Numerical investigation of dynamic free-fall penetrometers in soft cohesive marine sediments using a finite element approach

This paper represents the first stage in developing an algorithm for extracting the values of the undrained shear strength from the deceleration records of the STING penetrometer. A brief summary of the STING penetrometer and its processing algorithm is given. Then, we focus on the direct simulations of the probe velocity decay with depth, using simple soil constitutive models in a fully-dynamic elasto-plastic analysis. Much attention is devoted to alleviating severe numerical problems when analyzing a problem with extreme deformation, leading to mesh distortions and thus necessitating efficient remeshing methods. Arbitrary Lagrangian-Eulerian, ALE, remeshing mechanics of ABAQUS5 software is effectively utilized, allowing the solution to proceed and yielding good agreement with the velocity profile recorded by the decelerating STING penetrometer in situ. The soil is modeled as von Mises material with yield strength derived from a combination of laboratory vane and fall-cone tests and assuming a strength profile linear with depth. The methodology developed allows for the large-deformation penetration to proceed, and yields good agreement with the in-situ data. The future work will focus on the ultimate goal of the project, i.e. of developing an algorithm for extracting the strength profile from the field-measured deceleration record via inverse solutions in ABAQUS.