Soil Engineering: Common Terms and Definitions

Soil Engineering Common Terms (A-Z)

ABSORBED WATER

Absorbed Water – water held mechanically in a soil mass and having physical properties not much different from ordinary free water at the same temperature and pressure.

ACTIVE ZONE

Active Zone – the layer of expansive soil subjected to shrinking and swelling. This zone extends from the ground surface to the maximum depth of significant moisture fluctuation.

ADHESION

Adhesion – shearing resistance between soil and another material such as steel, concrete, etc., under zero externally applied pressure.

ADSORBED WATER

Adsorbed Water – water in a soil held by physiochemical forces. Its physical properties are substantially different from absorbed water at the same temperature and pressure.

AEOLIAN DEPOSITS

Aeolian Deposits – wind-deposited material such as dune sands and loess soil deposits.

ALLOWABLE BEARING PRESSURE

Allowable Bearing Pressure – the maximum bearing pressure that satisfies both bearing capacity and settlement criteria.

ALLUVIAL SOIL

Alluvial Soil – soil that has been transported in suspension by flowing water and subsequently deposited by sedimentation.

ANGLE OF FRICTION

Angle of Friction – Angle whose tangent is the ratio of the maximum shear stress that resists slippage between two solid bodies at rest and the normal stress across the constant surfaces.

ANGLE OF INTERNAL FRICTION

Angle of Internal Friction – angle between the axis of normal stress and the tangent to the Mohr at a point corresponding to a given failure stress in soil.

ANGLE OF REPOSE

Angle of Repose – Angle between the horizontal and the maximum slope that soil assumes through natural processes. It generally applies to dry granular soils.

ANISOTROPIC SOILS

Anisotropic Soils – soils having different properties in different directions.

APPARENT COHESION

Apparent Cohesion – cohesion in fine granular soils caused by capillary forces.

AQUIFER

Aquifer – groundwater reservoir found in a water-bearing geologic formation.

ATTERBERG LIMITS

Atterberg Limits – the results of three tests, the liquid limit test, the plastic limit test, and the shrinkage limit test (only the first two are commonly performed). These tests are a measure of the plasticity of a soil.

AUGER

Auger – a helically shaped drill used to bore holes into the ground. These holes may be made for the purpose of obtaining soil samples or it may be filled with concrete and form a drilled shaft foundation.

BANK RUN

Bank Run – material, usually gravel or sand, that is not processed but is used in the as-found condition.

BEARING CAPACITY

Bearing capacity of soil is the value of the average contact pressure between the foundation and the soil which will produce shear failure in the soil. Ultimate bearing capacity is the theoretical maximum pressure which can be supported without failure. Allowable bearing capacity is what is used in geotechnical design, and is the ultimate bearing capacity divided by a factor of safety.

figure_35_differential-foundation-settlement_2-150x150

BEARING CAPACITY FAILURE

Bearing Capacity Failure – a foundation failure that occurs when the shear stresses in the adjacent soil exceed the shear strength.

BEARING WALL

Bearing Wall – a wall that carries a structural load, such as that from upper floors or a roof.

BEDROCK

Bedrock – the continuous body of rock of relatively great thickness that underlies the overburden soils.

BELL

Bell – the enlarged portion at the bottom of a drilled shaft foundation. (Not all drilled shafts have bells.) Also known as an underream.

BENTONITE CLAY

Bentonite Clay – soil with a high content of montmorillonite clay that is characterized by high swelling potential.

BENTONITE SLURRY

Bentonite Slurry – a mixture of a highly plastic clay, known as bentonite, with water to form a material with a consistency similar to that of pea soup. Sometimes used during drilling of borings as a means of preventing the adjacent soil from caving into the boring.

BLOW COUNT

Blow Count – (a) The number of hammer blows to drive a pile for a specified distance, such as one foot; (b) The number of hammer blows required to drive a soil sampler, especially a split-spoon sampler, for a specified distance.

BOREHOLE

Borrow Pit – a circular hole made with a rotary or diamond drill with an auger or other rotated cutting tools or bits for exploring rock or soil. Also called boring or drill hole.

BOULDERS

Boulders – usually round shapes an average dimensions of 12 in. or more that result when rocks are fragmented by weathering or abrasion.

