Glossary of Terms for Home Foundation Repair

Absorption Field – The affected area around a point of deposit, such as a roof line or soaker hose.

Active Zone – The active zone refers to the depth of soil instability or movement, usually due to moisture variation, sometimes referred to as the zone of seasonal fluctuations.

Allowable Load – The load, which may be safely transmitted to a foundation pier. Perma Jack piers have an 8 ft. allowable load.

Bearing Capacity of Soil – The maximum pressure that 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.

Bell Bottom Pier – A Bell Bottom Pier is a vertical structural support built to support concrete slab foundations and is built of concrete and steel rebar. The name is derived from the bottom of the pier, which resembles a bell and provides a greater area of support for the pier and the concrete slab above.

Clay – Clay is a naturally occurring earthy mineral that is plastic when wet but becomes permanently hard when heated. It 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. Clays are formed by the weathering of feldspathic rock and are composed of hydrated aluminum silicates.

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 a vertical angle until the pier can no longer support the structural load.

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

Concrete Slab – A concrete slab (foundation) is an area or strip of concrete laid as a single unjointed piece to serve as the foundation for a home or building. Texas does not regulate the constructing of neither the slab nor the type of concrete/steel that is used in the slab. Without regulation of residential foundations, insurance companies can (and do) opt not to cover the cost of foundation repairs.

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, with bedrock being the most solid deep foundation.

Differential Moisture Content – Adjacent areas of soil with different moisture content can cause concrete slab and home foundation movement. Trees and drainage problems are the most common causes of differential moisture.

Elevation – Elevation is a series of measurements to determine the difference in height between a central point and other points. These measurements are taken by instruments to establish grades.

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

Footing – A footing is any physical object that provides support for a home foundation by distributing the weight over a greater area of the supporting soil.

Foundation – The part of the structure that is in direct contact with the ground; it transmits the load of the structure to the ground.

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.

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%.

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

Gumbo – Gumbo refers to a variety of fine-grained silty soils (usually clays) found in the western and southern portions of the United States. (See “Clay” above)

Interlayer 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.

Load Bearing Capacity – This term refers to the maximum load or weight that can be applied to the soil before movement or failure (also called shear failure). The soil under the home foundation is under constant pressure from the weight of the home.

Mudjacking/Mud Pumping – Mudjacking is a process used to fill voids and add additional support under home foundations. It is 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 elevation.

Plasticity Index (PI) – A dimensionless constant that 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.

Point of Deposit – The location on the soil where water is landing from a source such as a rooftop, sprinkler, or soaker hose

Refusal – The condition reached when a pile that is 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.

Sink/collapse – A sink/collapse (a negative elevation) in the foundation is the opposite of a heave (positive elevation). A loss in elevation to the point where the foundation will crack is the likely a result of many sources. However, if builders and foundations were regulated and residential buildings were built to meet ACI codes and standards, many of the other elements would not affect a satisfactory foundation as much.

Slab – A concrete foundation that is supported entirely by the surface soils. It probably constitutes the majority of new residential construction in Texas and areas with high-clay soils.

Soaker Hoses – A unique rubber hose around the perimeter of a home or building that can be placed on top of the soil or up to 24 inches below the surface. These hoses are designed to distribute a low-volume, low-pressure flow of water around the perimeter of a slab foundation. The goal is to have a uniform level of moisture around the structure, which in turn, will minimize the potential of soil movement to damage the concrete slab. Watering effectively can arrest settlement brought about by soil shrinkage resulting from loss of moisture. (See “FAQ’s on foundation drainage)

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.

Upheaval – A heave (positive elevation) in the foundation is the opposite of a sink/collapse (negative elevation). The situation in which areas of the foundation are raised above the as-built position is called an upheaval. This term refers to a process or situation where part of a home’s foundation has moved ABOVE its original elevation. It usually results in interior and exterior cracks in various places throughout the home. A common cause of upheaval is the introduction of excessive moisture/water under the concrete slab. Excessive moisture/water under the concrete slab is likely from a plumbing leak in the drainage system.

Water table – The upper surface of water saturation in permeable soil or rock is a water table.

Water/Slab Leaks – Water leaks are a huge problem for home foundations. Usually, they result from leaks in the plumbing system, but other sources can contribute to water accumulation under a home’s concrete slab. Water leaks mostly cause upheaval, which is a swelling and expansion of the clay soil followed by collapse (soil compaction).

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