Sinkhole Repair

Sinkhole repair starts with a correct diagnosis. The same surface depression can come from cover-collapse over a karst throat, slow cover-subsidence over a raveling column, or a dropout caused by a broken sewer or stormwater line, and each diagnosis points to a different repair. We open every project with a geotechnical investigation: standard penetration test (SPT) borings on the affected pattern to locate raveling and competent bearing, cone penetration testing where soil response is needed in a continuous profile, and ground penetrating radar per ASTM D6432 to map shallow voids before we drill. The investigation report drives the treatment plan and the structural engineer's repair design.

Compaction grouting is the workhorse. Low-mobility mortar, typically at a 1 to 3 inch slump, is staged bottom-up in 1 to 2 foot lifts at packer pressures of 100 to 600 psi, forming an expanding bulb at each injection point that displaces and densifies the surrounding ground. The grouted column blocks further raveling and re-establishes bearing capacity beneath the affected slab or footing. Real-time pressure, flow, and volume monitoring at each injection prevents surface heave and confirms the treated zone matches the design.

Where the diagnosis points to a connected dissolution channel in the underlying carbonate, cement or microfine permeation grouting seals the bedrock throat itself, cutting off the loss pathway that originated the failure. This is most common in Florida, the Tennessee Valley, central Pennsylvania, and other karst regions where dissolution features intersect overburden directly.

When the foundation has already dropped, compaction grouting alone will not restore structural support. We add micropile underpinning to transfer load past the disturbed zone into competent strata, with low-headroom drill rigs that operate inside finished basements in as little as 6 feet of clearance. Critical piles are load-tested per FHWA GEC-7 before final lock-off. Where the throat is too large or the structure too compromised for grouting and underpinning to work alone, a reinforced concrete structural cap bridges across the affected area and transfers load onto stable ground at the perimeter.

Shallow sinkholes, generally less than 10 feet deep with a clear bottom, are often best treated by excavation and replacement with flowable fill or engineered compacted fill, since the cost of mobilizing grout and drill equipment outweighs the simpler open-cut approach.

Every project closes with verification: post-treatment borings or pressure-test rounds confirm the treated column, micropile load tests document underpinning capacity, and a sealed engineering report covers the diagnosis, design, and field record. The package satisfies homeowners insurance neutral-evaluation requirements under Florida Statute Chapter 627 and equivalent procedures in other states, and gives the structural engineer of record what they need to certify the repair.