Glossary of Geosynthetic Terms and Definitions

A

ACTINIC DEGRADATION

The strength loss of fibers and fabrics due to exposure to sunlight or an accelerated weathering light source.

ADHESION

The holding of two surfaces together - usually by chemical action.

AIR LANCE

A device used to test, in the field, the integrity of field-formed seams in plastic sheeting. It is a tube through which compressed air is blown.

ANCHOR TRENCH

An excavated ditch in which the edges of a plastic sheet are buried to hold it in place or to anchor the sheet.

APPARENT OPENING SIZE

A property which indicates the approximate largest particle that would effectively pass through the geotextile.

ARCHING

The structuring of soil particles on the 'inflow' side of a geotextile where the particles arch (or bridge) over the fabrics' voids.

ATMOSPHERE FOR TESTING GEOTEXTILES

Air maintained at a relative humidity of 65+5% and a temperature of 21+ 20 C.

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B

BERM

A soil ridge often forming the outer edge of a lagoon or pond.

BLINDING

The condition whereby soil particles block the inter-fiber openings at the surface of a geotextile, thereby reducing the permeability of the geotextile.

BLOCKING

The same as "blinding".

BREAKING STRENGTH

The ultimate tensile strength of a geotextile per unit width. Usually given in kN/meter width.

BRIDGING

The same as Arching - see above.

BUTYL RUBBER

A synthetic rubber based on isobutylene and a minor amount of isoprene. It is vulcanizable and is highly impermeable to gases and water vapor, with good resistance to ageing, chemicals, and weathering.

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C

CALENDAR

A machine equipped with multiple metal rollers between which materials such as geotextiles pass. The essential point of a calendar is that the rolls move at different speeds or even in opposite directions, thus imparting a surface finish to the materials passing between. The rolls may be heated or cooled.

CALENDARING

A method of stabilizing a fabric structure using calendar rollers on a calendar.

CARBON BLACK CONTENT TEST

A geosynthetic is weighed before and after burning the sample to determine the percentage of carbon black. Carbon black minimizes UV degradation.

CHEMICAL STABILITY

The ability of a geotextile to resist degradation from chemicals, such as acids, bases, solvents, oils and oxidation agents as well as chemical reactions, including those catalyzed by light.

CLOGGING

The movement by mechanical action or hydraulic flow of soil particles into the voids of a fabric and retention therein, thereby reducing its permeability.

COATED FABRIC

Fabric which has been impregnated and/or coated with a rubbery or plastic material in the form of a solution, dispersion, hot melt, or powder. The term also applies to materials resulting from the application of a pre-formed film to a fabric by means of hot pressure rollers.

COMPOSITE

A product made from the combination of two or more other identifiable products. The composite usually has improved or entirely different performance characteristics from its component parts.

CONTINUOUS FILAMENT

A synthetic yarn produced continuously by plastic extrusion through a spinarette or similar dye hole.

CREEP

The slow change in length or thickness of a material under prolonged stress.

CROSS MACHINE DIRECTION (WEFT)

The direction perpendicular to the direction of manufacture of a geotextile or geomembrane.

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D

D

Symbol representing particle diameter.

DEFORMATION

The change in size of a material under load from its original pre-loaded dimensions.

DENIER

The weight in grams of 9000 m of yarn.

DENSITY

The mass per unit volume.

DIRECTION – CROSS MACHINE

The direction perpendicular to the long, machine, or manufactured direction (synonyms: woven geotextiles, weft direction).

DIRECTION - MACHINE

In textiles, the direction in a machine-made fabric parallel to the direction of movement the fabric followed in the manufacturing process (synonym: lengthwise, or long direction, and for woven geotextiles, warp direction).

DRAINAGE MEDIUM

The material used in a drain (usually crushed stone) through which water passes.

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E

EFFECTIVE SIZE (DN)

The diameter of the largest particles found in the smallest n percent of a soil. Common examples D15, D50, and Dgs are used in the design of granular drains.

ELASTICITY

The property of matter by virtue of which it tends to return to its original size and shape after removal of the stress which caused the deformation.

ELASTOMER

See Rubber.

ELDEG

A system of electronic leak detection and location.

ELONGATION

The increase in length of a material.

