Bearing capacity of reinforced and unreinforced sand beds over stone columns in soft clay

A series of experiments on the unreinforced sand bed (USB) and geogrid-reinforced sand bed (GRSB) placed over a group of floating stone columns in soft clay and their numerical simulations have been conducted. Three-dimensional numerical simulations were performed using the finite-element package ABAQUS 6.12 for modeling the USB and GRSB placed over a group of stone columns floating in soft clay. In finite-element analysis, geogrid is modeled as an elasto-plastic material. Compared to unreinforced clay, 1.72-fold, 2.83-fold and 5.30-fold increases in bearing capacity can be achieved by the provision of only stone columns, stone columns with USB and GRSB, respectively. The critical thickness of USB and GRSB can be taken as equal to 0.3 times and 0.2 times the diameter of the footing; above this thickness, improvement in the bearing capacity is marginal. Both the improvement factor and stress concentration ratio of the stone columns with GRSB show an increasing trend with an increase in settlement. The optimum length of the group of floating stone columns with GRSB is six times the diameter of the column. Plastic strain developed in the stone column material is much higher than that in the geogrid planar sheet.