Bättre åtkomst till avverkningstrakter med anpassat marktryck från avverkningsmaskinerna

Sammanfattning: The global climate-change means increasing mean-temperature and higher precipitation in Sweden, which leads to shorter periods of frozen ground in the forest. At the same time the harvesting machines are getting bigger and more powerful. The forest industry aim at an even wood flow, and the ground damage has to be as low as possible. The two biggest causes for ground-damage is the bearing capacity of the forest ground and the ground-pressure of the harvesting machines. The aim of this study was to find out some rules for the machine choice considering ground pressure, when harvesting on ground with low bearing capacity.A field study, using a Valmet 890.3 forwarder, was carried out where different ground pressures and their effect on the ground were tested on two different types of ground.Additionally, an inventory of damaged harvesting grounds was made. The rut depth and soil density was measured and the ground pressure of the harvesting machines was calculated.These datas, as well as data from two previous studies was used to study a possible trend for the rut depth according to used ground-pressure.The result shows that rut depth as well as soil compaction is less if the ground pressure from the forwarder is reduced by using tracks. For forwarders with high ground pressure (> 80 kPa), the rut depth raised significantly when operating on ground with cone-index (0.70 MPa) or softer. The model for machine-choice is a guideline for machine-use that fits the carrying capacity of the forest ground.However it is important to point out that the forest ground is very complex in its composition, and that it is difficult to predict damage to it (e.g. rut depth). Heavy rain could for example lower the bearing capacity considerably.