Glossary of Terms

A

Aggregate
Sand, gravel, cobble and boulder size particles in well-defined mixtures used in paving, concrete and other applications where specified properties are needed. Aggregates are typically inorganic, natural (e.g. gravel), processed (e.g. crushed rock) or man-made (e.g. air-cooled blast furnace slag and expanded shale).

Aggregate base course
Compacted layer of aggregate beneath a pavement.

Aperture
An opening, such as a hole, gap, or slit often referred to in geogrids.

Absorption
The process by which a liquid is drawn into and tends to fill permeable pores in a porous solid body, also, the increase in mass of a porous solid body resulting from penetration of a liquid into its permeable pores.

Asphalt pavement
A pavement consisting of a surface layer of mineral aggregate coated and cemented together with asphalt cement on supporting layers.

Anchor Reinforced Vegetation (ARV)
A soil protection system combining a Turf Reinforcement Mat (TRM) with earth percussion anchors to increase factors of safety in severe erosion control applications and to provide surficial slope stabilization.

B

Backfill
Earth or other material used to replace material removed during construction, such as in pipeline and culvert trenches and behind retaining walls.

Backslope
The non-horizontal finish grade of soils behind a wall; typically expressed as horizontal distance to vertical height (2:1 backslope); used in engineering calculations, backslope increases the design load on a wall. Also referred to as top slope.

Ballast
In railroads, gravel size material (normally an "aggregate") in which the railroad ties are held and supported.

Base reinforcement
The use of a geosynthetic within the aggregate base course to enhance the performance of a road structure.

Batter
As applied to walls, the difference between the wall face alignment and vertical. Batter can be expressed in degrees or ratio (vertical: horizontal). A lean of the wall face towards the retained fill is considered a positive batter, while an outward lean is considered a negative batter.

Batter is often built into a wall by off-setting (or "setting back") successive courses of a wall by a specified amount. (See Setback)

Best Management Practice (BMP)
Best Management Practice - often referred to in erosion and sediment control applications.

Biaxial (BX)
Having two axes; having strength in two directions.

Biodegradable
Capable of being decomposed by biological organisms or processes.

Blinding
The condition in which soil particles block the voids at the surface of a geotextile, thereby reducing the hydraulic conductivity of the geotextile.

Bonded Fiber Matrix (BFM)
A hydraulically-applied matrix containing organic defibrated fibers and cross-linked insoluble hydro-colloidal tackifiers to provide erosion control and facilitate vegetation establishment on steep slopes and designed to be functional for a minimum of 6 months.

Breakwater
An offshore structure generally aligned parallel to the shore (sometimes connected to the shore) designed to protect the shoreline from waves.

 

C

Calendaring
Smoothing or polishing a sheet of polymer between revolving rollers.

Chemical stabilization
Making something stronger or less affected by outside conditions with the addition of chemicals.

Example: Lime and cement are used for Chemical Stabilization of soils.

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

Compaction
The densification of a soil by a mechanical process.

Composite Turf Reinforcement Mat
A rolled erosion control product composed of non-degradable synthetic fibers, filaments, nets, wire mesh and/or other elements, processed into a permanent, three-dimensional matrix of sufficient thickness. Composite Turf Reinforcement Mats (C-TRM), which may be supplemented with degradable components, are designed to impart immediate erosion protection, enhance vegetation establishment and provide long-term functionality by permanently reinforcing vegetation during and after maturation.

Note: C-TRMs are typically used in hydraulic applications, such as high flow ditches and channels, steep slopes, stream banks and shorelines, where erosive forces may exceed the limits of natural, un-reinforced vegetation or in areas where limited vegetation establishment is anticipated.

Confinement
Geosynthetic improvement of an aggregate structure by the ability to resist lateral movement of the aggregate.

Contour line
An imaginary line, or its representation on a map, following all points at the same elevation above or below a given datum.

Core fill
Defines the granular rock material used in the open cell of the retaining wall units and the zone directly behind the wall. Core fill has the ability to free flow water while providing friction in the wall.

