Comparision of Casagrande aparatus, falling cone and extrusion methods in the determination of Atterberg limits

Plasticity index is one of the main soil properties used to make correlation with some other soil parameters and in soil classification. Traditionally, hand rolling method is used to determine plastic limit. Moreover, Casagrande apparatus and falling cone methods are used to determine liquid limits. Methods used in liquid limit and plastic limit determination include many uncertainties depending on the person who perform experiment and the apparatuses used. Deviation of these values due to these uncertainties influence the plasticity index. Generally, due to the fact that repeatability of these two experiments is very low and comparability between persons, who perform the experiment, is difficult many attempts have been made for providing alternative methods. This study is also one of them. As an alternative to these methods inverse extrusion method has been proposed. A series of extrusion tests has been made to get rid of these uncertainties and to reduce the operator dependency of the hand rolling, Cassagrande Dropping Bowl and falling cone methods.For this aim, eighty eight different inorganic soil samples are used. Hand rolling, Casagrande apparatus and falling cone experiments are made with the same soil samples to compare the results and to obtain the optimal extrusion pressure corresponding to consistency limits. When the results are evaluated on histograms, the pressure corresponding to plastic limit is obtained roughly as 3000 kPa, and the pressure corresponding to liquid limit is obtained roughly as 40 kPa. by the equipment of this workout.Key Words: Atterberg limits, plastic limit, liquid limit, fall cone,Casagrande, ekstrusion