CAPILLARY RISE

Capillary Rise – the height above a free water elevation to which water will rise due to capillary action.

CASING

Casing – a steel pipe that is temporarily inserted into a boring or drilled shaft in order to prevent the adjacent soil from caving.

CLAY SOIL

Clay Soil – fine-grained soil finer than 0.002 mm (0.005 mm in some cases) that exhibits plasticity with a range of water contents. It usually exhibits considerable strength depending on the presence of other soil materials when air-dried.

COBBLE

Cobble – a rock fragment, usually rounded, with an average diameter of 3 to 12 inches.

COEFFICIENT OF COMPRESSIBILITY

Coefficient of Compressibility – the rate of change of void ratio relative to applied pressure. It applies to cohesive soils.

COEFFICIENT OF CONSOLIDATION

Coefficient of Consolidation – a soil parameter used in the theory of consolidation that contains physical constants of a soil affecting its volume change.

COEFFICIENT OF PERMEABILITY

Coefficient of Permeability – the rate of discharge of water under laminar flow conditions through a unit cross-sectional area of porous medium such as soil under a unit hydraulic gradient and standard temperature and pressure conditions.

COEFFICIENT OF PERMEABILITY₁₂

Coefficient of Uniformity, C₁₂ – the ratio of discharge of water under laminar flow conditions through a unit cross-sectional area of porous medium such as soil under a unit hydraulic gradient and standard temperature and pressure conditions.

COHESION

Cohesion – Normally applies to cohesive soils and is defined as shear resistance at zero normal stress.

COLLOIDS

Colloids – small particles in suspension that will not settle out due to gravity.

COLLUVIAL SOIL

Colluvial Soil – soil transported downhill by gravity, such as by landslides or creep.

COMBINED FOOTING

Combined Footing – a spread footing that supports more than one column.

COMPACTIBILITY

Compactibility – a spread footing that supports more than one column.

COMPACTION

Compaction – the densification of a soil through mechanical means.

COMPACTION CURVE

Compaction Curve – the curve showing the relationship between dry unit weight and water content of a soil for a given compactive effort.

COMPACTION TEST

Compaction Test – laboratory compacting procedure in which a soil mass at a known water content is placed in a specified manner into a mold of standard dimensions, subjected to a standard compactive effort, and the resulting dry unit weight is determined.

COMPRESSIBILITY

Compressibility – property of soil and rock pertaining to their susceptibility to decrease in volume when subjected to external load.

COMPRESSIVE STRENGTH

Compressive Strength – the load per unit area at which an unconfined cylindrical soil specimen will fail in a simple compression test.

CONE PENETRATION TEST (CPT)

Cone Penetration Test (CPT) – an in-situ test for determining soil properties. It consists of slowly pressing a steel cone into the soil and measuring the penetration resistance.

CONSOLIDATION

Consolidation – the process of gradual reduction in volume of a soil mass resulting from an increase in compressive stress.

CONSOLIDATION TEST

Consolidation Test – a test in which the soil specimen is laterally confined in a ring and is compressed vertically between porous stones.

CONSOLIDOMETER

Consolidometer – testing device used to measure the consolidation of a soil sample.

CONSTANT HEAD PERMEAMETER

Constant Head Permeameter – device used to determine the permeability of a soil sample at a constant water pressure or head.

CORE

Core – a cylindrical sample of soil or rock recovered in the field using a core bit.

CORE BIT

Core Bit – a bit used to extract a core for testing.

CORE DRILLING

Core Drilling – a rotary drilling technique that cuts out cylindrical rock samples.

CRUSHED STONE

Crushed Stone – granular material, resulting from the mechanical crushing of rock, boulders or large cobble stones, of which substantially all faces have been fractured by the crushing operations.

CUMULATIVE PERCENT RETAINED

Cumulative Percent Retained – the total percentage of the soil grain distribution that is equal to or larger than the size under consideration.

DEGREE OF CONSOLIDATION

Degree of Consolidation – the ration, expressed as a percentage, of the amount of consolidation at a given time within a soil mass to the total amount of consolidation expected under a given stress condition.

DEGREE OF SATURATION

Degree of Saturation – the degree to which the voids in a soil mass contain fluid (water, gas, or oil.) Usually expressed as the ratio of water volume to total void volume.

