Richmond, Virginia – CJGeo has used TerraThane geotechnical polyurethane foam from NCFI to repair a New York City building with significant structural problems.
The 12-storey building is near Madison Square Garden in Manhattan, New York.A building inspection found it had floors which had dropped by over an inch (25 mm).
An engineer from environmental services specialist DPC discovered that this was caused by voids beneath the slab. The voids formed as the building settled into its foundations. These were built on fine silt, sediment, and back-fill from a previous building.
CJGeo was called in to use geotechnical polyurethane foam to fix the problem. ‘Second and third generation buildings in Manhattan were often constructed over poorly-placed fills used to cover previous structures,’ said CJGeo’s chief estimator Kirk Roberts.
Exploratory holes were drilled in the building’s slab. These allowed inspectors to see that and the cavity underneath was nearly a metre in depth. ‘The void was under the entire slab, which must have been held up by magic,’ Roberts said.
The void was filled by drilling 15mm holes in diameter into the slab. These were used to pump low-exotherm TerraThane from NCFI into the void. ‘We needed to keep the heat low in the space so we chose NCFI’s TerraThane,’ Roberts explained. ‘It’s the only low exotherm foam we choose for three-foot lifts.’
The job was completed in two days. There was minimal disruption to the building’s occupants.
The foam was a good choice for remediation, Roberts said, as it is simple to apply, clean, quick, and light. ‘If we’d used the old mud slurry method it would have added at least 450-lbs per square foot (2.2 T/m2)to the soil around it. That’s just asking for more settlement.’