Geogrids
Encyclopedia
A geogrid is geosynthetic material used to reinforce soils and similar materials. Geogrids are commonly used to reinforce retaining walls, as well as subbases or subsoils below roads or structures. 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 otherwise be the case.
Geogrids are commonly made from polymer
materials, such as polyester
or polystyrene
. They may be wovern or knitted from yarns, heat-welded from strips of material, or produced by punching a regular pattern of holes in sheets of material, then stretched into a grid.
The development of methods of preparing relatively rigid polymer
ic materials by tensile
drawing , in a sense "cold working
," raised the possibility that such materials could be used in the reinforcement of soils for walls, steep slopes
, roadway bases
and foundation soil
s. Used as such, the major function of the resulting geogrids is in the area of reinforcement. This area, as with many other geosynthetics, is very active, with a number of different products, materials, configurations, etc., making up today's geogrid market. The key feature of all geogrids is that the openings between the adjacent sets of longitudinal and transverse ribs, called “apertures,” are large enough to allow for soil strike-through from one side of the geogrid to the other. The ribs of some geogrids are often quite stiff compared to the fibers of geotextiles. As discussed later, not only is rib strength important, but junction strength is also important. The reason for this is that in anchorage situations the soil strike-through within the apertures bears against the transverse ribs, which transmits the load to the longitudinal ribs via the junctions. The junctions are, of course, where the longitudinal and transverse ribs meet and are connected. They are sometimes called “nodes”.
Currently there are three categories of geogrids. The first, and original, geogrids (called unitized or homogeneous types) were invented by Dr Frank Brian Mercer
in the United Kingdom
at Netlon, Ltd., and were brought in 1982 to North America by the Tensar
Corporation. A conference in 1984 was helpful in bringing geogrids to the engineering design community . A similar type of drawn geogrid which originated in Italy
by Tenax is also available, as are products by new manufacturers in Asia
.
The second category of geogrids are more flexible, textile-like geogrids using bundles of polyethylene
-coated polyester
fibres as the reinforcing component. They were first developed by ICI Linear Composites LTD in the United Kingdom around 1980. This led to the development of polyester yarn geogrids made on textile weaving machinery. In this process hundreds of continuous fibers are gathered together to form yarns which are woven into longitudinal and transverse ribs with large open spaces between. The cross-overs are joined by knitting or intertwining before the entire unit is protected by a subsequent coating. Bitumen, latex
, or PVC
are the usual coating materials. Geosynthetics
within this group are manufactured by many companies having various trademarked products. There are possibly as many as 25 companies manufacturing coated yarn-type polyester geogrids on a worldwide basis.
The third category of geogrids are made by laser
or ultrasonically
bonding together polyester or polypropylene rods or straps in a gridlike pattern. Two manufacturers currently make such geogrids.
The geogrid area is extremely active not only in manufacturing new products, but also in providing significant technical information to aid the design engineer
.
Geogrids are commonly made from polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
materials, such as polyester
Polyester
Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...
or polystyrene
Polystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
. They may be wovern or knitted from yarns, heat-welded from strips of material, or produced by punching a regular pattern of holes in sheets of material, then stretched into a grid.
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
ic materials by tensile
Tension
Tension may refer to:* The Void , also known as Tension in some regions* Tension , a factor that affects knitting gauge...
drawing , in a sense "cold working
Work hardening
Work hardening, also known as strain hardening or cold working, is the strengthening of a metal by plastic deformation. This strengthening occurs because of dislocation movements within the crystal structure of the material. Any material with a reasonably high melting point such as metals and...
," raised the possibility that such materials could be used in the reinforcement of soils for walls, steep slopes
Slope stability
The field of slope stability encompasses the analysis of static and dynamic stability of slopes of earth and rock-fill dams, slopes of other types of embankments, excavated slopes, and natural slopes in soil and soft rock...
