Geotextiles are permeable synthetic membranes specifically designed to be used in conjunction with other construction materials. The methods of manufacture usually consist of weaving polymeric tapes to produce a uniform fabric or by bonding together a matrix of polymetric fibres.

The characteristics of the two methods are as follows:

WOVEN	NONWOVEN
Very strong	Stronger as thickness increases
Do no elongate or stretch very much when a force is applied	Highly permeable
Made of woven synthetic fabric (usually polypropylene or polyester) by weaving yarns together	Able to stretch and take the shape of the adjacent surface

There are four primary uses of geotextiles in roadway construction and maintenance:-

• Stabalisation or separation

• Drainage

• Erosion control

• Reinforcement

Stabalisation or separation

The geotextile is used to permanently separate two layers of soil. This keeps the soft, underlying soil from working its way up into the top layer (i.e. gravel) and keeps the top layer from working down into the soft soil. This ensures a harder top surface remains in place for many years.

Both woven and non woven materials are used for this purpose.

Drainage

Geotextiles act as a filter through which water passes but fine soil does not pass through. This is useful for sports pitches ensuring good drainage but no loss of surface materials.

For this purpose mainly nonwoven fabrics are used because of their small pore size and high flow capacity.

Erosion control

Geotextiles place along culverts, ditches etc. provides an anchorage for a stabilising rock layer and also protects the underlying soil.

Reinforcement

Geotextiles can be used in construction where foundation soils are too weak to support a structure. The Geotextiles add reinforcement to the foundations.