Stone Columns

Technology Overview

Stone columns are commonly installed by water jetting or air jetting cylindrical vibrating probes into the ground to form holes, which are backfilled with gravel or crushed rock densified by the vibratory probe as it is withdrawn from the ground.  Water jetting is part of the vibroflotation technology, which is often referred as vibro-replacement or wet, top feed method.  Air jetting is part of the vibro-displacement or dry, top or bottom feed method.  Sometimes, pre-augering is used to reduce the amount of ground displacement during the installation.  The vibro-replacement method has less displacement and vibration disturbance to the surrounding ground than the vibro-displacement method, however, it has other environmental impacts due to slurry generated during the installation.  Stone column technologies have been used since 1970s in the United States.

Stone columns have been used to increase bearing capacity, shear strength, and rate of consolidation, reduce settlement, and increase liquefaction resistance.  Stone columns have demonstrated excellent performance in increasing liquefaction resistance of cohesionless soil as demonstrated in recent large magnitude earthquakes, such as Loma Prieta, CA (1989), Hokkaido, Japan (1993), Northridge, CA (1994), and Kobe, Japan (1995).  Design of stone columns is typically done by determining the layout pattern of columns (triangular or rectangular), spacing, and depth of stone columns to meet design requirements.  The main design principle is to treat stone columns and the surrounding soils as a composite foundation.  Stone columns carry more load than the surrounding soils due to their greater stiffness.  Stress concentration ratio (ratio of stress carried by the column to that carried by the in-situ matrix soil) and area replacement ratio (ratio of column cross section area to total treatment area) are two key design parameters.  The typical stress concentration ratio for stone columns in weak soils ranges from 2.0 to 5.0.

The Collin Group has utilized stone columns for the support of MSE walls for bridge approach embankments on numerous projects across the United States.

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