落石防護柵に衝撃荷重が載荷した場合におけるコンクリート基礎および柵の動的挙動に関する実規模実験

抄録

Many rockfall protection fences have been constructed along the cliffs and slopes in the mountain areas to prevent the rockfall disasters. The fences which are composed of steel posts, diamond-shaped steel nets and steel wire ropes, are set on the concrete foundation and/or rockfall protection walls. Now, stabilities of the structure have been checked following the design guideline for rockfall countermeasure. However, the guideline has been constituted based on not those dynamic response characteristics but statics. In order to investigate dynamic behavior of the structure and to consider validity of the guideline, the impact tests for prototype fences with 2 m height set on the concrete foundation having cross section of 1 m square were conducted by using about 1-ton steel weight. In this experiment, two types of anchoring systems for the posts were tried: conventional embedding type; and base-plate type, and two loading heights were considered: 1.4 m; and 0.6 m. The results obtained from this study were as follows: (1) even though the foundation cannot ensure the overturning stability following the guideline, all of these ensured experimentally; (2) the stability may be able to be checked by using Ushiro et al.'s equation with coefficient of restitution e=0 in the safety side which was derived by assuming rigid-body motion and using law of conservation of angular momentum; (3) the maximum impact force may be estimated by using the guideline; (4) the weight can be restrained from passing through the nets due to space keeping members even though the wire ropes break out of anchoring device; and (5) the base-plate type posts may be applicable for the practical use.