Behaviour of model stone column subjected to cyclic loading

Behaviour of saturated soft clay deposits subjected to cyclic stresses is of considerable importance in the design of railway infrastructure, since these deposits are characterised by very low bearing capacity and excessive settlement. Stone column is a well-established method that used to improve both bearing capacity and reduce settlement of such soil. However, much of the work to date has dealt with the behaviour of stone columns under static loading. Little is known about their response to cyclic loading. A laboratory based study was undertaken to investigate the response of both column and the surrounding soft soil to cyclic loading using a series of static and cyclic loading triaxial tests under undrained condition. Testing was performed on normally consolidated specimens of soft clay (undrained shear strength of ≈ 12 kPa, diameter 100 mm, and 200 mm height) reinforced with 28 mm diameter stone columns. Effects of loading frequencies at range of cyclic stress ratios were examined. It was found that the cumulative strain developed was dependent on the cyclic stress ratio, but independent of frequency from 0.5 to 3 Hz. Overall, stone columns have shown the potential to strength subgrade when exposed to cyclic loading, and hence reduce both capital costs (reduce the ballast needed for subbase), and operational cost through extended maintenance period.