Assessment of clay consistency through conventional methods and indirect extrusion tests

The consistency of fine-grained soil is an essential parameter in soil mechanics. The most relevant consistency indices are the liquid limit and the plastic limit. The liquid limit is commonly determined through the Casagrande test or the fall cone test, while the plastic limit is determined through the hand rolling method. The greatest issue with some of these techniques is their low repeatability and operator dependency. In order to minimize those issues, an indirect-extrusion-based technique was evaluated as an alternative method to determine both consistency limits. The experimental work was carried out on mixtures of kaolin and bentonite to cover a wide range of plasticity. The results suggested that there is a specific extrusion pressure linked to each consistency limit and that the results are repeatable. The liquid limit obtained through the extrusion method closely matches the results of the fall cone test. Similarly, the plastic limit out of extrusion closely matches the results of the hand rolling method.