ELONGATION AT BREAK

The percentage elongation corresponding to the maximum load.

ELONGATION, PERCENT

For geosynthetics, the increase in length of a specimen expressed as a percentage of the original gauge length.

EXTRUDER

A machine with a driver screw for continuous forming of polymeric compounds by forcing through a die; regularly used to manufacture geomembranes.

EXTRUSION WELDING

The application of molten polyethylene welding rod to the surface of two geomembrane sheets to be joined. The panels are then routed through a series of rollers that fuse the material together.

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F

FABRIC, COMPOSITE

A textile structure produced by combining different types of geotextiles into a single unit. One example is a fin drain, where geotextiles and meshes are combined into a planar drain composite.

FABRIC, KNITTED

A textile structure produced on knitting machines. Virtually all geotextiles are produced on Warp Knitting machines. Rarely is Weft Knitting used for geotechnical purposes. Warp knitted fabrics can be designed dimensionally stable. Weft knitted fabrics are usually easily deformed.

FABRIC, NONWOVEN

Nonwoven geotextiles are usually either needle punched or heat bonded fabrics.

FABRIC REINFORCEMENT

Usually an open weave textile mesh, called a scrim, which is used to add structural strength to another textile or geomembrane. In the Case of nonwoven fabrics, the scrim is usually needled into the nonwoven at the time of manufacture. In the case of geomembranes, the scrim is usually enclosed between two membrane sheets which are bonded together.

FABRIC, WOVEN

A planar textile structure produced by interlacing two or more sets of fibers on a loom, usually at right angles. The warp threads pass continuously through the loom in the machine direction, whilst the weft threads are inserted across the loom by a shuttle.

FABRIC-WRAPPED DRAIN

A two-layer drain comprising an inner core of usually granular drainage medium with a geotextile wrapped round the outside.

FIBER

A basic element of fabrics characterized by having a length at least 100 times its diameter or width which can be spun into a yarn or made into a fabric.

FILAMENT YARN

A yarn made from continuous filament fibers.

FILL

Same as weft.

FILLING

Same as weft.

FILM

A very thin sheet of plastic.

FILTER CAKE

The graded soil structure developed upstream of the bridging particles on a geotextile acting as a soil filter.

FILTER CLOTH

A geotextile whose immediate engineering function is to act primarily as a soil filter.

FILTRATION

The placing against a soil of a permeable material containing pores sufficiently fine to allow water to pass out of the soil, but not to permit the passage of soil particles. The permeable material is called a 'filter' or 'filter fabric' in the case of a geotextile; if it is granular, then it is usually referred to as the filter medium

FLOW REGIME

This term can either describe the steady ground water conditions at any particular locality, or it can describe the micro-flow conditions adjacent to a soil/filter interface, e.g. laminar, turbulent, radial, planar.

FRICTION ANGLE

An angle, the tangent of which is equal to the ratio of the friction force per unit area and the normal stress between two materials.

FUSION WELDING

Heat is applied directly to the geosynthetic panels by a motorized hot wedge welder. The panels are then routed through a series of rollers that fuse the material together.

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G

GEOCELL

A three-dimensional geosynthetic structure filled with granular material to form a contained mattress for increased bearing capacity over soft subsoils.

GEOCOMPOSITE

A manufactured material using geotextiles, geogrids, and/or geomembranes in laminated or composite form.

GEOGRID

This term refers to a usually rectangular grid made of polymer, which although it is rather rigid and unlike a textile in the conventional sense, still comes under the heading of geotextile in many definitions. It is probably more suitably referred to as a 'geosynthetic'.

GEOMEMBRANE

An impermeable membrane used primarily in the construction of lagoon or waste disposal liners.

GEONET

A netlike polymeric material formed from intersecting ribs integrally joined at the junctions used for drainage with foundation, soil, rock, earth or any other geotechnical-related material.

GEOPIPE

Any plastic pipe used with foundation, soil, rock, earth, or any other subsurface related material as an integral part of a humanmade project, structure, or system.

GEOSYNTHETICS

The generic classification of all synthetic materials used in geotechnical engineering applications; it includes geotextiles, geocells, geogrids, geomembranes, and geocomposites. It would naturally not include natural fabrics such as jute or bamboo products.

