報告書番号

V05009

タイトル（和文）

模型実験に基づく砕波を伴うソリトン分裂津波の波力評価

タイトル（英文）

Estimation of Tsunami Force with Breaking of Split Waves Based on Model Tests

概要 （図表や脚注は「報告書全文」に掲載しております）

大型造波水路を用いて，津波がソリトン分裂する場合さらに分裂波が砕波する場合について，防波堤に作用する津波波力の実験を実施し，波力評価法の検討を行った．その結果，注目すべき波力特性として，津波波力が最大になり得るのは，分裂第1波衝突時（分裂第1波砕波開始点での波力に対応）と第2波目以降の分裂波を含む津波本体重複波形成時（分裂第1波の砕波後の波力に対応）であることがわかった．入射津波本体の波長が短くなると，浅水変形により前傾し先端波形が切り立って発達しやすく，その上に顕著な分裂波が重畳しやすくなる．このため，分裂波の砕波前後で大きな波圧が発生しやすくなる．実験結果に基づき，新たな津波波圧算定式を提案した．本津波波圧算定式を用いると，日本海中部地震津波来襲時に被災した建設途上の能代護岸ケーソンが分裂波を伴う津波第1波で滑動し得ることが説明できる．

概要 （英文）

Using the CRIEPI large wave flume, tsunami force experiments were performed subject to breakwater. Tsunami with soliton fission and breaking of split waves were focused on. Tsunami force and vertical distribution of dynamic pressure were investigated in detail experimentally. As some remarkable features of tsunami force in experiments, tsunami force can show the maximum values at either the attack moment of the first split wave (corresponding to wave force at the starting point of breaking of the first split wave) or the formation moment of the standing waves of tsunami body and split waves on and after the second wave (corresponding to wave force post breaking of the first split waves). As the wavelength (the wave period) of incident tsunami body is shorter, tsunami profile can be deformed asymmetrically and the wave front can be steepened more significantly, and tsunami can split more largely by soliton fission.So, larger wave pressure can act on the breakwater under the breaking and pre-breaking conditions of split waves. Considering the above remarkable features, new formulae of wave pressure of tsunami with soliton fission and breaking of split waves are proposed, which are more reasonable to evaluate stability of coastal structure. The present wave pressure formula was applied to stability evaluation of seawall caissons at Noshiro Thermal Power Plant site, which was being constructed and damaged when Nihonkai-Chubu Earthquake Tsunami occurred and act in 1893. It was found that the proposed wave pressure formula could explain sliding of the seawall caissons by the first wave of tsunami with split waves.

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