Considerations on the Experimental Calibration of the Fall Cone Test

The fall cone test is widely used in soil mechanics to determine the liquid limit of fine-grained soils as an aid to soil classification. The test can also be used to obtain the undrained shear strength of a fine-grained soil, based on the cone factor, K. Reports from different authors show K values ranging from 0.4-1.33. Differences are mostly attributed to the cone surface roughness. This article presents a reinterpretation of several experimental observations available in the literature. It is observed that besides the cone roughness, testing methods have a clear influence when calibrating the fall cone for determining the undrained shear strength of materials with low and very low consistency. The results show that existing K reports should be extrapolated with care. Finally, we propose a series of recommendations and good practices for future calibrations.