Glossary of Slab Foundation Terms

Active soil zone

The depth below the surface to the depth at which soil moisture is stable. In Southeast Texas, the active soil zone is anywhere from 8 to 20-feet below the surface. 

Bell bottom pier

A pier which is belled at the bottom. The bell increases the bearing load capacity of the pier. It also restrains the pier from being pushed upward by swelling soil. The bell diameter is usually around three times the diameter of the shaft. If the drilled shaft is 12-inches, the bell diameter is usually around 36-inches, but that can vary depending on the load on the piers and the soil.

Clay soil

Clay soils are comprised of very thin particles called plates. When they come in contact with water, the water molecules will, over time get between the plates causing the apparent volume of the clay to increase or swell. 

Elevations or elevation measurements

Such measurements can be used to estimate how much a slab foundation has bent and judge what type of distortion mode the foundation surface is in: center lift or edge lift. 

Epoxy crack injection

A technique for repairing cracks in concrete.  Epoxy crack injection is considered a structural repair. We do not normally recommend epoxy injection for slab-on-ground foundations for several reasons: most companies providing epoxy injection have no interest in residential work, most homeowners have unrealistic expectations concerning epoxy injection, and it usually fails to get at the root cause of excessive bending. 

Expansive soil

Expansive soil is a clayey soil that swells and shrinks as it absorbs water and drys out. These soils are common in the City of Houston and throughout Southeast Texas.

Slab-on-ground foundation

A foundation is a structure for transferring loads to the supporting soil. If the supporting soil is overloaded, the superstructure will suffer structural damage.   

French drain

A French drain is a term of art that refers to any type of underground drain.

From Wikipedia: French drains are primarily used to prevent ground and surface water from penetrating or damaging building foundations and as an alternative to open ditches or storm sewers for streets and highways. 

Non-shrink grout

From Wikipedia: Non-shrink grout is a hydraulic cement grout that, when hardened under stipulated test conditions, does not shrink, so its final volume is greater than or equal to the originally installed volume.

Gumbo clay

Slang term for expansive clay soil



Water table

As you go deeper into the ground it is normal to reach a point where the soil is filled with water.

From Wikipedia: The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water.



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