An Unique Formula for the Stone-Column Group Efficiency-Paper

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The paper develops a group interaction factor (GIF) to account for how neighbouring stone columns affect settlement beneath large, uniformly loaded foundations. Conventional unit-cell methods model an isolated column and may therefore underestimate settlement when applied to column groups: adjacent columns constrain one another’s lateral bulging, reducing column deformation and increasing vertical settlement.

The author analysed hydrotest settlement data from 12 oil-storage tanks founded on stone-column-reinforced ground at Haldia and Kandla, India. Settlements predicted using existing analytical methods were consistently lower than measured values. From these field data, the paper defines a GIF that adjusts the settlement-reduction factor for the effects of group interaction, considering the composite ground’s equivalent deformation modulus and the area ratio.

Regression analysis produced the empirical relationship <strong>α = 2.2346 Ar⁻⁰·²⁹⁸⁷</strong>, where α is the interaction factor and Ar is the area ratio. The proposed relationship was compared with model tests on groups of two, three and four columns in soft clay, reported in earlier research. The comparison supported its applicability across different group sizes, column spacings and soil conditions.

The paper concludes that settlement estimates based on unit-cell analyses can be made more representative by applying the proposed interaction factor. The associated group-efficiency factor is the inverse of the GIF. The formulas offer a practical means of incorporating group effects into stone-column foundation design, though the relationship is empirical and derived from the cited field and experimental data.

Keywords

group interaction factor

stone columns

settlement prediction

unit-cell method

foundation settlement

oil storage tanks

Haldia

Kandla

area ratio

empirical regression