Compression Index: Misleading Parameter?

The limitations of the compression index $C_c$ as an indicator of soil compressibility are demonstrated and the usefulness of the relationship $C_c$ = 0.007(LL. - 10) is questioned. (Note: LL = liquid limit.) Using experimental data from three soil groups of widely differing properties, it is shown that soils having the highest values of $C_c$ and LL are not necessarily those of the highest compressibility. The parameters CR [+$C_c$/(1 + $3_o$)] or $m_v$ are better indicators of compressibility and peak values of these parameters do not coincide with peak values of $C_c$. The plasticity index, or position on the plasticity chart, is shown to provide a more reliable guide to soil compressibility than the liquid limit.