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

Cross-machine direction
In textiles, the direction perpendicular to the long, machine, or manufactured direction (for woven geotextiles: weft direction). (See Machine Direction)

Cross-plane
The direction of a geosynthetic which is perpendicular to the plane of its manufactured direction.  Referred to in hydraulic situations.

Cross section
A diagram of an element of construction showing the position of the components inside the normally visible face, as in a slice of a layered cake.

 

D

Detention basin (dry pond)
An area made to collect storm water runoff from a management system for the purpose of reducing peak flow and controlling rate of flow. A retention basin can be defined as having a permanent pool, whereas, a detention basin is normally dry.

Defibrated
Verb (used with object), to break (wood, paper, garbage, etc.) into fibrous components; reduce to fibers.

Dewatering
To remove water from.

DOT
Department of Transportation (U.S.)

Down slope
The area directly in front of, and below, a retaining wall, expressed in horizontal distance to vertical distance (4:1 down slope). Impacts retaining wall engineering design.

Drain inlet
A grate on top of a pipe riser that allows water runoff to enter directly into a drain pipe.

Drainage
The act or process of draining using a system of man-made or natural conveyances.

Interception and removal of surface or groundwater.

Conveyance of unwanted water from one point to another.

Drainage zone
The zone immediately behind a retaining wall that is designed to free flow water from the retaining wall and its surroundings. Designed to relieve associated pressure build-up and to not be prone to clogging.

 

E

Earth Percussion Anchors
Made of corrosion resistant aluminum alloy, earth percussion anchors hold the Turf Reinforcement Mat (TRM) in place through unstable surficial soil layers and into the underlying competent soil.

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

Elongation at break
The elongation corresponding to the maximum load.

Elongation, percent
For geosynthetics, the increase in length of a specimen expressed as a percentage of the original gage length (i.e., engineering strain).

Embedment
The buried depth requirements of a retaining wall where sufficient "Horizontal Line to Daylight" is maintained. Embedment is included in total wall height.

EPA
Environmental Protection Agency (U.S.)

Erosion
Detachment and movement of soil or rock fragments by water, wind, ice or gravity.

Erosion Control Blanket (ECB)
A temporary degradable rolled erosion control product composed of processed natural or polymer fibers mechanically, structurally or chemically bound together to form a continuous matrix to provide erosion control and facilitate vegetation establishment.

Excavation
A cavity formed by, or as if by, cutting, digging or scooping.

Extended-term RECP
A Rolled Erosion Control Product designed to provide erosion protection for longer than 12 months and up to 24 months. These products are used in areas where vegetation establishment may take up to two full growing seasons. These products are often used in semi-arid locations.  (See Rolled Erosion Control Product).

 

F

Fatigue cracking
The tendency for a material to crack under repeated stress.

Fiber Reinforced Matrix (FRM)
A hydraulically-applied matrix containing organic defibrated fibers, cross-linked insoluble hydro-colloidal tackifiers, and reinforcing natural and/or synthetic fibers to provide erosion control and facilitate vegetation establishment on very steep slopes and designed to be functional for a minimum of 12 months.

Filament yarn
The yarn made from continuous filament fibers.

Filling
The yarn running from selvedge to selvedge at right angles to the warp in a woven fabric.

Filling direction
See Cross-machine Direction. Note: For use with woven fabrics only.

Filter cake
The soil structure developed upstream of a geotextile by separating the suspended soil from liquid as the mixture attempts to pass through a soil-fabric system.

Filter cloth
A deprecated term for geotextile.

Filtration/Drainage
Fabric to soil system that allows for free liquid flow (but no soil loss) across or through the plane of the fabric over an indefinitely long period of time.

Footing
The soils, gravel and/or engineered materials used directly below a retaining wall upon which its concrete units rest.

Free water
Soil water that moves by gravity, in contrast to capillary and hydroscopic water.

Full height concrete panel
Concrete facing extending the full height of the wall without horizontal joint or breaks, but for a limited distance along the wall. Such panels are several inches to a foot thick and are one type of facing for a Mechanically Stabilized Earth (MSE) wall.

