Key benefits

Weighs less than soil. At one to three pounds per cubic foot, EPS geofoam is 100 times lighter than soil, reducing soft soil loads.

Extremely strong. Compressive resistance values range from 317 to 2,678 pounds per square foot at a 1% strain. Westergaard modulus of subgrade reaction “k” values confirm that geofoam has better bearing capacity than most foundation soils.

Predictable engineered values simplify design and construction. Contractors don’t have to compact soil in phases to a percentage of dry density and pay for multiple samples and laboratory tests to confirm results.

Uniform. Unlike other lightweight fills, the material’s homogenous composition provides uniform load transfer and eliminates differential settlement.

Very low maintenance. None is needed under normal conditions throughout its life. Geofoam is inert and highly stable; it won’t decompose or produce undesirable gases or leachates. It’s not affected by freeze-thaw cycles, moisture, or road salts, making it suitable for demanding conditions. It can be ordered with recycled content.

EPS geofoam cost vs. other fills

The unit price of EPS geofoam is typically higher than soil fill. But that installation doesn’t require earth-moving and/or compaction equipment. Also, since one truckload contains 120 cubic yards, construction traffic and transportation costs are lower than those of soil fill.

Nico Sutmoller ( is a geofoam specialist for Insulfoam (, Puyallup, Wash., a division of Carlisle Construction Materials.

Four common uses for expanded polystyrene (EPS) geofoam

1. Soft soil remediation

Ground with soft soils or soft clay makes construction difficult. Soft clay soils are notoriously poor foundations for public works projects, and require extensive remediation. To eliminate or greatly reduce the need for time-consuming and costly surcharging of soft soils, EPS geofoam provides high-load support at a low weight for projects of all sizes.

Example 1: Renovating an existing office building into a city hall for Renton, Wash. To meet building codes, new handicap ramps were required. The building is surrounded by extremely soft soils, so the ramps needed a very lightweight fill material to avoid post-construction settlement. The city installed 5,000 cubic yards of EPS geofoam, helping complete the project two months ahead of schedule and nearly $600,000 under budget.

Example 2: Widening the I-80 / I-65 interchange in Gary, Ind. At the south end of Lake Michigan, the project site had soft glacial soils. The Federal Highway Administration recommended a net-zero load methodology for the roadbed to prevent post-construction settlement. To enable a shallower excavation of the high-organic content soils, the contractors used EPS geofoam blocks. In addition to providing a solid foundation for the roadway, using the material reduced construction truck traffic on a very congested set of roads. Only 32 flatbed truckloads — equivalent to more than 400 dump truck loads of traditional earthen fill — were needed. A six-member crew installed 700 cubic yards in one week working four- to five-hour days.

“There’s no comparison to using traditional fill,” says Walsh Construction Site Supervisor Gary Walsh. “There are no lifts needed; we just unloaded the blocks and it installed fast.”

2. Slope stabilization

EPS geofoam can stabilize steep slopes without needing to change the final slope geometry. It can reduce the weight of a slope’s driving block as well as lower the risk of slope failures. The nature of the material also enables crews to move and place it without heavy earth moving and compaction equipment.

Example: Hillside road projects that used EPS geofoam for slope repair include:

  • U.S. 101 near Willets, Calif.
  • U.S. 50 near Montrose, Colo.
  • Window Rock Highway, Ariz.
  • State Highway 12 near White Pass, Wash.

3. Lateral load reduction on retaining structures

Similar to reducing the load on a slope-driving block, EPS geofoam significantly reduces lateral loads on retaining walls and building foundations. The material has an extremely low Poisson’s ratio (.05) and high coefficient of friction (.60), which helps enable placement of the blocks in a way that replaces the sliding soil wedge above the angle of repose. The need for geogrids or mechanical tiebacks is reduced, or sometimes eliminated, and project teams can construct a wall that acts more like a fence than a retaining wall. The material also allows for taller walls in narrower rights-of-way.

Example: Widening the Pacific Street Bridge over I-680 in Omaha, Neb. Typically, crews would have removed and replaced the existing abutment walls, which weren’t designed to withstand increased lateral loads induced by fill for additional lanes. Instead, the project team excavated the soil between the existing abutment wall and the soldier piles, then formed and extended the wall. The crew used about 2,000 cubic yards of EPS geofoam as lightweight back fill for the bridge approach.

4. Lightweight structural void fill

EPS geofoam works as structural void fill in concrete forming, enabling crews to fabricate virtually any shape or slope. The material eliminates separate concrete pours for vertical wall sections and topping slabs. Applications include bridge column formwork, stadium seating in auditoriums and sports arenas, stairways, podiums, loading docks and rooftop pool decks.

Example: Water channel walls in the Fairfield-Suisun Sewer District (Calif.) treatment plant. Typical construction of these types of walls involves two-sided forming then filling the void with soil, sand or concrete slurry and completing a second concrete pour for a topping slab. To simplify and speed the work, the contractor used 90 cubic yards of EPS geofoam as fill material. The geofoam blocks constituted half of the form, which simultaneously filled the void and carried the weight of the concrete topping slab. This enabled a monolithic pour of the channel tops and walls at the same time.