CPT Soil Behavior Type & Correlation Calculator

Robertson (1990/2009/2016) CPT SBT Equations

Normalized Cone Resistance (Qtn) & Friction Ratio (Fr): $$Q_{tn} = \left(\frac{q_t - \sigma_{vo}}{p_a}\right) \left(\frac{p_a}{\sigma'_{vo}}\right)^n, \quad F_r = \left(\frac{f_s}{q_t - \sigma_{vo}}\right) \times 100\%$$

Soil Behavior Type Index (Ic): $$I_c = \left[ (3.47 - \log_{10} Q_{tn})^2 + (\log_{10} F_r + 1.22)^2 \right]^{0.5}$$

Correlations: $$N_{60} = \frac{q_t / p_a}{8.5 \cdot (1 - I_c / 4.6)}, \quad s_u = \frac{q_t - \sigma_{vo}}{N_{kt}}, \quad \phi' = 17.6^\circ + 11.0^\circ \log_{10}(Q_{tn})$$