渗流是引起土石混合填料中细颗粒流失，致使土体结构变化引起路基变形及失稳的关键因素。采用自行研发的颗粒流失试验装置，对不同级配的土石混合填料进行渗流试验，监测渗流作用下填料的透水质量、细颗粒流失量和沉降量的变化过程，分析土体结构演变过程；采用PFC^3D （Particle Flow Code in 3D）对细颗粒流失过程进行数值模拟，分析填料孔隙和粒径动态变化特性。研究结果表明：透水质量和细颗粒流失率可以反映土石混合填料结构对水分的敏感程度。填料骨架结构对水分的敏感程度越低，可及时有效地排出水分，渗流对结构的破坏越小。渗流条件下土石混合填料的结构演化过程可分为细颗粒快速流失、骨架重塑和相对稳定3个阶段，其中骨架重塑阶段是引起其结构演化的关键阶段。细颗粒快速流失阶段，每小时透水量增长速率较快，细颗粒大量流失，沉降量很小；骨架重塑阶段，每小时透水量变化速率减缓，细颗粒流失量减少，但骨架结构重组导致颗粒产生明显的相对位移，沉降量增长较快；相对稳定阶段，每小时透水量变化缓慢，沉降量基本保持不变。颗粒流失数值模拟的过程表明细颗粒组分的迁移引起填料孔隙率产生变化，致使土体结构发生改变。上述结果表明，在所研究的几种填料中，n=0.55级配下土石混合填料的骨架结构最稳定，对水分的敏感性最弱。

Seepage is a key factor that causes the loss of fine particles in soil-rock mixture fillers and leads to changes in soil structure and subgrade deformation and instability. In this paper, the self-developed particle loss test device was used to carry out the seepage test of soil-rock mixture fillers with different gradations. The change process of permeable quality, fine particle loss and settlement of fillers under seepage was monitored, and the evolution process of soil structure was analyzed. Particle Flow Code in 3D (PFC^3D) was used to simulate the process of fine particle loss, and the dynamic change characteristics of soil porosity and filler particle size were analyzed. The results show that the permeability quality and fine particles loss rate can reflect the sensitivity of soil-rock mixture fillers structure to water. The lower the sensitivity of filler skeleton structure to water, the less the damage of the seepage to the structure, because the water can be discharged timely and effectively. The structural evolution process of soil-rock mixture fillers under seepage conditions can be divided into three stages, namely, stage of rapid loss of fine particles, skeleton remodeling stage, and relatively stable stage. The skeleton remodeling stage is the key stage to cause structural damage. In the stage of rapid loss of fine particles, the growth rate of per hour permeable quality is fast, a large number of fine particles are lost, and the settlement is small. In the skeleton remodeling stage, the change rate of per hour permeable quality slows down, and the loss of fine particles decreases. However, the reorganization of skeleton structure leads to obvious relative displacement of particles, and the settlement increases rapidly. In the relatively stable stage, the per hour permeable quality changes slowly and the settlement remains basically unchanged. The process of particle loss numerical simulation shows that the migration of fine particles causes the change of porosity of fillers, resulting in the change of soil structure. The results show that, among the studied fillers, the soil-rock mixture fillers with n=0.55 has the most stable skeleton structure and the weakest sensitivity to water.