![Kliffende, Island Sylt, 1999](https://upload.wikimedia.org/wikipedia/commons/7/79/Kliffende%2C_Island_Sylt%2C_1999.jpg)
Geosynthetics are synthetic products used to stabilize terrain. They are generally polymeric products used to solve
civil engineering
Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads, bridges, canals, dams, airports, sewage ...
problems. This includes eight main product categories:
geotextiles
Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain. Typically made from polypropylene or polyester, geotextile fabrics come in two basic forms: woven (r ...
,
geogrid
A geogrid is geosynthetic material used to reinforce soils and similar materials. Soils pull apart under tension. Compared to soil, geogrids are strong in tension. This fact allows them to transfer forces to a larger area of soil than would other ...
s,
geonets A geonet is a geosynthetic material similar in structure to a geogrid, consisting of integrally connected parallel sets of ribs overlying similar sets at various angles for in-plane drainage of liquids or gases. Geonets are often laminated with g ...
,
geomembranes
A geomembrane is very low permeability synthetic membrane liner or barrier used with any geotechnical engineering related material so as to control fluid (liquid or gas) migration in a human-made project, structure, or system. Geomembranes are ...
,
geosynthetic clay liners
Different types of fabric used for geosynthetic clay liners.
Geosynthetic clay liners (GCLs) are factory manufactured hydraulic barriers consisting of a layer of bentonite or other very low-permeability material supported bgeotextilesand/or geom ...
,
geofoam
Geofoam is expanded polystyrene (EPS) or extruded polystyrene (XPS) manufactured into large lightweight blocks. The blocks vary in size but are often . The primary function of geofoam is to provide a lightweight void fill below a highway, bridg ...
,
geocells and
geocomposites
Geocomposite is a composition / combination of two or more geosynthetic materials to perform multiple number of geosynthetic functions for specific civil engineering application(s) the purpose of providing this composition is to minimize the app ...
. The
polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
ic nature of the products makes them suitable for use in the ground where high levels of durability are required. They can also be used in exposed applications. Geosynthetics are available in a wide range of forms and materials. These products have a wide range of applications and are currently used in many civil,
geotechnical
Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics for the solution of its respective engineering problems. It al ...
,
transportation
Transport (in British English), or transportation (in American English), is the intentional movement of humans, animals, and goods from one location to another. Modes of transport include air, land (rail and road), water, cable, pipeline, ...
, geoenvironmental,
hydraulic
Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counte ...
, and private
development
Development or developing may refer to:
Arts
*Development hell, when a project is stuck in development
*Filmmaking, development phase, including finance and budgeting
*Development (music), the process thematic material is reshaped
* Photograph ...
applications including
road
A road is a linear way for the conveyance of traffic that mostly has an improved surface for use by vehicles (motorized and non-motorized) and pedestrians. Unlike streets, the main function of roads is transportation.
There are many types of ...
s,
airfield
An aerodrome ( Commonwealth English) or airdrome (American English) is a location from which aircraft flight operations take place, regardless of whether they involve air cargo, passengers, or neither, and regardless of whether it is for pub ...
s,
railroad
Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a pre ...
s,
embankments,
retaining structure
Retaining walls are relatively rigid walls used for supporting soil laterally so that it can be retained at different levels on the two sides.
Retaining walls are structures designed to restrain soil to a slope that it would not naturally keep to ...
s,
reservoir
A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation.
Reservoirs can be created in a number of ways, including contro ...
s,
canal
Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface flow un ...
s,
dam
A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...
s,
erosion control,
sediment control
A sediment control is a practice or device designed to keep eroded soil on a construction site, so that it does not wash off and cause water pollution to a nearby stream, river, lake, or sea. Sediment controls are usually employed together with e ...
,
landfill
A landfill site, also known as a tip, dump, rubbish dump, garbage dump, or dumping ground, is a site for the disposal of waste materials. Landfill is the oldest and most common form of waste disposal, although the systematic burial of the waste ...
liners, landfill covers,
mining
Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic via ...