DESSICATION

Desiccation – the drying of a soil. When soils are dried, either naturally or artificially, their engineering properties change. As the soil dries, the pore water is drawn to the particle contact points and a soil suction force develops. This causes the soil to become overconsolidated. Thus, simply rewetting the soil will not restore its original properties. Although this effect is most pronounced in fine-grained soils, it is also present in sandy soils.

DEWATERING

Dewatering – the process of removing water from a construction area, such as by pumping from sumps or from wells. Normally, a temporary measure.

Water pump being used to dewater mining location

DILATANCY

Dilatancy – the phenomenon of expansion of cohesionless soils when subjected to shearing deformation.

DIRECT SHEAR TEST

Direct Shear Test – Shear test in which soil or rock under an applied normal load is stressed to failure by moving one section of a soil sample relative to another section.

DISTURBED SOIL SAMPLE

Disturbed Soil Sample – this type of soil sample has been changed from its naturally occurring condition in the ground in some way. These changes may be due to the methods used in sampling, handling, transportation, storing or testing the sample. However, changes in the conditions of the soil are usually due to the type of sampling techniques used. A disturbed soil sample can still preserve many of the properties of the soil in the ground and can be used in testing.

EFFECTIVE DIAMETER

Effective Diameter – soil particle diameter corresponding to 10% finer on the grain-size curve

EFFECTIVE PRESSURE, EFFECTIVE STRESS

Effective Pressure, Effective Stress – the average normal force per unit area transmitted from grain to grain of a soil mass

ELASTICITY

Elasticity – property of material that returns to its original form after applied force is removed.

Here is an excellent resource to measure Soil Elasticity utilizing a triaxal apparatus. Link

By Pierre-Yves Hicher, (Prof., Lab. of Mech., Soils, Struct., Mat., CNRS URA 850 Ecole Centrale de Paris, 92295, Chateney-Malabry, France)

Journal of Geotechnical Engineering, Vol. 122, No. 8, August 1996, pp. 641-648, (doi:  http://dx.doi.org/10.1061/(ASCE)0733-9410(1996)122:8(641))

EXCESS PORE WATER PRESSURE

Excess Pore Water Pressure – the portion of the pore water pressure that is due to transient effects such as consolidation.

EXPANSIVE SOIL

Expansive Soil – a clayey soil that expands when wetted and contracts when dried.

FAILURE

Failure – Exceeding the maximum strength of material.

FAILURE CRITERION

Failure Criterion – mechanical condition under which solid materials fail by facturing or by deforming beyond some specified limit. Specification may be expressed in terms of stresses, strains, rate of change of stresses, rate of change of strains, or some combination of these parameters.

FAT CLAY

Fat Clay – a highly plastic clay with low values of liquid limits and high plasticity indices.

FILTER

Filter – a layer or combination of layers of pervious materials used to provide drainage yet prevent the movement of soil particles due to flowing water.

FINES

Fines – portion of a soil finer than a No. 200 U.S. standard sieve (0.075 mm).

FISSURES

Fissures – naturally occurring openings in rock formations.

FOOTING

Footing – portion of a structure that transmits loads directly to the soil

FOUNDATION

Foundation – Part of a structure that transmits load to soil or rock.

FREE WATER

Free Water – water that is free to move through a soil mass under the influence of gravity.

FREEZE

Freeze – an increase in the load capacity of a pile after it has been driven. Caused primarily by the dissipation of excess pore water pressures. Also known as setup.

FRIABLE

Friable – crumbles easily; brittle.

FROST HEAVE

Frost Heave – the heaving of the ground due to the formation of ice lenses.

FROST SUSCEPTIBLE SOIL

Frost Susceptible Soil – a soil that is capable of drawing in large quantities of water, usually by capillary action, and forming ice lenses. These lenses are the primary cost of frost heave

GAP-GRADED

Gap-Graded – a soil that is missing certain particle sizes.

GEOTEXTILES

Geotextiles – Man-made fabrics designed for use in soil stabilization and control.

GLACIAL TILL

Glacial Till – Man-made fabrics designed for use in soil stabilization and control.

GRADATION

Gradation – graph showing the proportions by mass of a soil or fragmented rock distributed in specified particle-size ranges.

GRAIN-SIZE DISTRIBUTION

Grain-Size Distribution – see gradation above.

