Abstract
In the Usui River, where sediment accumulation has been reduced due to the dam upstream, the soft rocks at the bottom of the river have been exposed. As a result, the riverbed soft rocks have been eroded resulting from slaking and the level of the river bottom is getting lower. This is the cause of problems such as damage to river banks and difficulties in agricultural water intake. In this study, we measure the slaking depth on the soft rock surface happened as a consequence of repetitive drying and water immersion using soft rock samples collected in this area. The results are as follows. One cycle of dry/wet repetition make about 3 mm of granulation on the soft rock surface. The thickness of this granulation become smaller if sufficient drying conditions are not provided. Remaining particles on the surface of the soft rock after slaking seems to delay the granulation. The soil classification of disintegrated particles is also shown.
