Lightening the Load

By Nico Sutmoller, Insulfoam Geofoam Specialist

Vinci Construction uses EPS geofoam simplifying engineering & construction of Trinidad freeway interchange

Adding or reconfiguring freeway interchange ramps often requires designers to carefully thread roads around existing support structures such as piers for overpasses and fly-over ramps. The challenge becomes how to support such new roads without expensive and time-consuming modifications to previously constructed engineered systems.

A new interchange at Valsayn, Trinidad, provides a clear example of the potential difficulties. Traffic growth in the island nation required the development of a new grade-separated interchange between two primary highways – the Churchill-Roosevelt Highway (CRH) and the Uriah Butler Highway (UBH).

One challenge the project team faced was that the north- and south-bound lanes of the UBH needed to pass adjacent to (and on both sides of) a support column for an existing flyover ramp. The new lanes required placement of 9.8 to 10.5 ft. (3 to 3.2 m) of embankment fill on top of the pier's pile cap on very soft soils. A concrete shaft around the pier would isolate it from the new fill to provide stability in case of any seismic activity. The concrete shaft also keeps the pier independent from the newfill.

To reduce the load applied to the pile cap under the pier, and to avoid any modification of the pier's seismic behavior, Vinci Construction GrandsProjets specified InsulFoam® GF expanded polystyrene (EPS) geofoam as a lightweight fill. Geofoam offers high compressive strength and predictability, yet weighs up to 100 times less than traditional soil fills, depending on the EPS density selected (see Table 1).

Table 1

Fill weight comparison

Pounds / cubic foot / kg/m3
EPS geofoam / 1 to 3 / 15.9 to 47.7
Soil / 120 / 1908

Vinci Construction crews placed 2,100 cy (1,600 m3) of EPS22 geofoam fill in an 80 by 89 ft (24.5 by 27 m) area surrounding the pier in only 3.5 days “Because of the ease and speed of installation, using geofoam allowed us to build this fill two times faster than a regular sand fill, especially in Trinidad, where heavy rains can interrupt back filling activities for days,” said Cecile Huillard, Construction Engineer with Vinci Construction GrandsProjets.

Huillard notes that the use of EPS fill provided a cost-effective and simple alternative to building a concrete slab founded on piles to support the load from the road and transfer it away from the pier pile cap. No heavy equipment was needed for the fill placement, as crews were able to install the geofoam blocks by hand. Additionally, the geofoam resulted in lower and smoother post-construction differential settlements of the roadway in both the transversal and longitudinal directions. The use of geofoam also eliminated the need for additional geotechnical investigation for potential additional piles.

“We selected Insulfoam as the geofoam supplier because of their expertise in this field and the numerous reference projects they have,” said Huillard. “From the beginning, they were really present in the design process to help us optimize the project. For instance, they modified the design in order to reduce the number of containers to be shipped. Insulfoam’s geofoam expert came on site, as well, for the installation; Nico Sutmoller organized an efficient training on site and the whole operation was done in less than a week.”

InsulFoam® GF EPS geofoam does not typically require surcharging, preloading, or staging often necessary with other fills. It resists moisture, freeze-thaw damage, insects, mold, and decomposition. The product is inert, does not emit undesirable gases or leachates, and is reusable or recyclable. EPS geofoam is available in multiple strengths suitable for a wide range of engineered applications. The EPS22 geofoam wasspecified in the CRH/UBH interchange project has a compressive resistance of 1,051 psf (50 kPa) at 1% deformation.

For more information on attributes and applications for EPS geofoam, visit Insulfoam at , or email

Geofoam road embankment fill at the Churchill-Roosevelt Highway / Uriah Butler Highway interchange in Valsayn, Trinidad.