Baldi et al. (1986) modified by Lune (2006)

$D_r=\frac{1}{C_2}\ln \left(\frac{q_c}{C_0{\left({{\sigma }^{\prime }}_{vo}\right)}^{C_1}}\right)$

C₀ = 157, C₁ = 0.55, C₂ = 2.41

(applicable for Normally Consolidated soils)

Jamiolkowski et al. (1985)

$D_r=-98+\left(66\ast {\log }_{10}\frac{q_c}{{\left({{\sigma }^{\prime }}_{vo}\right)}^{0.5}}\right)$

Kulhawy & Mayne (1990)

$D_r=100\sqrt{\frac{1}{305OC{R}^{0.2}}\left(\frac{\left(q_t/{\sigma }_{atm}\right)}{{\left({{\sigma }^{\prime }}_{vo}/{\sigma }_{atm}\right)}^{0.5}}\right)}$

where OCR = 1 for Normally Consolidated soils