Rammed Aggregate Piers and Soil Reinforcing

Ideal Support, Rammed aggregate piers ensure subgrade stability (Structural Engineer, May 2005) reports on a proprietary foundation system used to provide both foundation support and soils reinforcing. Rammed aggregate piers are constructed by drilling piers 24 to 36 inches in diameter, 7 to 30 feet in depth. Drilled holes are then filled with layers of compacted crushed rock or gravel. As each approximately 12-inch layer is placed, a vertical impact ram is used to densify the aggregate and compress it into the surrounding soil. When properly spaced, rammed aggregate piers can provide both direct structural support, as well as strengthening of the surrounding soil in which they are placed.

The diagram at left illustrates rammed aggregate piers directly supporting a shallow spread footing (left-most) as well as providing soils reinforcing below a slab on grade.

The diagram below shows rammed aggregate piers below a retaining wall, in this case designed to improve the underlying soil's resistance to shear failure during a seismic event.

More Info:

• Deep foundations, such as piers and piles, are  discussed on pages 43 through 52 of the textbook.
• Additional information on rammed aggregate piers is available at the manufacturer's web site www.geopier.com.