Glossary of Florida Sinkhole Terms

Activity: Commonly used as an indicator of the expansive potential of a clayey soil.  The activity of a soil is estimated by dividing the plasticity index by the clay fraction of the soil.

Aquifer: A geologic formation, group of formations, or part of a formation that is capable of storing, receiving, and transmitting water. The formation is capable of yielding enough water to support a well or spring.

Atterberg Limit: Tests performed on cohesive (clayey) soils to determine the range of moisture contents over which the soil changes from on physical condition to another. These limits are used as parameters to classify and estimate behavior of the clayey soils. See Liquid Limit, Plastic Limit, Plasticity Index.

Auger: An instrument for boring or perforating soils or rocks, for determining the quality of soils, or the nature of the rocks or strata upon which they lie, and for obtaining water.

Bearing Capacity: A measure of allowable bearing (load) placed on a given soil profile before a predetermined failure (yield) criteria is met.

Bentonite: clay formed by the decomposition of volcanic ash, having the ability to absorb large quantities of water and to expand to several times its normal volume.

Blow Count: The number of times a 140-lb hammer must fall 30 inches to drive a split spoon sampler 6 inches. 

Calcareous/Carbonate: Refers to earth materials composed of calcium carbonate (CaCO3)

Chemical Grouting: High density polyurethane expandable grout is installed under low pressure to fill voids immediately beneath foundations and/or concrete slabs.  This can gently raise foundations upward in a controlled and precise method.

Chert: Rock type composed of amorphous quartz (SIO2). The material is highly insoluble and usually found in the upper zones of the limestone bedrock. It is very hard and difficult to drill.

Cohesive: Soils which exhibit plastic behavior when moist which is generally comprised of clay minerals.

Compaction Grouting: Grout is pumped through steel casings into the ground under high pressure. This seals cavities in the limestone bedrock, compacts loose soils, and fills voids in the overlying soils.

Concrete Shrinkage: The volumetric change (shrinkage) of concrete due to the evaporation of water from the hardened concrete. Tensile stresses are generated and cracks are common.

Confining Unit: A geologic unit, primarily composed of clay minerals, which retards the flow or ground water.

Consolidation: The loss of volume of a cohesive soil mass due to loading (pressure) where water is “squeezed” out over time. Often misused interchangeably with settlement or deformation in sandy soils.

Cover Collapse Sinkhole: Develop abruptly (over a period of hours), and may cause catastrophic damage to houses, commercial buildings, and roadways.

Cover Subsidence Sinkhole: Tend to develop gradually where the covering sediments are permeable, and are transported into underlying carbonate rock, eventually forming a noticeable depression in the land surface.

Dissolution Sinkholes: Formed by rainfall and surface water percolating through joints in the limestone.

Epikarst: The zone of weathering found at the upper surface of the limestone bedrock. The weathering of the limestone surface results in an irregular surface and limestone pinnacles and boulders are common within the zone.

Erosion: The transportation of earth materials, usually accomplished by water, wind, or gravity.

Expansive Soil: A fine-grained clay that is subject to swelling and shrinkage of the soil, varying in proportion to the amount of moisture present in the soil.

Fill: Soils (generally sands) used to backfill excavations and to elevate site grades during construction.

Fly Ash: such ash recovered from the waste gases, used chiefly as a reinforcing agent in the manufacture of bricks, concrete, etc.

Footing: The portion of the foundation that transfers the structural load to underlying soils.

Foundation: That upon which anything is founded; that on which anything stands, and by which it is supported; the lowest and supporting layer of a structure; groundwork; basis.

Geologist: A person who specializes in geologic research and study.

Geotechnical: pertaining to practical applications of geological science in civil engineering, mining, etc.

Geotechnical Report: A report produced by geotechnical engineering firms used to communicate the soils conditions below a structure.  This report typically will contain ground penetrating radar analysis, soil boring (STP borings), and other specific soil related test.

Geotechnical Engineer: The branch of engineering dealing with the soil and bedrock, especially aspects of foundations and earthworks.