 

G

Gabion
A compartmented rectangular container made of steel wire mesh and filled with stone; used for erosion control and retaining wall purposes.

Geo-Cel
A three-dimensional structure filled with soil, thereby forming a mattress for increased stability when used with loose or compressible subsoils.

Geocomposite
A combination of two or more geosynthetics (geotextiles, geogrids, geonets and/or geomembranes) normally to accomplish multiple functions with a combined layer. The geosynthetics are normally bonded to facilitate installation.

Geogrid
A grid-like polymeric material formed by intersecting ribs joined at the junctions and with a regular network of openings (apertures) used for reinforcement with foundation, soil, rock, earth, or any other geotechnical engineering-related material as an integral part of a human-made project structure or system.

Geomembrane
A sheet of geosynthetic to act as a barrier to the movement of water or gas.

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.

Geosynthetic
The generic term for all synthetic materials used in geotechnical engineering applications; it includes  geotextiles, geogrids, geonets, geomembranes, and geocomposites.

Geosynthetic Clay Liner (GCL)
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 adhesives.

Geotextile
A woven or non-woven thermoplastic sheet material intended to allow the passage of water, but not fines, and without collecting fines at the soil-textile interface.

Global stability
The factor of safety against an overall failure of a retaining wall or slope, along a deep seated slip surface passing beneath and behind a structure.

Grade, finished
The completed surfaces of lawns, walks and roads brought to grades as designed.

Grade, natural
The undisturbed natural surface of the ground.

Grade, subgrade
The grade established in preparation for top surfacing of roads, lawns, etc.

Gradient
The degree of inclination of a surface, road or pipe, usually expressed as a percentage.

Grading
Modification of the ground surface by cuts and/or fills. Fine or finish grading is light or thin grading to finish a prepared earth surface.

Gravity wall
A retaining wall wherein the wall height, unit depth and weight are engineered to sufficiently serve the purpose of designing without use of reinforcement.

Groin
A shore protection structure extending from the backshore into a water body for the purpose of protecting the shoreline and the adjacent upland by influencing the movement of water and/or deposition of materials.

Groundwater
Water beneath the surface of the earth which saturates the pores and fractures of sand, gravel and rock formations.

 

H

Hardscape
A surface made of concrete, blacktop, wood or rock, such as sidewalks, driveways, patios, etc.

Height, reinforced
A retaining wall, or the portion of a retaining wall cross-section, that requires soil reinforcement to resist forces and loads.

Height, total wall
The vertically measured height of a retaining wall; includes the portion of the wall extending below the ground surface in front of the wall (subgrade).

Height, un-reinforced
A retaining wall or the portion of a retaining wall that does not require soil reinforcement.

Horizontal line to daylight
A horizontal line from the bottom of the wall to the intersection with the down slope.

Hydraulic Mulch (HM)
A hydraulically-applied material(s) containing defibrated paper, wood and/or natural fibers that may or may not contain tackifiers used to facilitate vegetation establishment on slopes and designed to be functional for up to three months.

 

I

In-plane
The direction of a geosynthetic that is parallel to its long, manufactured, or machine direction.  Referred to in hydraulic situations.

In-situ soils
Native, undisturbed soils.

Index test
A test procedure that may contain a known bias but which may be used to establish an order for a set of specimens with respect to the property of interest.

Infiltration
The slow passage of a liquid through a filtering medium, such as rainwater through the soil.

Interstitial

Being or relating to a crystalline compound in which usually small atoms or ions of a nonmetal occupy holes between the larger metal atoms or ions in the crystal lattice

IECA
International Erosion Control Association

Invert 
The lowest point of the internal cross section of a pipe or channel.

 

J

Jetty
On open seacoasts, a structure extending into a body of water, generally at the mouth of a river or an entrance channel to a bay, to direct and confine the stream or tidal flow to a selected channel, or to prevent shoaling.

Junction strength/efficiency
A geogrid's capacity at the intersections of longitudinal and transverse ribs.

