Numerical simulation of free-fall penetrometer dissipation tests in rate-dependent clay

The free-fall penetrometer (FFP) is a novel in-situ tool with potential of soil characterization in deep waters, owing to its low cost and high efficiency. The dissipation test of FFP in cohesive soil and then the determination of in-situ coefficient of consolidation are investigated numerically, where the entire ‘penetration-dissipation’ process of the FFP is reproduced using a large-deformation finite element approach incorporating the elastic-viscoplastic modified Cam-clay model. The large deformation approach is validated by comparing with the penetration profiles and dissipation curves measured in the existing centrifuge tests. The conventional interpretation of dissipation curve in the piezocone test is expanded to that against the FFP. A parametric study is then carried out varying the factors dominating the dissipation response, including the initial penetration velocity, mass, geometry and roughness of the FFP and the soil properties. It is observed that the effect of strain rate on the dissipation curve cannot be ignored reasonably. Thus, the equation to predict the consolidation coefficient for cone penetration test is expanded to obtain the coefficient of consolidation through the FFP.