Glossary of terms

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

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

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.

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

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

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

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

The same as "blinding".

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

The same as Arching - see above.

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

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.

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

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

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.

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.

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

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

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

Symbol representing particle diameter.

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

The weight in grams of 9000 m of yarn.

The mass per unit volume.

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

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.

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.

See Rubber.

A system of electronic leak detection and location.

The increase in length of a material.

The percentage elongation corresponding to the maximum load.

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

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.

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.

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

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.

A planar textile structure produced by interlacing two or more sets of fibres 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.

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

A yarn made from continuous filament fibres.

Same as weft.

Same as weft.

A very thin sheet of plastic.

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

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

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

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.

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

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

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'.

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

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.

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

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.

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

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

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.

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.

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

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

Will absorb water (attracts water).

Will not absorb water (repels water).

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.

See Fabric, knitted.

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

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.

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 metres wide to accommodate differential ground settlement.

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

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

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.

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

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 metre length is stressed by 1 kN and the metre is increased to 1.1 metre (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.

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

A synthetic fibre made from a single polymer.

This refers to a textile which has been mechanically bonded. Fibres are laid on a moving belt and then punched through repeatedly with barbed needles. The needles entangle the fibres, 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.

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

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

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.

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.

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

A commercial name for polyamide.

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.

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

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.

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.

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.

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.

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.

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

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

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

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

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

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

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

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

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

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.

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

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

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.

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.

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

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

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

Yarn made from staple fibres.

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

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.

A measure of fibre 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.

Denier divided by 9.

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.

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

Same as weft direction.

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

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

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.

The direction from which water is flowing.

The open spaces in a soil or geosynthetic material.

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

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

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

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

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

A fabric produced on a weaving loom.

A generic term for continuous strands of textile fibres or filaments in a form suitable for knitting, weaving, or otherwise intertwining to form a textile fabric. It may comprise (1) a number of fibres 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).