Jaeger Dirk, PhD. Assoc. Prof.

Steel flexible tracks (SFT) are regularly installed on bogie axles of forwarders to improve traction
and extend trafficability by increasing the contact area between machines and operating surface.
The study quantified dynamic peak loads exerted by a forwarder driving either on wheels or
using additional SFT on its rear bogie axle. To examine load distribution of a full-scale forwarder,
a load test platform was designed and constructed. Three scenarios were tested with the
forwarder unloaded and loaded to quantify load distribution between wheels driven directly over
the steel load test platform (Scenario 1) and SFT when either driven directly over the steel load
test platform (Scenario 2) or when driven over a 20 cm layer of sand placed over the platform
(Scenario 3). The platform proved to be an appropriate measuring device for full-scale tests.
Results indicate that, when operated on the sand layer, SFT (installed on the forwarder’s rear
unloaded axle) decreased dynamic peak loads by about 30% compared to wheels. The use of SFT
on bogie axles of forest machines is recommended to lower soil disturbances, especially through
a reduction of peak loads often responsible for negatively altering soil physical properties.

The impact of machines on forest soils is regularly assessed and quantified using absolute bulk density, which is most frequently obtained by soil cores. However, to allow for repeated measurements at the exact same locations, non-destructive devices are increasingly being used to determine soil bulk density and moisture content in field studies. An example of such a device is a nuclear moisture and density gauge (NMDG), originally designed as a control measurement for soil bulk density and moisture content in geotechnical applications. Unlike road construction or foundation projects that use mineral soil or gravel, forest soils have complex structures and the presence of organic matter, which can skew moisture and density readings from a NMDG. To gain further knowledge in this respect, we performed controlled tests in a sandbox to quantify the influence of varying amounts of saturated organic matter (3, 5, 10, and 15%) mixed with mineral soil in different layers (0–5, 0–10, 0–20 and 0–40 cm) on the accuracy of soil moisture content obtained by a NMDG and soil theta probe at varying depths. Main results illustrated that the presence of saturated organic matter per se was not problematic but moisture content overestimations and related underestimation of dry bulk density occurred when the tested measurement depth was below the created organic layer. Since forest soils often exhibit higher organic matter contents in the upper horizon, correction factors are suggested to minimize the moisture content variations between NMDG and reference method. With the use of correction factors, NMDG can present a non-destructive, fast, and accurate method of measuring soil moisture and bulk density in forestry applications.