Effects of strain rate and softening on the cone-tip resistance of CPT in soft clay

The Cone Penetration Test (CPT) is widely recognized as a prevalent in-situ testing technique during offshore site investigations, and the cone-tip resistance obtained from the CPT is treated as the representative of the engineering properties of soil. However, the behavior of soft clay, characterized by its strain rate dependency and strain softening properties, the corresponding cone-tip resistance in soft clay is still impossible to be predicted accurately. To address this, the penetration process of cone penetrometer is simulated by using the coupled Eulerian-Lagrangian (CEL) method in this study, the effect of strain rate, strain softening on cone-tip resistance and the evolution of soil strength enhance-softening around the cone penetrometer are analyzed. The corresponding results indicate that strain rate has a greater effect on cone-tip resistance compared to strain softening. The difference of the cone-tip resistance between the ideal Tresca soil and the strain-soften soil is 0-79%, but 0-16% with the strain-softening soil. Based on the numerical results, a prediction formula, in which the effect of strain softening and strain softening are considered, is proposed to predict the ultimate cone-tip resistance in soft clay.