松散土体中细颗粒运移的微观过程研究

Field observations show that loose soils are common deposit in gullies after an earthquake which provides ideal sources of material for debris flows and landslides. During rainfall infiltration process, pore structure provided by coarse soil skeleton provids a natural flow channel inside soil for fine particles to migrate, thus degrading the stability of soil structure and causing further slope failure. Pervious study of fine particle migration in soil mainly focused on seepage experiments, mid-scale flume test with rainfall as a boundary condition, and other macro-scale methods. However, these methods could not directly obtain the parameters such as pore structure, velocity of fine particles, and pore pressure inside soil sample to quantify the internal erosion process. In the current study, a series of one-dimensional cylinder microscopic seepage tests were designed, the coarse to fine particle size ratio was chosen as a controlling parameter, the three-dimensional computed tomography technology in Shanghai Synchrotron Radiation Facility (SSRF) was then used to quantify the characteristics of fine particle migration during seepage process. The numerical simulation using discrete element method (DEM) coupled with Darcy's flow was then used to back analysis the physical test. The results of CT and numerical calculations revealed that there existed preferential erosion in the inflow and outflow region of the soil sample. When the numerical simulation is calculated to 2.5s, 37.05% and 31.95% of the fine particles had been eroded in above two regions, respectively, while the erosion at other locations is relatively low. The form of fine particle erosion inside the soil in the direction of seepage includs the loss balance of loss and supply and gradual erosion. The average kinetic energy of the fine particles tends to increase along the seepage path. On the one hand, the forming of long-term clogging to flow channels is reflected by the decreasing of average kinetic energy and quantity of fine particles with time; On the other hand, the temporary clogging to flow channels is reflected by the rate of increase of the number of fine particles in the measurement region larger than the rate of increase of average kinetic energy. The fine particle migration characteristics in the soil on the microscopic scale are mainly affected by the fluid state and pore characteristics, and its research is of great value for understanding the mechanism of loose soil slope failure.