A century later: a bearing-capacity framework to extract Mohr-Coulomb parameters from penetration tests

This study reformulates classical bearing-capacity theory into a depth-resolved framework for extracting apparent Mohr–Coulomb parameters from quasi-static flat-punch penetration tests. The measured force–depth response is converted to the mean contact stress $$\varvec{q(z)}$$ and analysed as a function of depth, with cohesive, surcharge, and unit-weight contributions. Under homogeneous, axisymmetric conditions, the internal friction angle $$\varvec{\varphi }$$ and cohesion $$\varvec{c}$$ are obtained from the slope and intercept of the quasi-steady $$\varvec{q(z)}$$ relation. Applied to an inert montmorillonite–glycerin reference material, the method yielded reproducible results across punch diameters $$\varvec{D=20}$$ – $$\varvec{40~\textrm{mm}}$$ , giving $$\varvec{\varphi _{pen}\approx 4.8^\circ }$$ and $$\varvec{c_{pen}\approx 0.85~\textrm{kPa}}$$ . Independent vane tests gave $$\varvec{c_{\textrm{vane}}\approx 0.70~\textrm{kPa}}$$ , and direct shear box tests yielded $$\varvec{\varphi _{\textrm{dsb}}\approx 4.45^\circ }$$ and $$\varvec{c_{\textrm{dsb}}\approx 1.16~\textrm{kPa}}$$ . The friction angles from penetration and DSB testing were consistent, while the cohesion values differed in the ordering expected from their respective interface and deformation conditions. Within the quasi-static, low-stress regime examined here, the penetration-based approach provides an efficient method for quantifying apparent Mohr–Coulomb parameters of soft cohesive–frictional materials.