GRAVEL

Gravel – rounded or semirounded particles of rock that pass a 3-in. (76.2-mm) sieve and are retained on a No.4 U.S. standard sieve (4.75 mm).

GRIZZLY

Grizzly – a heavy-duty screen used in crushing plants.

GROUNDWATER LEVEL

Groundwater Level – the level below which the rock and subsoil, to unknown depths, are sturated.

HARDNESS

Hardness – resistance of a given material to indentation or scratching.

HARDPAN

Hardpan – a hard impervious soil layer which does not become plastic when mixed with water and limits the downward movement of water and roots.

HEAD

Head – energy of water in soil due to water pressure and position.

HEAVE

Heave – movement of soil caused by expansion or displacement resulting from phenomena such as moisture absorption, removal of pressure, driving of piles, frost action, and/or loading of an adjacent area.

HETEROGENEOUS SOIL MASS

Heterogeneous Soil Mass – a soil mass having different properties at different points.

HOMOGENEOUS SOIL MASS

Homogeneous Soil Mass – a soil mass having the same properties at different points.

HORIZON

Horizon – One of the layers of a soil profile, distinguished principally by its texture, color, structure and chemical content. These include the “A” horizon, the uppermost layer of a soil profile from which inorganic colloids and other soluble materials have been leached; the “B” horizon, the layer of a soil profile in which material leached from the overlying “A” horizon is accumulated; and the “C” horizon, which is an undisturbed parent material from which the overlying soil profile has been developed.

HUMUS

Humus – a brown or black material formed by the partial decomposition of vegetables, animal remains and organic fraction of soil.

HYDRAULIC FILL

Hydraulic Fill – a fill placed by transporting soils through a pipe using large quantities of water. These fills are loose because they had little or no mechanical compaction during construction.

HYDRAULIC GRADIENT

Hydraulic Gradient – The loss of hydraulic head per unit distance of flow. (critical*) Hydraulic gradient at which the intergranular pressure in a soil mass is reduced to zero by the upward flow of water.

HYDROMETER

Hydrometer – a device used for obtaining an indication of the specific gravity of a fluid or the particles within a fluid.

HYDROSTATIC PORE WATER PRESSURE

Hydrostatic Pore Water Pressure – the portion of the pore water pressure that is due to the force of gravity acting on the water above. The pore water pressure that would be present when the soil has reached equilibrium.

IN-SITU

In-Situ – referring to the in-place or undisturbed properties or state of a soil.

ISOTROPIC

Isotropic – an adjective used to describe materials with physical properties that are the same regardless of the direction of measurement. For example, the strength at a point in an isotropic soil is the same in the vertical, horizontal, or any other direction.

KIP

Kip – Kilopound; a unit of force equal to 1000 lb.

LANDSLIDE

Landslide – the downward and outward sliding or movement of a soil mass of earth or rock, or a mixture of both. Mass wasting.

LATERAL EARTH PRESSURE

Lateral Earth Pressure – the pressure exerted by an earth backfill against a wall or bulkhead; and calculated by an earth pressure coefficient (active, at rest, or passive) multiplied by the vertical soil pressure.

LEACHING

Leaching – the removal in solution of soluble materials by percolating or moving water.

LEAN CLAY

Lean Clay – a slightly plastic clay with low values of liquid limits and plasticity indices

LIQUEFACTION

Liquefaction – the sudden large decrease in shearing resistance of a cohesionless soil. It is caused by a collapse of structure by shock or other type of strain and is associated with a sudden but temporary increase in fluid pressure.

LIQUID LIMIT (AN ATTERBERG LIMIT, LL)

Liquid Limit (an Atterberg limit, LL) – the water content at which a pat of soil, cut by a groove of standard dimensions, will flow together for a distance of 1/2 in. under the impact of 25 blows in a standard liquid limit apparatus.

LIQUIDITY INDEX

Liquidity Index – the ratio, expressed as a percentage, of the natural water content of a given soil sample minus its plastic limit to its plasticity index.

LOAM

Loam – a mixture of sand, silt, or clay, or a combination of any of these, with organic matter.

LOESS

Loess – a uniform aeolian deposit of silty material having an open structure and relatively high cohesion due to cementation of grains. A characteristic of loess deposits is that they can stand with nearly vertical slopes.