 

L

Landform contour grading
A technique of earthwork construction to shape the ground to achieve a more natural appearance when compared to unnatural-looking geometric shapes. It is more commonly used in typical construction.

Landscape
Improvement of the natural beauty of a tract of land by grading, clearing or decorative planting.

Leveling pad
The compacted material upon which a wall directly rests; typically made of crushed gravel.

Load
(See Surcharge)

Load transfer platform
A platform built on top of a system of foundation columns to transfer embankment or other loads to the foundation columns (rammed aggregate piers, piles, etc.). Composite load transfer platform consists of one or more layers of geosynthetic reinforcement and select fill resulting in a relatively stiff structure usually 2-4 ft. thick.

Long term non-degradable RECP
A Rolled Erosion Control Product composed of non-degradable materials that furnishes erosion protection and extends the erosion control limits of vegetation for the design life of a project.

Lot
A unit of production, or a group of other units or packages, taken for sampling or statistical examination, having one or more common properties and being readily separable from other similar units.

 

M

Machine direction
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. For woven geotextiles - warp direction). (See Cross-Machine Direction)

Marine mattress
A compartmental structure filled tightly with aggregate for protection of waterfront structures against wave action and erosion.

Mass per unit area
The proper term to represent and compare to the amount of material per unit area (units are oz./yd.² or g/m²).

Mechanically Stabilized Earth (MSE)
A retaining wall or slope normally comprised of soil or aggregates stabilized by horizontal layers of reinforcement such as geogrids. The facing for structures can include precast concrete panels, concrete blocks, vegetation, rock or other options.

Modulus of elasticity
The initial linear portion of the stress-versus-strain test of a geosynthetic during its evaluation in a tensile strength test (units are lb./in.², kPa, lb./in., or kN/m).

Mulch Control Netting (MCN)
A planar woven natural fiber or extruded geosynthetic mesh used as a temporary degradable rolled erosion control product to anchor loose fiber mulches.


N

Natural
A class name of various general fibers, of animal, mineral or vegetable origin.

Needle-punched
Mechanically bonded by needling with barbed needles.

Nilexian
Person employed by the Nilex group. Generally recognized as being knowledgeable, caring and enthusiastic by nature.

Nonwoven
For geotextiles, a planar and essentially random textile structure produced by bonding, interlocking of fibers, or both, accomplished by mechanical, chemical, thermal, or solvent means and combinations thereof.

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

 

O

Open Weave Textile (OWT)
A temporary degradable rolled erosion control product composed of processed natural or polymer yarns woven into a matrix, used to provide erosion control and facilitate vegetation establishment.

Orientation/Orienting
The process in which the punched or formed holes in the calendared sheet or cast net is stretched to the desired aperture sizes via the use of an orienting machine at controlled temperatures, tensions and stretch ratios.

Overlay
A repair topping of asphalt or concrete placed on a worn roadway.

 

P

Packaged solution
A solution consisting of a variety of specialty products and engineering services, including engineering, technical assistance and specifications. Packaged solutions provide greater value to a customer because they remove the need to independently source each of the component materials. Also known as a "system". 

Pavement interlayer
A stress relief interlayer used in overlaying applications to control reflective cracking.

Permeability
A generic term for the property that reflects the ability of a material to conduct a fluid or vapor through a porous media such as soil or geotextiles.  Properly called hydraulic conductivity.

Performance test
A test that simulates as closely as practicable selected conditions experienced in the field and which can be used in design.

Permanent rolled erosion control products
For applications where natural vegetation alone will not sustain expected flow conditions and/or provide sufficient long-term erosion protection, furnish a permanent rolled erosion control product with the necessary performance properties to effectively control erosion and reinforce vegetation under the expected long-term site conditions.

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.

Pervious
The property of a material which permits movement of water through it under ordinary hydrostatic pressure.

Photodegradable
Capable of decaying or molecularly breaking down when exposed to ultra-violet light.

