Shear Strength Behavior of Soft Clay Reinforced with Ordinary and Geotextile-Encased Granular Columns

Large-scale direct shear tests were performed to examine the behavior of soft clay improved with ordinary and geotextile-encased granular column (OGC and EGC) subjected to shear loading. The relative density of aggregates, type of geotextile encasement, and the applied normal stresses were all varied aiming to investigate the shear response of the geocomposite (i.e., clay + column inclusion). Results showed that in the presence of granular column, the mobilized shear stress, the overall shear stiffness, and the shear strength parameters were significantly improved. Compared to OGC, the EGC further increased the lateral load capacity of geocomposite owing to the provision of the additional confinement along the granular column. However, this improvement was greatly influenced by aggregates relative density and normal stress. In addition, using either OGC or EGC led a great portion of the applied shear stress to be supported by the accumulative frictional resistance of aggregates as the internal friction angle of the geocomposite increased from zero for virgin clay to over 26° for EGC-improved soft clay model. Also, the effect of the relative density of column filling material on the shear strength became pronounced with increasing the normal stress or using a stiffer geotextile encasement.