,
aquaculture
Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...
and
agriculture
Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to ...
.
History
Inclusions of different sorts mixed with
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...
have been used for thousands of years. They were used in roadway construction in
Roman
Roman or Romans most often refers to:
*Rome, the capital city of Italy
*Ancient Rome, Roman civilization from 8th century BC to 5th century AD
*Roman people, the people of ancient Rome
*''Epistle to the Romans'', shortened to ''Romans'', a letter ...
days to stabilize roadways and their edges. These early attempts were made of natural
fibres,
fabric
Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, different fabric types, etc. At first, the word "textiles" only referred to woven fabrics. However, weaving is not th ...
s or
vegetation
Vegetation is an assemblage of plant species and the ground cover they provide. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic character ...
mixed with soil to improve road quality, particularly when roads were built on unstable soil. They were also used to build steep slopes as with several
pyramid
A pyramid (from el, πυραμίς ') is a structure whose outer surfaces are triangular and converge to a single step at the top, making the shape roughly a pyramid in the geometric sense. The base of a pyramid can be trilateral, quadrilat ...
s in
Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Mediter ...
and walls as well. A fundamental problem with using natural materials (
wood
Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...
,
cotton
Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus ''Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor perce ...
, etc.) in a buried environment is the
biodegradation
Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegrada ...
that occurs from
microorganism
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s in the soil. With the advent of polymers in the middle of the 20th century a much more stable material became available. When properly formulated, lifetimes of centuries can be predicted even for harsh environmental conditions.
Early papers on geosynthetics (as we know them today) in the 1960s documented their use as filters in the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
and as reinforcement in
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
. A 1977 conference in
Paris
Paris () is the capital and most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), making it the 30th most densely populated city in the world in 2020. S ...
brought together many of the early manufacturers and practitioners. The International Geosynthetics Society (IGS) founded in 1982 has subsequently organized a worldwide conference every four years and its numerous chapters have additional conferences. Presently, separate geosynthetic institutes, trade-groups, and standards-setting groups are active. Approximately twenty universities teach stand-alone courses on geosynthetics and almost all include the subject in geotechnical, geoenvironmental, and
hydraulic engineering
Hydraulic engineering as a sub-discipline of civil engineering is concerned with the flow and conveyance of fluids, principally water and sewage. One feature of these systems is the extensive use of gravity as the motive force to cause the mov ...
courses. Geosynthetics are available worldwide and the activity is robust and steadily growing.
Categories
Geotextiles
Geotextiles form one of the two largest groups of geosynthetics. They are textiles consisting of synthetic fibers rather than natural ones such as cotton, wool, or silk. This makes them less susceptible to bio-degradation. These synthetic fibers are made into flexible, porous fabrics by standard weaving machinery or are matted together in a random non woven manner. Some are also knitted. Geotextiles are porous to liquid flow across their manufactured plane and also within their thickness, but to a widely varying degree. There are at least 100 specific application areas for geotextiles that have been developed; however, the fabric always performs at least one of four discrete functions: separation, reinforcement, filtration, and/or drainage.
Geogrids
![Geogrid on a slope](https://upload.wikimedia.org/wikipedia/commons/3/32/Geogrid_on_a_slope.jpg)
Geogrids represent a rapidly growing segment within geosynthetics. Rather than being a woven, nonwoven or knitted textile fabric, geogrids are polymers formed into a very open, gridlike configuration, i.e., they have large apertures between individual ribs in the transverse and longitudinal directions. Geogrids are (a) either stretched in one, two or three directions for improved physical properties, (b) made on weaving or knitting machinery by standard textile manufacturing methods, or (c) by laser or ultrasonically bonding rods or straps together. There are many specific application areas; however, geogrids function almost exclusively as reinforcement materials.
