To carry out a soil stratification test effectively to assess the stability of cut slopes and the best location for high-density spur roads, estimates of soil particle size were made for silt- and clay-dominated colluvial soil layers over 50 cm thick that overlay weathered residual soil. Material exposed by road-cuts was classified as rock or soil, and the relationships between composition and local topography were analyzed. Using a 10-m digital elevation model (DEM), three topographic factors were assessed: (1) average slope; (2) horizontal openness (the degree of convergence/parallelism/divergence of contour lines); and (3) vertical openness (the degree of concavity/planarity/convexity of flow lines). The study area was divided into slope areas with roughly uniform characteristics with a limit angle between each grid. Soil samples from areas with slopes over 25 degrees and horizontal openness less than 140 degrees at a limit angle of less than 10 degrees, and slopes over 30 degrees and horizontal openness less than 145 degrees at a limit angle of less than 15 degrees contained significantly less silt and clay (p<0.05, by the t-test). The finding that points with comparatively high silt and clay content were generally located on gentle and divergent ground was verified by observations at other sites. Soil coverage was high on slopes of less than 25 degrees, but low on slopes steeper than 30 degrees. This study demonstrates that analysis of topographic characteristics using a 10-m gridded DEM is effective in assessing certain geological features and in estimating the silt and clay content of soil.

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The theory of the cumulative frequency distribution of catchment area of the valleys crossing a forest road are driven by expanding the first Horton's law about number of the valley order and the fourth Horton's law about catchment area. This theory, which is a modification of Hori's theory, does not contain Hori's restrictive conditions. The cumulative frequency distributions of catchment areas of the valleys crossing forest roads shown on topographical maps mostly agreed with the theoretical values. In addition, three types of random walk computer simulations of 90 hillsides showed that while some of the data were invalid, most of the data roughly agreed with theoretical values. When applying the theory practically, there must be a clear method for identifying parameters which are bifurcation ratio and drainage-area ratio.

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In order to establish safe and efficient logging operations in yarding with tower-yarders, we analysed for the cable tension of mainline, haulbackline and the rotation frequency of drums on a tower-yarder with a running skyline cable system. We also investigated for the safety of tower-yarders according to the relation of loading weight and midspan percent deflection. The running of unloaded and loaded carriages was confirmed to be efficient under the condition of inter-locking. Setting an angle of 45 degrees to the yarding direction was an efficient way to method for the dragging and hoisting of mainline in the lateral yarding. In the running of unloaded carriages, not accelerating the rotation frequency of the drum was safe and efficient in both the condition of inter-locking and uninter-locking. However, accelerating the rotation frequency of drum was safe and efficient in the running of loaded carriages. This showed us that the yarding with tower-yarder is operated to safe yarding.

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A brush cutter equipped with a shaft brake system interlocked with the accelerator lever was developed. Although the brake to stop blade rotation should be adjusted, improved with better parts, etc., it could nonetheless stop the blade in just a few seconds. And in brushing work, the new system had no adverse effect on operational efficiency. Brushing work will become safer by using brush cutters equipped with this brake system. Moreover, the increased use of this type of machine will probably reduce the number of labor-related accidents.

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