報告書番号

N05062

タイトル（和文）

圧力抜き開口部を有する護岸の遮水シート作用波圧に関する研究

タイトル（英文）

Dynamic pressure under waterproof sheet of seawall with opening space

概要 （図表や脚注は「報告書全文」に掲載しております）

ある火力発電所の灰捨場護岸の遮水シートが1999年に破損した．その復旧のために，遮水シート作用波圧を評価した．被災前の完全遮蔽タイプの護岸の遮水シートには非常に大きな圧力が作用すること，対策工として圧力抜き開口部を設置することにより圧力を低減できることを確認した．圧力抜き開口部の幅と圧力との関係を数値計算で評価し，開口部の幅を決定した．この対策工について規則波を用いて詳細な波浪条件の下で水理実験を行った．規則波による数値計算と水理実験から遮水シートに作用する波圧の発生メカニズムを明らかにし，透過波圧の変動成分と護岸前面の重複波の平均水位上昇による平均圧力を議論し，平均圧力の最大波圧への寄与が大きいことを示した．さらに現地観測により波の不規則性と3次元性の遮水シート作用波圧に及ぼす影響を調べた．設計波圧値は現地観測結果から推定される外力を上回るものと判断され対策工の安全性を確認した．

概要 （英文）

Thermal power stations using coal usually have ash disposal site which becomes reclamation land when it is completely filled. Bulkheads of the disposal site are constructed according to regulations of reclamation area of waste disposal in Japan. Waterproof sheet must be placed not to contaminate surrounding sea by leaking the waste. Waterproof sheet of the ash disposal site at one of the power plants was damaged by waves in 1999. The sheet was placed completely covering on backfilling layer and back face of the caisson. This type of sheet placement was usually done at waste disposal constructions so far. Pressure acting on the sheet in the backfilling layer becomes extremely high because no wave dissipation is expected in the rubble mound and backfilling layer when the porous media region was completely closed. Sometimes this type of pressure is missed to design weight on the rubber sheet, which is called the stagnation pressure. As a new restoration work, an opening band was constructed behind the caisson to release the stagnation pressure. The pressure acting beneath the waterproof sheet through rubble mound after constructing the opening band was estimated using a numerical simulation model, physical model tests and field measurements. The present paper describes a methodology and an experience of the new restoration work to the waterproof sheet of bulkhead. The physical phnomena acting on the waterproof sheets is also described: A standing wave is formed in front of the bulkhead. A rise of the mean water level at the anti-node causes a rise of a mean pressure through the rubble mound. By constructing the opening band, the pressure acting beneath waterproof sheet is reduced. A component of pressure by the transmitted wave is compatible to the mean pressure rise due to the standing wave in front of the bulk head. The present work shows that its contribution to the maximum pressure is not neglegible by the results of the experiments and field measurement.

報告者

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