Sinkholes 101

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A Quick Primer On A Common Problem

A sinkhole is a surface depression that may be caused by either geological conditions or man-made problems, like leaking storm sewers or buried trash. The man-made variety can certainly be disruptive and troublesome, but a geologic sinkhole can be downright devastating. What is a geologic sinkhole, and more importantly—what can be done about it?

Sinkhole Formation

About 25% of land mass in the world is characterized as karst.

Karst describes areas with sinkholes, caves, and underground streams which are formed by the slow dissolving of bedrock. When rainwater falls through the atmosphere and trickles through the soil, it becomes slightly acidic. In karst areas, this weak acid can dissolve holes in the bedrock or enlarge existing fractures, creating a “drain” for more groundwater.

As water flows into the feature, it takes some of the surrounding soil with it, sometimes resulting in significant soil loss. At the ground surface, this may appear as a slowly sinking circular depression, or a very sudden dropout into collapsing soil caverns. And so, a sinkhole is born.

Repairing a Sinkhole

Remediation options for sinkholes are fairly limited, and can be generalized into two basic methods: excavation and grouting.

One question that comes up often is this: What about just dumping several trucks of concrete down the hole? Although you might fill the depression, it is highly unlikely that dumped concrete will actually reach (and plug) any holes in the bedrock. This merely delays the problem and vastly complicates the eventual repair. Let’s look at the real options.

Excavation and Backfill

Sinkholes that form where the depth to bedrock is shallow (less than about 15 feet), can typically be remediated by excavation and backfill. All soil in the affected area must be removed from the bedrock surface to expose the hole or feature causing the problem.

Often, a sinkhole is actually a group of holes or an enlarged fracture, requiring additional exposure of the bedrock. Once located, the throats of these holes can be plugged with low-slump concrete to prevent water and soil from draining away.

Alternatively, a graded filter can be constructed of stone and filter fabric to allow water to pass into the feature, but retain the soil. Then the excavation is backfilled, with special attention to proper compaction. Excavation and backfill is a much more cost effective solution when indicated.

If bedrock is too deep, however, or if excavation would undermine or damage nearby structures, then grouting is the preferred approach.

Grouting

Remediation of sinkholes where bedrock is deep is accomplished by a process called “cap grouting.” Steel pipes are drilled or driven to bedrock on a grid pattern that covers the affected area. A thick cement-based grout is pumped down the pipes and injected at the bedrock surface. The grout spreads out on the surface and creates a concrete “cap” that covers the bedrock defects.

Cap grouting prevents further soil loss, but by itself does not address the disturbed and poorly compacted cone of soil from bedrock to the ground surface. So, as the grout pipes are slowly withdrawn, thick mortar-like grout is injected to displace and compact the surrounding soil. This “compaction grouting” restores the bearing capacity of the affected soil to prevent settlement of overlying structures.

Grouting is the best alternative when the problem is deep or occurs under or near an existing structure such as a roadway, bridge or building. This method creates much less disturbance to the surrounding area while accomplishing the two main objectives: stopping the soil loss and restoring the soil bearing capacity.

The Rembco Approach

Rembco specializes in repairing sinkholes by grouting. We have a history of success spanning almost 30 years. When you suspect sinkhole activity, make Rembco your first contact.

You’ll get a qualified assessment, straightforward conversation, and an unbiased recommendation. Then, if you choose Rembco to make the repair, you’ll get a fair price for an enduring solution. Click here to learn more about our sinkhole repair capabilities.

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About Rembco

Rembco is a geotechnical contractor that specializes in foundation support, soil stabilization and specialty grouting. Rembco offers micropiles, minipiles, soil nailing, rock anchors, pressure grouting, compaction grouting, compaction piles, chemical grouting, sinkhole repair, soil anchors and more. Headquartered in Knoxville, TN, Rembco has been providing geotechnical services (ground improvement, rock slide stabilization, excavation shoring, sinkhole remediation, hazardous material encapsulation, and underground liquid migration control) for over 30 years, serving clients throughout the nation.

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