Stone and soil-cement columns are often used to improve the liquefaction resistance of loose sandy ground potentially subjected to strong shaking. The shear stress reduction in the loose ground resulting from the reinforcing effect of these stiffer discrete columns is often considered as a contributing mechanism for liquefaction mitigation. Current design practice commonly assumes that discrete columns and soil deform equally in pure shear (i.e. shear strain compatible deformation). In addition, since the discrete column is stiffer than the soil, it is assumed to attract higher shear stress, thereby reducing the shear stress in the surrounding soil. In this paper, the shear stress distribution mechanism of discrete columns and the shear stress reduction in liquefiable soils are investigated using 3-D finite element analysis. From the analysis, it is found that discrete columns behave in both shear and flexure, such that the shear strain compatibility assumption can be significantly unconservative. The investigation indicates that the shear reinforcement of stiffer discrete columns is less effective than commonly used in current design practice. A revised design equation is proposed to conservatively estimate the shear stress reduction ratio.
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