Numerical Modeling of the Seismic Response of Columnar Reinforced Ground

Ground improvement using stiff columnar reinforcement, such as stone, jet-grout, and soil-mix columns, is commonly used for mitigation of seismic damage in weak ground. Seismic shear stress reduction in the reinforced soil mass is often counted on for reducing liquefaction potential. Current design methods assume composite behavior of the reinforced soil, where the shear stress reduction is based on the ratio of the columnar stiffness relative to the soil as well as the area replacement ratio. This implicitly assumes the stiff columns will deform in pure shear along with the soil. We performed 3-D dynamic finite element modeling to better understand the column deformation and shear stress reduction behavior. We found that the columns deform in both shear and flexure, providing little seismic shear stress reduction and current methods may be unconservative.