Case Studies- Soil Stab & Void Fill Pages

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Prime Flex 920 Used for Void Fill Under Bus Loop at Airport

Water-activated, rigid structural polyurethane foam fills a void and stabilizes loose soil under a busy bus loop without having to close the road to traffic.


Contractor: NEC Keystone, Inc. under contract with Turner Construction
Client: Florida Department of Transportation


The MIA Mover is a 1.25-mile-long automated people mover system linking the airport with its nearby Miami Intermodal Center, known as the MIC. The MIC is a common terminus for multicounty Tri-Rail service, in-county Metrorail heavy rail service, the MIA Mover, plus a consolidated rental car facility.


Credit: Patriarca12 – Own work, CC BY 3.0,


During construction of an adjacent facility, the vibration from the pile driving caused voids to form under the bus loop. The bus loop is made of six-inch thick high strength concrete to support the bus traffic for the multimodal transportation center.



Turner Construction subcontracted NEC Keystone to do the void filling and soil stabilization. The NEC Keystone crew injected Prime Resins Prime Flex 920, a single-part polyurethane to fill the voids beneath the slabs. They drilled holes in the slab in an offset grid pattern on 4-foot centers and injected the resin through 5/8” ports. Prime Flex 920, a hydrophobic, water-activated polyurethane grout, penetrated the void areas easily. Water in the substrate activated the grout causing it to expand and form rigid, rock-hard foam. The foam filled the voids and consolidated the loose, sandy soil to hardness similar to sandstone.



The process took just four days and the bus loop remained open the entire time. The work passed FDOT inspection without affecting operations or adjacent construction. Chemical grout injection for soil stabilization, in this case, saved the FDOT time, money, and public inconvenience.



The alternative was the replacement of the concrete slabs. That would have taken considerably more time and money, not to mention the major inconvenience to travelers for interrupted bus services.