Design of Short Aggregate Piers to Support Highway Embankments

When new embankments are constructed over soft soils and existing roadways and embankments are widened rapidly, stability and differential settlement problems often result. Past approaches to mitigate these problems include overexcavation and replacement, preloading, lightweight fill, piles and concrete caps, geosynthetic-reinforced soil and pile-supported embankment systems, stone columns, lime-cement columns, and deep soil mixing. The advantages and limitations of these approaches are well documented in the literature. An alternative approach to support highway embankments that is less well documented, but that has seen increased use in recent years, is short aggregate piers. Although the technique has been used to support shallow spread footings, design approaches and parameter values have not been widely available for embankment support applications and are not well known in the field. The engineering properties and an approach used to design short aggregate piers for the support of highway embankments are summarized, and the mechanisms of load-settlement behavior are described. Techniques for evaluating overall stability, control and time rate of settlement, and bearing capacity are summarized. Performance measurements are referenced for embankment support projects recently constructed in Iowa.