Development of a simplified method for the assessment of liquefaction mitigation via vertical gravel drains

Seismic–induced liquefaction of saturated sandy soils may cause severe damage to civil infrastructures, pushing the scientific community toward a more in-depth understanding of the physical phenomenon and the development of effective strategies for its mitigation. Vertical gravel drains and stone columns are often used as a mitigation measure against liquefaction as, depending on site conditions, they can be easier to install and more cost-effective with respect to other design solutions. Standard design methods of the gravel drains are usually based on the seminal work by Seed and Booker (1977), which relies on several simplifying assumptions about: the direction of water flow (purely horizontal axisymmetric flow towards the drains), the physical and mechanical properties of the drain material (virtually infinite permeability), and the rate of excess pore pressure (described through empirical relationships based on undrained cyclic tests). The present paper illustrates a comparison between the seminal work proposed by Seed and Booker, which was subsequently improved by Onoue (1988), and the results of a fully-coupled, nonlinear dynamic 3D Finite Element analysis, where the cyclic behaviour of the saturated sand layer is described through an advanced constitutive model.