Determining Intrinsic Compressibility of Fine-Grained Soils

Results of laboratory oedometer tests on reconstituted specimens of four clays prepared at different initial water contents, ranging from the liquid limit to 1.75 times the liquid limit, show that the intrinsic compression line may not be “unique” for a given soil. This suggests that the “intrinsic” parameter $I_v\text{,}$ which is based on the constants of intrinsic compressibility, $e_{100}^{*}\text{,}$ (void ratio corresponding to ${\sigma }_v^{\prime }=100 \mathrm{kPa})\text{,}$ and $C_c^{*}\text{,}$ $(e_{100}^{*}-e_{1000}^{*})\text{,}$ may in fact not be a truly intrinsic parameter of the soil, but is dependent on sample preparation. The positioning of the normalized compression curve in $e-\log -{\sigma }_v^{\prime }$ space is significantly influenced by the initial remolding water content, therefore resulting in differing values of $e_{100}^{*}$ for a given soil depending on the initial water content. The influence of initial water content was greater for kaolinitic and illitic clay than for montmorillonitic clay. It is hypothesized that the difference in behavior may be attributed to differences in mineralogy. The results illustrate that caution should be used when comparing tests results from widespread sources and suggest that a standard level of initial water content be used to evaluate the intrinsic compressibility.