Determination of controlling constriction size from capillary tube model for internal stability assessment of granular soils

Internal instability is associated with geotechnical structures such as earth dams and dikes, and involves movement of fine loose particles through the voids of the main soil skeleton. In this study, some methods to determine the delimiting particle size (DPS) were critically reviewed. The accurate determination of the values of DPS and the diameter of the controlling constriction size (dcont.) is essential for internal stability assessment. Here, a relationship is derived from the capillary tube model in order to determine the controlling constriction size, knowing that the diameter of the controlling constriction size should be smaller than the diameter of the loose fine particles to ensure the safety against internal stability. This derived relationship was verified with a large amount of data and it gave more accurate prediction than other methods.