The effects of an auxiliary axle on forwarder rut development – a Norwegian field study

Abstract

ABSTRACT The goal of this study was to compare wheel-rut development between a conventional 8-wheel forwarder and a 10-wheel forwarder. Two Ponsse Buffalo forwarders with 14 metric ton load capacity were compared; one with a standard double-bogie undercarriage and one with double-bogies plus an auxiliary back axle. Both forwarders were equipped with bogie-tracks front and back; the 8-wheeler with standard traction tracks on the rear bogie, the 10-wheeler with combi-tracks. The comparison was set up with two parallel forwarding trails leading down from the landing over marine sediments (coarse sand) to four parallel strip roads over a 4 m deep 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 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. Using linear regression, 79% of the variation in rut depth 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.