Glossary of Geosynthetic Terms and Definitions

A

Apparent opening size (AOS) - A geotextile property, which indicates the diameter of the approximate largest particle that would effectively pass through the geotextile. At least 95% of the openings apparently have that diameter, or are smaller, as measured by the dry sieve test (ASTM D-4751).

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

Blinding - A condition in geotextiles where soil particles block the openings on the surface of a geotextile thereby reducing hydraulic conductivity of the geotextile.

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C

Calendaring - The rolling of resin with the rollers in a series; used in the manufacturing of certain geomembranes.

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 - A movement by mechanical action or hydraulic flow of soil particles into the voids of fabric which are retained, thereby reducing the hydraulic conductivity of the geotextile.

Creep - The slow change in physical dimension of a material under prolonged stress.

Cross machine direction (weft) - The axis within the plane of a fabric perpendicular to the prominent axis of the direction of production.

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D

Deformation - The change in shape of a geosynthetic under load, frequently out of the normal plane of the material.

Denier - The weight in grams of 9000 meters of yarn.

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E

Elongation - The increase in length produced in the gauge length of the test specimen by a tensile load.

Elongation percent - The increase in the length of a geotexile specimen expressed as a percentage of the original gauge length.

Extruder - A machine with a driver screw for continuous forming of a 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

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.

Filter cloth - A term relating to geotextiles used in filtration applications but has also become a generic term to cover all geotextiles.

Filtration - In geotextiles, the process of retaining soil in place while allowing water to pass from the soil. Removal of particles from a fluid stream.

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 structure filled with soil, thereby forming a mattress for increased stability when used with loose or compressible soils.

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

Geogrid - An open grid structure of polymeric material used primarily for tensile reinforcement.

Geomembrane - An essentially impermeable membrane.

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.

Geosynthetics - The generic classification of all synthetic materials used in geotechnical engineering applications; it includes geotextiles, geocells, geogrids, geomembranes and geocomposites.

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

Geotextile - Any permeable textile used with foundation, soil, rock earth or any other geotechnical engineering- related material.

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).

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

Hydraulic conductivity - The rate of discharge of water under laminar flow conditions through a unit cross-sectional area of a porous membrane under a hydraulic gradient and standard temperatures (200C)

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M

Machine direction (warp) - The axis within the plane of the fabric parallel to the direction in which a fabric is processed onto rolls.

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 proper term to represent and compare the amount of material per unit area (units are oz/yd2 or g/m2) of a fabric.

Modulus - The slope of stress/strain curve; the stress on stretching a material to different elongations, the ratio of the change in force to the change in elongation.

Monofilament - A single filament of a fiber (normally synthetic), usually of a dernier higher than 15.

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 - A mechanical bonding of staple or filament fibers with barbed needles to form a compact fabric.

Needle-punched - Mechanically bonded by needling with barbed needles.

Nonwoven fabric - A textile structure produced by bonding or interlocking of fibers, or both, accomplished by mechanical, chemical or solvent means.

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P

Permeability - (1) A generic term for the property that reflects the ability of a material to conduct a fluid; (2) the capacity of a porous medium to conduct or transmit fluids; (3) The amount of liquid moving through a barrier in a unit time per unit area and per unit pressure gradient not normalized for, but directly related to thickness. Not to be used to compare fabrics since it is directly proportional to thickness. Use permittivity.

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 a material (ASTM D-4491).

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.

Polymer - A macromolecular material formed by the chemical combination of monomers having either the same or different chemical composition. Plastics, rubbers and textile fibres are all high molecular weight polymers.

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

Polypropylene - A polyolefin formed by solution polymerization.

Polyvinyl chloride (PVC) - A synthetic thermoplastic polymer prepared from vinylchloride. 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 as well as screens; flexible forms are used in manufacture of geomembranes.

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

Puncture resistance - A measure of a materials' resistance to puncture. It is measured by forcing a probe through the geosynthetic at a fixed rate.

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R

Resin bonded - The joining of fibers at their intersection points by resin in the formation of a nonwoven geotextile or composite.

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S

Seam strength - Strength of a seam of geosynthetic material.

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.

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 fabrics - Fabrics formed by continuous filaments which have been spun (extruded), drawn, layed into a web and bonded (chemical, mechanical or thermal bonding) together in one continuous process.

Staple fibers - Fibers of short lengths; for example 3"-6" in geotextiles. Frequently used to make needlepunched nonwoven fabrics.

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

Strength, tearing, F - The force required either 1) to start or 2) to continue or propagate a tear in a fabric under specified conditions.

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

Tenacity - The fiber strength in grams per denier.

Tensile strength - The maximum force required to tear a specified specimen; the force acting substantially parallel to the major axis of the test specimen.

Tex - Denier divided by 9.

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

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

Transmissivity - The volumetric flow rate of a geosynthetic per unit thickness under laminar flow conditions and in the in-plane direction of the geosynthetic.

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U

Ultraviolet (UV) radiation stability - The ability of a fabric to resist deterioration from exposure to sunlight.

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V

Voids - The open spaces in a geosynthetic material through which flow can occur.

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W

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.

Wicking - Fluid conduction into the geosynthetic.

Woven fabric - A planar textile structure produced by interlacing two or more sets of elements such as yarns, fibers, rovings or filaments where the elements pass each other usually at right angles and one set of elements are parallel to the fabric axis.

Woven monofilament - A woven fabric produced with single continuous filaments.

Woven multifilament - A woven fabric produced with bundles of continuous filaments.

Woven slit film - 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 strand strands of textile filaments, monofilaments or slit form suitable for knitting, weaving, intertwining or bonding to form a geotextile.

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This glossary contains portions from R. Koerner, Designing with Geosynthetics. Third Edition, 1994; ASTM Designation D-4439-98 Standard Terminology for Geosynthetic; Industrial Fabric Association International, A Design Primer: Geotextiles and Related Materials. 1990 and the glossary of Juteworld.com.