Precompression stress and compression index depend on the property used to represent the soil deformation in the compression curve

Pressão de preconsolidação e índice de compressão dependem da propriedade usada para representar a deformação do solo na curva de compressão

ABSTRACT:

During linear deformation (h) in a soil sample, the variation of the void ratio with respect to deformation (dε/dh) and the respective variation of soil bulk density (dρ/dh) are identical only for a specific value of h. Consequently, if two compression curves are drawn for the same soil sample, one using ρ and the other using ε, there are differences in both the calculated precompression stress (σp) and compression index (Ic). In this study, we highlight the causes by a mathematical analysis and an experimental investigation, quantifying the differences in σp and Ic when using ε and ρ. σp and Ic were calculated for 103 compression curves of an ultisol and 193 of an oxisol. The σp (kPa) using ρ (σp_ρ) was greater than when using ε (σp_ε), and differences were rather independent of the soil type. The relations found by linear regression relating σp_ρ to σp_ε were σp_ρ=0.8186σp_ε+34.202 for the ultisol and σp_ρ=0.8878σp_ε+34.875 for the oxisol. In contrast, the used soil property (ρ or ε) as well as soil type affected Ic. Ic calculated using ρ was greater than when using ε in almost all (96%) of the cases for the ultisol, and in only 12% of the cases for the oxisol. For a wide range of ρ, evidence from this study indicated that the use of ρ overestimates σp when compared to the use of ε.

Key words:
void ratio; particle density; soil bulk density