Analysis of Alternative Forest Road Retaining Technologies on Difficult Slopes in Japan

In Japan, soft and sandy soils and steep slopes were native problems and usually caused difficulties in forest road construction. In addition, there were many crushing zones in mountainous forested area, and underground water often sprung out from stones and rocks in these crushing zones. This underground water often caused road degradation and should be drained. Some forest road retaining technologies had been introduced recently for stabling spur roads. One is L-shaped steel retaining wall technology called L-shaped mesh wall. It is easy to construct and underground water can be drained easily. The other is reinforced soil wall using thinned logs and geotextile called TK wall. In this study, the bearing capacity and usage of these technologies were analyzed based on the points of terrain, bearing capacity, and future possibility. L-shaped mesh wall was effective when applied to cross the short section of crushing zone. TK wall was easy to construct on steep slopes with narrow clearing width for roadway by its perpendicular filling slope, and provided environmental friendly landscape with recovered vegetation from the seed contained at surface as well as using thinned woods. Both technologies made easier to construct spur roads on slopes with soft soils but it was clarified that they needed appropriate drainage systems and their regular maintenance for economical use.