All photos courtesy Ed Bell Construction
by Tom Huempfner
Large-scale construction requires making many decisions far in advance of the onsite construction work. Engineers and architects guide clients through myriad decisions while creating the drawings and specifications during the design phase of the project. Ultimately, successful projects are about making good decisions before even moving the first shovel of dirt, and then supplying skilled workers with detailed plans.
“Building roads and bridges is often about solving problems,” says Phillippe Falkner, operations manager for Ed Bell Construction, a heavy/highway and municipal contractor. “Experience is always a great asset in building confidence in the choices we make.”
Based in Dallas, Ed Bell Construction was working on a highway rehabilitation project for the Texas Department of Transportation (TxDOT) in 2010 when Falkner was presented with a rare opportunity.
“The US 67 bridge over SH 174 outside of Cleburne needed to be rehabilitated and they asked Ed Bell to add it to our scope of work on the adjacent section of highway,” says Falkner.
Due to deteriorating embankments, the pavement had bunched where the road connected to the bridge on either end. TxDOT attempted 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 as sort of an R&D project,” he explains.
The first task on the add-services contract was to rehabilitate the bridge over SH 174, which had been diminished by the failing embankments. Once the bridge was sound, the embankments were excavated in sections roughly 1.8 m (6 ft) deep and 36.6 m (120 ft) long. These fresh, wide trenches were fitted with alternative fill materials and paved over with new road, reconnecting both sides to the rehabilitated bridge. TxDOT requested two different structural fills to complete the work on either side of the bridge, and wanted electronic pressure monitors installed beneath the restructured embankments to independently monitor any future settlement.
Considering alternative fill options, TxDOT compared kiln-processed lightweight clay aggregate with solid, lightweight geofoam blocks. On the surface, Falkner expected the aggregate materials would behave similarly to soil, but the geofoam blocks caused him some concern.
“Using geofoam seemed so different from typical roadway building,” Falkner says. “I needed to know quite a bit more before I could order it.”
With the bridge remediated, the trenches were lined with a filter fabric and fitted with settlement sensors. Once prepared, Ed Bell Construction began filling the embankments and documenting the work. On the lightweight aggregate side, a truck backed up to the hole and dumped in the material—a material Falkner describes as texturally similar to kitty litter. The aggregate was graded flat and covered with more fabric, performing largely the same way soil would under the grader.
Before installing the geofoam, drafters produced shop drawings of the block configuration pattern, numbering each piece and ensuring the embankment was filled for structural soundness. Next, a sand-leveling course was put down to get a nice flat surface. The blocks were laid by hand with no specialized equipment or skilled labor involved. Two-person teams moved pieces as large as 2.4 m by 1.2 m (8 by 4 ft), weighing less than 45 kg (100 lb). Most blocks required no modification, but, when necessary, workers used a hand-held hotwire cutter to quickly customize blocks onsite. Once the geofoam was stacked and wrapped in fabric like the aggregate side, Falkner had two ready-to-pave embankments made from very different materials.
“With the embankments built, it was time to lay the road down,” says Falkner. “That went a lot differently than expected.”
The road plan called for a crushed limestone-based subgrade, covered with a hot asphalt mix and topped with a 254 mm (10 in.) concrete paving.
“I was worried about [the durability of] the geofoam side, but it was rock solid under the equipment as we pushed the base out with a dozer. Then on the aggregate side, everything was kind of squishy and it took a lot longer than we expected to get a smooth surface.”
Falkner, still concerned about damaging the embankments with heavy construction equipment, decided to use a lightweight truss screed bridge paver rather than a traditional concrete paver to install the final top.
Five years after installation, data suggests both alternative fills have performed adequately. On the lightweight aggregate side, the fill settled slightly—more than was originally expected, but within TxDOT’s acceptable tolerances. The geofoam side had a quick initial settlement, but no further movement, performing better than originally expected. Falkner continues to work on TxDOT projects with the area engineer, commenting that the department has been satisfied with the work, as well with the durability of the rehabilitation project.
Tom Huempfner is vice president of sales and marketing at ACH Foam Technologies. He has 30 years of experience in the molded polystyrene industry, specializing in product for architectural insulation, geofoam, and industrial applications. Huempfner can be reached at tomhuempfner@achfoam.com.
