Numerical modelling of stone columns in soft soils

Great areas all over the world with underlying deep deposits of soft clay have increased the pressure on geotechnical engineers and ground engineering practitioners into looking for various improvement techniques to overcome problems associated with construction on soft soil, due to its low shear strength and high compressibility. For lightly loaded low- rise structures supported by narrow shallow footings, the use of vibro stone columns is gaining acceptance in industry and in construction. In this paper, numerical analysis is used to examine the influence of various parameters such as vibro stone column length, spacing and founding depth on the footing performance. Comparisons are made with the published field trials at the Bothkennar research site in Scotland. It has been found that the upper crust of the Bothkennar profile has a significant impact on settlement performance. In addition, the settlement performance/reduction is more significant once column length to diameter ratio (L/d) exceeds around 8.3. Also, the depth of stone column bulging is between 1.85–2.5 m below ground level which is comparable to the bulging depth suggested by Hughes et al. (1976). Numerical analysis predicts a stress ratio of 2.9 to 3.4 which is comparable with the field measurements.