By Tom Savoy
When cracks appeared on the eastbound lanes of the heavily trafficked U.S. 36, which connects Boulder, Colorado with Denver, crews quickly found that they were facing a full-blown sinkhole. The sinkhole appeared in the middle of the high-traffic summer season for the popular stretch of highway, and a quick repair was critical to getting traffic moving again and also beating the impending winter weather.
Construction crews created an aggressive timeline to rebuild the damaged roadway in just three months’ time. In order to meet this tight schedule, the project’s team turned to expanded polystyrene (EPS) geofoam from Insulfoam to meet the structural requirements of stabilizing the roadway. By utilizing EPS geofoam, the Colorado Department of Transportation (CDOT) and its design team of RJ Engineering and Consulting, Inc. and David Evans and Associates, Inc., were able to keep the project on track.
In just 20 days, six Insulfoam EPS plants manufactured and coordinated logistics for more than 200 truckloads carrying in excess of 6,000 blocks of EPS geofoam during the busiest months of the year. Shortly following the installation, the U.S. 36 roadway was fully operational.
Geofoam offers lightweight performance
According to CDOT, engineers specified geofoam because it is “very strong, which means it can safely support highway loading and also lead to improved slope stability. Of the different options considered, (EPS geofoam) provides the best factor of safety.”
A defining feature of EPS geofoam is that it is ultra-lightweight compared to other fills. Geofoam weighs approximately 0.7 to 2.85 pounds per cubic foot, depending on the product type, compared to 99 to 116 pounds per cubic foot for soil. This is also significantly less than other low-weight fills such as cellular concrete (24 to 90 pounds per cubic foot) and wood chips (15 to 30 pounds per cubic foot). Unlike other fills, EPS geofoam offers predictable engineered density values, which simplifies design and construction.
Although it is lightweight, EPS geofoam has better bearing capacity than most foundation soils. The material’s compressive resistance ranges from about 317 to 2,678 pounds per square foot at a 1 percent strain. As long as combined dead/live loads do not exceed 1 percent strain, the material will not creep or experience plastic yield.
Filling in for traditional fill materials
EPS geofoam blocks offer one additional advantage: uniformity. This is not the case with soil and other fill materials, whose variable, inconsistent compositions can lead to non-uniform load transfer and differential settlement. This type of settlement can cause dangerous, uneven structure settling and lead to further damage. On the other hand, EPS geofoam uniquely disburses or spreads the load out across a wide area, minimizing post-construction settling and creating a more stable foundation.
As Kris Essex, Territory Sales Manager for Insulfoam in Colorado explains, “(EPS) geofoam is a stable compound right away, as you can engineer the right density. There’s settlement compaction with soil, and there’s not time for that when the main U.S. 36 thoroughfare closed down.”
According to the EPS Industry Alliance, EPS geofoam’s lighter load decreases stress, while sidestepping deformation-related construction problems. Or, as CDOT put it, “since geofoam is lightweight, it reduces pressure and stress to the underlying soil.”
With a closed-cell structure, EPS geofoam dries quickly compared with other fill materials. As a result, little, if any, weight gain is expected. These structural benefits made it the best solution for the U.S. 36 engineers and the ability to complete the project on time made geofoam the best solution for the project’s managers.
Filling in the timeline
The CDOT and the project’s engineering team created an aggressive timeline to restore all lanes of travel. In order to meet that deadline and get the road re-opened, the project’s EPS geofoam manufacturer utilized six multi-operational plants in Colorado, Nebraska, Arizona, Florida, Washington, and California to produce and ship the blocks.
Matt Hogan, project manager for the roadway contractor Kraemer North America, further explains, with EPS “geofoam, we could fabricate quickly and not need all the deep foundation work to support the load of the new wall system. Being able to use six different plants across the country helped. We were able to find the fastest producer to be able to meet the needs of this particular project.”
Pulling together the large-scale, multi-site effort was necessary to meet CDOT’s aggressive re-opening deadline. Additional time-savings came from the manufacturer’s ability to create 40″ x 48″ x 96″ customized EPS geofoam to meet CDOT’s exact requirements. These large block sizes saved crucial time and labor on the Colorado jobsite. What’s more, should a block’s dimensions need to be adjusted for any reason, road building teams can quickly and easily cut EPS geofoam to the proper size with hot wire tooling or saws. EPS geofoam further saves construction schedules by taking surcharging and preloading out of the equation, freeing crews up to focus on other tasks.
For Hogan and his team, the ease of installation was particularly noteworthy.
“The nice part is being able to train people very quickly, because it’s literally stacking blocks. We’re able to slide the foam right into place, (add) a little bit of detail on the edges, (identify) out-of-line blocks and slide them into place. Once you get the material up on top of that foam, it slides relatively easy, and it’s able to go right in.” Hogan said. We “couldn’t be happier with the simplicity of how to install the foam.”
In addition to the short-term benefits of time and cost savings, CDOT will see long-term value as well. Geofoam is a low-maintenance solution and will require minimal service throughout the fill system’s lifespan. For the CDOT and other engineers that are seeking a durable infill solution that can quickly fit a project’s needs, EPS geofoam is an ideal solution.
Tom Savoy is the technical director for Insulfoam, a division of Carlisle Construction Materials. He has worked in the EPS Industry for 33 years and in construction materials (manufacturing and testing) for 38 years. Tom actively participates in many trade organizations including ASTM, SPRI and EPS IA. He can be reached at firstname.lastname@example.org.