The Use of Landfill Tyre Drainage Layers

Leachate drainage layers are necessary in most waste landfill sites to minimise the accumulation of leachate within the site and they reduce the risk of contamination of surrounding ground and groundwater. A cheaper and environmentally preferable option is be the use of scrap vehicle tyres, but is their use permissible and what happens to them under pressure?

Normally layers of whole or shredded tyres exhibit excellent drainage properties, but if tyres are used as the main drainage layer at the base of a landfill the concern exists that they may compress under the overburden stress from the weight of the waste above and cease to act as an effective drainage layer.

Schredding Scrap Tyres - watch this video!



The results of a series of tests undertaken by the University of Southampton are reported by the above researchers as presented in their paper examining the compressibility and changes in hydrogeological properties of shredded and whole tyres subjected to a range of stresses typical of landfill conditions.

In the UK over 400,000 tonnes of used vehicle tyres are produced each year (Hird et al. The problem of disposing of used tyres has been made worse by the EU Landfill Directive which prohibited the disposal of whole used vehicle tyres to new landfills from 16 July 2003.

The Landfill Directive permits used tyres to be utilised as engineering material in landfills.

There is little published research indicating i) the extent to which tyre drainage layers will compress under such stresses, ii) the reduction in hydraulic conductivity due to compression and iii) the effect of tyre shred size on the compressibility and hydraulic conductivity of tyre layers.

The data demonstrated that tyre layers will compress under stress and this will result in a reduction of drainable porosity and hydraulic conductivity.

Countries that have specified a minimum hydraulic conductivity for landfill drainage layers generally give values of between 1 x 10^-3 and 1 x 10^-4 m/s.

However, this group found that shredded tyres would easily comply with requirements as low as 1 x 10^-3 m/s at stresses up to 600 kPa, but would only meet the most stringent requirements of some nations at stresses below 400 kPa.

The data presented in this paper demonstrate that the hydrogeological properties of whole and shredded tyres change according to the applied stress.

Therefore, by adding some more specification paramaters and sizes, it has been possible for the recycling industry from now on to produce anew (UK) tyre bale product which will serve a market in the secondary materials / recycling arena.
Steve Evans has provided more leading information on Landfill use of recycled Tyre Drainage layers at his blog. A full version of this article is available at Shredded Recycled Tyres.