Last reviewed 16 Sept 2026 · 9 min read
What are geosynthetics?
Geosynthetics are planar (or three-dimensional) products made from polymeric materials (and some natural fibres) used in contact with soil, rock or other geotechnical materials as an integral part of civil engineering projects.
Polymers used
Polypropylene (PP), polyester (PET), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), polyvinyl chloride (PVC), polyamide (nylon), and natural fibres (jute, coir) for biodegradable products.
Types of geosynthetics
| Type | Description | Main functions |
|---|---|---|
| Geotextiles | Permeable fabrics — woven (interlaced yarns, high strength), non-woven (needle-punched or heat-bonded fibres, good filtration and drainage), knitted | Separation, filtration, drainage, reinforcement (woven), protection |
| Geogrids | Open grid-like structures with apertures — uniaxial (strength in one direction — walls, slopes), biaxial (both directions — road bases), triaxial; extruded, welded or woven/knitted and coated | Reinforcement, stabilisation (interlock with aggregates) |
| Geonets | Net-like structures with parallel ribs forming in-plane flow channels | In-plane drainage (usually with geotextiles as geocomposites) |
| Geomembranes | Impermeable polymer sheets (HDPE, LLDPE, PVC) | Containment / barrier — landfill liners, canal and pond linings, tunnels |
| Geosynthetic clay liners (GCL) | Thin layer of bentonite between geotextiles (or on a geomembrane) | Hydraulic barrier (swells when hydrated) — landfills, ponds |
| Geocells | Three-dimensional honeycomb cellular confinement systems filled with soil or aggregate | Confinement/stabilisation of weak subgrades, slope and channel erosion protection, load support |
| Geocomposites | Combinations — e.g. drainage composites (geonet/core + geotextile), prefabricated vertical drains (PVDs) (band drains for consolidation), reinforced geotextiles | Drainage, consolidation, filtration + reinforcement |
| Geofoam | Large blocks of expanded polystyrene (EPS) | Lightweight fill on soft soils, bridge approaches, reducing earth pressure |
| Geopipes | Perforated or solid polymer pipes | Subsurface drainage |
| Geomats / erosion control blankets | Three-dimensional mats (synthetic or natural) | Erosion control and vegetation establishment |
| Geobags, geomattresses, geotubes | Geotextile containers filled with sand/slurry | River bank protection, coastal protection, dewatering |
| Natural geotextiles | Jute and coir fabrics, mats | Temporary erosion control, low-volume road separation, slope vegetation — biodegradable (India is a major producer of jute and coir) |
Functions of geosynthetics
| Function | Description | Example |
|---|---|---|
| Separation | Prevents intermixing of dissimilar materials (e.g. fine subgrade and aggregate base) | Geotextile between soft subgrade and granular sub-base of roads and railways |
| Filtration | Allows water to pass while retaining soil particles | Geotextile filter around drains, behind retaining walls, under riprap |
| Drainage | Conveys water within its plane (transmissivity) | Drainage composites behind walls, in landfill covers, below pavements |
| Reinforcement | Provides tensile strength to soil | Geogrids in reinforced soil walls, steep slopes, embankments on soft ground, pavement bases |
| Protection (cushioning) | Protects another material (geomembrane) from puncture | Thick non-woven geotextile over geomembrane liners |
| Containment (barrier) | Prevents migration of liquids or gases | Geomembranes and GCLs in landfills, ponds, canals |
| Erosion control | Protects soil surfaces from rain, wind and flowing water | Geomats, geocells, geobags on slopes and banks |
| Stabilisation / confinement | Improves bearing capacity through lateral restraint | Geocells and biaxial geogrids on weak subgrades |
Applications
Roads and railways
- Separation and stabilisation of weak subgrades — geotextiles and geogrids reduce aggregate thickness, rutting and contamination of base layers.
- Base reinforcement of flexible pavements with geogrids.
- Paving fabrics and grids in asphalt overlays — retard reflective cracking and act as moisture barriers.
- Drainage — geocomposite edge drains, filter wraps.
- Railway tracks — separation between ballast/blanket and formation soil; reduces mud pumping.
- IRC guidelines (e.g. IRC:SP:59 on geosynthetics in road pavements) and MoRTH specifications cover their use.
Reinforced soil walls and slopes
- Mechanically stabilised earth (MSE) walls — layers of geogrid/geostrip reinforcement in compacted fill with facing panels or blocks — widely used for flyover and bridge approaches (IRC:113 guidelines for reinforced soil walls).
- Reinforced steep slopes — allow steeper slopes than unreinforced soil, saving land.
- Advantages: flexible, tolerate differential settlement, faster and often cheaper than RCC retaining walls.
Embankments on soft soils
- Basal reinforcement with high-strength geotextiles or geogrids improves stability.
- Prefabricated vertical drains (PVDs) with preloading/surcharge accelerate consolidation of soft clays.
- Geocell mattresses, geofoam lightweight fills, geosynthetic-encased stone columns.
Landfills and containment
- Composite liner systems — geomembrane (HDPE) over a compacted clay liner or GCL.
- Leachate collection — geonets/drainage composites, geopipes; protection geotextiles.
- Final covers (caps) — geomembranes, GCLs, drainage layers, erosion control.
- Also: secondary containment, tailings dams, sewage lagoons.
Water resources and hydraulic works
- Canal and pond linings with geomembranes to reduce seepage.
- Filters under riprap and revetments.
- River bank and coastal protection — geobags, geomattresses, geotubes.
- Dams — geomembrane facings, drainage and filtration.
Other uses
Tunnel waterproofing, green roofs, sports fields, erosion control of highway cuttings and embankments (geomats, coir/jute nets with vegetation), dewatering of sludge (geotubes).
Properties and tests
| Property group | Examples |
|---|---|
| Physical | Mass per unit area (g/m²), thickness, specific gravity, aperture size (geogrids) |
| Mechanical | Wide-width tensile strength (kN/m) and elongation, grab tensile, CBR puncture resistance, trapezoidal tear, seam strength, creep, junction strength (geogrids), interface shear with soil |
| Hydraulic | Apparent opening size (AOS, O₉₀ or O₉₅), permittivity (cross-plane flow), transmissivity (in-plane flow), soil retention, long-term clogging (gradient ratio test) |
| Endurance and durability | UV resistance, creep, installation damage, chemical and biological resistance, oxidation (polyolefins), hydrolysis (polyester in high pH) |
Basic design concepts
Geotextile filter criteria
A geotextile filter must:
- Retain soil (retention criterion): the opening size must be small enough — typically (soil), with depending on soil grading and flow conditions (often about 1 for conservative design).
- Allow water to pass (permeability criterion): permeability of the geotextile greater than that of the soil (often by a factor of about 10 in critical applications).
- Resist clogging over time (select non-woven or woven products with suitable porosity, check by gradient ratio tests for problematic soils).
- Survive installation (strength requirements).
Long-term design strength of reinforcement
FormulaLong-term design strength
= ultimate tensile strength; = reduction factor for creep; = reduction factor for installation damage; = reduction factor for durability (chemical and biological degradation). An additional overall factor of safety is applied in design.
Reinforced soil wall (internal stability — simplified)
FormulaTension in a reinforcement layer
= active earth pressure coefficient; = unit weight of fill; = depth of the layer; = vertical spacing of reinforcement. Requirement: allowable reinforcement strength; pull-out resistance beyond the failure wedge must also be adequate, along with external stability (sliding, overturning, bearing, global stability).