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Highway reconstruction on soft soils not a problem with geofoam

Case Studies | April 1, 2011 | By:

Once a thriving industrial suburb of Chicago that was sometimes called the Steel City, Gary, Ind., has seen a gradual decline in its industrial base and population.

Indiana’s fifth-largest city was hard hit by the decline in steel mill employment but has recently found an economic boon in the light manufacturing and tourist industries. Its location on the south shore of Lake Michigan is ideal for casino boats and provides a place for Chicagoans who are looking for weekend getaways.

The increase in industry and tourism led to a growing number of vehicles using the highways surrounding Gary. Most of the highway system was constructed in the 1950s and clearly was not aging well or able to withstand the increase in traffic.

The Indiana Department of Transportation (INDOT) recognized the need for major improvements to the highway system and approved the reconstruction of the Borman Expressway (I-80/I-94) from Gary westward to the Illinois state line, a project that has been under way since 2004.

The last element of the project is the $189 million Major Moves New Construction Interchange Modification that included the reconstruction and widening of the I-80/94–I-65 interchange.

Gary’s location at the southern tip of Lake Michigan contributes to its extremely soft soils and presents a challenge for road projects, which must withstand the constant vehicle traffic.

The Federal Highway Administration (FHWA) recommended the use of expanded polystyrene (EPS) geofoam as a soil stabilizer for this project because of the soft soils adjacent to the existing roadway. INDOT followed the FHWA’s recommendation and placed the project out for bid with a specification to use geofoam.

EPS geofoam is a lightweight, rigid foam plastic that has been used worldwide as a fill for more than 30 years. It’s approximately 100 times lighter than most soil and at least 20-30 times lighter than other lightweight fill alternatives. Because it is a soil alternative, EPS geofoam embankments can be covered to look like normal sloped embankments or finished to look like a wall.

Since this was the general contractor’s first experience using geofoam, the knowledge of the salespeople and the available technical support was critical for them. They provided shop drawings and technical support from the initial design phase through the project’s completion.

A partnering workshop 10 months before the start of this project offered a geofoam educational presentation for the engineers and project managers. Geofoam representatives were at the jobsite on the first day to coordinate truck deliveries and to review the layout and installation techniques with the on-site crews.

The INDOT project specifications called for a blend of sand and shredded tires with the geofoam. This was put in place first and mechanically stabilized earth (MSE) wall sections with metal straps were sandwiched between the blend of the sand and shredded tires to further reduce the overburden loads on top of the soft soils.

The geofoam installation began with 32 flatbed trucks delivering 115 cubic yards of geofoam per truck that were unloaded by a heavy-equipment operator using a retrofitted forklift. The trucks pulled up beside the concrete construction barriers and were unloaded from one side.

The volume of geofoam delivered on the 32 flatbed trucks was equivalent to more than 400 dump truck loads of traditional earth fill. The reduction in deliveries in the tightly congested jobsite area allowed for fewer disruptions and a close adherence to the construction schedule.

The EPS foam blocks were initially placed in a staging area before they were unloaded into the work area. They were then hand placed by workers to prevent vertical or horizontal joints in the stack. Barbed metal plates were used to prevent the layers from shifting prior to covering with the overburden.

The lightweight nature of the geofoam blocks contributed to the speed and ease of installation, according to the contractor, with each block maneuvered into place by two workers.

“For as much geofoam as we put down, the project went really quick,” said Gary Walsh, the general contractor. “There’s really no comparison to using traditional fill. There are no lifts needed. We just unloaded the blocks and got it installed fast.”

Each of the large blocks weighed less than a standard bag of ready-mix concrete and a crew of six was able to install 700 cubic yards working four to five hours a day during a one-week period. Using geofoam reduced the total overburden weight on the soft soils by more than 10.3 million pounds.

The installation crew overcame the challenge of cutting around stormwater drainage penetrations by using a hot-wire cutter. Though the crew had assorted thicknesses of geofoam, including some tapered pieces, maintaining the grade change required some curved and tapered field fabrication that was simplified by using the hot-wire cutter.

After the geofoam was in place, a course of leveling sand was installed to smooth out stair-stepped areas. A load distribution slab, 28-mil geomembrane, road base, and concrete paving slab were then placed over the geofoam.

The completion of this project brings Gary, Ind., one step closer to providing the transportation infrastructure necessary to support its existing industrial base and to accommodate its growing tourism industry. As this city reinvents and revitalizes itself, its major thoroughfares can now carry the burden of an increased traffic load.

David Shong and Nico Sutmoller are geofoam specialists with Insulfoam, Tacoma, Wash.

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