Effects of Geomorphological Settings on Salt Weathering of Sandstone in the Coastal Spray Zone

点击翻译按钮获取中文摘要

The effects of waves on salt weathering of sandstone blocks used for a masonry bridge piers in the coastal spray zone has been studied since 1999. Four piers of Yayoi Bridge, connecting Aoshima island with Kyusyu island in Japan, are the frustum of a pyramid in shape. The piers are called as P1, P2, P3 and P4 respectively. Most of the sandstone blocks, which cover all side walls of the piers, have a tafoni-like depression on their surface. The average depression depth of each wall is the largest on P4 and gradually becomes smaller on P3 and P2 in due order, then the smallest on P1. Therefore, the amount of sea water supply to sandstone blocks by waves has been measured in order to elucidate the role of sea spray in the formation of the tendency mentioned above.Results obtained are summarized as follows;1. On the north-facing walls, the amount of sea water supply to sandstone blocks shows the largest on P1, then gradually decreases toward P4. This indicates that the average depression depth are inversely proportional to the amount of sea water supply.2. On the south-facing walls, the amount of sea water supply shows the largest on P2. This is related to the fact that the depression depth in the spray zone is the smallest on P2.3. Because waves approach from the north under normal sea conditions, the amount of sea water supply shows notable difference between north and south-facing walls. Also this difference in the amount of sea water supply is the largest on P1.4. The amount of sea water supply on each wall of P2 is the largest on the north-facing wall and decreases on the south-facing wall, then becomes the smallest on the east and west-facing walls.These results suggest that the sea water supply to sandstone blocks plays an important role in the formation of depressions.