反粒序砂土体内侵蚀及渗流特性变化规律试验研究

Experimental study on the change law of internal erosion and seepage characteristics of inverse grading sand accumulation

反粒序堆积体常见于高速远程滑坡的流通区和堆积区。针对其粒径上大下小的特殊结构和较强透水性而诱发堆积体不稳定的问题,采用自制的渗流侵蚀试验装置对颗粒粒径为0.075~20 mm的7组连续及间断颗粒级配反粒序土样进行了试验,研究了反粒序砂土体渗流侵蚀过程中参数变化和细颗粒迁移模式及规律。结果表明:在反粒序堆积土样中,细颗粒含量和不均匀系数对反粒序砂土体的渗流侵蚀有重要影响,细颗粒含量越高,不均匀系数越大,则起始渗流系数越小。反粒序砂土体发生管涌颗粒跃层后,底层颗粒流失量最多,且粒径为0.075~0.125 mm的颗粒流失比最大。反粒序堆积体整体的渗流能力主要取决于底部的细颗粒含量,细颗粒含量越高,临界水力梯度越大。在连续级配土样中,水力梯度与渗流系数呈二次函数关系;在间断级配反粒序土样中,细颗粒含量超过45%时,土样趋于稳定。反粒序堆积体发生管涌后,其颗粒呈现剥离-沉淀-剥离-沉淀中下层颗粒交替侵蚀的运移模式。研究结果对于该类灾害形成机理与防治研究具有理论和实际应用意义。

Inverse grading deposits are commonly found in circulation and accumulation areas of high-speed and long-distance landslides.Due to its special structure of large particle size at the top and small at the bottom and strong permeability,the accumulation is highly susceptible to unstable failure.In this study,using a self-designed device,seepage erosion tests were conducted on seven sets of inverse grading soil samples with continuous and discontinuous particle gradation of particle size 0.075-20 mm to investigate the parameter changes and fine particle migration patterns and laws during seepage erosion of inverse grading sand mass.The results show that the fine particle content and nonuniformity coefficient have an important influence on the seepage erosion of the inverse grading soil samples.The higher the fine particle content,the greater the nonuniformity coefficient and the lower the initial seepage coefficient.After the occurrence of cross-layer tube surge particles,the bottom layer of particle loss is the most,and the particle size of 0.075-0.125 mm particle loss ratio is the largest.The seepage capacity of the inverse grading sand mass depends mainly on the content of fine particles at the bottom.The higher the content of fine particles is,the greater the critical hydraulic gradient will be.In continuous graded soil samples,the relationship between the hydraulic gradient is quadratically related to the percolation coefficient.Soil samples with discontinuous particle gradation are stabilized when the content of fine particles exceeds 45%.After tube gushing occurred in the reverse grain sequence accumulation body,the particles show a migration pattern of stripping-precipitation-stripping-precipitation alternately eroded particles in the middle and lower layers.The study has theoretical and practical significance for the formation mechanism and prevention of such disasters.