Abstract
When water flows through broadly graded soil, the small particles within the soil may erode, thereby leading to a narrowing of the grading. An important goal in geo-engineering is to gain a better understanding of the mechanical consequences of this type of event, with attention directed particularly toward the potential for ground deformation or failure due to erosion.
In this study, we focused on the mechanism of internal erosion and, from the viewpoint of instability, defined such erosion as the increase in particle movement and in the extent of macroscopic erosion. On this basis, when a given particle erodes, the pore structures of the rest of the particles should enable exit from a movable void, and their interparticle contact structures should enable egress by seepage force. Pore structure primarily pertains to void size and void continuity. Contact structure is estimated by average coordination number and fabric tensor. To illustrate internal erosion accompanied by changes in grading, we conducted experimental and computational analyses. Through a seepage test with particle erosion, we obtained the grading shaped-induced quantitative difference and trend in the weight of leached particles. With regard to permeability, all the grading values indicate a decreasing trend. Because specimen height was kept constant during the experiment, permeability could have increased given the rise in voids due to particle erosion. On the basis of the decreasing trend, however, the increased permeability can be regarded as a case of particle clogging. The pore structure analysis indicates that at the logarithmic scale, the index shows qualitatively good agreement with the extent of erosion from various grading conditions. As for the contact structure, the average coordination number of the particles and the particle voids also exhibit good agreement with erosion behavior.
