降雨击溅下鄂尔多斯松散砒砂岩粒径分选特性及其敏感性分析

Grain size sorting characteristics of loose Pisha-sandstone in Ordos under rainfall splash and its sensitivity analysis

为揭示降雨初期鄂尔多斯砒砂岩区松散砒砂岩的溅蚀机理,在室内开展人工降雨击溅侵蚀试验,研究降雨强度、坡度对松散砒砂岩溅蚀的影响。结果表明:1)利用变动率指标反映各粒级区间颗粒数量的变动幅度,能够更清晰直观反映溅蚀土样中各粒级颗粒数量受坡度、降雨强度的影响程度;2)坡度、降雨强度是砒砂岩发生溅蚀的主要影响因子,坡度在<30°时,降雨强度是影响降雨溅蚀的最敏感因子,随着坡度的不断增大,坡度对砒砂岩溅蚀的敏感性增强;3)松散砒砂岩表土颗粒在20°坡面上最易发生降雨溅蚀;4)溅蚀对砒砂岩散土颗粒中的细砂分选作用最为显著,其次是中砂、极细砂、粉砂。松散砒砂岩发生溅蚀的严重程度是降雨强度、坡度、土壤颗粒大小等多因素共同耦合作用的结果。深入分析溅蚀对松散砒砂岩粒径的分选规律,可为后续深入研究砒砂岩区的水力侵蚀机理提供参考。

[Background]Soil erosion is very serious in the Pisha-sandstone area of Inner Mongolia Ordos,and rainfall erosion is an important factor causing soil erosion in Pisha-sandstone,while rainfall splash is the main erosion mode of soil at the early stage of rainfall.Since splash dispersion changes soil particles in the parent material,it is important to investigate the sorting law of rainfall splash on the particle size of loose Pisha-sandstone and the sensitivity to the sorting of particle size at all levels to reveal the mechanism of erosion of loose Pisha-sandstone at the beginning of rainfall.[Methods]Indoor artificial rainfall simulation was used to conduct spattering experiments on loose Pisha-sandstone.In order to reveal more clearly and intuitively the sorting degree of each particle size in the splash erosion samples by rainfall intensity and slope,the magnitude of the absolute value of the change rate was introduced to indicate the variation of the number of particles in each grain size interval,and the trend of the variation was reflected by the positive or negative rate of change.[Results]The slope and rainfall intensity are the main influencing factors for the occurrence of spattering erosion of Pisha-sandstone.On the slope with slope less than or equal to 20°,rainfall intensity is the most sensitive factor for splash erosion of loose Pisha-sandstone,in which the percentages of medium sand,fine sand and very fine sand particles increase with the increase of rainfall intensity,and the percentages of up-slope quantity are always larger than those of down-slope;while the percentages of powder sand quantity decrease with the increase of rainfall intensity,and the percentages of up-slope quantity are smaller than those of down-slope.In the slope with slope greater than or equal to 30°,the sensitive factors of spattering of loose Pisha-sandstone are slope and rainfall intensity,and the increase of rainfall intensity makes the size of soil particles that can be migrated gradually increase;when the slope and rainfall intensity are the same,the percentage change of the number of fine sand particles is the largest,and the effect of spattering on the sorting of fine sand is the most significant,then the medium sand,very fine sand,and silty sand in order.[Conclusions]The severity of spatter erosion occurring in loose Pisha-sandstone is the result of the combined coupling of multiple factors such as rainfall intensity,slope,and soil particle size.Among them,rainfall intensity and ground slope have the greatest effect,but the sensitivity of these two factors can vary depending on the size of different particles.