This study was conducted to clarify the relationships between placements of existing spur roads and topography. For this purpose, 13 areas where the inclinations were within the range of 14-32 degrees and forest road densities were 70-250m/ha were investigated. The spur roads were classified into two depending on their purpose: either operational or transportation purposes. This classification is based on the longitudinal slopes of the spur roads and contour lines. The inclination angle and slope profile were analyzed for each function. Our investigation revealed that the ratio of the roads for operation to those for transportation approaches a constant according to the forest road density in the area where the inclination is more than 20 degrees. The ratio tends to value of about 5:5 regardless of inclination. While roads for logging operations are generally laid out in are irrespective of inclination, those for traffic are laid out on gentle slopes where the inclination is less than 20 degree except for flat areas where the average inclination is less than 15 degrees. Slope profiles are classified as convex rectilinear or concave. While the roads for logging operations were evenly distributed among the three types of slop profiles, those for transportation were placed mainly on convex slopes.

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In recent years, many low-cost high-efficiency logging systems with very high forest road network densities, e.g., over 200m/ha, have been developed in moderate and steep mountain areas in Japan. This study involved basic research to establish appropriate earth engineering for skidding road construction. For 27 months, we investigated the capacity of new skidding roads constructed on Neogene period gravelly soils in the North Tohoku district. The CBR value of the road surface increased linearly by about three times during the experimental period. These increases occurred in the shoulder (from 1.4% to 4.0%), the rut (from 2.7% to 7.8%), and the center part (from 1.7% to 5.6%)of roads. It was estimated that the bearing capacity of the road surface will increase over a 10-year period. This increase will be rapid immediately after construction and will take more than 2 years to stabilize. The conversion-N value of the road bearing capacity ranged from about 0 to 5. This value did not vary much during the 27 months. Our research indicates that tamping is very important to the bearing capacity of a newly constructed skidding road.

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