Glossary

Active Zone
The depth of seasonal soil moisture variation. Sometimes referred to as the zone of seasonal fluctuations.

Adequate Watering
Watering sufficient to stop or arrest settlement brought about by soil shrinkage resulting from loss of moisture.

Allowable Load
The load which may be safely transmitted to a foundation member.

Bearing Capacity of Soil
The maximum pressure which can be applied to a soil mass without causing shear failure. The pressure or stress is created by applied loads and transmitted to the soil by the foundation.

Caisson or Caisson Pile
A large-diameter shaft hand- or machine-excavated to bearing stratum inside a protective casing. The shaft may require a cutting shoe to penetrate obstructions.

Clay
A soil that has the finest possible particles, usually smaller than 1/10,00 in (2.5X10-4 cm) in diameter, and often possesses the capacity for extreme volume changes with differential access to water.

Clay Bearing Failure
The result of expansive soils exerting non-uniform pressure against a constant downward loading. Such loading causes a pier to deviate further from vertical until the pier can no longer support the structural load.

Collapsible Soil
Soil susceptible to substantial reduction in void ratio upon addition of water.

Cut and Fill
Removal of excess existing soil (cut) to low or deficient areas (fill) for contouring purposes.

Deep Foundation
A design whereby structural load is transmitted to a soil at some depth, usually through piers, piles, or caissons.

Evaluations
Measurements taken by instruments (usually optical) to establish grades.

Fill
Soil added to provide a level construction surface or desired grade.

Footing
A member, usually concrete, that distributes the foundation load over an extended area and thus provides increased support capacity on any bearing soil.

Foundation
The part of a structure in direct contact with the ground which transmits the load of the structure to the ground.

Free Water
Water which can be taken on or lost by the soil without corresponding soil volume change.

French Drain
A perforated pipe installed in a cut to intercept and divert the underground water. The cut is below the level of the intruding water, and it is graded to drain the accumulated water away from the site. Sometimes a catch basin and discharge pump are required if a natural grade does not exist.

Grade
The level of ground surface. Also, the rise or fall per given distance (often per 100 ft or 30 m).

Gumbo
Highly plastic clay from the southern and/or western United States.

Inter Layer Moisture
Water that is situated within the crystalline layers of the clay and provides the bulk of the residual moisture contained within the intermediate belt.

Jacking
Controlled lifting of structure using hydraulic or mechanical systems.

Mud Jacking
A process whereby a water and soil cement or soil-lime-cement grout is pumped beneath the slab, under pressure, to produce a lifting force which literally floats the slab to desired position.

Plastic Index or(PI)
A dimensionless constant which bears a direct ratio to the affinity of the soil for volumetric changes with respect to moisture variations. The PI is determined as the difference between the liquid limit (LL) and the Plastic Limit (PL).

Poorly Graded Soil
A coarse-grained soil in which a majority of particles are of one size. Often described as uniform or gap-graded.

Settlement
The drop of some portion of the foundation below the original as-built grade.

Slab
One or another variety of concrete foundation that is supported entirely by the surface soils. It probably constitutes the majority of new residential construction in areas with high-clay soils.

Soil
All the loose material constituting the earth’s crust in varying proportions and including air, water, and solid particles. The solid particles have been formed by the disintegration of rocks.

Soil Stabilization
A procedure for improving natural properties of soil to make it a more adequate base for construction.

Spread Footings
Footings that generally consist of two structural components: (1)steel-reinforced pads that are of sufficient size to adequately distribute the foundation load over the supporting soil and are poured at a depth to be relatively independent of seasonal soil moisture variation and (2) a steel-reinforced pier tied into the footing with steel and poured to the bottom of the foundation beam.

Transpiration
The removal of soil moisture by vegetation.

Uniform Soil
Soil that contains a high proportion of particles with narrow size limits.

Upheaval
The situation in which areas of the foundation (usually internal) are raised above the as-built position.

Water Leaks
Water from any domestic source which is accumulated under the foundation. Any water under the foundation, regardless of source, tends to accumulate in the plumbing ditch. Usually of greater concern with slab foundations.

Water Table
The upper surface of water saturation in permeable soil or rock.

Well-graded Soil
A soil with a fairly even distribution of grain sizes-no excess of one size and no intermediate sizes lacking.