饱和状态下黄绵土坡面细沟侵蚀可蚀性和临界剪切应力特征

土壤可蚀性参数和临界剪切应力是评价土壤易侵蚀程度和抗水流剪切变形能力的重要指标，目前在黄绵土坡面细沟侵蚀过程中，土壤饱和条件下可蚀性参数和临界剪切应力的变化尚不明确。该研究采用室内土槽模拟冲刷试验确定不同坡度（5°、10°、15°、20°）和流量（2、4、8 L/min）下饱和黄绵土坡面的最大细沟剥蚀率，基于数值法、修正数值法和解析法计算土壤可蚀性参数和临界剪切应力。结果表明，3种方法所得最大细沟剥蚀率均随坡度和流量增加而增大，其中修正数值法和解析法计算的最大细沟剥蚀率更接近。土壤可蚀性参数分别是0.485、0.283和0.268 s/m，土壤临界剪切应力分别为1.225、1.244和1.381 N/m2。修正数值法可提高数值法近似计算的精度，使近似计算结果更接近解析法计算获得的理论值。饱和较未饱和黄绵土的土壤可蚀性参数略有减小（16.83%），而临界剪切应力减小了66.97%，表明土壤饱和对黄绵土土壤可蚀性参数影响很小，但大幅度削弱了土壤临界剪切应力，使得黄绵土坡面饱和后土壤侵蚀更为强烈。此外，饱和黄绵土边坡的临界剪切应力比饱和紫色土坡面大6.38%，而细沟可蚀性参数大2.35倍，表明土壤饱和对2种土壤临界剪切应力影响程度相似，但黄绵土较紫色土对土壤侵蚀的敏感性更高。研究结果可为饱和状态下不同土壤坡面细沟侵蚀模型参数的优化提供参考。

Characteristics of soil erodibility parameter and critical shear stress on saturated loess soil slope

Soil erodibility parameter and critical shear stress are important indicators to evaluate the degree of soil erosion sensitivity and the resistance to the shear deformation of water flow. To date, the change of soil erodibility parameter and critical shear stress is unclear in the rill erosion process of saturated loess soil slope. In this study, the maximum rill detachment rates of saturated loess soil slope were determined by a series of soil scouring experiments in the laboratory under different slopes (5°, 10°, 15°, and 20°) and flow rates (2, 4, and 8 L/min). Then, the numerical, modified numerical, and analytical approaches were utilized to calculate the soil erodibility parameters and critical shear stresses. The results showed that the maximum rill detachment rates calculated by the three methods increased with the increase of slope and flow rate over saturated loess soil slope, and the maximum rill detachment rates calculated by the modified numerical method were similar with those calculated by the analytical method. The soil erodibility parameters were 0.485, 0.283, and 0.268 s/m, respectively, and the critical shear stresses were 2.225, 1.244, and 1.381 N/m2, respectively. The modified numerical method improved the calculation accuracy, thus the modified numerical calculation was close to the theoretical value calculated by the analytical method. The soil erodibility parameters of saturated loess soil slope decreased by 16.83%, and the critical shear stresses decreased by 66.99%, compared with those of non-saturated loess soil slope in the same study area. Soil saturation had no significant effect on the soil erodibility parameters, while greatly reducing soil critical shear stress, and then leading to serious soil erosion on loess soil slope. Besides, the critical shear stresses of the saturated loess soil slope were 6.38% larger than those of the saturated purple soil slope, and the soil erodibility parameters of the saturated loess soil slope were 2.35 times those of the saturated purple soil slope. These results indicated that the soil saturation had similar effects on the critical shear stress of the two soils, while the saturated loess soil was more sensitivity on soil erosion than the saturated purple soil. These findings can provide some references to optimize the rill erosion model parameters in different soil slopes under the condition of saturations.