Sinkhole Terminology

  • Anomaly

A deviation from uniformity in physical properties; a perturbation from a normal, uniform, or predictable field. An anomaly represents an area or volume of geologic materials that have unusual physical properties that can be detected by ground penetrating radar, electrical resistivity, seismic, or other investigation methods.

  • Blow Counts

In a Standard Penetrating Test, a blow count represents the number of times the 140 pound hammer must fall 30 inches onto the anvil in order to drive the split-spoon 6 inches. The blow counts for the second and third, 6-inch intervals are added up to obtain N-value.

  • Collapse Sinkhole

This is a sinkhole formed by the collapse of cover materials such as sediment, soil, or rock. These cover materials collapse into an underground void created by the dissolution of limestone or dolostone.

  • Ground Penetrating Radar

A geophysical method for mapping interfaces underground by reflecting frequency radar waves off the interfaces and recording their reflections at the ground surface. This method is often used to detect shallow soil conditions that might represent sinkhole activity.

  • Limestone

A sediment rock composed primarily of calcite. This rock is soluble and often develops karst features when weathered.

  • Pier

A column used to support a structure and transfer its load to the soil through a footing as opposed to direct embedment in the soil.

  • Solution Sinkhole

This is a sinkhole formed by the slow subsidence of sediment or soil as the upper surface of the underlying, water-soluble rock or sediment is removed by dissolution.

  • Standard Penetration Test (SPT)

A geotechnical investigation technique that is widely used in which a split-spoon sampler is driven into a soil or sediment by a 140-pound hammer dropping 30 inches. The number of blows required to drive the sampler one footed is called the blow count (N).

  • Subsidence Sinkhole

A subsidence sinkhole forms when the upper surface of the limestone is dissolved away, and the thin cover overburden slowly subsides to occupy the space once occupied by limestone. Because of the continued downward movement of cover materials, voids may not be well developed.

  • Weight of Rod

This is an event that occurs during a standard penetration testing when the drill string (drilling rod and split spoon sampler) are allowed to rest on the bottom of the borehole and they sink under their own weight. This event may reflect a void, naturally weak soils, or excessive weight of drill string.


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