, roadway bases
Base course
Base Course in pavements refers to the sub-layer material of an asphalt roadway and is placed directly on top of the undisturbed soil so as to provide a foundation to support the top layer of the pavement...
and foundation soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
s. Used as such, the major function of the resulting geogrids is in the area of reinforcement. This area, as with many other geosynthetics, is very active, with a number of different products, materials, configurations, etc., making up today's geogrid market. The key feature of all geogrids is that the openings between the adjacent sets of longitudinal and transverse ribs, called “apertures,” are large enough to allow for soil strike-through from one side of the geogrid to the other. The ribs of some geogrids are often quite stiff compared to the fibers of geotextiles. As discussed later, not only is rib strength important, but junction strength is also important. The reason for this is that in anchorage situations the soil strike-through within the apertures bears against the transverse ribs, which transmits the load to the longitudinal ribs via the junctions. The junctions are, of course, where the longitudinal and transverse ribs meet and are connected. They are sometimes called “nodes”.
Currently there are three categories of geogrids. The first, and original, geogrids (called unitized or homogeneous types) were invented by Dr Frank Brian Mercer
Frank Brian Mercer
Frank Brian Mercer OBE FRS was an English chemist and businessman.He was born into a Blackburn family, which for generations had been involved in the textile industry and which owned and controlled companies engaged in spinning, weaving, dyeing and finishing and educated at the Queen Elizabeth's...
in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
at Netlon, Ltd., and were brought in 1982 to North America by the Tensar
Tensar
-History:In the late 1970s, Netlon’s founder, Dr Brian Mercer, invented and patented the Tensar stiff polymer geogrid, now used worldwide. Throughout the 1980s and 1990s, the company developed, refined and researched Tensar uniaxial and biaxial geogrids, and expanded the range of construction...
Corporation. A conference in 1984 was helpful in bringing geogrids to the engineering design community . A similar type of drawn geogrid which originated in Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
by Tenax is also available, as are products by new manufacturers in Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
.
The second category of geogrids are more flexible, textile-like geogrids using bundles of polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
-coated polyester
Polyester
Polyester is a category of polymers which contain the ester functional group in their main chain. Although there are many polyesters, the term "polyester" as a specific material most commonly refers to polyethylene terephthalate...
fibres as the reinforcing component. They were first developed by ICI Linear Composites LTD in the United Kingdom around 1980. This led to the development of polyester yarn geogrids made on textile weaving machinery. In this process hundreds of continuous fibers are gathered together to form yarns which are woven into longitudinal and transverse ribs with large open spaces between. The cross-overs are joined by knitting or intertwining before the entire unit is protected by a subsequent coating. Bitumen, latex
Latex
Latex is the stable dispersion of polymer microparticles in an aqueous medium. Latexes may be natural or synthetic.Latex as found in nature is a milky fluid found in 10% of all flowering plants . It is a complex emulsion consisting of proteins, alkaloids, starches, sugars, oils, tannins, resins,...
, or PVC
Polyvinyl chloride
Polyvinyl chloride, commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl groups having one hydrogen replaced by chloride. Polyvinyl chloride is the third most widely produced plastic, after polyethylene and polypropylene. PVC is widely used in...
are the usual coating materials. Geosynthetics
Geosynthetics
Geosynthetics is the term used to describe a range of generally polymeric products used to solve civil engineering problems. The term is generally regarded to encompass eight main product categories: geotextiles, geogrids, geonets, geomembranes, geosynthetic clay liners, geofoam, geocells and...
within this group are manufactured by many companies having various trademarked products. There are possibly as many as 25 companies manufacturing coated yarn-type polyester geogrids on a worldwide basis.
The third category of geogrids are made by laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
or ultrasonically
Ultrasonics
Ultrasonics is a term meaning the application of ultrasound. It is often used in industry as a shorthand term for any equipment employing ultrasonic principles....
bonding together polyester or polypropylene rods or straps in a gridlike pattern. Two manufacturers currently make such geogrids.
The geogrid area is extremely active not only in manufacturing new products, but also in providing significant technical information to aid the design engineer
Design engineer
Design Engineer is a general term that covers multiple engineering disciplines including electrical, mechanical, industrial design and civil engineering, architectural engineers in the U.S...
.