3D numerical analyses of geosynthetic encased stone columns

Stone columns are commonly used as ground improvement elements since they act as reinforcing inclusions. However, due to the lack of sufficient lateral confinement for the columns, this technique is not applicable for the improvement of grounds that consist of very soft soils. In order to provide lateral confinement and increase the load bearing capacity of stone columns installed in very soft clay soils, they are usually encased with suitable geosynthetic materials, forming geosynthetic-encased columns (GECs). In this paper, a 3D numerical approach is used to study the effect of varying the encasement length of different columns of a group of GECs on the overall group behavior. These results are compared with those obtained from a group of fully encased columns, through comparison of the settlements and lateral deformations (bulging) of the columns. The analyses are calibrated through modeling the behavior of GECs used in a ground reclamation project in Hamburg, Germany. Parametric studies are also carried out to investigate the effects of factors such as stiffness of the geosynthetic encasement, column diameter, and modulus of elasticity and friction angle of the column material on the overall behavior of the GEC group. The results indicated that encasing only the outer columns of the stone column group is sufficient in providing an optimal design. It was also shown that increasing the stiffness of the encasement and the column diameter enhance the overall behavior of the GEC group through increasing the overall stiffness of the stone columns and the ratio of the soft soil replaced by the stone columns (i.e. the area replacement ratio), respectively. Moreover, it was observed that the performance of GECs is comparatively less sensitive to the internal friction angle of the column material, and that, in general, the modulus of elasticity of the column material has only a small effect on the group behavior. (C) 2012 Elsevier Ltd. All rights reserved.