In this study, we developed a soil model using the 3D Distinct Element Method and examined parameters used in the method. This was done by comparing results of simple examinations with their simulation results. First, we selected parameters by trial and error to show the experimental results and then changed the friction coefficient, particle size, and spring constant based on these parameters in order to examine them. The friction coefficient had a positive relation with soil deformation and reaction force, and the spring constant had a positive relation with only reaction force while particle size did not have a relation with them. In addition, the spring constant could be estimated using previously proposed equations. However, the friction coefficient can not be estimated using the internal friction angle. Digging experiments were conducted with a 20-cm wide soil bin and a 7.5-cm wide leg. Three dimensional particle movement could be expressed with the above parameters. Furthermore, this simulation could also express the reaction force which was reduced during digging due to three-dimensional particle movements.

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We planned road routes and assigned road construction priorities for the next decade based on forest operations conducted during the previous decade in Toei, Aichi Prefecture, Japan. Five basic forest operations conducted between 1991 and 2000 were considered: planting, weeding, pruning, cleaning, and thinning. Work sites with longer mean access distances from roads than sites worked over the previous decade were targeted for development. For each sub-compartment, we considered one route, which would be constructed using strip roads from the centers of the targeted work sites to the nearest road. The total reduction in the length of the access distance to the work sites was used as an index to determine the order of road construction. As a result, 189 alternative routes were planned; the total road length and cost were about 107 km and 960 million yen at 9000 yen/m, which corresponded to the cost of actual road construction in Toei over 7 years. This should cut access distance for work sites and the labor burden to half of that for the previous decade. Even if only the 30 km of roads with the highest priority were constructed, constituting 41 of the planned routes, which equals the total length of road constructed over the previous decade, the cost reduction is expected to exceed 30%, versus a 10% reduction for the actual roads constructed in the previous decade. The construction would enable intensive forestry, because more than half of the work sites would be within 100 m of a road.

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Trends in the maintenance and repair costs over time of high performance forestry machines in Japan were analyzed, and maintenance and repair cost curves were formulated. There were four types of acceleration trends of maintenance and repair costs, and maintenance and repair cost curves were approximated as involution functions that have a range of maximum and minimum values. The highest maintenance and repair costs were for the largest harvesters, followed by skidders, forwarders, processors, grapple saws and tower-yarders (including swing-yarders). Usable life was derived from the actual years a machine is replaced or abandoned, and for-the-year operation time, and the ratios maintenance and repair costs for every machine were calculated. Consequently, the ranges of the ratios mean values of maintenance and repair cost of a high performance forestry machine were 34-63%. The ratios of maintenance and repair costs where the range of fluctuation was not taken into consideration became about 1/3-2/3 of conventional forestry machines (vehicle-type logging machines), and brought the result near the values of a construction machine (back hoe, bulldozer).

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