Effective stress and suffusion onset at local and global scales in centrifuge permeameter tests

This study presents the results from a series of centrifuge tests conducted in a novel permeameter capable of measuring both global and layer permeability. Six tests were undertaken at gravitational accelerations ranging from 10 to 40g. Using a parametric modeling approach, the research examined the influence of effective stress gradient on the onset and progression of suffusion in an underfilled, gap-graded soil. At a specimen scale, increased effective stress gradient appeared to increase suffusion susceptibility in identically prepared models. However, analysis of the permeability response of individual layers indicated that initial microscale variability and hydraulic loading history had more impact on the suffusion behavior than did effective stress. At the layer scale, suffusion and clogging events occurred from the onset of seepage flow, and there was no observed influence of effective stress level on suffusion onset. The study found that the definition of suffusion onset is highly dependent on experimental design, and critically evaluated the concept of threshold hydromechanical conditions for suffusion onset.