MANHOLE

Manhole – a hole, usually with a cover, through which a person may enter a sewer, drain, steam boiler, etc., especially one located in a city street.

MENISCUS

Meniscus – the curved, film-like layer at the surface of a liquid at rest within a container.

MODULUS OF ELASTICITY

Modulus of Elasticity – the ratio of stress to strain for a material under given loading conditions. It is equal to the slope of the tangent or the secant of a stress-strain curve.

MOHR FAILURE ENVELOPE

Mohr Failure Envelope – the envelope of a sequence of Mohr circles representing different stress conditions at failure for a given material.

MOISTURE CONTENT

Moisture Content – the amount of water contained within a soil, usually expressed as a percentage. It is found for a sample by dividing the weight of the water by the weight of the solid particles.

MOISTURE-DENSITY CURVE

Moisture-Density Curve – the curve showing the relationship between dry unit weight and water content of a soil for a given compactive effort.

MUCK

Muck – stone, dirt, debris or an organic soil of low consistency.

MUD

Mud – a mixture of soil and water in a fluid state.

NORMAL FORCE

Normal Force – a force directed perpendicular to a surface element upon which it acts.

NORMALLY CONSOLIDATED SOIL

Normally Consolidated Soil – soil that has never been subjected to an effective pressure greater than the existing effective overburden pressure.

OPTIMUM MOISTURE CONTENT

Optimum Moisture Content – water content at which a soil can be compacted to a maximum dry unit weight using a specific compactive effort.

ORGANIC SOIL

Organic Soil – soil with a high organic content, normally greater than 25% by weight. In general, organic soils are highly compressible and have poor load-sustaining properties.

OUTCROP

Outcrop – Exposed portions of bedrock at ground surface.

OVERBURDEN

Overburden – loose soil that overlies bedrock; also refers to all material overlying point of interest in a given soil deposit, such as the soil that must be moved to get to a level where construction of foundation components may begin.

OVERCONSOLIDATED SOIL

Overconsolidated soil – soil that has been subjected to an effective pressure greater than the existing effective overburden pressure.

PARENT ROCK

Parent Rock – rock from which a soil has been derived.

PEAT

Peat – fibrous organic matter in various stages of decomposition, generally darkbrown to black in color and of spongy consistency.

PENETRATION RESISTANCE (SPT)

Penetration Resistance (SPT) – Number of blows (N) required to drive a standard sampler a distance of 1.0 ft into soil using a hammer weighing 140 lbs, falling a 30-in. distance.

PENETROMETER

Penetrometer – Device used fot testing a soil’s load-carrying capacity indirectly by measuring its resistance to an object being forced into the soil with a standard force.

PERCENT COMPACTION

Percent Compaction – The ratio, expressed as a percentage, of dry unit weight of a soil to maximum dry unit weight obtained in a laboratory compaction test.

PERCHED WATER TABLE

Perched Water Table – groundwater separated from an underlying body of groundwater by a concave and relatively impervious soil or rock layer. It is located at a higher elevation than the groundwater table.

PERCOLATION

Percolation – Movement, under hydrostatic pressure, of water through soil or rock, excluding movement through large openings such as solution channels.

PERCOLATION ("PERC") TEST

Percolation (“perc”) Test – a test used to determine the water absorption capability of a soil.

PERMAFROST

Permafrost – perennially frozen soil found at varying depths

PERMEABILITY

Permeability – the capacity of soil and rock to conduct liquid or gas.

PH

pH – an index of the acidity or alkalinity of a solution expressed in terms of the logarithm of the reciprocal of the hydrogen ion concentration.

PIEZOMETER

Piezometer – an instrument for measuring pressure head in soil deposits.

PILE

Pile – relatively slender structural element that is driven or otherwise introduced into soil for the purpose of providing vertical or lateral support for a structure.

PIPING

Piping – the progressive removal of soil particles from a deposit by percolating water, leading to the development of channels and ultimately failure.

PLASTIC LIMIT (AN ATTERBERG LIMIT, PL)

Plastic Limit (an Atterberg Limit, PL) – the water content corresponding to an arbitrary limit between the plastic and the semisolid states of consistency of a soil. It is equivalent to the water content, expressed in percentage, at which a soil will begin to crumble when rolled into a thread 1/8 in. diameter.

