Geosynthetics are a modern class of manufactured products integral to civil engineering and construction projects worldwide. They are specifically designed materials placed in contact with soil, rock, or other geotechnical materials to enhance performance and durability. Their use allows for innovative and cost-effective solutions to common infrastructure challenges, such as building roads over weak subgrades or managing water flow beneath structures. By modifying the properties of soil masses, geosynthetics contribute to the longevity and stability of infrastructure like roadways, embankments, and retaining walls.
Defining Geosynthetics and Their Composition
Geosynthetics are defined as planar, sheet-like products manufactured from synthetic, polymeric materials for use in geotechnical applications. The “geo” prefix signifies their earth-related application, while “synthetic” highlights their man-made composition, distinguishing them from natural materials like timber or stone. These materials are derived from petrochemical-based polymers chosen for their specific physical and chemical properties.
The most common polymers used include polypropylene (PP), polyester (PET), and high-density polyethylene (HDPE). Polypropylene is valued for its low cost, though it is vulnerable to ultraviolet (UV) light degradation. High-density polyethylene offers excellent chemical and impact resistance, making it suitable for containment. Polyester is selected for its high strength and resistance to creep under sustained load. These synthetic materials are preferred because they are biologically inert, resisting decomposition and ensuring long service life within the ground.
Primary Classifications
Geosynthetics are categorized primarily by their physical form and structure, which dictates their interaction with the surrounding soil.
Geotextiles
Geotextiles are the largest and most versatile category. They are permeable, flexible fabrics made from synthetic fibers. They can be either woven, resembling a stable, cloth-like material with uniform threads, or non-woven, which have a felt-like appearance with randomly oriented, bonded fibers.
Geogrids
Geogrids are characterized by a regular, open network of integrally connected, high-tensile polymeric ribs, creating large apertures. These net-like structures are often made from high-density polyethylene or polyester and are designed to interlock with soil particles. Their physical structure makes them highly effective at resisting tensile forces.
Geomembranes
Geomembranes are continuous, thin, and highly impermeable sheets, typically manufactured from polymers like high-density polyethylene (HDPE) or polyvinyl chloride (PVC). Unlike geotextiles and geogrids, geomembranes are designed to be a barrier, preventing the passage of liquids or gases.
Geonets
Geonets are formed from two sets of coarse, parallel polymeric strands extruded over one another at a constant angle, creating a sheet with distinct in-plane porosity. This structure gives geonets a thick, open network designed primarily to allow fluid or gas to flow easily within the plane of the material.
Geocomposites
Geocomposites represent a combination of two or more geosynthetic types, such as a geotextile bonded to a geonet, to achieve multiple functions in a single product.
Essential Engineering Functions
Geosynthetics perform a set of distinct, yet often combined, functions that address specific geotechnical challenges in construction.
Separation
Separation is the action of placing a geosynthetic material between two dissimilar materials to prevent them from mixing. This is common in road construction where a geotextile keeps the fine subgrade soil from contaminating the granular base course, maintaining the design integrity and load-bearing capacity of the upper layers.
Reinforcement
Reinforcement involves the geosynthetic material interacting with the soil to increase the overall strength and stability of the soil mass. Geogrids are widely used to add tensile strength to soil, allowing it to withstand greater loads or be constructed at steeper slopes. This function is accomplished by the material absorbing the tensile stresses that the soil cannot resist.
Filtration
Filtration is the process where the geosynthetic allows liquid to pass through while retaining fine soil particles. A permeable geotextile acts as a filter medium, preventing the migration of soil into a drainage system, thereby maintaining the system’s hydraulic efficiency and preventing clogging.
Drainage
Drainage is the function of collecting and conveying water or other liquids within the plane of the geosynthetic. Geonets and geocomposites are engineered with a high in-plane transmissivity to expedite the removal of excess moisture from the soil structure, which reduces hydrostatic pressure and increases stability.
Containment
Containment, or barrier function, is the use of an impermeable geosynthetic, such as a geomembrane, to prevent the migration of fluids or gases. This is critical in environmental applications like landfill liners, where the material must reliably isolate waste from the surrounding environment.