土壤理化性质测定和原状土冲刷试验,分析不同坡位土壤结构特征、径流泥沙量及抗冲系数差异。结果表明:沉陷后表层土壤质地类型未发生改变,仍为粉质壤土,但颗粒组成和结构稳定性发生变化。与对应CK相比,坡顶、坡中和坡脚砂粒质量分数分别增加8.8%、2.9%和2.8%,黏粒质量分数分别降低1.1%、6.9%和7.0%,土壤孔隙度分别增加4.1%、2.1%和1.4%;>0.25 mm水稳性团聚体质量分数分别降低25.3%(p<0.05)、15.5%(p<0.05)和3.1%,有机质质量分数分别降低7.7%、6.8%和3.3%。原状土冲刷结果显示,不同坡位径流泥沙量随冲刷时间延长均呈“速增-缓增-稳持”变化,0~4 min泥沙量占10 min总泥沙量的90%以上。相较CK,沉陷坡面累积径流泥沙量增加,1 min时坡顶、坡中和坡脚增幅分别为14.4%、10.2%和6.0%;抗冲系数则整体降低,退化程度表现为坡顶>坡中>坡脚。相关性分析显示,4 min累积径流泥沙量与砂粒质量分数、孔隙度呈极显著正相关(p<0.01),与黏粒和有机质质量分数呈极显著负相关(p<0.01);4 min抗冲系数与上述指标呈相反关系。综上,采煤沉陷通过促进颗粒粗化、孔隙度升高、团聚体稳定性下降和有机质减少,削弱坡面表层土壤抗冲性,其中坡顶响应最为明显。研究结果可为陕北煤矿区沉陷坡面水土流失分区防控提供依据。

       

      Abstract: 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.

       

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