Stone Column

A stone column is a vertical column of compacted crushed stone/gravel installed in soft clay or loose sand to reinforce and stiffen the ground, designed and constructed per IS 15284 Part 1. Working as a group beneath rafts/embankments, stone columns increase composite bearing capacity, reduce and accelerate settlement (the granular column also acts as a vertical drain shortening clay consolidation paths), and mitigate liquefaction of loose sands by densification and drainage.

They are installed by the vibro technique — vibro-replacement (wet, top-feed) or vibro-displacement (dry, bottom-feed) — typically on a triangular/square grid, with the area replacement ratio, column diameter/spacing and stone gradation set by the design to achieve the target settlement reduction (settlement-improvement factor) and bearing pressure. Performance is verified by load tests on single/group columns and post-treatment soundings, and load transfer relies on the surrounding soil providing lateral confinement — so very soft, sensitive clays may need geosynthetic-encased columns.