Determination of Atterberg limits
With the Atterbergs limits the process ability (plasticity) of cohesive samples is determined. Three areas can be determined: the solid, the plastic, and the liquid areas. The Atterberg limits show the boundaries between these areas. The liquid limit is the boundary between plastic and liquid state. The plastic limit is the boundary between solid and plastic. The difference between the liquid limit and the plastic limit is called the “ plasticity index” (Pi).
With this method the Casagrande device is used. The sample is put in a percussion cup and a standard groove is cut with a grooving mold. The cup is raised to a predetermined height and dropped with a fixed frequency. The liquid limit is the moisture content at which the groove, after 25 blows, closes up over a length of 1 cm. There is a slight difference between the BS method and the ASTM method. The ASTM method is the more customary method in the Netherlands.
As an alternative for the determination of the liquid limit, the fall-cone method is also available. This method is frequently used abroad.