Abstract: An area of soil having an initial low bearing strength, such as an alluvial or sandy area, or an area formed by hydraulic fill, is compacted to provide an improved area of high bearing strength by forming a plurality of granular particulate (e.g., crushed stone, pebbles or sand) columns in pre-compacted holes in the area. The pre-compacted holes are formed by vibratorily driving a hollow probe having openable closure means set in closed position at its lower end, vertically downwardly to form each vertical hole, the soil around the probe thus being compacted. Thereafter, the probe is vibratorily extracted and granular particles are passed downwardly through the probe with the adjustable closure means open. Desirably, the granular material is compacted, i.e.