Unseen Asset

Civil infrastructure challenges of all shapes and sizes rely on Molded Polystyrene Geofoam solutions

By Sean O’Keefe

Infrastructure is an asset; one that likely goes largely underappreciated by the public that accesses it. While it may be hard to miss the mid-rise office buildings sprouting up across suburbia or the cool new mixed-use retail and entertainment amenities surrounding them, few beyond the design and construction industry recognize the vast array of interconnected civil infrastructure that gets us to and from wherever we’re going. Equally vital and often every bit as challenging as any urban infill office tower, civil infrastructure construction often necessitates similarly high levels of innovation and problem-solving.

When Bay Area, heavy-civil engineering contractor Maggiora & Ghilotti, Inc. of San Rafael, California was hired to work on a wetlands levee reinforcement project just north of San Francisco, Vice President, Scott Ghilotti knew that innovation would be essential to any effective solution.

“Restoring a wetland requires a combination of construction know-how and an appreciation for the long-term impacts on the natural environment,” said Ghilotti. His firm’s primary scope of work was to reinforce a roadway levee supporting State Route 37, which was undertaken as part of a broader effort to restore some 1,500 acres of tidal wetlands in the San Pablo Bay National Wildlife Refuge. To effectively support the two miles of roadway traversing the levee, the plan called for reinforcing the embankment. However, maintaining an appropriate transitional zone between the roadway and the wetlands to support natural use by birds and other wildlife necessitated creating a long, gentle slope rather than a steep grade. Doing so meant adding a substantial amount of slope-fill material between the elevated levee and the wetlands area below.

Due to the area’s very soft soils, known locally as Bay Mud, engineers at the California Department of Transportation were concerned about adding a substantial amount of weight to the embankment. Using soil or even a lightweight concrete fill would likely lead to settlement over time, potentially damaging the long-term stability of the levee and roadway above. When project partners at Ducks Unlimited suggested using molded polystyrene as a structural fill, Ghilotti was initially skeptical.

“We hadn’t ever used Geofoam before, but the guys at Atlas Molded Products were really helpful,” he said. “They detailed the manufacturing process including performance specifications, available block sizes, and how they were willing to pre-cut the blocks to individual dimensions as long as the cuts were straight lines.”

At about one percent of the weight of soil, molded polystyrene Geofoam is a cellular plastic material with a compressive resistance up to 18.6 psi at one percent deformation, making it an ideal solution to a complex problem. Ultimately, more than 15,000 cubic yards of EPS 29 Geofoam were used. Ghilotti estimates that his team installed an average of 1,500 yards of material a day along the two-mile stretch of levee without any complications. Once in place, the blocks had to be covered with soil and there Ghilotti had concerns as well.

“The overfill, compaction, and grading process happening on top of the foam blocks seemed like it would be a very delicate operation,” he shared. “Moving the amount of dirt required for this project meant using machines that weigh around 35 tons fully loaded with dirt. It just didn’t seem possible that equipment that heavy could move around on top of an embankment supported by foam blocks without damaging them.”

To his surprise with a layer of dirt of just 18 inches deep, even the heaviest machines were supported just as they would be on solid ground.

Phillippe Falkner had a similar discovery around the problem-solving power of molded polystyrene Geofoam when he was asked to put it to the test on a bridge embankment reconstruction project in Texas.

“Building roads and bridges is often about solving problems,” said Falkner, who is a Business Service Specialist for Ed Bell Construction, a north Texas heavy highway and municipal contractor based in Dallas. Ed Bell Construction was working on a highway rehabilitation project for the Texas Department of Transportation when their client asked them to rehabilitate a failing bridge along US-67 over SH-174 just outside of Cleburne, TX. The bridge’s headers were settling because deteriorating embankments at either end were causing the pavement to bunch up where the road connects to the bridge. TxDOT had already tried to rehabilitate the embankments using traditional soil stabilization methods but moisture issues and settlement continued.

“Since traditional methods hadn’t worked, they asked us to do a side-by-side comparison of two different fill materials,” continued Falkner.

After rehabilitating the bridge being diminished by the failing embankments, the next step was to excavate each side and refill the trenches with two very different alternatives. On one side of the bridge, TxDOT wanted the embankment rebuilt with a kiln-processed, lightweight clay aggregate. On the other side, molded polystyrene Geofoam blocks were the material of choice.

