Failure of Ring Foundations on Soft Clay Reinforced with an Annular Stone Column

Abstract

The pressure–settlement response of ring foundations placed on soft clay and reinforced with an annular stone column was determined both experimentally and numerically. The mean diameters of the ring footing and the stone column were kept equal. The experimental work was carried out based on a series of small-scale model tests. The concrete ring footing was tested by placing it on soft clay with and without an annular stone column. The numerical assessment was based on: (i) an axisymmetric linearly elastic–perfectly plastic finite-element (FE) analysis for both associated and nonassociated flow rule materials; and (ii) an axisymmetric FE limit analysis (FELA) for the explicit determination of the collapse loads for an associated flow rule material. From the model tests, it was revealed that the employment of the stone column increased the bearing capacity of the ring foundations to almost double its magnitude. Employment of the stone column also led to a decrease in the magnitude of the footing settlement. When the inner portion of the ring footing was left unfilled, the footing was found to tilt. This footing tilt was avoidable by filling the inner hollow portion of the ring footing with a compacted soil mass, which also led to a marginal increase in the bearing capacity. The results obtained from the FE analysis compared reasonably well with the corresponding experimental data. The failure loads for an associated flow rule material from the FELA and FE analysis compare well with each other.