Modelling T-bar penetration in soft clay using large-displacement sequential limit analysis

T-bar penetrometers are commonly used for the measurements of undrained strength profiles for clay (e.g. intact shear strength, sensitivity, ductility). The adoption of a constant resistance factor in the absence of a full-flow failure mechanism, coupled with the strain-softening effect, usually leads to considerable underestimation of soil strength within the depth of up to several T-bar diameters. This paper presents a numerical investigation into the vertical penetration behaviour of a T-bar using a sequential limit analysis (SLA) technique. The T-bar is penetrated from the mudline to a maximum of eight diameters to capture the behaviours related to differing failure mechanisms. The robustness of the SLA is demonstrated through comparisons between lower- and upper-bound solutions and between the SLA and the coupled Eulerian-Lagrangian results, in terms of penetration resistance and failure mechanism. The influences of unit weight, strain softening and strain rate are then examined, based on which an analytical model is developed for more accurate quantification of soil strength back-calculated from T-bar penetration resistance.