Design of DSM Grids for Liquefaction Remediation

Deep soil mixing (DSM) to form in-ground shear walls has been used to remediate against the potential effects of earthquake-induced liquefaction on many projects. A grid pattern of soil-cement walls act as a confined shear box, which can provide additional shear stiffness and strength for sites to withstand liquefaction. Current design practice for DSM grids commonly relies on the strain compatibility assumption, where the DSM walls and confined soil are assumed to experience the same shear strain. In this paper, the distributions of shear stresses and strains in liquefiable soil deposits treated with DSM grids are investigated using three-dimensional linear elastic finite-element analyses of unit cells. Parametric analyses are performed for a range of geometries, relative stiffness ratios, and dynamic loadings. These linear elastic results provide a baseline against which future nonlinear modeling results can be compared, but they are also sufficient for demonstrating that shear stress reductions are less than predicted by the assumption of shear strain compatibility. Modifications to the shear strain compatibility equation are presented, which improve its agreement with the results of these analyses.