Theory and practice of the fall cone test

The fall cone is considered as a more reliable method for determining the l iquid limit than the Casagrande method, and is standardised in many countri es as the preferred liquid limit test method. In this paper the theory and practice of the fall cone test are described. First the penetration mechani sm of a fall cone into clay is analysed, introducing the concept of dynamic strength to the static results. Next the applicability of dynamic analysis to the fall cone test is examined with regard to Hansbo's cone factor, K, for various cone angles. The theoretical K value for the 60 degrees cone wi th a semi-rough surface is found to agree better with experimental results than is the case for the 30 degrees cone. It is proposed that the liquid li mit be redefined internationally as the water content at which a 60 degrees , 60g fall cone penetrates 10 mm. Finally the applicability of the fall con e test as a device to relate the strength of a clay with the index properti es is examined.