Evaluation of the Liquefaction Hazard for Sites and Embankments Improved with Dense Granular Columns

Abstract

Dense granular columns (DGC) have become a common soil improvement strategy for critical embankment structures founded on potentially liquefiable deposits. The state-of-practice for the design of DGCs is limited to simplified methods that consider, separately, the three-primary liquefaction-mitigation mechanisms provided by these columns: (i) installation-induced densification; (ii) enhanced drainage; and (iii) shear reinforcement. Critical aspects, such as the effects of soil-column-embankment interaction, site characteristics and layer-to-layer interaction, ground motion characteristics beyond the peak ground acceleration, and the total uncertainty, are not included in current engineering design procedures. In this work, we present results from a numerical parametric study, previously validated with dynamic centrifuge test results, to evaluate the liquefaction hazard in layered profiles improved with DGCs. The criteria for various degrees of liquefaction are based on peak excess pore pressure ratios and shear strains observed within each layer. Our study includes different properties and geometries for both soil and DGCs, various confining pressures induced by an overlying embankment, as well as a large collection of ground motions from shallow crustal and subduction earthquakes. We performed a total of 30,000 3D, fully coupled, nonlinear, dynamic finite-element (FE) simulations in OpenSees using a state-of-the-art soil constitutive model (PDMY02), whose properties were calibrated based on both element level laboratory tests and a free-field boundary-value problem modeled in the centrifuge. The results from this parametric study are used to develop a probabilistic predictive model for the triggering of liquefaction in embankment sites treated with DGCs.