Assessment of internal stability of granular soils

The evaluation of the internal stability of a granular soil in contact with a filter is a very important aspect for the design of filtering systems widely used in the geotechnical (eg. earth dams, embankments, drainage trenches, etc.) and environmental (eg. landfills, permeable reactive barriers, etc.) works. A granular soil is defined internally unstable if a fraction of fine particles of the material is free to move, under the action of a drag filtration force, through existing pores and constrictions between the particles which constitute the solid skeleton. In the paper, the main methods available in the literature to evaluate the internal stability of granular soils are described and critically discussed. Therefore, the recent research developments on internal stability achieved by the authors are illustrated. In particular, two methods, considering the grain size distribution of granular base soil, both validated by long term filtration tests, are described in detail.