Experimental investigation on erosion progression and strength reduction of gap-graded cohesionless soil subjected to suffusion

Suffusion is a typical mode of internal erosion that leads to the deterioration of earthen structures. A stress-controlled experimental apparatus has been developed, which is adopted to investigate the characteristics of the erosion process and strength reduction of gap-graded cohesionless soil subjected to suffusion. Experimental results reveal that the critical hydraulic gradient significantly relates to the relative content of fine and coarse particles. Besides, under the same stress condition, the suffusion process is divided into three typical stages, i.e., the steady seepage stage (S1), the suffusion initiation stage (S2), and the suffusion equilibrium stage (S3). The suffusion process and the responses of the soil strength are explored with a newly defined coefficient, i.e., erosion ratio (ER). The coefficient ER is defined as the percentage of the cumulative weight of the eroded fine particles to the initial fine particle content in the specimen. The experiment results reveal that when ER is smaller than 6%, the effect of particle erosion on the strength of the soil is negligible. Nevertheless, the strength reduction is remarkable if the ER continuously increases. When the ER reached 35%, the critical friction angle decreased by 12.04 degrees, and the strength decreased by 27.38% compared with the intact specimen. Moreover, the internal stability assessment and fine particle migration characteristics of gap-graded cohesionless soil are further analyzed according to particle-size distribution criteria. The diversity of the strength reduction trend is attributed to the differences in soil skeleton structure.