Types of Geosynthetics and Their Geotechnical Functions

Geosynthetics are factory-made polymer products used in structures that interact with soil, rock or other geotechnical engineering materials. The types of geosynthetics most commonly used are geotextile, geocell, geogrid, geomembrane, geocomposite, geomat, geosynthetic clay liner, geopipe and others. Geosynthetic materials come from the plastics industry: polymers, rubber, fibreglass and other materials. All geosynthetics are generally made from strong, durable materials whose base resists chemical reactions, weathering and ageing, and geosynthetics also have special specifications, such as resistance to temperature or ultraviolet light.

Common abbreviations for the base polymers used to make geosynthetics are: PET (polyester), PP (polypropylene), PE (polyethylene), HDPE (high density polyethylene), LDPE (low density polyethylene) and PVC (polyvinyl chloride). Geosynthetic base materials consist mainly of carbon and hydrogen, and sometimes nitrogen and chloride, and are produced by processing coal and oil.

Types of Geosynthetics

Geotextile

One of the most widely used geosynthetic materials is geotextile. Geotextile is a water-permeable, factory-made textile produced from synthetic materials such as polypropylene, polyester, polyethylene, nylon and polyvinyl chloride. Geotextile can be used as a cushion or protection for other materials, for example as protection for geomembrane. The level of protection a geotextile cushion provides varies with the thickness, purpose and strength of the geotextile.

Read also: How Geotextile Is Made

Geotextile applications include:

• Slope reinforcement, to increase slope stability.
• Reinforced soil wall structures, where geotextile acts as reinforcement/anchors that keep stable a wall formed from geotextile and backfill.
• Road pavement structures, where geotextile separates the subgrade from the subbase of the pavement.
• Railway structures, with the same function as in pavements. Here the geotextile is placed at the interface between subgrade and ballast.
• Erosion control structures, where geotextile is placed behind gabions or rip-rap.
• Protection against seepage, to prevent fine soil particles being washed out by seepage flow.
• Separation between different materials, in road pavement structures, where geotextile is placed between the subgrade and the aggregate base course.
• As a filter, where geotextile is often wrapped around stone aggregate or collector pipes in subsurface drains.

Geocell

Geocell is made from HDPE (High Density Polyethylene) strips joined into a single honeycomb-like structure. Geocell is usually used to protect slopes or banks against erosion. It is also often used as a road base layer over soft subgrade, where it spreads vertical pressure over a wider area and increases the bearing capacity of the (soft) soil.

Geogrid

Geogrid is a sheet with relatively large openings. The openings are usually square, elliptical, triangular or other shapes. They allow the grid ribs to interlock with the surrounding soil or aggregate. Geogrid ribs are stronger and stiffer than geotextile. Geogrids are made from polymer sheets, usually polyethylene, punched with uniform square holes (closely spaced, with hole sizes ranging from 1.25 to 5 cm) and stretched in one direction (uniaxial) or equally in two directions (biaxial). Geogrid is a material that functions as reinforcement.

Geomembrane

Geomembrane is a waterproof material used mainly to protect bases or slopes, as a structural barrier, and to contain liquids or water. In principle, geomembrane serves as a liner for drinking water, protection against leaks in water reservoirs, protection of soil from landfill leachate, protection in agriculture, protection of water channels against leaks, a barrier to seepage flowing through the subgrade or under buildings, a vertical barrier to control the damaging effects of expansive soil, and more. Geomembrane is made from raw materials including the polymer resin itself plus additives such as antioxidants, plasticisers, carbon black and lubricants used as processing aids. These raw materials are then processed by the manufacturer into geomembrane sheets in various widths and thicknesses.

Geocomposite

Geocomposite is a material that combines geotextile and geogrid, geogrid and geomembrane, geotextile, geogrid and geomembrane, or combinations of these three materials with other materials. The main purpose of a geocomposite is to combine several materials for a specific purpose so that they perform optimally. For example, if geotextile is bonded to one or both sides of a geomembrane, the product becomes more resistant to puncture and tearing and its tensile strength increases. Geocomposite applications cover many kinds of work, including reinforcement, filtration, drainage, separation and moisture barriers.

Read also: Saving Installation Time with Geocomposite

Geomat

Geomat is a type of geosynthetic with a three-dimensional structure, thermally bonded together. It is made from synthetic filaments arranged into a layer. Geomat is typically used to establish vegetation on hillsides, roadside slopes and similar areas to prevent surface erosion.

Geosynthetic clay liner (GCL)

Geosynthetic clay liner (GCL) is a hydraulic barrier against the flow of liquids (water or waste). It acts as a waterproof layer equivalent to a thicker layer of compacted natural clay. This factory-made material combines a layer of natural clay with polymer materials. A GCL sheet consists of a layer of bentonite clay (or another impermeable material) sandwiched between two geotextiles or bonded to a geomembrane. GCL is used as a base liner for landfills, channel lining, pond surface lining, waste containment and more.

Main functions of geosynthetics

In civil engineering, the types of geosynthetics manufactured from polymers have several main functions: separation, filtration, drainage, reinforcement and protection. These functions can be single or a combination of several, depending on the application.