The findings of this research are presented in NCHRP Report 529, "Guideline and Recommended Standard for Geofoam Applications in Highway Embankments" and NCHRP Web Document 65". NCHRP Report 529 consists of two parts, a design guideline and a material and construction standard for EPS-block geofoam. NCHRP Web Document 65 consists of the project final report and four appendixes.

Geofoam (expanded polystyrene) is a super-lightweight soil substitute material. Originally patented in the United States, the first widespread application of geofoam technology in highway construction was for insulation and pavement frost damage mitigation, but geofoam is now used in a broad variety of transportation-related applications in both the United States and other countries.

One geofoam application receiving increased attention is as super-lightweight fill in highway embankment construction. In the United States, a 1995 project in Oahu, Hawaii, used 17,000 cubic meters of geofoam in an embankment constructed over very soft organic soils. Reconstruction of I-15 around Salt Lake City, Utah, will incorporate 100,000 cubic meters of geofoam in embankments constructed on soft lake bed silts. A bridge approach constructed in Issaquah, Washington, employed geofoam to reduce the downdrag on the pile-supported foundation. Another related geofoam application is slope stabilization. An example is a recently completed New York State DOT project where geofoam was used as super-lightweight fill to reduce the forces causing slope instability. These examples illustrate the use of geofoam to solve serious geotechnical problems facing the design engineer.

The use of geofoam in embankment construction avoids the problem of excessive settlements and affords benefits including reduction of overburden pressure, reduction in the magnitude of ultimate settlement, and savings in construction time. Differential settlements between the approach fill and bridge abutments can be reduced. Lateral pressure from approach fills onto abutments and wing walls can be lessened significantly with geofoam fill. Long-term maintenance requirements can be minimized, and ride quality of roads crossing swamps or bog areas can also be improved by geofoam use.

The research conducted under this project resulted in the development of guidelines and a recommended standard for the use of geofoam as a super-lightweight fill in embankments and bridge approaches over soft ground.

Status: Research is complete.

The NCHRP research oversight panel requested continuation funds in the amount of $300,000 to study the use of geofoam in landslide stabilization and to study time-dependent creep in geofoam. The continuation research will conducted as NCHRP Project 24-11(2).

Product Availability: The design guideline and recommended standard have been published as NCHRP Report 529. The final report and supporting appendixes are available online as NCHRP Web Document 65.