Analytical Method of Stone Columns compared with an analysis as per Rowe Dilatancy Theory-Paper

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The paper compares two analytical methods for predicting the settlement and stress response of foundations on stone-column-reinforced soil: Saha’s mechanistic method, which incorporates dilation using the Schanz–Vermeer relation, and Pulko and Majes’ method, based on Rowe’s stress–dilatancy theory.<br /><br />Both methods use an axisymmetric unit-cell model. The surrounding soil is treated as elastic, while the stone column is modeled as a rigid-plastic Mohr–Coulomb material that can yield and dilate. The analysis considers column geometry, area replacement ratio, column length, applied stress, and the extent of column bulging near its head.<br /><br />The results show that dilation can substantially improve settlement reduction and increase stress concentration in the column. Even small amounts of dilation may have a notable effect. Within the practical area-replacement range of approximately 10–25%, the predicted stress concentration ratios are about 4–7 for short columns and 5–8 for long columns. Long columns generally provide greater settlement reduction, while greater dilation increases the column’s stiffness and load-bearing contribution.<br /><br />Saha’s predictions of dilatancy angle agree closely with the Rowe-based method at low area-replacement ratios and for short columns. Across the practical design range, the settlement predictions also compare favorably with other analytical methods and published field measurements, including tests on soft Bangkok clay. Differences among field results are attributed to varying soil conditions, installation methods, and column dilation behavior.<br /><br />The study concludes that accounting for granular-column dilation is important for design: densification and the resulting increase in initial stiffness can improve the performance of reinforced ground.

Keywords

stone column reinforcement

settlement prediction

stress concentration ratio

dilatancy angle

axisymmetric unit-cell model

Mohr-Coulomb material

Rowe stress-dilatancy theory

Saha mechanistic method

Pulko Majes method

foundation analysis