GEOSYNTHETIC CLAY LINER

Factory-manufactured hydraulic barriers consisting of a layer of bentonite clay or other very low permeability material supported by geotextiles and/or geomembranes, and mechanically held together by needling, stitching, or chemical adhesive.

GEOTECHNICAL ENGINEERING

Geotembined application of geology, soil mechanics, rock mechanics, hydrology and civil engineering.

GEOTECHNICS

The application of scientific methods and engineering principles to the acquisition, interpretation, and use of knowledge of materials of the earth's crust to the solution of engineering problems; it embraces the field of soil mechanics, rock mechanics, and many of the engineering aspects of geology, geophysics, hydrology, and related sciences.

GEOTECHNICAL ENGINEERING

An application of civil engineering technology for the use of soil or rock as construction materials.

GEOTEXTILE

Any permeable textile, mesh, net or even grid, used in contact with soil or rock.

GRAB TENSILE STRENGTH

The strength at a specific width of fabric together with the additional strength contributed by adjacent areas. Typically, grab strength is determined on a 4-inch-wide strip of fabric, with the tensile load applied at the midpoint of the fabric width through 1-inch-wide jaw faces (ASTM D-4632). GRANULAR DRAIN

A traditionally designed drain incorporating a graded granular material to filter out the surrounding soil whilst permitting water to enter and be transported away.

GRADIENT RATIO

The ratio of the average hydraulic gradient across the fabric and the 1-inch of soil immediately next to the fabric to the average hydraulic gradient across the 2-inch of soil between 1 and 3 inches above the fabric, as measured in a constant head permeability test.

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H

HEAT BONDED

This term describes a textile that has been subject to heat and pressure, whereby the individual fibres have partially melted and bonded at their intersection points.

HEAT SEAMING

The process of joining two or more thermoplastic films of sheets by heating areas in contact with each other to the temperature at which fusion occurs. The process is usually aided by a controlled pressure. In dielectric seaming the heat is induced within films by means of electromagnetic radiation.

HETEROFILAMENT

A synthetic filament comprising a core of one polymer surrounded by a sheath of different material.

HYDRAULIC CONDUCTIVITY

The capacity of a drain to transport a certain volume of water in a certain time.

HYDROPHILLIC

Will absorb water (attracts water).

HYDROPHOBIC

Will not absorb water (repels water).

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I

IN-PLANE

Refers to the plane of a geotextile. Usually associated with hydraulic conductivity in connection with how much water can be conducted along, within the geotextile, as opposed to the ease with which a geotextile can permit water to pass across its thin dimension.

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K

KNITTED

See Fabric, knitted.

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L

LAMINAR FLOW

Fluid follows specific flow paths, obeys Darcy's Law when seeping through porous media.

LAPPED JOINT

A joint made by placing one edge of a textile or membrane partly over another surface and bonding or sewing the overlapping portions. The purpose of joining may be to waterproof a membrane lining of a lagoon, or to save money over a large textile area by saving lap fabric, or to provide a continuous structural strength in the weft direction of a textile layer by sewing adjacent geotextile sheets together.

LAPPED JUNCTION

Wade by placing one edge of a textile or membrane partly over another surface but not joining, bonding or sewing. Lapped junction-are common in many civil engineering designs. For example, on landfill designs, the lap may well be up to 0.5 meters wide to accommodate differential ground settlement.

LENO FABRIC

An open mesh fabric in which two warp yarns wrap around each weft yarn to provide a simple stability to the open structure.

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M

MACHINE DIRECTION (WARP)

The direction in a geotextile parallel to the direction of movement of the finished fabric during the manufacturing process.

M.A.R.V. (Minimum Average Roll Value)

Until the 1980’s, geotextile values were reported as “typical.” A typical value is an average or mean value, which means that 50% of the results can be expected to exceed the typical value and 50% can be expected to fall below the typical value. ASTM D4759 “Standard Practice for Determining the Specification Conformance of Geosynthetics” requires using M.A.R.V. values. The “minimum average roll value” is a middle ground between the absolute minimum value and the typical value. The MARV is derived statistically as the typical (mean or average) value less two standard deviations. A standard deviation is a measure of the width of the spread of the values, or their variance (dispersion) from the mean. The standard deviation is determined by taking the square root of that variance. The variance takes into account all possible values (not just the extremes which give the range). It is interesting to note that values reported ABOVE the mean count as a negative in the same manner as a value reported below the mean counts as a negative.

