Influence of elastic strains during plastic deformation of encased stone columns

This paper studies the significance of elastic strains of encased stone columns during their plastic deformation. A new analytical solution that includes these elastic strains is presented to study the deformation and consolidation around encased stone columns, which are a common ground improvement technique for soft soils. The analytical solution models only a unit cell, i.e. an end-bearing column and its surrounding soil, in axial symmetry under a rigid and uniform load. The soft soil is treated as an elastic material and the column as an elastic-perfect plastic material using the Mohr-Coulomb yield criterion and a non-associated flow rule, with a constant dilatancy angle. The solution is presented in a closed form and is directly usable in a spreadsheet. The elastic strains during plastic deformation of the column are added as an extension of a previous solution by the authors. This inclusion complicates the formulation of the analytical solution. The differences with the previous solution, and therefore, those elastic strains, are important only for high encasement stiffnesses. The analytical solution is used to study the encasement length. The presented approach, which considers soil consolidation, is compared with a loading process in drained conditions. Numerical analyses are included for validation.