Abstract
We conducted a realities analysis of a spur road network. Results are summarized as follow. 1) Slopes were divided into two categories: those with an inclination of less than 30 degrees, and those with an inclination of 30 degrees or more. Slopes of 30 degrees or more were parts of the surfaces of spur roads (3m wide with cutting height of 1.5m) that were filled in when the spur roads were constructed. Such slopes are officially classified as steep hillsides and measures are taken to prevent landslides and other disasters. In geomorphological terms, the inclination conversion line between the low-relief surface and the slope is called convex break of slope (erosion front). 2) At the study area in Shimanto-Cho, 52% of the total road network has been constructed on relatively gentle slopes of less than 30 degrees, which cover 35% of the area. Since road construction becomes more difficult at steeper inclinations,it is important to know where the gentler slopes are for road network development. 3) The results of compaction tests and road surface CBR values obtained in the present study indicated that steep hillsides in the area are composed of soil with a high tampability (that is, it becomes denser and harder when compacted). Thus, roads on steeper slopes are constructed by compacting and hardening the subbase. 4) It was concluded that compaction tests can be used to assess the soil of slopes that are targeted for regular road construction. However, in the case of spur road, construction plans should be evaluated based on the CBR value of the spur road surfaces.
