Last month, we presented the ground pressure simulation that was carried out by Dresden Technical University. Terranimo from Switzerland has also been working on this subject for a very long time. Here are a few insights. 

KEEPING IT BRIEF

  • The Terranimo simulation program can compute the effects of a wheel load deep in the soil.
  • Tyre lugs have an effect on the ground pressure only in the top depth zone.
  • You can use the system to learn about your own conditions (www.terranimo.ch).

Measuring the ground pressure in field conditions is both costly and time-consuming. Thankfully, there are simulation programs that can recreate the amount of compaction relative to the tyres fitted and the load being carried by the wheel. However, it takes a lot of work, with countless measurements, to develop such a program. 

Complex experiments…

The Bern University of Applied Sciences was able to use a 1.0m by 1.0m sensor mat with an incredible 37,000 measuring points. For the tests, the mat was placed directly under the tyre (VF600/70 R30), which was inflated to 1.6 bar and loaded with 4.6t. To determine the effect of this wheel load at depth, some additional measurements were taken. For these, the mat was covered with 10, 20 and 30cm of soil at a corresponding density.

The results of these test measurements are shown in the pictures below: In picture 1, the lugs cannot sink into the soil, and the pressure is up to 10 bar. At the same time, the lugs are only just visible at a depth of 10cm. Farther down, at a depth of 20cm or 30cm, we can hardly detect a difference between the footprint of the lugs and the area between the lugs. This explains why the Terranimo simulation doesn’t consider the lugs separately.

The left pictures show the pressure measurements of a sensor mat at various depths. The tyre was a VF600/70 R30 tyre inflated to 1.2 bar; the wheel load was 4.6t. The right pictures show the visualized results of the corresponding simulations with Terranimo. Note the different scaling in the top pictures. The measurement here was taken directly under the lugs, as the pressure here is consistently higher than 2 bar and up to 10 bar. Yet, at a depth of just 10cm, the lugs are blurred.

…for good simulations

By comparing the measurements that were taken with Bolling probes (see the diagrams below) and the simulation, we learn how accurately a simulation reflects reality. At soil depths of 20, 40 and 60cm, both the pressures measured and computed are always at a comparable level. This applies to high tyre pressures (left pair of graphs) and low tyre pressures (right pair). 

This means that the terranimo.ch program can predict the soil pressure (and thus the risk of soil compaction) without having to make any complex measurements. 

Hubert Wilmer

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