A note on the vertical stresses near the soil-tyre interface

Abstract

Whether the magnitude and distribution of stress in the soil-tyre interface is controlled by the tyre inflation pressure or by the wheel load is still a source of dispute. Due to the scarcity of measured data on surface stress, inputs to models that predict stresses in the soil profile are based on uncertain and non-validated assumptions of the magnitude and distribution of stresses in the soil-tyre interface. To clarify this issue we measured the contact area and the distribution of vertical stress near the soil-tyre interface for two radial-ply tyres with 83 kN wheel load at rated inflation pressures. A battery of 17 stress transducers was installed in a sandy soil at approximately field capacity and covered with 0.1 m loose soil. We used a recently developed model for fitting the measured stress pattern across the footprint. We combined the new data with previously published tests at 30 and 60 kN wheel load at rated inflation pressures and tests at three non-rated inflation pressures at 60 kN wheel load. The combined data set indicates that the level of maximum vertical stress in the contact area–for the tyres tested and for one specific soil condition–could be fully described by the tyre inflation pressure. The mean ground pressure was near identical to the inflation pressure for both tyres at the 30 kN load, but about 15 and 60 kPa lower than the inflation pressure for the 60 and 83 kN loads, respectively. Our results therefore indicate that the mean ground pressure cannot be estimated from the inflation pressure by adding a contribution from the tyre carcass stiffness, although this approach is often used in state-of-the-art models for soil compaction. The general validity of our conclusions should be evaluated for other tyres and at different soil strengths.