Studies on Transportation Mechanics of Sakurajima Volcanic Ash Drifted Over the Fixed Bed Open Channel

Research Project

Project/Area Number	01460236
Research Category	Grant-in-Aid for General Scientific Research (B)
Allocation Type	Single-year Grants
Research Field	農業土木
Research Institution	Kagoshima University
Principal Investigator	KAWAHARADA Reijirou Kagoshima University. Faculty of Agriculture Professor, 農学部, 教授 (80041599)
Co-Investigator(Kenkyū-buntansha)	CHO Katsushi Kagoshima University. Faculty of Agriculture Assistant Professor, 農学部, 助教授 (20038235)
Project Period (FY)	1989 – 1990
Project Status	Completed (Fiscal Year 1990)
Budget Amount *help	¥5,400,000 (Direct Cost: ¥5,400,000) Fiscal Year 1990: ¥1,200,000 (Direct Cost: ¥1,200,000) Fiscal Year 1989: ¥4,200,000 (Direct Cost: ¥4,200,000)
Keywords	Critical tractive force / Ripple / Sediment transport / Settling velocity / 掃流砂 / 滞積 / 砂レン
Research Abstract	This experimental investigation have been carried out clarify the transportation mechanics of Sakurajima volcanic ash drifted over the fixed bed open channels, with taking physical properties of ash particles into account. The main findings of the present study can be summarized as follows : 1. The ash particles are very angular and jagged, the particle sizes range approximately 0.1 mm to 1.0 mm in diameter in Kagoshima city. The specific gravity of ash range 2.65 to 2.71, these values are a little large than ordinary sand. The settling velocity of ash particles in water are slightly slower than sand. 2. The distributions of the velocity over ashed bed channels show the log-law except the near water surface regions. Ordinary ashed bed channels and their turbulence intensities are classified as a smooth channel surface. 3. The critical tractive force of ash over the fixed bed is little larger than that of sand, because of the difference of particle feature. Smaller ash particles usually set each other and increase flocculation during dry-process, however the difference between ash and sand tractive force can not be seen in this experiment. 4. A free surface flow over the ashed bed generates sediment transportation and ripple form. Ash particles roll and run over the ripple crest and fall at the leeward because of separation, and continues scour and deposition toward the downstream. Ripple length and height do not depend on flow depth, but particle diameter. 5. Bed sediment load of ash change according to particle diameter, the smaller, the fewer amount, ash-sediment can not be transported and cleared away in the drainage channel during short period because of changeable hydraulic conditions.