Geonets/Geospacers
Geonets, and the related ''geospacers'' by some, constitute another specialized segment within the geosynthetics area. They are formed by a continuous extrusion of parallel sets of polymeric ribs at acute angles to one another. When the ribs are opened, relatively large apertures are formed into a netlike configuration. Two types are most common, either biplanar or triplanar. Alternatively many very different types of drainage cores are available. They consist of nubbed, dimpled or cuspated polymer sheets, three-dimensional networks of stiff polymer fibers in different configurations and small drainage pipes or spacers within geotextiles. Their design function is completely within the drainage area where they are used to convey liquids or gases of all types.
Geomembranes
Geomembranes represent the other largest group of geosynthetics, and in dollar volume their sales are greater than that of geotextiles. Their growth in the United States and Germany was stimulated by governmental regulations originally enacted in the early 1980s for the lining of solid-waste landfills. The materials themselves are relatively thin, impervious sheets of polymeric material used primarily for linings and covers of liquids- or solid-storage facilities. This includes all types of landfills, surface impoundments, canals, and other containment facilities. Thus the primary function is always containment as a liquid or vapor barrier or both. The range of applications, however, is great, and in addition to the environmental area, applications are rapidly growing in geotechnical, transportation, hydraulic, and private development engineering (such as aquaculture, agriculture, heap leach mining, etc.).
Geosynthetic clay liners
Geosynthetic clay liners, or GCLs, are an interesting juxtaposition of polymeric materials and natural soils. They are rolls of factory fabricated thin layers of
bentonite clay
Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-mon ...
sandwiched between two geotextiles or bonded to a geomembrane. Structural integrity of the subsequent composite is obtained by needle-punching, stitching or adhesive bonding. GCLs are used as a composite component beneath a geomembrane or by themselves in geoenvironmental and containment applications as well as in transportation, geotechnical, hydraulic, and many private development applications.
Geofoam
Geofoam is a polymeric product created by processing polystyrene into a foam consisting of many closed cells filled with air and/or gases. The skeletal nature of the cell walls resembles bone-structures made of the unexpanded polymeric material. The resulting product is generally in the form of large, but extremely light, blocks which are stacked side-by-side and in layers providing lightweight fill in numerous applications.
Geocells
Geocells (also known as Cellular Confinement Systems) are three-dimensional honeycombed cellular structures that form a confinement system when infilled with compacted soil. Extruded from polymeric materials into strips welded together ultrasonically in series, the strips are expanded to form the stiff (and typically textured and perforated) walls of a flexible 3D cellular mattress. Infilled with soil, a new composite entity is created from the cell-soil interactions. The cellular confinement reduces the lateral movement of soil particles, thereby maintaining compaction and forms a stiffened mattress that distributes loads over a wider area. Traditionally used in slope protection and earth retention applications, geocells made from advanced polymers are being increasingly adopted for long-term road and rail load support. Much larger geocells are also made from stiff geotextiles sewn into similar, but larger, unit cells that are used for protection bunkers and walls.
Geocomposites
![Geocomposite drain installation2](https://upload.wikimedia.org/wikipedia/commons/4/4b/Geocomposite_drain_installation2.jpg)
A geocomposite consists of a combination of geotextiles, geogrids, geonets and/or geomembranes in a factory fabricated unit. Also, any one of these four materials can be combined with another synthetic material (e.g., deformed plastic sheets or steel cables) or even with soil. As examples, a geonet or geospacer with geotextiles on both surfaces and a GCL consisting of a geotextile/bentonite/geotextile sandwich are both geocomposites. This specific category brings out the best creative efforts of the engineer and manufacturer. The application areas are numerous and constantly growing. The major functions encompass the entire range of functions listed for geosynthetics discussed previously: separation, reinforcement, filtration, drainage, and containment.