MASS PER UNIT AREA

The usual term representing the weight of a textile or membrane per unit area. This is usually quoted in oz/yd? or g/m? (Alternatively written g.s.m.). A typical separation geotextile will weigh about 120 g.s.m. The general range of geotextile weights is 100 to 500 g.s.m.

MEMBRANE

A continuous sheet of material. Usually, it carries the connotation of being impermeable, although this is not strictly true.

MODULUS

The stiffness of a material when subject to stress. The higher the modulus, the less strain is generated by any given stress. The modulus is calculated by dividing the increase in dimension by the original dimension for any unit of stress. If 1 meter length is stressed by 1 kN and the meter is increased to 1.1 meter (i.e. increased by 0.1m), then the modulus will be 1/0.1 = 10 kNm/m. Since geotextiles do not often have perfectly linear stress/strain responses, the modulus at any given strain is usually required for engineering purposes. The modulus at 10% strain would be referred to as K10.

MODULUS OF ELASTICITY

The ratio of stress to strain within the elastic range, also known as Young's modulus.

MONOFILAMENT

A synthetic fiber made from a single polymer.

MULLEN BURST

Hydraulic bursting strength of geotextiles (ASTM D-3786-87).

MULTIFILAMENT

 A yarn consisting of many continuous filaments or strands.

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N

NEEDLE-PUNCHED

This refers to a textile which has been mechanically bonded. Fibers are laid on a moving belt and then punched through repeatedly with barbed needles. The needles entangle the fibers, causing them to form into a continuous textile having tensile strength. Because of the nature of the construction, nonwoven geotextiles of this kind usually exhibit high elongation before rupture.

NEEDLE-PUNCHING

A process for producing non-woven fabrics using barbed needles to entangle the fibers.

NEOPRENE (POLYCHLOROPRENE)

Generic name for a synthetic rubber. Resistant to ozone, to ageing and to some oils.

NITRILE RUBBER

A family of copolymers of butadiene and acrylonitrile that can be vulcanized into tough oil-resistant compounds. Blends with PVC are used where ozone and weathering are important requirements in addition to its inherent oil and fuel resistance.

NONWOVEN

Note that this is correctly a single word. It is commonly hyphenated in error. This term, by common usage, refers to needle-punched and heat bonded fabrics only. Knitted fabrics are technically not woven but are not usually covered by this word.

NORMAL DIRECTION

For geotextiles, the direction perpendicular to the plane of a geotextile.

NYLON

A commercial name for polyamide.

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P

PARTICLE SIZE DISTRIBUTION

A term describing the range of particle sizes in a soil. A Particle Size Distribution Curve is a graph showing the percentage fractions by weight of different sizes of particles in a particular soil sample. It is obtained by undertaking the laboratory sieving of a soil.

PERCENTAGE FREQUENCY OF PORES/UNIT AREA

A measure of the free space within the structure of a non-woven fabric (its porosity).

PERCENTAGE OPEN AREA (% OA)

A measure of the effectively presented pore space as a percentage of the total area of the fabric. In simple terms, it describes the percentage area of the holes in the fabric. On its own, it is a meaningless number, since it must be used in conjunction with the pore sizes to properly describe the void structure of a textile.

PERMEABILITY

In the context of geotextiles, this usually means the ease or otherwise with which water can travel within or pass through a textile or granular medium. A high permeability means that water passes through easily. A low permeability means that water passes (if at all) with difficulty.

PERMITTIVITY

For a geotextile, the volumetric flow rate of water per unit cross-section area, per unit head, under laminar flow conditions, in the normal direction through the fabric.

PH

A measure of the acidity or alkalinity of a material, liquid or solid. PH is represented on a scale of 0 to 14; 7 represents a neutral state; 0 represents the most acid, and 14 the most alkaline.

PICKING

In the geotextile manufacturing process, the operation of projecting the shuttle from one side of the loom slay to the other.

