Researchers examined the effectiveness of number of wheels during soft ground extraction.
The goal of the research was to compare rut development between a conventional 8-wheel forwarder with traction bogie-tracks and a 10-wheel forwarder with combi-tracks on soft forest ground conditions during typical summer/autumn conditions. Two Ponsse Buffalo forwarders with 14 t load capacity were compared; one with a standard double-bogie undercarriage (8-wheel) and one with a double-bogie undercarriage with an auxiliary axle behind the rear bogie (10-wheel).
The standard unloaded weight of the 8-wheeled Buffalo is 19.8 tons. The unloaded weights for the 8- and 10-wheeler with tracks was 22.7 and 25.2 tons, respectively. The auxiliary axle on the 10-wheel forwarder is hydraulically lifted and lowered with variable axle pressure when in use. Both machines were equipped with 710 mm (28 in) wide Trelleborg Twin forestry tires. The 8-wheeler had universal tracks on the front bogie (Pewag Bluetrack Duro, wide-rib) and traction tracks on the rear bogie (Olofsfors OF, narrow-rib) for more difficult terrain. The 10-wheeler had all-round tracks on the front bogie (Olofsfors Kovax-Soft, M-rib) and combi-tracks (Olofsfors Max-Magnum with alternating M-plates and narrow-ribs) on the rear bogie. Based on the contractor’s experience from an earlier 10-wheeler, non-pneumatic tires were used on the auxiliary axle to avoid punctures along the rim edge.
A side-by-side comparison of the two forwarders was set up with two parallel forwarding trails (250 m / 820 ft) leading down from the landing on an undulating slope (0–10% inclination) to a lower bog. These led to four parallel strip roads (200 m / 200 ft) over the lower bog (4 m / 13 ft deep). The harvester used 50% wider cutting zones on the bog to provide a sufficient reinforcement of the trails with harvest residues. The forwarder load stakes were marked at heights specifying a 12 m3 (424 ft3) load, due to the low bearing capacity of the bog.
Seven blocks with three transects per block were laid out to follow the breakdown of the harvest residue layer (above the humus surface) and development of rut depth (below the humus surface) after each loaded pass. Ruts deeper than 10 cm (4 in) were found on 19% and 31% of transects after 5–10 and 15–20 passes for the 8-wheel forwarder, respectively. The corresponding figures for the 10-wheel forwarder were 7% and 12%, respectively. Most of the rut depth variation could be explained by pass interval, forwarder type, and pre-harvest soil moisture content. The auxiliary axle with suitable bogie-tracks offers increased site availability in moderate terrain during frost-free periods.
In summary, the auxiliary axle matched with a suitable bogie-track served as an effective aid when passing sections of marginal bearing capacity. Given suitable harvest residue matting, it reduced the initial risk of breaking through the peatland root mat and subsequent rut development.
The researchers were D Fjeld & Ø Østby-Berntsen. The research was titled “The effects of an auxiliary axle on forwarder rut development – a Norwegian field study”. It was published in the International Journal of Forest Engineering, 2020. Source