金沙江干热河谷冲沟区优先流影响下的土壤力学特性

Soil Mechanical Properties Under the Influence of Preferential Flow in the Gully Area of Jinsha River′s Dry-hot Valley

为探究金沙江干热河谷冲沟区优先流与土壤力学的相关机理,揭示优先流影响下土壤抗剪强度特征规律,丰富干热河谷冲沟发育区沟侵蚀机理,为该地区进一步开展沟蚀治理提供理论依据。在典型冲沟发育区选择完整冲沟为研究对象,基于染色示踪、土壤理化、原状土直剪试验,利用RDA等统计方法分析优先流与土壤力学指标间的相关性,明晰优先流和抗剪强度的关系。结果表明:(1)由于冲沟发育使冲沟内由集水区到沟底优先流发育程度逐渐降低。土壤含水率、容重、总孔隙度、有机质含量均呈优先流区大于基质流区,机械组成分形维数整体上基质流区(2.680~2.874)大于优先流区(2.746~2.893)。(2)冲沟区优先流通过影响土壤黏聚力和内摩擦角进而对抗剪强度产生影响,一定程度上会降低土体抗剪强度。集水区、沟头抗剪强度大于沟床和沟底。优先流区黏聚力(1.24~2.65 kPa)小于基质流区黏聚力(1.91~4.27 kPa),优先流区内摩擦角(19.52°~22.47°)略大于基质流区内摩擦角(17.68°~22.35°),优先流区抗剪强度(36.66~43.68 kPa)整体小于基质流区抗剪强度(38.74~47.32 kPa)。(3)优先流与土壤黏聚力和内摩擦角有不同程度的相关性。土壤黏聚力与染色面积比、基质流深度呈显著负相关,内摩擦角与优先流百分数、优先流区染色面积比呈负相关;抗剪强度与染色面比、最大染色深度、优先流百分数、优先流区染色面积比呈负相关。

In order to explore the correlation mechanism between preferential flow and soil mechanics in the gully area of the dry-hot valley of Jinsha River and reveal the characteristics of soil shear strength under the influence of priority flow,to enrich the mechanism of gully erosion in the development area of hot and dry river valleys and provide theoretical basis for further gully erosion control in this area,the intact gully in the typical gully development area were selected as the study object,and based on staining tracer,soil physicochemical and intact soil straight shear experiments,the correlation between priority flow and soil mechanical indexes were analyzed by statistical methods such as RDA,and to clarify the relationship between preferential flow and shear strength.The results showed that:(1)Due to the development of ditch,the preferential flow development degree from the catchment area to the bottom of the ditch was gradually reduced.The soil moisture content,bulk density,total porosity and organic matter content in the preferential flow area were higher than that the matrix flow area,and the fractal dimension of mechanical composition in the matrix flow area(2.680~2.874)was greater than that in the preferential flow area(2.746~2.893).(2)The preferential flow area in the gully area affects the soil cohesion and strength,which will reduce the soil shear strength to a certain extent.The shear strength of the water catchment area and the trench head was greater than that of the ditch bed and the ditch bottom.The cohesive in the preferential flow region(1.24~2.65 kPa)was smaller than that in the matrix flow area region(1.91~4.27 kPa),the internal friction angle in the preferential flow region(19.52°~22.47°)was slightly larger than that in the matrix flow area region(17.68°~22.35°),and the shear strength of the preferential flow area region(36.66~43.68 kPa)was generally smaller than that of the matrix flow area region(38.74~47.32 kPa).(3)The preferential flow had different degree of correlation with soil cohesion and internal friction angle.Soil cohesion was significantly negatively correlated with dyeing area ratio and stroma flow depth,while internal friction angle was negatively correlated with the percentage of the preferential flow and dyeing area ratio of preferred flow area.The shear strength was inversely correlated with the ratio of staining surface,the maximum dyeing depth,the percentage of preferential flow and the dyeing area of the preferential flow area.