不同雨强和覆盖度条件下崩积体侵蚀泥沙颗粒特征

崩积体坡面侵蚀泥沙颗粒的变化特征及过程研究是揭示崩岗崩积体侵蚀机理的关键。基于崩岗崩积体土质疏松、粗颗粒含量高、极易被侵蚀的特性,通过室内人工模拟降雨试验,研究30°坡度条件下,不同覆盖度(0,25%,50%,75%,100%)和雨强(60,90,120 mm h-1)组合坡面侵蚀泥沙颗粒特征。结果表明:降雨过程中,坡面径流优先搬运的是粒径较小的泥沙颗粒;侵蚀泥沙中粗颗粒(砾石和粗砂)泥沙含量随着覆盖度的增加呈先减小后增大趋势;侵蚀泥沙颗粒的平均重量直径(MWD)与覆盖度之间呈极显著相关;当覆盖度达到50%时,坡面粗颗粒泥沙的减少效果最明显,75%覆盖度坡面较容易发生崩塌。以上结果表明,侵蚀泥沙颗粒的大小与坡面秸秆覆盖度的高低密切相关,50%左右的秸秆覆盖度可以达到较好的减沙效果。

Particle Size Composition of Erosion Sediment from Colluvial Deposits of Collapsing Hill as Affected by Rainfall Intensity and Coverage

AbstractObjective]Collapsing hills are widely distributed in granite-covered areas of tropical and subtropical South China,characterized by being high in erosion rate,strong in explosiveness and difficult to control. Colluvial deposits,formed of materials accumulated at the foot of the collapsing wall,are an important component of a collapsing hill,and meanwhile as they are loose in texture,high in content of coarse particles and high in erodibility,they become the main source of erosion sediment in the area. The erosion of colluvial deposits has aroused widespread attention,however,the current study on colluvial deposits still has some shortages. For instance,so far nothing has been reported on characteristics of the disturbed soil of colluvial deposits and laws of the erosion thereon.Method]Therefore,to study properties of erosion sediment from colluvial deposits,an indoor rainfall simulation experiment was carried out on slopes of colluvial deposits,30° in gradient,different in coverage(0,25%,50%,75%,100%)and different rainfall intensity(60,90,120 mm h-1),SPSS18. 0 was used to analyze relationships of the characteristics of particle size composition with coverage.Result]Results show as follow:(1)The mean content of coarse sand was much lower,and the mean content of fine silt much higher than that in the test soil. During the process of rainfall,runoff on the slopes carried long with it soil,particles small in size first;The mean enrichment rates of fine sand,coarse silt,fine silt and clay were all higher than 1 in the sediment.(2)The content of coarse particles(gravel and coarse sand)reduced first,then rose again and the content of fine particles(fine sand,coarse powder,fine silt and clay)did not very much with increasing coverage.(3)On slopes,varying in the range of 0~25% in coverage,the content of fine particles reduced slowly,while the content of gravel and coarse sand rose gruadually with the rainfall going on;on slopes 50% in coverage,the content of fine particles remained high,while the content of coarse particles stayed low throughout the rainfall event;and on slopes reaching 75% in coverage,the content of soil particles various in size fluctuated sharply during the course of a rainfall event,and in this case,collapse of the slopes occurred readily.(4)And the mean weight diameter(MWD)of the erosion sediment decreased first and then increased with increasing coverage.Conclusion]MWD of sediment particles was found to be significantly related to coverage of the slope,rather than rainfall intensity. When the coverage of the slopewas around 50%,the effect of sediment reducing was better. Therefore,in the process of prevention of erosion,we should pay attention to the control of the coverage on slopes.