Demand and production
Functions
The juxtaposition of the various types of geosynthetics just described with the primary function that the material is called upon to serve allows for the creation of an organizational matrix for geosynthetics; see table below. In essence, this matrix is the “scorecard” for understanding the entire geosynthetic field and its design related methodology. In the table the primary function that each geosynthetic can be called upon to serve is seen. Note that these are primary functions and in many cases (if not most) cases there are secondary functions, and perhaps tertiary ones as well. For example, a geotextile placed on soft soil will usually be designed on the basis of its reinforcement capability, but separation and filtration might certainly be secondary and tertiary considerations. As another example, a geomembrane is obviously used for its containment capability, but separation will always be a secondary function.
The greatest variability from a manufacturing and materials viewpoint is the category of geocomposites. The primary function will depend entirely upon what is actually created, manufactured, and installed.
Geosynthetics are generally designed for a particular application by considering the primary function that can be provided. As seen in the accompanying table there are five primary functions given, but some groups suggest even more.
Separation is the placement of a flexible geosynthetic material, like a porous geotextile, between dissimilar materials so that the integrity and functioning of both materials can remain intact or even be improved. Paved roads, unpaved roads, and railroad bases are common applications. Also, the use of thick nonwoven geotextiles for cushioning and protection of geomembranes is in this category. In addition, for most applications of geofoam and geocells, separation is the major function.
Reinforcement is the synergistic improvement of a total system’s strength created by the introduction of a geotextile, geogrid or geocell (all of which are good in tension) into a soil (that is good in compression, but poor in tension) or other disjointed and separated material. Applications of this function are in mechanically stabilized and retained earth walls and steep soil slopes; they can be combined with masonry facings to create vertical retaining walls. Also involved is the application of basal reinforcement over soft soils and over deep foundations for embankments and heavy surface loadings. Stiff polymer geogrids and geocells do not have to be held in tension to provide soil reinforcement, unlike geotextiles. Stiff 2D geogrid and 3D geocells interlock with the aggregate particles and the reinforcement mechanism is one of confinement of the aggregate. The resulting mechanically stabilized aggregate layer exhibits improved loadbearing performance.
Stiff polymer geogrids, with very open apertures, in addition to three-dimensional geocells made from various polymers are also increasingly specified in unpaved and paved roadways, load platforms and railway ballast, where the improved loadbearing characteristics significantly reduce the requirements for high quality, imported aggregate fills, thus reducing the
carbon footprint
A carbon footprint is the total greenhouse gas (GHG) emissions caused by an individual, event, organization, service, place or product, expressed as carbon dioxide equivalent (CO2e). Greenhouse gases, including the carbon-containing gases carbo ...
of the construction.
Filtration is the equilibrium soil-to-geotextile interaction that allows for adequate liquid flow without soil loss, across the plane of the geotextile over a service lifetime compatible with the application under consideration. Filtration applications are highway underdrain systems, retaining wall drainage, landfill
leachate collection systems, as
silt fence
A silt fence, sometimes (misleadingly) called a "filter fence," is a temporary sediment control device used on construction sites to protect water quality in nearby streams, rivers, lakes and seas from sediment (loose soil) in stormwater runof ...
s and curtains, and as flexible forms for bags, tubes and containers.
Drainage is the equilibrium soil-to-geosynthetic system that allows for adequate liquid flow without soil loss, within the plane of the geosynthetic over a service lifetime compatible with the application under consideration. Geopipe highlights this function, and also geonets, geocomposites and very thick geotextiles. Drainage applications for these different geosynthetics are retaining walls, sport fields, dams, canals, reservoirs, and capillary breaks. Also to be noted is that sheet, edge and
wick drains are geocomposites used for various soil and rock drainage situations.
Containment involves geomembranes, geosynthetic clay liners, or some geocomposites which function as liquid or gas barriers. Landfill liners and covers make critical use of these geosynthetics. All hydraulic applications (tunnels, dams, canals, surface impoundments, and floating covers) use these geosynthetics as well.
Advantages
* The manufactured quality control of geosynthetics in a controlled factory environment is a great advantage over outdoor soil and rock construction. Most factories are ISO 9000 certified and have their own in-house quality programs as well.
