Abstract
A deterioration survey and bending strength test were carried out on thinned softwood logs used as shock absorbing pads of a debris fall defense hedge.
As the result of the annual deterioration survey of logs measured by PILODYN, it was found that the logs greatly deteriorated for 3 to 4 years, especially in certain places where they were installed. The striking depth PILODYN value of logs placed in the third or fourth layer in the pad was almost the same as that of logs touching the steel frame of the defense hedge. Thus, the thickness direction of the pad had little effect on deterioration. On the other hand, the striking depth value of the logs was influenced by the longitudinal direction, decreasing from the butt end to the center.
The bending strength of the logs was 85% after 2 years, and 20% after 5 years. A negative correlation was recognized between the striking depth value and the gap fraction of the forest behind the defense hedge.