Piggyback/Piggybacking
Building a new lined landfill on the roof (vertical) or side slope (lateral) of a closed landfill. Geogrids are commonly installed to support the liner system over anticipated settlements associated with decomposition in the old waste.

Polyethylene
A polymeric substance formed by the addition of long chain molecules made up of repeat carbon and hydrogen atoms, belonging to the polyolefin family of thermoplastics.

Products formed with high-density polyethylene include automobile battery casings, gasoline containers and polymeric liners for hazardous waste.

Polymer
A substance or compound that features high molecular weight derived by the addition of many smaller molecules of the same kind.

Polyolefin
A family of polymeric materials that includes polypropylene and polyethylene.

Polypropylene
A polymeric substance formed by the addition of long chain molecules made up of repeat carbon, hydrogen and methyl atoms, belonging to the polyolefin family of thermoplastics.

Porosity
The ratio of the volume of air or void contained within the boundaries of a material to the total volume expressed as a percentage.

Positive mechanical connection
Structural connection of retaining walls specifically designed to mechanically connect facing elements to geogrid reinforcement with a low-strain, end-bearing connection device that is not dependent on friction for connection strength.

Precast concrete retaining wall
Gravity or semi-gravity retaining walls composed of prefabricated concrete modules with or without fill material placed within these elements.

Pressure relief wall
A retaining wall built to prevent the application of lateral earth pressure loads to a below-grade concrete structure. By preventing lateral earth pressure loads, the concrete structure may be designed and constructed at a much thinner cross section, thereby greatly reducing the cost. Generally, the pressure relief wall is separated from the concrete wall by 12-24 inches.

Punching
Punching is the process in which a cooled extruded sheet is perforated in a specified pattern and shape of holes prior to stretching of this perforated sheet to form a geogrid.

PVC pipe
A type of smooth wall thermoplastic pipe manufactured using Polyvinyl Chloride, which is widely accepted for drainage applications due to its cost, longevity and chemical resistance.

 

R

Rammed Aggregate PierTM (RAP)
An intermediate foundation system.  RAPs are constructed by densely compacting successive thin lifts of high quality crushed rock in a 2 to 3 foot cavity of varying depth using patented ramming equipment. The vertical ramming action increases the lateral stress and improves the soils surrounding the cavity, which results in foundation settlement control and greater bearing pressures for design.

Reciprocating die
The equipment in which the holes are formed in cast net during extrusion via the alternately up and down movement of the mated piston with a slotted die.

Reflective cracking
The presence of cracks extending into the interior of a structure, usually produced by overstressing the structural material. In roadways, this can be caused by heavy traffic or thermal loads.

Regrading
Earthwork construction to level or smooth the existing ground surface to a desired or horizontal grade.

Reinforced fill
Retaining wall backfill that contains reinforcing material to create the structure. Used in engineered applications.

Reinforced slope
(See Steepened slope)

Reinforcement
Improvement of the system strength created by the introduction of a geosynthetic into a soil/aggregate system.

Retaining wall
A wall built to hold back earth allowing adjacent areas to be at different elevations. Wall inclinations are typically 70 to 90 degrees with respect to the horizontal.

Retention basin
An area made to collect storm water runoff from a management system for the purpose of reducing peak flow and controlling rate of flow. A retention basin can be defined as having a permanent pool, whereas, a detention basin is normally dry.

Revetment
A facing of armor stone, riprap, etc. used to protect an embankment, or shore structure, against erosion from waves or currents.

Rib and junction thickness
The vertical, top-to-bottom dimension(s) of geogrid.

Note: Geogrid must be sufficiently thick to secure aggregate particles (which strike through the geogrid plane) in place, and thus restrict their lateral movement. Geogrid thickness also relates to robustness; the geogrid must be sufficiently robust to withstand heavy earthwork construction-induced stresses.

Riprap
Stones or other material placed on a slope or in a channel to prevent erosion by water.

Rolled Erosion Control Product (RECP)
A temporary degradable or long-term non degradable material manufactured or fabricated into rolls designed to reduce soil erosion and assist in the growth, establishment and protection of vegetation.

