Embankment Supported by Low Area Replacement Ratio Stone Columns, Monitoring and Numerical Studies

The focus of this study was to evaluate the behaviour of a test embankment supported on vibro stone columns (VSCs) installed with a low area replacement ratio (7.56%) based on data obtained from field instrumentation complemented by analytical and numerical methods. The test embankment is 5.35 m high and was built on top of a soft soil treated with VSCs arranged in a 10-column × 10-column square grid. Analytical and two-dimensional finite element methods using the axisymmetric unit cell approach were also employed in the study to analyse the instrumentation data. The measured settlement-time curves, for the embankment axis, were compatible with finite element analysis in which the coefficient of permeability was continuously updated with the void ratio. Comparison was also favourable regarding measured and predicted values of settlements and improvement factors. All evidence indicates that VSCs installed with a low area replacement ratio (<10%) were quite effective in reducing the time for settlement stabilization and in providing adequate short-term stability against failure, but less effective in reducing the long-term settlement magnitude.