Effect of side shear zones on T-bar penetration resistance in clay—upper bound analysis

The full-flow T-bar penetrometer has been widely used in laboratory tests and field site investigations to obtain the undrained strength of seabed sediments. The soil failure mechanism of a full-flow T-bar penetrometer at deep penetration is consistent with that of the laterally loaded circular pile in cohesive soil, where the soil flows around the cylinder from the bottom to the top. On each side of the T-bar, however, two side shear zones exist between the full-flow zone and the adjacent soil, which may generate additional energy dissipation and thus contribute to the resistance. This study provides significant insight into the analysis of the contribution of the side shear zones to the resistance of the T-bar penetrometer in undrained clay. According to the full-flow failure mechanism presented by Randolph and Houlsby (1989), a quantitative relation between the resistance of the T-bar penetrometer and the soil undrained shear strength is derived using the upper bound theorem. The resistance factor N s is introduced to revise the traditional calculation method. Theoretical results demonstrate that the resistance factor N s increases from 1.666 for a smooth interface to 3.099 for a rough interface, and are further validated against a series of numerical simulation results from finite element analyses.