Vibro stone columns – model tests vs. fem calculations

Research on the group action of stone columns points out that the behaviour of an isolated single column is quite different from the one of a stone column in a group of columns under a rigid footing. To highlight the differences, model tests of a rigid footing on a single sand column in clay and model tests of a rigid footing with various numbers of sand columns in clay are compared. A re-calculation of model tests has been performed by means of the finite element method taking into account the mean grain diameter. Beginning with a single isolated column, the deformation mechanism of the column has been reproduced, detecting a wedge shaped shear zone below the footing. Furthermore, the same footing has been analysed to study the group effect in a section of 5 columns. Again the same deformation mechanism as in the model test has been observed displaying a wedge shaped area below the footing. The influence of the length of the columns and an additional row of columns outside the footing has been investigated and recommendations are given