Determination of the plasticity index from flow index

The flow index (I-f), which is the slope of the water content versus log(10 ) (number of blows) plot in the percussion cup method or the slope of the w ater content versus log(10) (depth of penetration) plot of the cone penetra tion method of determining the liquid limit of soils is a measure of soil p lasticity. Hence, the plasticity index of a soil that represents the soil p lasticity can be correlated with the now index. Analysis of test data pertaining to soils of widely varying plasticity char acteristics and geological origin indicates that there is an excellent corr elation between the plasticity index and the flow index, particularly in th e cone penetration method. In this paper, a simple equation has been sugges ted to obtain the plasticity index of a soil from the flow index, thereby e liminating the dependence of the plasticity index determination on the time -consuming and unrefined plastic limit test.