Pavingexpert - Geo-synthetics

Geo-synthetics

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Introduction
Types
Uses
Specification
Suppliers

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.

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

Separation: -to prevent bedding layers disappearing into sub-bases/subgrades
-to keep sub-bases from mixing into sub-grades
-to minimise/prevent soil-pumping

Filtration:
Reinforcement:
-as drainage composites or lagging to filter drains
-to inhibit reflective cracking in asphalt courses
-strengthening of poor sub-grades

Railway Construction

Separation: -similar uses to those in road construction
-separation of ballast from sub-grade to minimise 'pumping'
pumping

Filtration:
Reinforcement:
- track-edge drainage
-sub-grade and sub-base reinforcement

Ground Engineering

Separation: - weed control; root barriers
Root Barriers protect drainage and foundations

Filtration: - usually as a drainage composite but also as a filter membrane for land drains

Reinforcement: - used to stabilise topsoils
- to stabilise earth banks

Other Uses

Erosion 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

Vapour/Gas membranes: - impermeable to protect part of a structure
- damp-proofing; radon barriers

Landfill Sites: - containment and filtration
- leachate and gas collection

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

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:

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

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

Other Geo-sheet pages on this site

Geo-sheets
Landscape Fabrics
FAQ - is a membrane necessary
Sub-grades
Sub-bases
Aggregates

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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 sub-base integrity
Separation:	-to prevent bedding layers disappearing into sub-bases/subgrades -to keep sub-bases from mixing into sub-grades -to minimise/prevent soil-pumping
Filtration: Reinforcement:	-as drainage composites or lagging to filter drains -to inhibit reflective cracking in asphalt courses -strengthening of poor sub-grades
Railway Construction
Separation:	-similar uses to those in road construction -separation of ballast from sub-grade to minimise 'pumping'
Filtration: Reinforcement:	- track-edge drainage -sub-grade and sub-base reinforcement
Ground Engineering
Separation:	- weed control; root barriers	Root Barriers protect drainage and foundations
Filtration:	- usually as a drainage composite but also as a filter membrane for land drains
Reinforcement:	- used to stabilise topsoils - to stabilise earth banks

Other Uses
Erosion 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
Vapour/Gas membranes:	- impermeable to protect part of a structure - damp-proofing; radon barriers
Landfill Sites:	- containment and filtration - leachate and gas collection

Introduction

Some definitions

Uses

Specification

Suppliers:

Related Pages

Other Geo-sheet pages on this site