Cavity Effect on the Penetration Resistance of the T-Bar Penetrometer in Undrained Clay

The full-flow T-bar penetrometer has been extensively employed in centrifuge model tests and offshore site investigations to measure the undrained shear strength of soft clays. A rigorous correlation between T-bar resistance and undrained shear strength relies heavily on the elucidation of the resistance factor Nt, which has been widely pursued utilizing classical plasticity according to a full-flow mechanism. However, the adoption of a constant resistance factor Nt in the absence of a full-flow mechanism at shallow penetration due to the cavity above the T-bar cylinder has been identified to underestimate the soil strength. Thus, to accurately interpret T-bar penetration data, this paper presents theoretical investigations into the resistance factor of the T-bar penetrometer considering the cavity effect. A generalized theoretical solution of the resistance factor Nt is deduced in terms of roughness factor α at the T-bar-soil interface and sidewall inclination δ of the cavity, which will degenerate to the well-known plasticity solutions of Randolph and Houlsby (1984) when the cavity vanishes. Theoretical results show that the resistance factor Nt increases with increasing roughness factor α, but decreases with increasing sidewall inclinations δ. Finally, the rationality of the proposed failure mechanism and theoretical results are verified against finite element limit analysis (FELA) conducted in this study, as well as the numerical results and theoretical solutions in the existing literature.