Abstract
A hypothesis was performed on the A- line in the plasticity chart proposed by Casagrande for
laboratory classification of fine- textured soils.
By examining the results of tests on both the liquid and plastic limit published earlier on Bentonite,
Illite and Kaolinite which are typical clay minerals, it was found that the relationship between
the liquid limit (WL.) and plastic limit (Wp) could be expressed by the equation:
WP 0.30WL +15.85 (WL≤120%) and
Wp 69.8 ( constant) (WL>120%).
On the basis of this linear relationship and the definition of the plasticity index (Ip), the following
equation, which is closely similar to that of the A- line, was obtained as follows:
IP 0.70 (Wl-22.6) (W≤120%).