* The low thickness of geosynthetics, as compared to their natural soil counterparts, is an advantage insofar as light weight on the subgrade, less airspace used, and avoidance of quarried sand, gravel, and clay soil materials.
[
* The ease of geosynthetic installation is significant in comparison to thick soil layers (sands, gravels, or clays) requiring large earthmoving equipment.][
* Published standards (test methods, guides, and specifications) are well advanced in standards-setting organizations like ISO, ASTM, and GSI.
* Design methods are currently available from many publication sources as well as universities which teach stand-alone courses in geosynthetics or have integrated geosynthetics in traditional geotechnical, geoenvironmental, and hydraulic engineering courses.
* When comparing geosynthetic designs to alternative natural soil designs there are usually cost advantages and invariably sustainability (lower CO2 footprint) advantages.][
]
Disadvantages
* Long-term performance of the particular formulated resin being used to make the geosynthetic must be assured by using proper additives including antioxidants, ultraviolet screeners, and fillers.
* The exposed lifetime of geosynthetics, being polymeric, is less than unexposed as when they are soil backfilled.
* Clogging or bioclogging Bioclogging or biological clogging is clogging of pore space in soil by microbial biomass; their body and their byproducts such as extracellular polymeric substance (EPS). The microbial biomass blocks the pathway of water in the pore space, forming ...
of geotextiles, geonets, geopipe and/or geocomposites is a challenging design for certain soil types or unusual situations. For example, loess soils, fine cohesionless silts, highly turbid liquids, and microorganism laden liquids (farm runoff) are troublesome and generally require specialized testing evaluations.
* Handling, storage, carrying and installation must be assured by careful quality control and quality assurance.
References
Further reading
*Van Zanten, R. V. (1986). ''Geotextiles and Geomembranes in Civil Engineering'', A. A. Balkema Publ., Rotterdam, The Netherlands.
*Industrial Fabrics Association International (1990). ''A Design Primer: Geotextiles and Related Materials'', IFAI Publ., Roseville, MN, US.
*Van Santvoort, G. P. T. M., Translator (1995). ''Geosynthetics in Civil Engineering'', A. A. Balkema Publ., Rotterdam, The Netherlands.
*Jewell, R. A. (1996). ''Soil Reinforcement With Geotextiles'', CIRIA Publishers, London, England.
*Holtz, R. D., Christopher, B. R. and Berg, R. R. (1997). Geosynthetic Engineering, BiTech Publishers, Ltd., Richmond, B.C., Canada.
*Pilarczyk, K. W. (2000). ''Geosynthetics and Geosystems in Hydraulic and Coastal Engineering'', A. A. Balkema Publ., Rotterdam, The Netherlands.
*Rowe, R. K. (Ed.) (2001). ''Geotechnical and Geoenvironmental Engineering Handbook'', Kluwer Academic Publishers, Boston, US.
*Dixon, N., Smith, D. M., Greenwood, J. R. and Jones, D. R. V. (2003). ''Geosynthetics: Protecting the Environment'', Thomas Telford Publ., London, England.
*Shukla, S. K. and Yin, J.-H. (2006). ''Fundamentals of Geosynthetic Engineering'', Taylor and Francis Publishers, London, England.
*Sarsby, R. W. Ed. (2007). ''Geosynthetics in Civil Engineering'', Woodhead Publishing Ltd., Cambridge, England.
External links
International Association of Geosynthetic Installers
International Geosynthetics Society Website
Engineering Use of Geotextiles
Geosynthetic Materials Association
Geosynthetic Institute
geosyntheticsystems
Geosynthetics magazine
Geosynthetica – Free digital geosynthetics publication
Composite Behavior of Geosynthetic Reinforced Soil Mass
Federal Highway Administration
The Federal Highway Administration (FHWA) is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two programs, the Federal-aid Highway Program a ...
VERUS Certification – Notified Body nº 2449 for CE Marking of Geosynthetics Products
{{Geotechnical engineering