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Sinkhole/Karst Remediation

Karst is formed by the dissolution of soluble, carbonate rocks, including limestone, gypsum, and dolomite, by the flow of slightly acidic groundwater through natural weaknesses in the rock, creating sinkholes, sinking streams, closed depressions, subterranean drainage, and caves. Sinkhole formation is often triggered after the collapse of a soil bridge caused by the gradual internal erosion of the overburden into the cavities below, typically the result of an active water source moving particles of soil until the bridge collapses. Property within the zone of influence of the depression can undergo substantial damage; however, this natural geologic hazard is a normal consideration for construction within karst regions like Florida and Kentucky and is remediated routinely when identified during a geological survey. Sinkhole warning signs include a localized area of deeper bedrock overlain by very soft, wet soil; gradual localized ground settlement; bowing walls; and foundation cracks.

Much of central Florida and Kentucky are underlain by the distinctive geologic formation known as karst, which is prone to sinkhole activity. New reports have increased significantly in recent years, which can be directly linked to rapid population growth. The increase in population also affects the water table. As demand for fresh water increases, ground water levels are lowered, accelerating sinkhole formation.

In the 1970s, Hayward Baker pioneered the use of compaction grout to stabilize ground subsidence that occurred during soft ground tunneling for the Baltimore subway. Realizing that naturally occurring sinkholes were very similar to those caused by the tunneling process, the Tampa office of Hayward Baker pioneered the use of compaction grout (Portland cement, sand, and water) for solutions to sinkholes in central Florida. Compaction grout offered the benefit of filling the larger voids and compacting loosened soil while at the same time, its stiff nature would limit unnecessary grout takes in the thin cracks of the limestone formation. This helps control sinkhole repair cost for the owner or sinkhole insurance company.

When geotechnical surveys indicate potential collapse, several other sinkhole solutions are available depending on subsurface conditions and site restrictions. Pre-construction treatment to reduce the risk of sinkhole damage includes vibro replacement and vibro compaction to precollapse sinkholes and densify and reinforce loose overburden soils; and dynamic compaction to densify underlying soils and collapse voids

When the confining layer has been breached by the underlying void and soils have raveled into the cavity creating a surface depression, compaction grout is typically the most effective long-term sinkhole remediation technique. The evaluation for potential additional collapse requires surface and subsurface investigations and studying historical geological surveys by an expert geologist. Soil borings can be drilled to explore the cavity and underlying soils. Continuous survey monitoring is often utilized to detect any signs of additional movement after a collapse. Hayward Baker has experience with sinkhole remediation techniques to provide solutions for your home or building.

Learn more about shoring and implementing an earth retention system which includes best practices when providing support of excavation.

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