Foundations

Must transmit building loads to the rock or soil on which they rest.

Dead Loads

Permanent loads that remain constant over time.

Live Loads

Loads that change over time.

Uniform Settlement

Settlement that may disrupt building services, entrances, or site elements without distorting the structure.

Differential Settlement

Settlement that causes distortion and damage to finishes, cladding, and other building components.

Earth Material

A construction material that is naturally heterogeneous and less predictable than manufactured materials.

Rock

A continuous mass of solid mineral material that provides excellent foundation support.

Soil

A particulate earth material whose behavior depends on particle size, shape, mineral content, and moisture.

Index Properties

Physical characteristics used to identify and classify soils without directly measuring strength.

Boulder

A soil particle too large to lift with one hand.

Cobble

A soil particle that can be lifted with one hand.

Gravel

Particles that can be lifted between the thumb and forefinger.

Sand

Particles too small to be individually picked up between fingers.

Silt

Fine-grained soil with roughly spherical particles that are too small to see individually.

Clay

Soil particles smaller than silt with a plate-shaped structure.

Organic Soils

Soils containing decomposed plant material such as humus, muck, or peat and generally unsuitable for foundations.

Unified Soil Classification System USCS

A system used to classify coarse-grained, fine-grained, and organic soils.

Coarse-Grained Soils

Non-cohesive soils whose strength comes from friction and interlocking of particles.

Fine-Grained Soils

Cohesive soils whose properties are highly sensitive to moisture content.

Shear Strength

The resistance of soil particles to sliding past one another.

Cohesive Soil

Soil whose particles stick together because of electrostatic forces.

Non-Cohesive Soil

Soil whose strength depends mainly on particle friction and interlocking rather than cohesion.

Consolidation

The gradual compression of soil under sustained loads that causes long-term settlement.

Shrinkage Limit SL

The water content below which further drying causes no additional volume reduction.

Plastic Limit PL

The lowest water content at which soil remains plastic.

Liquid Limit LL

The water content at which a clay soil changes from plastic behavior toward liquid behavior.

Atterberg Limits

Tests used to determine the shrinkage, plastic, and liquid limits of soils.

ASTM D4318

Standard test procedure used to determine the plastic limit of soils.

Well-Graded Soil

Soil containing a wide distribution of particle sizes.

Well-Sorted Soil

Soil containing a limited range of particle sizes and typically more void space.

Field Density Test

A test used to determine the in-place density of soil at a construction site.

Sand Cone Method

A field density test that uses calibrated Ottawa sand to determine hole volume and soil density.

Ottawa Sand

Uniform calibrated sand used in the Sand Cone density test.

Nuclear Density Gauge

A device that measures in-place soil density and moisture using radioactive sources.

ASTM D1556

Standard governing the Sand Cone Method field density test.

ASTM D2922

Standard governing the Nuclear Method field density test.

Maximum Dry Density

The highest dry density a soil can achieve under a given compaction effort.

Optimum Moisture Content OMC

The moisture content that produces maximum dry density during compaction.

Proctor Curve

A graph showing the relationship between dry density and moisture content.

R. R. Proctor

The engineer who developed the concept of maximum dry density and optimum moisture content.

Standard Proctor Test

A compaction test using a 5.5-lb hammer and ASTM D698 procedures.

Modified Proctor Test

A higher-energy compaction test using a 10-lb hammer and ASTM D1557 procedures.

ASTM D698

Standard specification for the Standard Proctor Test.

ASTM D1557

Standard specification for the Modified Proctor Test.

Soil Investigation

The exploration of subsurface soil conditions to evaluate foundation suitability.

Invasive Soil Investigation

Methods involving direct penetration or excavation of the ground.

Non-Invasive Soil Investigation

Geophysical methods that evaluate subsurface conditions without excavation.

Soil Borings

Holes drilled into the ground to obtain soil samples and investigate subsurface conditions.

