Performance of encased granular columns considering shear-induced volumetric dilation of the fill material

This numerical study investigates the behaviour of geosynthetic-encased sand columns. Based on an elastic-plastic constitutive model used with the non-associated flow rule, the prominent expansive behaviour of medium to dense sands is characterised. Numerical analysis results are verified via laboratory triaxial tests on encased sand columns, where the sand mechanical properties are extracted from simple experimental tests. The tested sand columns in the experiments consist of two sands, encased by sleeves fabricated from two geotextiles. This verification demonstrates that the sand volumetric strain profoundly affects the induced confining pressure of an encased column. Exactly how the encasement stiffness, strength and diameter of the granular column influence encased column response is also studied using numerical analyses. Numerical results indicate that the encasement induces additional confining pressure, subsequently preventing strength yield in the encased columns before the encasement reaches its yield strength. These results further demonstrate that the ratio of encasement stiffness to column diameter significantly affects the response of a granular column. Moreover, it may be unnecessary to encase a small-diameter column with a stiff encasement, whereas encasing a large diameter column with a low-stiffness encasement may produce a limited reinforcing effect.