PICKS

The weft or filling yarn, which lies across the length of the fabric.

PICKS PER MINUTE

In the geotextile manufacturing process, the number of times per minute the shuttle traverses the loom slay.

PIPING

The washing out of fine particles from a soil by water emerging from the soil. Adjacent to drains, the piping of ground soil can cause surface settlement, and the clogging of the drains. Beneath dams, piping can cause the outwash of fine soil, resulting in increasing permeability and increased groundwater flows, possibly culminating in failure.

PLASTIC

A material that contains as an essential ingredient one or more organic polymeric substances of large molecular weight, is solid in its finished state, and at some stage in its manufacture or processing into finished articles, can be shaped by flow.

PLASTICIZER

A plasticizer is a material added to a plastic or a rubber to increase its ease of working or its flexibility.

POLYESTER

A material in which the fiber-forming substance is any long-chain synthetic polymer composed of an ester of a dihydric alcohol and terephthalic acid.

POLYMER

A material formed by the chemical combination of monomers with either the same or different chemical compositions. Plastics, rubbers, and textile fibers are all high-molecular-weight polymers.

POLYMERIC LINER

Plastic or rubber sheeting used to line waste disposal sites, ponds, lagoons, or canals.

POLYOLEFIN

A family of polymeric materials that includes polypropylene and polyethylene, the former being very common in geotextiles, the latter in geomembranes. Many variations of each exist.

POLYPROPYLENE

A polyolefin formed by solution polymerization as was described for high-density polyethylene

POLYVINYL CHLORIDE (PVC)

A synthetic thermoplastic polymer prepared from vinyl chloride. PVC can be compounded into flexible and rigid forms through the use of plasticizers, stabilizers, fillers, and other modifiers; rigid forms are used in pipes and well screens; flexible forms are used to make membranes.

PORE, SLOT, APERTURE

The holes through a pipe, a mesh or a geotextile.

PORE SIZE DISTRIBUTION

The range of opening sizes within a geotextile or a soil. This is usually expressed in the form of a graph.

POROSITY

The ratio of the volume of void space to the total volume. Is usually expressed as a percentage of the volume.

PUNCTURE RESISTANCE

The extent to which a geotextile can withstand the penetration of an object without perforation.

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R

RESIN BONDED

The joining of fibers at their intersection points by an applied resin. Geotextiles may be coated in resin to provide adhesion between fibers, thus making the textile more stable and giving a stiffer feel to the product.

RUBBER

A polymeric material which, at room temperature, can recover substantially in shape and size after removal of a deforming force. Refers to both synthetic and natural rubber. Also called an elastomer.

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S

SCREEN

A word used to describe a porous sheet physically separating two soils.

SCRIM

A woven, open-mesh reinforcing fabric made from continuous-filament yarn, used to reinforce nonwoven geotextiles or geo-membranes.

SEAM STRENGTH

Strength of a sewn, glued, or bonded junction between two sheets of textile or membrane. Seam strength is reported either in absolute units (e.g. kN/m length of seam) of as a percent of the strength of the sheeting, or both.

SELF-INDUCED FILTRATION

Filtration of a soil by the development of a filter layer within that soil. This is generated by permitting a limited soil migration to take place through a filter fabric which holds the face of the soil stable. Within the soil, the slow re-distribution of particles adjacent to the geotextile forms a filter cake which then slows down and ultimately prevents the passage of any further soil particles out of the soil. Self-filtration is thus achieved.

SELVEDGE

The longitudinal edges of a fabric are formed in such a way to prevent unraveling.

SEPARATION

The function of a fabric as a partition between two adjacent materials (usually dissimilar) to prevent mixing of the two materials.

SOIL-FABRIC FRICTION

The resistance to sliding between a fabric and a soil, excluding the resistance from soil cohesion. Soil-fabric friction is usually quantified in terms of a friction angle.

SOIL MIGRATION

The transportation of soil particles within a soil, caused by the internal flow of water.

SPECIFIC GRAVITY

The ratio of the density of a fabric or a polymer to the density of water obtained by weighing both items in air. A specific gravity less than one implies that the fabric or polymer will float.

