Infrastructure is an asset; one that likely goes largely underappreci- ated 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 neces- sitates similarly high levels of innovation and problem-solving. When Bay Area, heavy-civil engineering contractor Maggiora & Ghi- lotti, 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 ef- fectively 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 road- way 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 manufac- turing 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 Geo- foam 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. Unseen Asset Civil infrastructure challenges of all shapes and sizes rely on Molded Polystyrene Geofoam solutions By Sean O’Keefe
“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 heavi- est 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 stabiliza- tion 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 embank- ments, 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, how- ever, 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 Lightweight, yet incredibly strong, the geofoam blocks from Atlas Molded Products served as the base material on an embankment project for the Texas Department of Transportation.
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october 2020
csengineermag.com
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