Grout: A specially designed blend of cement, fine sand, fly ash, water, and sometimes small gravel that is used in the grouting process.  When pumped in the ground at high pressure grout will compact loose soils, fill voids in overlying soils, and seal of cavities in the limestone bedrock.

Incipient: beginning to exist or appear; in an initial stage. This is generally used to describe the initial stages of cover subsidence sinkhole activity that may not have resulted as a surface expression.

Indurated: Cemented or compacted sediments.

Kaolinite: Clay sized mineral with a low expansion potential.

Karst: An area of limestone terrain characterized by sinks, ravines, and underground streams.

Limestone: A sedimentary rock consisting primarily of calcium carbonate, often in the form of the minerals calcite or aragonite, and sometimes with magnesium carbonate in the form of dolomite.

Lintel:  a horizontal architectural member supporting the weight above an opening, as a window or a door.

Liquid Limit (LL): The moisture content at which a cohesive soil (clay) ceases to behave plastically and flows (as a viscous fluid).

Loss of Drilling Fluid Circulation (LOC):  Occurs when drilling fluid is lost to voids or openings in underlying geologic units. In addition, drilling fluid may be lost due to drilling conditions (clogging or drill bit, etc.)

Masonry: Stone, brick, concrete, or similar building materials bonded together with mortar to form a wall.

Moisture content:  Water content or moisture content is the quantity of water contained in a material, such as soil (called soil moisture), rock, ceramics, or wood on a volumetric or gravimetric basis.

Monolithic Slab: One of the four types of foundations.  Foundations were footings and slabs are poured together.

Montmorillonite: Any of a group of clay minerals characterized by the ability to expand when they absorb large quantities of water.

N-Value: The sum of the blows required to drive a split spoon sampler 12 inches of soil.

Overburden Soils: The sediments located directly over the bedrock. These soils are generally composed of sand and clay in Florida.

Peat: An organic-rich soil or sediment with greater that 50% by dry weight organic component.

Plastic Limit (PL): The moisture content at which a cohesive soil (clay) ceases to be brittle and becomes plastic (able to be molded).

Plasticity Index (PI): The range of moisture over which a cohesive soil behaves plastically. The PL is calculated as the liquid limit minus the plastic limit and is expressed as a whole number.

Potentiometric Surface: A hypothetical surface representing the level to which groundwater would rise if not trapped in a confined aquifer.

Raveling: An erosional process where groundwater transports soil particles by seepage forces (drag) downward into fractures and openings in underlying geologic units.

Settlement: Deformation of soil in the (downward) vertical direction. Settlements observed in soils may be the results of several conditions, including loading, drag forces from moving water, and erosion.

Shallow Grouting: Grout is pumped at low pressure in low volumes at 6-8 feet below a structure. This will compacted loose soils, stabilizing a structure.

Sinkhole: Formed when soluble limestone and dolomite are dissolved by acidic rainwater. This creates solution channels, fissures, and interconnected void veins within the limestone formation. As water percolates through the overburden soils into the limestone formation, part of the soil is transported into the limestone formation.

Soil Series: A classification derived by the USDA originally used for agricultural purposes. In general, the upper 6 or 7 feet of soils are described in the soil series.

Solution Sinkhole: A small diameter opening in the limestone bedrock. The small opening may be in-filled with sediment from above or (if the limestone is sufficiently shallow) may produce a small “hole” in the ground surface. The latter is often referred to as a “chimney sinkhole”.

Surficial Aquifer: The ground water contained in the upper sequences of sands or other overburden sediments in general, the upper surface is free to move with changes in ground water volume change (due to increases/decreases in rainfall, evaporation).

Water Table: The planar, underground surface beneath which earth materials, as soil or rock, is saturated with water. The upper surface of the surficial aquifer.

Weathering: The various mechanical and chemical processes that cause exposed rock to decompose.

Weight of Hammer (WHO): An event where the drilling hammer, rod, and bit are allowed to rest on the bottom of the borehole and advance under their own weight.

Weight of Rod (WOR): An event where the drilling rod and bit (before the placement of the hammer on the anvil)