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.
Anchor Pier or Pile – A pile or pier connected to a structure by one or more ties to furnish lateral support or to uplift. Also, a reaction pile or pier for load testing.
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 nonuniform 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.
Earth Anchor – A steel shaft containing one or more helixes which is screwed into the earth to provide a retention system against uplift forces.
Elevations – 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.
Frost Heaving – Expansion that results when a mixture of soil and water freezes. Upon freezing, the total volume may increase by as much as 25 percent, depending on the formation of ice lenses at the boundary between the frozen and unfrozen soil.
Gap-Graded Soil – A coarse-grained soil containing both large and small sizes but relatively low proportion of intermediate sizes.
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
Interlayer Moisture – Water that is situated within the cyrastalline layers of the clay and provides the bulk of the residual moisture contained within the intermediate belt.
Jacking – A means of imposing a static driving force on a pile by jacks. Used extensively to install piles in underpinning existing structures and in a static load testing.
Mudjacking – 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.
Non-cohesive Soil – A soil in which there is no attraction or adhesion between individual soil particles.
Plasticity Index (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.
Refusal – The condition reached when a pile being driven by a hammer has zero penetration per blow (as when the point of the pile reaches an impenetrable bottom such as rock) or when the effective energy of the hammer blow is no longer sufficient to cause penetration. When so stipulated, the term refusal or substantial refusal may be used to indicate the specified minimum penetration per blow. Overdriving of piles after essential refusal can damage them seriously.
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 Belt – The vertical section that can contain capillary water available from rains or watering. Unless this moisture is continually restored, the soil will eventually desiccate through the effects of gravity, transpiration, and/or evaporation.
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.
Void Ratio – The ratio of combined volume of water and air to the total volume of the soil sample.
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 sizesâ€”no excess of one size and no intermediate sizes lacking.