Auger Borings

A soil investigation method using hand or power augers.

Rotary Drilling

A drilling technique used for soil investigation and rock coring.

Standard Penetration Test SPT

A drive-tube boring method used to evaluate soil resistance and properties.

Shelby Tube Sampler

A device used to obtain relatively undisturbed soil samples.

Dutch Cone Penetrometer

A tool used to evaluate soil resistance and subsurface conditions.

Ground Penetrating Radar GPR

A geophysical method that uses radar waves to investigate subsurface conditions.

DC Resistivity

A geophysical soil investigation technique based on electrical resistance.

Seismic Refraction

A geophysical method that uses seismic waves to study subsurface layers.

Seismic Reflection

A geophysical method that analyzes reflected seismic waves to identify subsurface features.

Geotechnical Report

A report describing subsurface soils, properties, and laboratory testing results.

Bearing Capacity

The ability of soil to support structural loads without failure.

Structural Fill

Imported, well-graded coarse-grained soil used to improve site conditions and raise grades.

Drainage Fill

Uniformly graded gravel used around foundations or beneath slabs to improve drainage.

Benched Excavation

An excavation with sloped or stepped sides that is generally less expensive than sheeted excavation.

Sheeted Excavation

An excavation supported with temporary retaining systems where space is limited.

Tiebacks

Anchors extending into stable soil or rock to support excavation walls.

Soldier Beams

Vertical structural members used to support excavation walls.

Lagging

Timber or precast concrete panels placed between soldier beams to retain soil.

Steel Sheet Piling

Interlocking steel sheets driven into the ground for earth retention and groundwater control.

Dewatering

The removal or control of groundwater during excavation and foundation construction.

Foundation

The part of a structure that transfers loads safely to supporting soil or rock.

Shallow Foundation

A foundation located near the bottom of the substructure that transfers loads to near-surface soils.

Deep Foundation

A foundation extending to deeper, more competent soil or rock.

Spread Footing

A shallow foundation that supports individual columns or piers by spreading loads over a larger area.

Strip Footing

A shallow foundation that supports continuous load-bearing walls.

Slab-on-Grade Foundation

A concrete slab cast directly on prepared soil with thickened areas for support.

Crawl Space Foundation

A shallow foundation with an elevated floor system above an open space.

Basement Foundation

A fully enclosed below-grade space requiring waterproofing and drainage.

Mat Raft Foundation

A large reinforced concrete slab supporting an entire structure and reducing differential settlement.

Caisson Pier

A drilled deep foundation element reinforced and filled with concrete.

Pile

A deep foundation element driven into the ground to transfer loads through end bearing and skin friction.

End Bearing

Load transfer mechanism where piles rest on competent soil or rock.

Skin Friction

Load transfer mechanism through friction between pile surfaces and surrounding soil.

Pile Cap

A reinforced concrete element that distributes structural loads among a group of piles.

Grade Beam

A beam spanning between piers or pile caps to support walls above.

Mini Piles Pin Piles

Small piles pressed or rammed into the ground for stabilization and load transfer.

Helical Piles

Screw-like piles installed by rotation to transfer loads to competent soils.

Rammed Aggregate Piers

Ground-improvement elements made of compacted aggregate that strengthen weak soils.

Underpinning

A process used to strengthen, repair, or replace an existing foundation.

Drainage Mat

A material that allows groundwater to flow downward toward drainage systems.

Drain Piping

Perforated pipe installed at foundation bases to collect and remove groundwater.

Damp-Proofing

A coating that limits moisture penetration into concrete but does not resist hydrostatic pressure.

Waterproofing

A system that prevents water penetration even under hydrostatic pressure.

Waterstop

A material installed in concrete joints to prevent water passage between separate pours.

Hydrostatic Pressure

Water pressure exerted against foundation walls below grade.

Free-Draining Backfill

Granular material placed around foundations to promote drainage and reduce water pressure.