SPUN-BONDED

A fabric manufacturing process wherein continuous or staple monofilaments are spun, formed into a sheet and then subject to heated pressurized rollers which weld the filaments together at their contact points.

STAPLE FIBERS

This refers to fibers that have been chopped up from continuous filaments. They are referred to as staple fibers. Staple can be long or short depending upon the cutting process.

STAPLE YARN

Yarn made from staple fibers.

STRAIN

The change in length per unit of length in any specific direction.

STRIKETHROUGH

A term generally used to describe the penetration of an applied chemical through a geotextile. Sometimes this is desirable and sometimes not.

SUBGRADE INTRUSION

Localized aggregate penetration of a soft cohesive subgrade and resulting displacement of the subgrade into the cohesionless material.

SUBGRADE PUMPING

The displacement of cohesive or low-cohesion fines from a saturated subgrade into overlying aggregate as the result of hydraulic forces created by the transmittal of wheel-load stresses to the subgrade.

SURVIVABILITY

The ability of a fabric to be placed and to perform its intended function without undergoing degradation.

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T

TEAR STRENGTH

The force required to tear a specimen of geotextile or geomembrane. Test results are dependent on direction of tear, specimen geometry and rate of tear.

TENACITY

A measure of fiber strength.

TENSILE STRENGTH

This term means the maximum tensile stress per unit of original Cross-sectional area applied during the stretching of a specimen to break. It is described in units of force per unit area of specimen cross section.

TEX

Denier divided by 9.

TEXTURED GEOMEMBRANES

The use of induced textured surfaces to increase the interface friction between containment membranes and adjoining material.

THERMOPLASTIC

Capable of being repeatedly softened by increase of temperature and hardened by decrease in temperature. Most polymeric membranes are supplied in thermoplastic form because the thermoplastic form allows for easier seaming.

TRANSMISSIVITY

For a geotextile, the volumetric flow rate per unit thickness under laminar flow conditions, in the plane of the fabric.

TRANSVERSE DIRECTION

Same as weft direction.

TRAPEZOIDAL TEAR TEST

 A test method to measure the tearing strength of geotextiles (ASTM D-4533)

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U

ULTIMATE ELONGATION

The elongation of a stretched specimen at the time of break. Usually reported as percent of the original length. Also called elongation at break.

ULTRA-VIOLET DEGRADATION

The breakdown of a geotextile's fibers or a geomembrane's polymer when exposed to light.

UNIFORMITY COEFFICIENT

The ratio of the D60 to D10 sizes of the soil, i.e. a measure of the spread of soil particle sizes within a soil.

UPSTREAM

The direction from which water is flowing.

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V

VOIDS

The open spaces in a soil or geosynthetic material.

VULCANISATION

A chemical process through which a rubber compound's physical and chemical properties are improved.

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W

WARP

Filaments running in the long direction of a weaving loom. i.e. the direction in which the fabric moves during manufacture.

WARP DIRECTION

See Direction, machine; this term is commonly used for woven fabrics only.

WATER TABLE

(1) The upper limit of the part of the soil or underlying rock material that is wholly saturated with water. (2) The upper surface of the zone of saturation in ground water in which the hydrostatic pressure is equal to atmospheric pressure.

WEFT

Filaments running usually at 90° to the warp direction of a weaving loom. The weft fibers are placed between the warp fibers by means of a shuttle.

WICKING

Fluid conduction into the geosynthetic.

WIDTH

For a geotextile, the weft (or cross-direction) edge-to-edge measurement of a fabric in a relaxed condition on a flat surface.

WOVEN

A fabric produced on a weaving loom.

WOVEN MONOFILAMENT

A woven fabric produced with single continuous filaments.

WOVEN MULTIFIAMENT

A woven fabric produced with bundles of continuous filaments.

WOVEN SLITFILM

A woven fabric produced with yarns formed by longitudinally splitting a polymeric film to form a slit tape yarn.

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Y

YARN

A generic term for continuous strands of textile fibers or filaments in a form suitable for knitting, weaving, or otherwise intertwining to form a textile fabric. It may comprise (1) a number of fibers twisted together, (2) a number of filaments laid together without twist (a zero-twist yarn), (3) a number of filaments laid together with alternating twist, or (4) a single filament with or without twist (a monofilament).