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 q(z) and analysed as a function of depth, with cohesive, surcharge, and unit-weight contributions. Under homogeneous, axisym- metric conditions, the internal friction angle φ and cohesion c are obtained from the slope and intercept of the quasi-steady q(z) relation. Applied to an inert montmorillonite–glycerin reference material, the method yielded reproducible results across punch diameters D = 20–40 mm, giving φpen ≈ 4.8° and cpen ≈ 0.85 kPa. Independent vane tests gave cvane ≈ 0.70 kPa, and direct shear box tests yielded φdsb ≈ 4.45° and cdsb ≈ 1.16 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 defor- mation 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.