Running bond
In retaining wall installation, the pattern of unit placement wherein units are stacked such that the ends of units are positioned over the center of the units below.

Runoff
The part of precipitation that flows off the area on which it falls. Also, the rate of surface discharge of the above.

Rutting
A sunken track or groove along the roadway in pavements caused by the passage of vehicles.

 

S

Sample
A portion of material, which is taken for testing or for recorded purposes and used in the laboratory as a source of individual specimens.

Scour protection
Protection against erosion of the seabed, or embankment, in front of the toe.

Secant Aperture Stability Modulus (a.k.a. Torsional Stiffness)
A geogrid's resistance to deformation under torque - specifically a given torque (moment) of 20 cm-kg.

Note: This test quantifies the geogrid's capacity to maintain its aperture(s) configuration. Since each aperture is created by a junction of ribs at each corner, the procedure essentially amounts to holding a junction node and then twisting it in its horizontal plane, as one can demonstrate with thumb and forefingers. Torsional stiffness provides the single-best correlation with Traffic Improvement Factor (a.k.a. Traffic Benefit Ratio) from full-scale independent tests of Geogrid Base Reinforcement.

Segmental retaining wall
A Mechanically Stabilized Earth (MSE) retaining wall system consisting of soil stabilized by horizontal layers of reinforcement attached to a near vertical facing of dry-stacked concrete blocks.

Separation
Geotextile placed between dissimilar materials so that the integrity of both can remain intact or be improved.

Setback
The "backward" placement of segmental concrete units, one on another, altering the position of units from 5/8 inches to near vertical to create a batter of the wall face.

Shimming
Compensate for variations in two adjoining surfaces.

Slope
The face of an embankment or cut section; any ground whose surface makes an angle with the horizontal plane.

Slope stability
Consideration of a slope's propensity to fail as a result of several potential failure mechanisms including rotational slips, compound slips and translational slides.

Soil reinforcement
Tensile reinforcing elements usually placed in horizontal layers within soil so that the resulting composite soil is stronger than the original unreinforced soil.

Soil stabilization
The act of improving soil properties by the inclusion of reinforcing elements such as geosynthetics, chemical substances, compaction or other methods.

Specific gravity
The ratio of the density of the substance in question to the density of a reference substance at specified conditions of temperature and pressure.

Specimen
A specific portion of a material or laboratory sample upon which a test is performed or which a measurement is taken for that purpose.

Stabilized Mulch Matrix (SMM)
A hydraulically-applied matrix containing defibrated organic fibers with, at a minimum, one of the following additives: soil flocculants, crosslinked hydro-colloidal polymers, tackifiers. Utilized to provide erosion control and facilitate vegetation establishment on moderate slopes and designed to be functional for a minimum of three months.

Stacked bond
The pattern of unit placement wherein units are stacked directly over one another so that the vertical edges form a single plane. Generally not advisable in segmental retaining walls as it inhibits the wall strength.

Standing water
Water that is not in motion and remains in place for some time after a hard rain due to poor surface and subsurface drainage problems. If not absorbed, evaporated or drained, it can become stagnant water.

Steepened slope
Man-made Mechanically Stabilized Earth (MSE) slopes consisting of soil stabilized by planar reinforcing elements. Facing treatments ranging from natural vegetation to welded-wire are applied to prevent erosion. MSE slopes can be built much steeper than ordinary slopes due to the inclusion of the reinforcing elements and are therefore also called "steepened slopes". Slopes are normally considered to be inclined at 70 degrees or less with respect to the horizontal.

Stiffness
A resistance to bending.

Subgrade
The grade established in preparation for top surfacing of roads, lawns, etc.

Subgrade improvement
A technique used to provide a competent temporary road surface or a stable foundation layer for a permanent road when weak subgrade conditions are encountered.

Surcharge
Weight or load acting in, on, or near a retaining wall that impacts its ability to perform. Surcharge loads must be included in the design and engineering of retaining walls.

Surface water
Water that is deposited by rainfall or irrigation which has not permeated the soil, flowing on top of turf, landscapes and hardscapes. 

