Mine Shaft Sinkhole Repair Beneath a Home

The Challenge

A large sinkhole opened up beneath a home in Rockaway, New Jersey.

Old-timers report that iron ore mined from this part of the state was the highest quality iron ore mined anywhere in North America. But for one homeowner in Rockaway, New Jersey, this source of local pride became the source of much stress when a large sink hole opened up under his home. Local legend has it that the old iron ore mines were capped and filled back in the late 1700’s. But with the passage of time, voids opened in the horizontal shafts running 50-feet below the surface, and the overburden soils gradually moved downward to fill those voids. Up at the surface, just beneath the home, a 15-foot by 15-foot void formed beneath the slab and the homeowner reached out for help.

Key Facts

The Solution

Groundworks crews arrived on the scene and began work on a three-phase plan, void fill, soil stabilization and polyurethane injections.

CTL Engineering of Morgantown, WV, a company specializing in mining consulting and mine forensics, put together a solution after studying the situation at the Rockaway residence. A local construction company would fill the sinkhole beneath the home with flowable fill material. However, given the known weight of such material, this would only be a temporary fix without a proper support matrix beneath the fill. Groundworks was suggested to supply the support matrix. The unique nature of URETEK’s 486 Star^® polymer material would offer the desired soil improvement at depth, while creating a “bridge” on which to support the new fill and the home’s concrete slab above.

Groundworks crews arrived on the scene and began work on a three-phase plan. The first phase involved a local construction company filling the void with flowable fill. Once completed, Groundworks crews stabilized the soil beneath the new fill material with the polyurethane injection process, providing the desired compressive strength while adding minimal weight to overburden soils.  Lastly, in order to bring the cured fill material into contact with the home’s slab, Groundworks crews injected additional polymer resin through holes previously drilled in the slab, effectively filling any and all voids, and fully restoring the base beneath the home.

The Impact

Polyurethane injections and solid geo-engineering practices led to a quick and affordable solution to a problem that took over 200 years to develop.

For the Rockaway homeowner, disaster was averted thanks to polyurethane injections and the experience of Groundworks’ crews with sink hole problems not just in New Jersey, but nationwide. When a large sinkhole opened up beneath this home, polyurethane injections and solid geo-engineering practices led to a quick and affordable solution to a problem that took over 200 years to develop.