Strain softening parameters estimation of soft clay by T-bar penetrometers

The T-bar penetrometer is a key tool to estimate the strain softening parameters by repeating penetration and extraction. In this study, the cyclic penetration process of T-bar is simulated using the large deformation finite element (LDFE) method, considering the strain softening behavior of clay. The criteria to estimate the critical depth during initial penetration are discussed. A new equation of the critical depth is proposed to consider the effect of soil strain softening. The characteristics of the T-bar resistance curves are discussed, and they can also be used to judge whether the soil reaches the full-flow mechanism. The soil flow mechanisms for shallow cyclic T-bar penetration are discussed. It is found that a cavity is formed during T-bar extraction and it leads to the following resistance gradually decreases. This means that, for shallow cyclic tests, the measured cyclic penetration or extraction resistance cannot be used to estimate the clay sensitivity. Moreover, a simple method is proposed to estimate the strain softening parameters of soil. The proposed method is verified by comparing the estimated values with the numerical simulation results and the field test data.