Interpretation of T-Bar Penetration Data in Two-Layer Clays

This paper explores the interpretation of undrained shear strength and layer boundaries from T-bar penetration resistance profiles in layered soft-stiff and stiff-soft clay sediments. The proposed interpretation framework was based on extensive parametric large deformation finite-element analyses by varying the strength ratio between the two layers, and the relative thickness of the top layer. For soft-stiff clay deposits, the squeezing mechanism dominated the behavior when the T-bar approached the layer interface. No soil plug was trapped at the base of the T-bar. The interface can be identified as the kink point with a sharp increase in resistance profile sensing the stiff layer. For stiff-soft clay deposits, a stiff soil plug was trapped at the base of the T-bar and penetrated into the soft layer. Resistance profiles dropped before reaching the layer interface being influenced by the soft layer. A minimum thickness of 25D was needed to mobilize the ultimate resistance of the top layer. The layer boundary can be identified as 4.2D above the kink point on the resistance profile in the bottom layer. The stabilized resistance in the bottom layer increased with increasing the strength ratio owing to the thicker stiff soil plug at the base of the T-bar.