Exploring Advanced Soil Constitutive Models for Simulation of Flexible Barrier Piles Under Vehicle Impact

The nonlinear dynamic soil-pile interaction plays a key role in the performance of the roadside piled-barrier systems during vehicle collisions. Only a few studies have focused on the soil-pile interaction under the impact, and mostly evaluated soil-pile interaction under quasi-static and low-frequency loads. To achieve a more optimum design of soil-embedded piles subjected to vehicle impact, advanced soil constitutive models are required that can capture the nonlinear interaction between soil and pile, hence the energy dissipation throughout the impact. Historically, simple soil constitutive models, such as Mohr–Coulomb, have been mostly considered due to the complexity of defining soil input parameters of advanced material models in numerical simulations. More advanced soil constitutive models, such as elastic-viscoplastic models, have been developed and proposed in recent years. However, several shortcomings have been identified with their implementation for simulation of pile barriers under impact such as artificial stiff behaviour in soil and instability in large deformations. In this paper, the most relevant soil constitutive models used for simulation of embedded barrier piles in LS-DYNA are reviewed, particularly for two of the most commonly-used ones: MAT_FHWA and MAT_Hysteretic_Soil. The gaps and shortcomings are demonstrated, and initial steps in development of a more accurate soil constitutive model are discussed based on the results of element-scale and full-scale numerical simulations. A number of modifications for these two constitutive material models are recommended to better capture the strain-rate dependency of stiffness and strain-softening effects as the key source of energy dissipation in soil during vehicle impact.