Suffusion is the phenomenon responsible for internal erosion, and is the process by which finer soil particles are moved through the constrictions between the larger soil particles by seepage forces. Generally, gap-graded soil is known to be susceptible to suffusion. Meanwhile, suffusion of well-graded silty sand and the resulting soil behavior are not well understood. Moreover, the previous researches on laboratory suffusion tests focused on the study of the critical hydraulic gradient, which triggers the internal instability of the soils within a short period of time. Therefore, in this study, long-term suffusion tests were conducted on well-graded silty sand under a hydraulic gradient lower than the critical value. As a result, abrupt increases in permeability and amount of soil discharged were observed due to the progressive migration of the soil particles, resulting in suffusion even at a relatively low hydraulic gradient.

溢流是造成内部侵蚀的现象，是细粒土壤通过渗流力穿过较大土壤颗粒之间的收缩的过程。一般而言，已知间隙级配的土壤易受溢流影响。同时，对细粒级粉砂的泛滥和由此产生的土壤行为还不是很了解。此外，以往的实验室泛滥试验研究主要集中在临界水力梯度的研究上，临界水力梯度会在短时间内触发土壤的内部不稳定。因此，在本研究中，在低于临界值的水力梯度下，对级配良好的粉砂进行了长期注水试验。因此，