IMPROVEMENT OF SOFT SOIL CHARACTERISTICS USING STONE COLUMNS

Abstract

Due to rapid increase in construction activities over the past few decades, the importance of ground improvement techniques has increased manifold. Ground improvement techniques are numerous but the basic aim is to improve the engineering parameters of problematic soils so as to achieve desired properties. Stone columns reinforce soft soil owing to their high stiffness, strength and increase in drainage path. Different models have been used to predict load-settlement behavior of soil treated by stone columns. The load carrying capacity of stone columns is dependent on various parameters which provide an insight into their load-sharing mechanism. This research aims at investigating the effects of floating stone columns in clayey soil with silty deposits by developing small-scale laboratory models. A comparison is made between untreated and single stone column treated soil by varying the undrained shear strength of soil and L/D ratio of stone column. Effect of group columns is investigated in terms of varying spacing among them. Based on rigorous testing conducted in laboratory, soil parameters have been identified to develop accurate numerical models in PLAXIS 2D software. It is inferred from comparison between the two that results of small-scale laboratory testing are in close agreement with results from FEM. The undrained shear strength of soil affects the applicability of stone columns as a ground improvement technique and the stone columns are effective in the range of low to medium shear strength soil (Su<54KPa). There exists a critical length of column beyond which the load carrying capacity does not significantly increase. (L/D= 4 – 5.5). Group effect of columns is more pronounced at closer spacing and is found negligible beyond S/D=3. Bulging failure is observed in single stone column loaded in compression and the effect of bulging is prominent at 1.5–2D from the top. However group columns do not fail by bulging. The small scale testing is effective to predict load settlement behavior of stone columns in field however controlled environment should be vi available for conducting testing. Further research is needed to address the effects of curing time, encasing of columns and varying diameter of stone columns.