Evaluating suffusion in dam core soil of glacial till using empirical methods

Glacial till, a broadly graded soil formed by the action of glaciation, is used in many parts of the world as dam core material. Statistically these show higher frequency of internal erosion incidents in dams than other types of core soils. One mechanism that may be influential is suffusion as caused by internal instability, which is one initiation mode of internal erosion. A compilation of 23 laboratory tests on suffusion of glacial till core soil has been compiled of which 13 performed unstable. An assessment of the potential for internal instability is made using five empirical methods that evaluates the shape of the particle size distribution. Evaluation of the database indicates on the methods’ applicability to glacial till gradations, and, furthermore, it reveals that the Kenney-Lau approach and its Li-Fannin adaptation provide predictions relatively more accurate in identifying unstable gradations due to suffusion. A stricter assessment is suggested by extending the Li-Fannin adaptation so that it incorporates a transition zone defined by the range 0.68≤H/F<1.0.