Ground pressure forwarder trials: assess benefits in reducing wheel rutting

Reduced tyre inflation pressure has been extensively used in timber haulage industry, with significant benefits in the control of rutting on forest roads during timber haulage. Research in Canada and Sweden has shown significant reduction in the rutting caused by haulage trucks on forest roads, when used with reduced tyre pressures vis-à-vis normal tyre pressures. Reduced tyre pressures also allow for timber haulage to be carried out over a longer time during the 'thaw period' in winter. Research in Ireland has also quantified the potential benefits of reduced tyre pressures in minimisation of fatigue damage on forest access roads, i.e., significant increase in the number of wheel passes prior to failure by cracking and rutting. The benefits and best practices in the use of reduced tyre inflation pressures on forwarders are as yet unclear for many forest roads with varying soil substrata and moisture regimes. The aim of this study was therefore to provide data that could be useful in determining the best practice. Timberjack 810 forwarder was used. This is the most common forwarder type in Irish Forestry and in other European country. The forwarder was fitted with both 600mm wide tyres (4 of) and 700mm wide tyres (4 of). The forwarder, together with a full load of timber was transferred to the site and payload was accurately measured so that trials can be run with full payload and with half payload. Analysis of the soil (moisture content, cone penetrometer measurements, shear vane tests) were carried out so that a detailed description of the site could accompany the results. Trial location was in Ireland in the Midlands, near Clonaslee in Slieve Blooms Forest, a highly forested area, close to where the forwarder operates generally. This has been typical of a soft, shallow peat based site described as peat podzol. The work was funded by COFORD (Council for Forest Research and Development in Ireland) and conduct in cooperation between the University of Florence, Coillte (the Irish forestry board) and CNR (National Research Council - Italy). The aims of this study were: a) to quantify the effects of reduced tyre pressures on rutting on soft soils, when compared to normal recommended pressures; b) to quantify the significance of load size variation on rutting potential, in order to assess the potential benefits of using reduced load size as a strategy to minimise rutting; and c) to assess the effect of tyre size (600 mm and 700 mm wide tyres) in the potential control of rutting.