CHANGES IN SUBSOIL POROSITY CAUSED BY HEAVY VEHICLES

Previous Swedish studies led to a recommendation to limit the toad on a single axle to 6 Mg and on a tandem axle unit to 8 Mg in order to avoid permanent subsoil compaction in wet soil. In recent years large tyres that can carry large toads at low inflation pressure have been available. In a new project it was studied whether the use of such tyres may change the recommended load limits. Loads of 8-12 Mg on a single axle or 10-20 Mg on a tandem axle unit significantly reduced the porosity in the 300-400 and 400-560 mm soil layer. In the 400-500 mm soil layer an inflation pressure of 50 or 100 kPa compared with 150 kPa did not substantially reduce compaction. The results indicate that no important increase in the previously recommended limits can be proposed.