An experimental study to increase bearing capacity and reduce bulging of stone columns using geogrid reinforced sand bed

Stone columns are normally used to improve a soft clay deposit by increasing the bearing capacity and reducing the compressibility. However, the settlement of the soft clay cannot be substantial-ly reduced due to bulging of the stone columns. It is therefore needed to develop a technique so that the expected settlement of the soft clay reinforced with stone columns is greatly reduced under an imposed load. In the present study a series of laboratory model tests were carried out to observe the effect of nor-mal sand bed (NSB) and geogrid-reinforced sand bed (GRSB) resting over a group of geotextile wrapped stone columns floating in soft clay. Significant improvement in the load-carrying capacity and reduction in settlement were observed. Due to placement of geogrid reinforced sand bed, the depth of bulging of the stone columns increases while the bulge diameter reduces. As compared to unreinforced clay, 1.72 fold, 2.83 fold and 5.48 fold increases in bearing capacity were achieved by the provision of only stone col-umns, stone columns with NSB and stone columns with GRSB, respectively. The critical thicknesses of NSB and GRSB were found to be 0.3 times and 0.2 times the diameter of the footing. The critical diame-ter of the geogrid layer is 2.5 times the diameter of the footing. The optimum length of the stone column is 6 times the diameter of the column. The observations showed that the stone columns with GRSB exhib-it negligible settlement under vertical load