Surficial
Relating to a surface.

Swale
A constructed or natural drainage channel used to direct surface flow. Constructed swales typically have parabolic, trapezoidal or triangular cross sections.

 

T

Temporary degradable
An RECP composed of biologically, photochemically or otherwise degradable materials that temporarily reduces soil erosion and enhances the establishment of vegetation.

Temporary rolled erosion control products
For applications where natural vegetation alone will provide sufficient permanent erosion protection, furnish a temporary rolled erosion control product with the necessary longevity and performance properties to effectively control erosion and assist in the establishment of vegetation under the anticipated immediate site conditions.

Tensile modulus of elasticity
The tensile modulus is the ratio of stress to elastic strain in tension. A high tensile modulus means that the material is rigid - more stress is required to produce a given amount of strain. In polymers, the tensile modulus and compressive modulus can be close or may vary widely. This variation may be 50% or more, depending on resin type, reinforcing agents, and processing methods.

Tensile strength
The resistance to deformation developed for a specific material and subsequent modulus and elongation when subjected to tension by an external force.

Tiered walls
Multiple retaining wall structures constructed in elevation with a horizontal or gradual break between wall faces; also referred to as superimposed walls.

Top slope
(See Backslope)

Torsional stiffness
(See Secant Aperture Stability Modulus)

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

Transverse direction
The direction in the plane of the fabric perpendicular to the direction of manufacture. Often referred to as the "cross-machine direction."

Trench drain
A linear drain structure with grate used to collect sheets of runoff water in paved areas.

Turf Reinforcement Mat (TRM)
A rolled erosion control product composed of non-degradable synthetic fibers, filaments, nets, wire mesh and/or other elements, processed into a permanent, three-dimensional matrix of sufficient thickness. TRMs, which may be supplemented with degradable components, are designed to impart immediate erosion protection, enhance vegetation establishment and provide long-term functionality by permanently reinforcing vegetation during and after maturation. Note: TRMs are typically used in hydraulic applications, such as high flow ditches and channels, steep slopes, stream banks, and shorelines, where erosive forces may exceed the limits of natural, unreinforced vegetation or in areas where limited vegetation establishment is anticipated.

 

U

Uniaxial (UX)
Having one direction; or relating to, or affecting one axis.
Having tensile strength in one direction only.
Example: Uniaxial (UX) Geogrid (polymeric grid material that carries loads applied in one main direction in the plane of the geogrid).

Unit drainage fill
Free-draining fill placed in the openings within segmental block units.

Ultra-short term products
An RECP designed to last three months or less. They are used in areas where vegetation can be quickly established and will be mowed soon after installation. The netting and bonding materials (e.g. stitching thread) on ultra-short term products degrade quickly to prevent entanglement with mowing equipment.

Ultraviolet degradation
The breakdown of polymeric structure when exposed to natural light.

Utility
A buried pipe or cable supplying water, gas, electricity, etc.



W

Wall Batter
(See Batter)

Warp
The yarn running the length of the fabric in the machine direction when manufacturing woven fabrics.

Warp direction
The machine direction when manufacturing woven geotextiles.

Water table
The upper limit of water in saturated soil or underlying material.

Watershed
The region or area contributing to the supply of a stream or lake.

Weft
The yarn running the length of the fabric perpendicular to the machine direction when manufacturing woven or knitted fabrics.  Often referred to as the "cross-machine direction".

Weft direction
The cross-machine direction when manufacturing woven geotextiles.

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

Wire-formed retaining wall
Mechanically Stabilized Earth (MSE) retaining wall with facing elements manufactured from welded wire mesh.

Woven geotextile
A planar textile structure produced by interlacing two or more sets of elements, such as yarns, fibers, roving's, 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
The woven fabric produced with monofilament yarns.

Woven, multifilament
The woven fabric produced with multifilament yarns.

Woven, slit-film
The woven fabric produced with yarns produced from slit film.

 

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. Yarn may refer to (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 more or less twist, or (4) a single filament with or without twist (a monofilament).