PLASTICITY

Plasticity – the property of a soil that allows it to be deformed beyond the point of recovery without cracking or appreciable volume changes.

PLASTICITY INDEX (PI)

Plasticity Index (PI) – numerical difference between the liquid limit and the plastic limit.

PORE WATER PRESSURE

Pore Water Pressure – pressure transmitted through pore water in saturated soil deposits.

POROSITY

Porosity – the ratio of volume of voids in a rock or soil to its total volume.

PRECONSOLIDATION PRESSURE

Preconsolidation Pressure – the greatest effective stress to which a soil has been subjected.

PRELOADING

Preloading – the densification of a soil by placement of a temporary surface load.

PROCTOR CURVE

Proctor Curve – the curve showing the relationship between dry unit weight and water content of a soil for a given compactive effort.

QUICK CLAY

Quick Clay – a sensitive clay that, when remolded, loses strength and resembles a viscous fluid.

REFUSAL

Refusal – the condition reached when a pile or a soil sampler being driven by a hammer has negligible penetration from each blow of the hammer. Occurs when very hard soil or rock is encountered. Also applies to cone penetration tests when the cone cannot advance further.

RELATIVE DENSITY

Relative Density – the ratio of the difference between the void ratio of a cohesionless soil in the loosest state and any given void ratio to the difference between void ratios in the loosest and in the densest states.

REMOLDED SOIL

Remolded Soil – soil that has had its natural structure modified by mechanical manipulation

RESIDUAL SOIL

Residual Soil – soil found in place, formed by weathering of the underlying material.

RIPPABLE / RIPPABILITY

Rippable / Rippability – the relative ease or difficulty of ripping soil and rock formations with a dozer equipped with a ripping tool.

RIPPER

Ripper – a long, chisel like tool attached to a dozer or other equipment used to loosen hard-packed material

ROCK

Rock – any naturally formed and cemented aggregate of mineral matter occurring in large masses or fragments.

SAND

Sand – soil particles that will pass the No. 4 (4.75-mm) sieve and be retained on the No. 200 U.S. standard sieve.

SAND BOIL

Sand Boil – the ejection of sand and water resulting from piping.

SAND CONE METHOD

Sand Cone Method – a method of determining in-place density using a sand cone apparatus.

SEEPAGE

Seepage – the infiltration or percolation of water through rodk or soil. The term seepage is usually restricted to the very slow movement of groundwater.

SEEPAGE FORCE

Seepage Force – the frictional drag of water flowing through voids or interstices in soil, causing forces on individual soil grains.

SELECT FILL

Select Fill – soil especially selected for its physical characteristics and used as a construction base, or to replace soil removed during excavation.

SHEAR

Shear – a force applied to a soil sample perpendicular to the long axis of the sample. The shear force tends to tear the sample apart along a plane referred to as the shear plane.

SHEAR FAILURE

Shear Failure – failure in which movement caused by shearing stress in a soil or rock mass is of sufficient magnitude to seriously endanger the safety of a structure.

SHELBY-TUBE SAMPLER

Shelby-Tube Sampler – device used for obtaining soil samples, usually undisturbed and from some depth beneath the surface. The Shelby-tube sampler is a tube that is pressed into the soil to be sampled, usually by a drilling rig. The sample is removed from within the Shelby-tube by pushing or extruding it from the tube.

SHRINKAGE LIMIT (AN ATTERBERG LIMIT, SL)

Shrinkage Limit (an Atterberg limit, SL) – the maximum water content at which a reduction in water content will not cause a decrease in volume of a soil mass.

SIEVE

Sieve – a device, similar in concept to a strainer, that has openings in the wire mesh of a designated size.

SIEVE ANALYSIS

Sieve Analysis – use of a series of sieves to determine the particle size distribution of a soil.

SILT

Silt – Material passing the No. 200 U.S. standard sieve that is nonplastic or very slightly plastic and exhibits little or no strength when air-dried.

SLAKE DURABILITY

Slake Durability – the degree to which rock comes apart when soaked in water and agitated.

SOIL

Soil – sediments or other unconsolidated accumulations of solid particles produced by the physical and chemical disintegration of rocks, and which may contain organic matter.

