Sinkholes: A Homeowner's Unsettling Settling Problem

Dominick Amari, P.G.

 

Sinkholes and land subsidence have long plagued urban development by undermining foundations and causing extensive and costly damage to residential and commercial structures. Sinkhole (Karst) activity occurs throughout Tennessee and Kentucky where clay soils exist above and around areas underlain by soluble limestone and dolostone bedrock. Sinkhole development across these states is a natural process which can be more easily understood if recognized during the initial stages of land development.

"The causes of sinkhole (Karst) activity such as land subsidence under and around home foundations are both varied and complicated."

Soil settlement and soil migration into a sinkhole is often misunderstood and misdiagnosed due to the complex nature of the problem. The presence of shallow depressions and land subsidence under home foundations is subtle and occasionally manifest unnoticed by the homeowner.

Often the first indications the homeowner may observe are cracks or fissures in exterior home fascia materials such as brick, concrete block or stucco siding. Also, obvious openings such as interior cracks and separations in wall board especially over doors and windows become evident. Floor elevation changes resulting from floor system support pier shifting can give an indication that subsidence may be occurring under the central portions of the home.

The effect of the upward migration of the voids present in clay soils usually first develop as shallow surface depressions. When these develop under homes they often cause foundation failures because of the differential settlement under the concrete footings.

It is important to note that while sinkhole (Karst) activity can cause or contribute to differential settlement related issues, it is not always responsible for every settlement related condition. Many of our investigations have found different non-sinkhole (Karst) conditions that were contributing to differential settlement. These have included:

  • hand dug water wells abandoned improperly
  • trash pits that have been settling over time
  • buried organic rotting tree logs and rotting tree root systems
  • abandon septic tanks not properly backfilled

These are among the more common causes of differential settlement other than sinkhole (Karst) activity.

That is why subsurface soil evaluation is an important tool to evaluate both the presence of sinkhole (Karst) activity and to further evaluate when or more specifically where that activity has influenced a structure and if so specifically what part of the structure it has influence.

 


 

 

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VCE Investigative

2604 Foster Ave.
Nashville, TN 37210

Phone: (800) 747-3844

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