The lightweight aggregate only came from one manufacturer in Texas, so there wasn’t a lot to consider,” Falkner said. “Using Geofoam, however, seemed so different from typical roadway building that I needed to know quite a bit more before I could order it.”

Falkner decided to engage two different Geofoam suppliers to gain as much insight as he could while staying competitive in material procurement. Ultimately, blocks of molded polystyrene Geofoam from Atlas Molded Products were chosen. Working closely with the Atlas product representative, Falkner selected EPS 22Geofoam, which offers a compressive strength of 7.3 psi at one percent deformation. Shop drawings of the block configuration pattern were produced to validate structural soundness before placement. Atlas packaged pre-numbered blocks and followed a specified delivery sequence to ensure easy, precise installation of each block according to plans.

Once the Geofoam arrived, laborers were easily able to move the 40” x 48” x 96” blocks by hand. Most of the blocks required no modifications, but where needed, a hand-held hot wire cutter was used to quickly customize the Geofoam to fit around the bridge’s superstructure.

“With the embankment built, it was time to lay the road, and that went a lot different than expected,” continued Falkner. The road plan called for a crushed limestone base subgrade, covered with a hot asphalt mix to be topped with ten inches of concrete paving. “On the aggregate side, everything was kind of squishy and it took a lot longer than we expected to get a smooth surface. I was worried about the Geofoam side, but it was rock solid under the equipment as we pushed the base out with a dozer.”

Just as civil infrastructure challenges come in a variety of flavors, so do the possibilities for solutions innovation. For general contractor, WW Clyde, of Springville, Utah, one such opportunity presented itself on a road and bridge project in Pocatello, Idaho. Known as the Cheyenne South Valley Connector, the project involved a new two-lane roadway connecting the east and west sides of Pocatello. The main feature of the project was a 430-foot long bridge traversing the Portneuf River that also crosses six sets of active railroad tracks, South 2nd Avenue in Pocatello, and several bike and pedestrian paths. Minimizing community impact during construction was a key consideration for WW Clyde and project manager, Bryson Clyde, a licensed Professional Engineer, and fourth-generation builder in the Clyde family.

“In almost every construction project cost, schedule, and resources are the three primary variables,” shared Clyde. “As the project manager, it’s my responsibility to balance the allocation of each, which often requires some innovative thinking.”

On the Cheyenne South Valley Connector, innovation came in the form of an unusual application of Atlas Molded Products’ molded polystyrene Geofoam. Regularly used as a structural fill, in the case of the Pocatello bridge, WW Clyde’s structures manager suggested that the Geofoam could be used to create the formwork for the bridge’s three concrete piers.

“We never used Geofoam as concrete formwork before, but this project opened our eyes to the possibilities of this dynamic product and its ability to help solve construction challenges in the future,” Clyde continued. Typically, builders use wood or metal to construct concrete forms, which in custom applications like bridge piers can be very time consuming and expensive. Clyde calculated that using Geofoam as the concrete formwork saved the project an estimated $7,800 in formwork material costs alone. Add to that some 200 manhours saved in not having to build wooden forms by hand and the benefits were measurably obvious.

Once the shop drawings for the formwork were approved, the foam blocks were cut and shaped to the engineering specifications. Curved fillets were attached to the foam blocks to add an artistic fluted flair to the finished surface. The foam blocks were then delivered to the site, secured in place, and the concrete was poured from the top to fill the carefully constructed void of each pier.

“Using molded polystyrene geofoam not only saved money but is also save a lot of time,” finished Clyde. “We shaved more than a week off a very tight construction schedule by using Geofoam to make the concrete forms. Truthfully, most of the work was done by Atlas in shaping the product to our specifications. When it arrived on site, putting it in place was quite easy and things were very efficient.”

Though much of what is accomplished with Geofoam goes largely unnoticed by the everyday public, builders, engineers, and owners across the country have long realized the benefits of this strong, lightweight, adaptable material and know they have a trusted ally in Atlas Molded Products.

Sean O’Keefe is an architecture and construction writer who crafts stories and content based on 20 years of experience and a keen interest in the people who make projects happen. He can be reached at sean@sokpr.com.