Predicted site behaviour of geogrid encased stone columns

Where lightly loaded structures such as embankments are to be founded on soft compressible soils, stone columns are often used to improve the engineering properties of the bearing layer. Stone column treatment can provide a significant reduction in the magnitude of both primary and creep settlement, in addition to accelerating consolidation. With recent research aimed at reinforcing columns with geosynthetics, a technique of partial encasement using geogrid has been investigated to further reduce settlements. Small-scale testing of model columns has indicated that significant reductions in vertical settlement can be achieved by steadily increasing the percent encased length of the column. Based on these findings, a parametric study using numerical modelling was undertaken, indicating that similar reductions in vertical settlement may be achieved in full-scale. It is expected that geogrid encasement could be used to extend stone column treatment to sites with strict settlement control or to reduce the ‘step’ in differential creep settlement that can occur off piled structures such as bridge abutments.