Large Deformation Explicit Finite Element Simulations of Drop Tower Experiments on Clay

Abstract

Results of a high strain rate unconfined compression test on a clay soil sample and corresponding finite element simulations are presented. A drop tower was adapted to drop weights onto a saturated cylindrical kaolin clay soil sample. The engineering stress-strain response was found using piezoelectric load cells and a high-speed camera. Remolded cylindrical clay samples were prepared by the static compaction of hydrated clay in a cylindrical mold. The drop tower experiment featured a mass of 13.4 kg dropped from a height of 1.5 m, resulting in an impact velocity of 4.15 m/s and a constant strain rate of 56/s on the soil sample. Results of the high strain rate experiments revealed that the saturated kaolin clay strength, as quantified using the unconfined compressive strength, exhibited significant strain-rate dependence. An approximately 100% increase in the unconfined compressive strength was observed at a strain rate of 56/s compared to the quasi-static strength. Three-dimensional finite element simulations of the drop tower setup were then used to replicate the observed response. A penalty contact algorithm, available in the commercial finite element code Abaqus/Explicit, was used to simulate the soil-loading ram interactions. Elastic-purely plastic extended Tresca constitutive equations with strain rate and strain softening inclusions were used to capture the strain rate dependence of clay. A comparison of the experiments and the simulations revealed that the modeling procedures and the constitutive model used were able to capture the salient features of the response observed from the drop tower experiments.