Load transfer mechanism of geotextile-reinforced sand layer over semirigid column-improved soft soil

Many design guidelines have been proposed for piled embankments, most of which consider piles or columns as rigid inclusions. In this study, a small-scale physical model test was performed to investigate the load transfer mechanism of a geotextile-reinforced sand layer over a soft subsoil improved by semirigid columns. A multi-stage load was applied at the top of the sand layer until the columns started to yield. When the columns yielded, a reverse load transfer was observed. Vertical stresses were measured and analyzed in terms of efficacy and stress reduction ratio (SRR) with a comparison of existing design guidelines for assessing soil arching. Among the reviewed guidelines, the approach recommended by the Dutch guidelines provided the closest results to the experimental data, whereas the one adopted by the American guidelines predicted well the change in efficacy and SRR under different surcharge loads. However, the load transfer mechanism after the yielding of columns is beyond the scope of the existing design guidelines. In addition, it was found through regression analysis that the increment of vertical stresses on columns and surrounding soil followed an inclined line under partially undrained conditions during loading stages and a curve during consolidation.