延安地区降雨引发黄土泥流的试验研究

在野外模拟降雨条件下,研究了黄土粒度分布和微结构在降雨前后的变化及其对泥流启动的影响.结果表明,采自径流沉积物的降雨后土样中的细黏粒、粗黏粒体积含量分别相对增加了22％和18％,而粗粉粒、微砂体积含量分别相对减少了7.6％和3.3％.坡面残余土的粒度“粗化”,降雨后土骨架连接松散,这些由降雨引起的黄土的粒度和微结构变化说明降雨后黄土的抗剪强度和抗压能力将降低,导致泥流启动的可能性增加.随着降雨入渗,当沿坡面的黄土重力分力与抗剪强度间的平衡被打破,黄土开始滑移并发展成泥流.有效防止坡面土粒度“粗化”是遏制水土流失的关键.

Experimental Study on Loess Mudflow Induced by Rainfall in Yan'an Area

The changes of grain size distribution and microstructure of loess after rainfall were investigated inthis study,as well as their effects on the initiation of mudflow.A simulated rainfall experiment was conducted in field for this purpose.We found that after rainfall,the volumetric percentages of fine and rough clayparticles increase approximately 22% and 18%,and those of silt and fine sand decreased 7.6%and 3.3%,respectively,in the samples collected from the sediment deposits.Consequently,the grain size of residual loess on the slope coarsened and the connection of loess skeleton became loose after rainfall.Such changes ofgrain size and microstructure of loess induced by rainfall implies that both of the shear and pressure resistanceof loess will decrease after rainfall.Thus,the probability of the mudflow initiation increases.Once the balance between the gravitational component of loess along the slope and the shear resistance is broken as therainfall penetrates,the loess begins to slip and possibly develops into mudflow.Preventing the loess on theslope effectively from being coarsened is the key to mitigate water loss and soil erosion.