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Geo-synthetics

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geosynthetics
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Introduction

Reading the trade press, it would seem that civil engineers are finding a new use for geo-synthetics on an almost daily basis. Although the term 'geo-synthetics' is used here, this group of ground engineering products includes geo-fabrics, geo-membranes, geo-textiles, landscape fabrics, geo-grids, and geo-matrices. Basically, they are all sheet products of synthetic or natural origin that are used in some way to 'improve' the natural ground or earthworks.
 

Some definitions

Geo-synthetics is a 'catch-all' term used to describe sheets of a man-made material that may be knitted, woven or non-woven.

spacer geotextile Geo-textiles are woven, non-woven or knitted, permeable sheets, usually, but not exclusively, non-biodegradable.

Landscape fabrics are an example of a light-use geo-textile commonly used in the horticultural and soft-landscaping trades.

geomembrane Geo-membranes are impermeable and usually non-woven, ie a film or solid sheet.

Typical use would be as a vapour or damp barrier.

geo-composite Geo-composites normally refers to a sheet that combines two or more layers of geo-synthetics.

For example, a drainage composite usually combines a permeable geo-textile with an impermeable geo-membrane.

geogrid Geo-grids are tough, non-woven synthetic sheets with large (100mm+) rectanglar holes.

Used for ground stabilisation. They are also known as geo-nets.

geomatrix Geo-matrices can be thought of as 3-dimensional geo-grids, in that they are cellular and used to stabilise surface soil, gravels etc.

More commonly used as a form of Grass Paving

See also Cellular Paving Systems page.

Many types of materials may be used to manufacture geo-fabrics, depending on the end use. The two main distinctions are between woven and nonwoven products.

Geo-synthetics are manufactured from synthetic materials, but there are some applications that call for biodegradable, natural materials such as coir or jute. Polypropylene is a popular choice for geo-grids or geo-matrices, as it is strong and chemically inert. Polyester is chosen for its strength and flexibility.

There are permeable woven geo-textiles commonly used for filtration purposes and impermeable membranes to resist mud-pumping. Some fabrics offer high puncture resistance, an important consideration in road and rail construction projects, or where the integrity of the sheet is essential, as in landfill sites.

 


Uses

Geo-synthetics have three main roles in the construction industry. They are used to provide...
  • Separation
  • Filtration (liquids and gases)
  • Reinforcement
...either singly or in combination.

Geo-synthetics have literally hundreds of uses, but the most common include...

Roads & Pavements maintaining bedding
Maintaining sub-base integrity
spacerSeparation: -to prevent bedding layers disappearing into sub-bases/subgrades

-to keep sub-bases from mixing into sub-grades

-to minimise/prevent soil-pumping

spacerFiltration:

spacerReinforcement:

-as drainage composites or lagging to filter drains

-to inhibit reflective cracking in asphalt courses

-strengthening of poor sub-grades

Railway Construction
spacerSeparation: -similar uses to those in road construction

-separation of ballast from sub-grade to minimise 'pumping'

pumping
spacerFiltration:

spacerReinforcement:

- track-edge drainage

-sub-grade and sub-base reinforcement

Ground Engineering
spacerSeparation: - weed control; root barriers root barrier
Root Barriers protect drainage and foundations
spacerFiltration: - usually as a drainage composite but also as a filter membrane for land drains
spacerReinforcement: - used to stabilise topsoils

- to stabilise earth banks

Other Uses
spacerErosion Control: - to prevent coastal or fluvial erosion
- to counter scour by wind and rain and surface run-off
- may be biodegradable and intended to last only until vegetation has established itself
spacerVapour/Gas membranes: - impermeable to protect part of a structure
- damp-proofing; radon barriers
spacerLandfill Sites: - containment and filtration
- leachate and gas collection

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FAQ "Do I really need a membrane or a layer of polythene underneath my paving?"           [Click Here]

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Specification

Separator geo-fabrics are the most commonly specified geo-synthetics used in the construction of roads and pavements. These are often non-woven, permeable materials primarily used to prevent the various layers of a pavement mixing or disappearing into lower layers.

DTp Clause 609 lists four essential qualities for separator geo-textiles:

  1. Pore size O90 - a measure of average hole size - lower figure means finer particles trapped
  2. Permeability, as measure in litres per m² per second
  3. Tensile strength - usually an abitrary minimum of 10 kN per m²
  4. Puncture resistance (CBR)
 

Suppliers:

Contact details for many of the larger maufacturers and suppliers of geo-synthetics can be found on this page

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Related Pages

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Other Geo-sheet pages on this site

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