Needlepunching is the most common web bonding method. It is the method of consolidation of fibrous webs by the repeated insertion of barbed needles into the web as shown in Figure 1.21. The needling can be done either from one side or from both (top and bottom) sides of the web. This process consolidates the structure of fibrous web without any binder by interlocking of fibres in the third or ‘Z’ dimension. Continuous filaments or short staple fibres are initially arranged in the form of a fibrous web in various orientations (random, cross, parallel, or composite). This forms a three-dimensional intermingled structure which fulfils the necessary requirements of geotextiles.
Needlepunched nonwoven geotextiles are extensively used in civil engineering applications including road and railway construction, landfills, land reclamation and slope stabilization. Such applications require geotextiles to perform more than one function including filtration, drainage, and separation. The properties of needle-punched nonwoven depend on parameters like fibre type, web aerial density, needle penetration depth, punch density (number of punches/cm2) and number of needling passages.