Assessing the internal erosion sensitivity of earth-fill-dam soils based on the phenomena of suffusion and suffosion

Suffusion and suffosion are the process of internal instability which involves the migration of finer soil particles by the seepage forces, and it is known as a major cause of dam failures. Internal instability of the soils has been studied by a number of researchers, and through the laboratory seepage tests, criteria on grain size distribution to evaluate the internal stability were suggested. Seepage tests conducted by early researchers, however, are different in terms of the details, fine contents, relative density of the soils, applied hydraulic gradients and boundary conditions (filter system). Such discrepancies can lead to a problem of applicability of existing criteria on fill-dams. Therefore, in this study, laboratory seepage tests were conducted on fill-dam materials in Korea with the consideration of various testing conditions, and based on the test results, potential behavior of internal instability was evaluated. Test results showed that the soils with small fraction of fines (10%, passing sieve no. 200) are susceptible to suffusion. On the other hand, soils with significant amount of fine contents (40%) are vulnerable to suffosion, and it is dependent on the relative density. Thus, the susceptibility of fill-dam materials in Korea to internal erosion is highly affected by the fines and relative density of the soils.