A Novel Uncoupled Approach to Design Vertical Gravel Drains for Liquefaction Mitigation

This paper presents a comparative assessment of uncoupled approaches for the analysis and design of vertical gravel drains for mitigating the risk of seismic-induced soil liquefaction. The study first recalls the analytical formulation by Onoue [1] and the novel extension recently proposed by Boccieri et al. [2], who introduced more realistic assumptions about the non–uniform cyclic loading and the frequency shift induced in the soil deposit by the pore pressure build–up. The reliability of the numerical implementation of the novel uncou-pled approach is checked against fully coupled 3D Finite Element Analyses performed in the OpenSees framework, for the selected benchmark case of an indefinitely extended vertical drain system installed in a homogeneous liquefiable sand deposit. The good comparison with the 3D coupled analyses clearly highlights the need for the hypotheses introduced in the uncoupled approach by Boccieri et al. [2]. The improvement with respect to the classical Onoue charts [1] highlights the enhanced predictive accuracy of the proposed uncoupled approach, while maintaining a low computational cost. These results support the use of the proposed uncoupled method as a design tool for liquefaction mitigation, providing a good compromise between accuracy and computational efficiency.