SOIL MECHANICS

Soil Mechanics – the application of the laws and principles of mechanics and hydraulics to engineering problems dealing with soil as an engineering material.

SOIL PROFILE

Soil Profile – vertical section of soil, showing the nature and sequence of various layers, as developed by deposition or weathering, or both.

SOIL STABILIZATION

Soil Stabilization – chemical or mechanical treatment designed to improve stability of a soil mass or to deposition or weathering, or both.

SPECIFIC GRAVITY OF SOLIDS

Specific Gravity of Solids – ratio of the weight in air of a given volume of solids at a stated temperature to the weight in air of an equal volume of distilled water at a given temperature.

SPLIT-SPOON SAMPLER

Split-Spoon Sampler – device used for obtaining soil samples in a predrilled hole and from some depth beneath the surface. The split-spoon sampler is a tube that is driven into the soil to be sampled. The sampler is opened by splitting it longitudinally to retreieve the soil sample from within. Part of the Standard Penetration Test (SPT).

STANDARD PENETRATION TEST (SPT)

Standard Penetration Test (SPT) – field test in which a split-spoon sampler is driven a distance of 1.0 ft. into soil using a hammer weighing 140 lbs falling a 30-in. distance, and the number of hammer blows (N) are noted.

STONE

Stone – crushed or naturally angular particle of rock that will pass a 3-in. (75 mm) sieve and be retained on a No. 4 (4.75-mm) U.S. standard sieve.

STRAIN

Strain – the changes in length per unit length in a given direction.

STRESS

Stress – the ratio of force to area upon which it acts.

SUBSIDENCE

Subsidence – sinking of a part of the earth’s crust and downward displacement of the overburden (rock, soil, or both) lying above an underground excavation.

TEXTURE

Texture – the arrangement in space of soil particles and of the boundaries between these particles within a soil mass.

THIXOTROPY

Thixotropy – the property of a material that enables it to stiffen in a relatively short time, but upon agitation or manipulation to change a very soft consistency or to a fluid of high viscosity. The process is completely reversible.

TILL

Till – Unstratified glacial drift of clay, sand, gravel and boulders.

TOPSOIL

Topsoil – dark surface soil, usually containing organic matter.

TRANSPORTED SOIL

Transported Soil – soil transported from the place of its origin by wind, water or ice.

TRIAXIAL COMPRESSION TEST

Triaxial Compression Test – compression test in which soil, encased in a rubber membrane under applied normal load and lateral confining pressure is stressed to failure, either with or without permitting drainage.

UNCONFINED COMPRESSION TEST

Unconfined Compression Test – test method in which only a vertical load is applied to the specimen.

UNCONFINED OR UNIAXIAL COMPRESSIVE STRENGTH

Unconfined or Uniaxial Compressive Strength – the load per unit area at which an unconfined cylindrical soil specimen will fail in a simple compression test.

UNDISTURBED SAMPLE

Undisturbed Sample – a soil sample that has been obtained by methods in which precaution has been taken to minimize disturbance.

UNIFORMLY-GRADED

Uniformly-Graded – a soil having a large part of its components of the same (or similar) particle size.

VANE SHEAR TEST

Vane Shear Test – a shear test in which a rod with thin radial vanes at the end is forced into the soil and the resistance to rotation of the rod is determined.

VARVED CLAY

Varved Clay – alternating thin layers of silt or fine sand and clay formed by variations in sedimentation during the various stages of deposition and formation, often exhibiting contrasting colors when partially dried.

VOID

Void – space in a soil or rock mass not occupied by solid mineral matter. This space may be occupied by air, water, or other gaseous or liquid material.

VOID RATIO

Void Ratio – the ratio of the volume of voids to the volume of solids in a soil or rock mass.

WASH BORING

Wash Boring – the process of drilling a bore hole by using the jet action of water or high pressure steam.

WATER CONTENT

Water Content – the amount of water contained within a soil, usually expressed as a percentage. It is found for a sample by dividing the weight of the water by the weight of the solid particles.

WEATHERING

Weathering – the process of disintegration and decomposition of rock as a consequence of exposure to the atmosphere, to chemical action, and/or to the action of frost, water and heat.

WELL-GRADED

Well-Graded – a soil composed of a variety of different particle sizes.