Mine Shaft beneath a Home in Rockaway, New Jersey

Problem

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.

Analysis

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. URETEK 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.

Solution

URETEK 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, URETEK crews stabilized the soil beneath the new fill material with the URETEK Deep Injection® (UDI) 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, URETEK 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.

Result

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

URETEK Deep Injection® (UDI)

Widely referenced throughout our industry, UDI involves the injection of structural polymer into base and subgrade soils to increase the load bearing capacity. This is achieved by injecting the polymer through small holes drilled directly through the pavement structure to depths determined by site-specific analysis. Our URETEK 486 Star® material flows easily into voids and weak zones within the soil mass below. Through a controlled chemical reaction, the expanding polymer compacts surrounding soils and applies a controlled pressure on targeted areas of the affected pavement above. If needed, a multi-injection design plan is utilized to gently return the pavement to its original grade. The composite material quickly cures into a strong, dimensionally stable, and water-resistant geo-material, providing years of reliable service.

URETEK 486 Star®

URETEK 486 Star® polymer is a two-component, high-density, expanding thermoset polyurethane system. It was developed to be the ideal solution for under-sealing, void filling, lifting of settled pavement, stabilization and stiffening of weak soils, and for encapsulating and sealing buried infrastructure. URETEK 486 Star® is environmentally inert, non-toxic, and resists underground water erosion or weakening due to its industry-leading hydrophobic properties.

A large sinkhole opened up beneath the resident’s home.
Injecting 486 Star® through small passages beneath the home.