| Leachate drainage layers are necessary in most | | | | The Landfill Directive permits used tyres to be utilised |
| waste landfill sites to minimise the accumulation of | | | | as engineering material in landfills. |
| leachate within the site and they reduce the risk of | | | | There is little published research indicating i) the |
| contamination of surrounding ground and | | | | extent to which tyre drainage layers will compress |
| groundwater. A cheaper and environmentally | | | | under such stresses, ii) the reduction in hydraulic |
| preferable option is be the use of scrap vehicle tyres, | | | | conductivity due to compression and iii) the effect of |
| but is their use permissible and what happens to | | | | tyre shred size on the compressibility and hydraulic |
| them under pressure? | | | | conductivity of tyre layers. |
| Normally layers of whole or shredded tyres exhibit | | | | The data demonstrated that tyre layers will |
| excellent drainage properties, but if tyres are used as | | | | compress under stress and this will result in a |
| the main drainage layer at the base of a landfill the | | | | reduction of drainable porosity and hydraulic |
| concern exists that they may compress under the | | | | conductivity. |
| overburden stress from the weight of the waste | | | | Countries that have specified a minimum hydraulic |
| above and cease to act as an effective drainage | | | | conductivity for landfill drainage layers generally give |
| layer. | | | | values of between 1 x 10^-3 and 1 x 10^-4 m/s. |
| The results of a series of tests undertaken by the | | | | However, this group found that shredded tyres |
| University of Southampton are reported by the | | | | would easily comply with requirements as low as 1 x |
| above researchers as presented in their paper | | | | 10^-3 m/s at stresses up to 600 kPa, but would only |
| examining the compressibility and changes in | | | | meet the most stringent requirements of some |
| hydrogeological properties of shredded and whole | | | | nations at stresses below 400 kPa. |
| tyres subjected to a range of stresses typical of | | | | The data presented in this paper demonstrate that |
| landfill conditions. | | | | the hydrogeological properties of whole and shredded |
| In the UK over 400,000 tonnes of used vehicle tyres | | | | tyres change according to the applied stress. |
| are produced each year (Hird et al. The problem of | | | | Therefore, by adding some more specification |
| disposing of used tyres has been made worse by | | | | paramaters and sizes, it has been possible for the |
| the EU Landfill Directive which prohibited the disposal | | | | recycling industry from now on to produce anew |
| of whole used vehicle tyres to new landfills from 16 | | | | (UK) tyre bale product which will serve a market in |
| July 2003. | | | | the secondary materials / recycling arena. |