Abstract:

A series of fall cone tests are performed to determine the liquid limits and the plastic limits of fine grained soil. The result shows that the log-log relationships between penetration depth of fall cone and water content of some fine grained soil are clearly nonlinear; and the liquid limits and the plastic limits can not be obtained according to the linear relation. Effective test data can not be measured within the three ranges of water contents proposed by the present standards. The dependability is necessary to discuss about the liquid-plastic limit test results obtained from three ranges. It is possible that the contradictory and wrong classification results exist by using the liquid limits and the plastic limits obtained from the test data with straight line. The further test results show that the fall cone test is suitable for the silts over 13 % clay particles content since the shear strength is mainly controlled by cohesion; and the plasticity is available from the plasticity indexes. On the contrary, the fall cone test is not suitable for the other silts and the silty sands which are similar to silts, because the shear strength is mainly controlled by particle friction. At last, some opinions about the fine grained soil classification are given.

Key words: fall cone test, silt, soil classification, liquid limit, plastic limit, plasticity, clay particles, shear strength