Volume 43, N. 4

October-December 2020

The influence of the fluid dielectric constant on the shear strength of a unsaturated soil


Volume 43, N. 4, October-December 2020 | PDF (120 downloads)


Results of triaxial tests performed in saturated and unsaturated compacted soil specimens with different interstitial fluids are presented. Tests were carried out in order to study the influence of the fluid relative dielectric constant, εr, on the soil shear strength of a granite-gneiss clayey residual soil from Salvador, Bahia, Brazil. It is shown that the soil shear strength is affected not only by the interstitial fluid saturation degree (or suction) but it is also a nonlinear function of the interstitial fluid value of εr. The shear strength of the saturated samples decreased with εr, following the order (air εr = 1, diesel εr = 2.13, ethanol εr = 24.3 and water εr = 80), whereas fluids with higher dielectric constants presented a more pronounced increase in shear strength under drying (replacement of the interstitial liquid with air). An empirical model is proposed to predict soil shear strength as a function of (εrw - εf), the difference between the relative dielectric constant of the water and the interstitial fluid. Good adherence between experimental and fitted results was obtained.

Keywords: Dielectric constant, Napl, Shear strength, Unsaturated soils,

Submitted on December 14, 2018.
Final Acceptance on June 10, 2020.
Discussion open until March 31, 2021.
DOI: 10.28927/SR.434535